GFCI breaker in panel vs spa panel

[ajdelange]

I'm completely rational... There is one simple rule with electricity.... It takes THE PATH OF LEAST RESISTANCE to ground.

If you believe the last sentence that proves the first to be untrue. Given a set of paths p1, p2, p3... and an impressed voltage of E across each of them the current that flows through each is I1 = E/R1; I2 = E/R2; I3 = E/R2... where R1, R2 and R3 ... are the resistance of the paths. The current does not select the path of least resistance. It divides itself among the paths according to their resistances. In the current example we might have a heater in a circuit with resistance such that 50 amps flows through it with, in this example, the resistance being 240/50 = 4.8 Ω. This is clearly less than the resistance of a path consisting of someone with dry unbroken, skin to ground which is perhaps a couple K Ω. At 120V (we've got a bi-phase system here) that means a current of only 60 mA. Thus not all the current takes the path of least resistance. 60 mA, a very small fraction of the current, takes the much higher resistance path through the person contacting the hot wire. Though it is not a large amount of current it is, nevertheless, enough to do you a mischief.

The function of the GFCI is, of course, to detect that the high resistance path is there and remove power from the circuit thereby relieving the insurance company of the burden of having to pay out a benefit. The code requires GFCIs in certain locations for a good reason. It is written by the insurance companies.

 

[doug293cz]

If you believe the last sentence that proves the first to be untrue. Given a set of paths p1, p2, p3... and an impressed voltage of E across each of them the current that flows through each is I1 = E/R1; I2 = E/R2; I3 = E/R2... where R1, R2 and R3 ... are the resistance of the paths. The current does not select the path of least resistance. It divides itself among the paths according to their resistances. In the current example we might have a heater in a circuit with resistance such that 50 amps flows through it with, in this example, the resistance being 240/50 = 4.8 Ω. This is clearly less than the resistance of a path consisting of someone with dry unbroken, skin to ground which is perhaps a couple K Ω. At 120V (we've got a bi-phase system here) that means a current of only 60 mA. Thus not all the current takes the path of least resistance. 60 mA, a very small fraction of the current, takes the much higher resistance path through the person contacting the hot wire. Though it is not a large amount of current it is, nevertheless, enough to do you a mischief.

The function of the GFCI is, of course, to detect that the high resistance path is there and remove power from the circuit thereby relieving the insurance company of burden of having to pay out a benefit. The code requires GFCIs in certain locations for a good reason. It is written by the insurance companies.

Touche!

Brew on

 

[itsnotrequired]

in fairness to owly, code doesn't explicitly call for gfci protection for electric brewing systems. code calls out specific requirements for gfci protection and it is limited to 125 volts, 15 and 20 amp receptacles in specific locations. so if you are running a 240v system, code does not require gfci protection. applications that would require gfci protection by code would include 120v systems that are plugged into receptacles which require gfci protection (e.g. kitchen countertop, outdoors, garage, etc.) it doesn't matter if you are plugging in a brewing controller, appliance, power tool, whatever. the receptacle itself requires gfci protection so your brew controller will have the protection.

all this being said, code describes minimum requirements only. absolutely nothing wrong with adding gfci protection where it is not required. it is of course not a substitute for proper wire sizes, proper installation techniques, good electrical practices, etc. but man, it sure is some cheap insurance.

 

[Owly055]

As another poster wrote "touche"................ I've worked with electronics all my life, and am well aware of how networks of resistors work. Most folks here are pretty ignorant about electricity, hence the oversimplification......The reality in this case is that the path to ground has virtually no resistance, where your body has very high resistance. I just now moistened my finger tips and measured my internal resistance at 229K ohms. That's wet finger tip to wet finger tip.............. do the math. One resistor at essentially zero ohms, another at 229K ohms.......... 50 amps flowing to ground, how much current is going to flow through your body??? Essentially none. This assuming you have some sort of good ground. So you have your hand on the brewstand, and suddenly the element shorts out.......... Where is the path to ground? You not only have a very high internal resistance, but you likely are not connected to any ground except the brew stand itself, but even if you are barefoot standing in a puddle of wort over a clogged floor drain made of iron, your relative resistance is so high compared to the grounded brew stand that there will be essentially no current flow through you...... You won't feel a thing.
Again I give the analogy of the grounded pliers pulling off sparkplug wires with 40,000 volts running through them. I've done this literally hundreds of times. You can watch the spark jump to the pliers, but you don't even feel a tickle even though you are bare handed.
How many of your large appliances are on GFCI? I've NEVER seen a large appliance connected to GFCI, yet you don't cringe every time you touch your kitchen range, drier, water heater, etc. Even your refrigerator is usually not on GFCI, though 120 can kill you just as dead as 240.

I'm not against GFCI except in so far as it leads to the mindset that whatever I do GFCI will protect me. A person should always design something like a brew stand as if
GFCI didn't exist.

H.W.

If you believe the last sentence that proves the first to be untrue. Given a set of paths p1, p2, p3... and an impressed voltage of E across each of them the current that flows through each is I1 = E/R1; I2 = E/R2; I3 = E/R2... where R1, R2 and R3 ... are the resistance of the paths. The current does not select the path of least resistance. It divides itself among the paths according to their resistances. In the current example we might have a heater in a circuit with resistance such that 50 amps flows through it with, in this example, the resistance being 240/50 = 4.8 Ω. This is clearly less than the resistance of a path consisting of someone with dry unbroken, skin to ground which is perhaps a couple K Ω. At 120V (we've got a bi-phase system here) that means a current of only 60 mA. Thus not all the current takes the path of least resistance. 60 mA, a very small fraction of the current, takes the much higher resistance path through the person contacting the hot wire. Though it is not a large amount of current it is, nevertheless, enough to do you a mischief.

The function of the GFCI is, of course, to detect that the high resistance path is there and remove power from the circuit thereby relieving the insurance company of the burden of having to pay out a benefit. The code requires GFCIs in certain locations for a good reason. It is written by the insurance companies.

 

[UndeadFred]

I have a GFCI on my system (in a "spa panel"). However, I have to agree that GFCI's are no substitute for adequate grounding. There can be situations with a lost ground that the GFCI then becomes completely worthless. But yes, if a hot shorts to the properly connected ground, or outside of the kettle, both sides, both hots are disconnected. For $50, that and having a big enough shutoff is worth it. But I often wonder if it gives an electric brewing system owner a false sense of security. I do know people who are much more careless with water and electricity because they think the GFCI will simply trip if they start to get hit with AC. True, but depending on how wet you are, it still could be too late.

I check my grounds about every other brew on my system, just in case. I would go out on a limb and say that IF you checked your grounding with a meter every time you used the system, you could safely get away without a GFCI. But in the grand scheme of things it's a cheap ($50) secondary insurance policy against stupidity. But the good ground still needs to be there for it to have a return path to trip.

 

[Owly055]

Check out the new thread I just started on GFCI failure rates......... and Google it yourself!

H.W.

 

[Owly055]

I have a GFCI on my system (in a "spa panel"). However, I have to agree that GFCI's are no substitute for adequate grounding. There can be situations with a lost ground that the GFCI then becomes completely worthless. But yes, if a hot shorts to the properly connected ground, or outside of the kettle, both sides, both hots are disconnected. For $50, that and having a big enough shutoff is worth it. But I often wonder if it gives an electric brewing system owner a false sense of security. I do know people who are much more careless with water and electricity because they think the GFCI will simply trip if they start to get hit with AC. True, but depending on how wet you are, it still could be too late.

I check my grounds about every other brew on my system, just in case. I would go out on a limb and say that IF you checked your grounding with a meter every time you used the system, you could safely get away without a GFCI. But in the grand scheme of things it's a cheap ($50) secondary insurance policy against stupidity. But the good ground still needs to be there for it to have a return path to trip.

Unfortunately it is NOT cheap insurance, it's a false sense of security. You should check your GFCI EVERY TIME......... Checking grounding is as simple as having a push button that routes a significant load through the ground from one leg. If the ground carries the load (120 volt load), it works, and will protect you. There are a number of clever ways to do this.

H.W.

 

[stevehaun]

I am not getting into this deliberation. However, IMHO, this is a very wise statement:

A person should always design something like a brew stand as if
GFCI didn't exist.

 

[passedpawn]

As another poster wrote "touche"................ I've worked with electronics all my life, and am well aware of how networks of resistors work. Most folks here are pretty ignorant about electricity, hence the oversimplification......The reality in this case is that the path to ground has virtually no resistance, where your body has very high resistance. I just now moistened my finger tips and measured my internal resistance at 229K ohms. That's wet finger tip to wet finger tip.............. do the math. One resistor at essentially zero ohms, another at 229K ohms.......... 50 amps flowing to ground, how much current is going to flow through your body??? Essentially none. This assuming you have some sort of good ground. So you have your hand on the brewstand, and suddenly the element shorts out.......... Where is the path to ground? You not only have a very high internal resistance, but you likely are not connected to any ground except the brew stand itself, but even if you are barefoot standing in a puddle of wort over a clogged floor drain made of iron, your relative resistance is so high compared to the grounded brew stand that there will be essentially no current flow through you...... You won't feel a thing.
Again I give the analogy of the grounded pliers pulling off sparkplug wires with 40,000 volts running through them. I've done this literally hundreds of times. You can watch the spark jump to the pliers, but you don't even feel a tickle even though you are bare handed.
How many of your large appliances are on GFCI? I've NEVER seen a large appliance connected to GFCI, yet you don't cringe every time you touch your kitchen range, drier, water heater, etc. Even your refrigerator is usually not on GFCI, though 120 can kill you just as dead as 240.

I'm not against GFCI except in so far as it leads to the mindset that whatever I do GFCI will protect me. A person should always design something like a brew stand as if
GFCI didn't exist.

H.W.

That multimeter test isn't valid. Impedence goes down pretty fast as the the frequency increases - I'm not sure what it typically is at 60Hz. People do get electrocuted all the time so, regardless of what you think your multimeter is telling you, electrocution is a reality.

The "can't let go" current level at 60 Hz is about 15mArms - I imagine that's why the GFCI level is set at 5mA. So, ohms law, if the body impedence gets below 8kohms, you're a goner (at 120Vac). On split phase, both lines are 120V to gnd.

Like you said, grounding exposed metal is a given. If there is a direct short from L->N or L->GND, the breaker will trip. But if the fault is NOT a direct short, IOW if the fault does not exceed 30A (or whatever the breaker is), it'll just sit there patiently waiting for you. If a live ckt comes into contact with the wort, will the resistance of the wort allow 30A? Maybe, maybe not. Do you feel lucky today?

 

[GilaMinumBeer]

I'm completely rational, have been working with high voltage electricity for over 50 years including working in the field with centerpivot irrigation systems that run on 480 3 phase which have no such protection.

Now wait a minute here. In another thread you claimed to have been unemployed for 40 years, subsisting on 1-2 hours a day of public internet trading.

 

[Owly055]

Now wait a minute here. In another thread you claimed to have been unemployed for 40 years, subsisting on 1-2 hours a day of public internet trading.

I've been self employed for about 40 years. The last few of years I've been semi retired day trading in the stock market. I think I said I've not had a "job" for 40 years. That's not the same as "unemployed".

H.W.

 

[doug293cz]

in fairness to owly, code doesn't explicitly call for gfci protection for electric brewing systems. code calls out specific requirements for gfci protection and it is limited to 125 volts, 15 and 20 amp receptacles in specific locations. so if you are running a 240v system, code does not require gfci protection. applications that would require gfci protection by code would include 120v systems that are plugged into receptacles which require gfci protection (e.g. kitchen countertop, outdoors, garage, etc.) it doesn't matter if you are plugging in a brewing controller, appliance, power tool, whatever. the receptacle itself requires gfci protection so your brew controller will have the protection.

all this being said, code describes minimum requirements only. absolutely nothing wrong with adding gfci protection where it is not required. it is of course not a substitute for proper wire sizes, proper installation techniques, good electrical practices, etc. but man, it sure is some cheap insurance.

It's not surprising that code doesn't say anything about brewing systems. In the grand scheme of things, electric brewing systems are pretty rare compared to other household installations/appliances. If they were common, I'm pretty sure code would add something about them.

Does code really not say anything about spa installations requiring GFCI? I've never seen a spa that didn't use 240V.

Brew on

 

[Owly055]

I think you need to come back to "reality land"........ Remember what you've written here next time you are stirring a pot on your kitchen range, or loading wet clothes into your dryer. I'm imagining you running back and shutting off the circuit breaker every time you need to stir a pot, or touch the clothes drier. I sure hope you don't have copper pipe to your water heater!! Seems to me that you are dancing with death every single day....... or your wife and children are!!

Please explain to me the difference between stirring a pot on the stove...... which does not have a GFCI, and brewing.......... You depend entirely on good grounding on both the range and the drier...... How's that different from your brew stand?

H.W.

That multimeter test isn't valid. Impedence goes down pretty fast as the the frequency increases - I'm not sure what it typically is at 60Hz. People do get electrocuted all the time so, regardless of what you think your multimeter is telling you, electrocution is a reality.

The "can't let go" current level at 60 Hz is about 15mArms - I imagine that's why the GFCI level is set at 5mA. So, ohms law, if the body impedence gets below 8kohms, you're a goner (at 120Vac). On split phase, both lines are 120V to gnd.

Like you said, grounding exposed metal is a given. If there is a direct short from L->N or L->GND, the breaker will trip. But if the fault is NOT a direct short, IOW if the fault does not exceed 30A (or whatever the breaker is), it'll just sit there patiently waiting for you. If a live ckt comes into contact with the wort, will the resistance of the wort allow 30A? Maybe, maybe not. Do you feel lucky today?

 

[UndeadFred]

Unfortunately it is NOT cheap insurance, it's a false sense of security. You should check your GFCI EVERY TIME......... Checking grounding is as simple as having a push button that routes a significant load through the ground from one leg. If the ground carries the load (120 volt load), it works, and will protect you. There are a number of clever ways to do this.

H.W.

I actually said "secondary insurance". I don't think my comment contradicted anything you said or anything in your quoted reply above.

Having a trip circuit like that is a great idea. In a system like mine with the GFCI, the indication would be that the GFCI trips. I'll have to add that in the next iteration of the design. I'm about to RaspberryPi control my setup anyway, so the iteration will probably make it in after the next brew.

Interestingly enough, when I suggested this exact trip circuit as an emergency off (instead of a contactor) I was poo pooed in a major way on this very site. I don't use a contactor in my single kettle setup, I either hit the "test" button or flip the breaker to turn the system off. I'm still quite alive...

I should add that the TEST button on the GFCI only tests the GFCI itself, it does noting to verify the proper grounding in the system. It would only fail if the downstream ground (the input to the spa panel) was bad.

Fred

 

[itsnotrequired]

It's not surprising that code doesn't say anything about brewing systems. In the grand scheme of things, electric brewing systems are pretty rare compared to other household installations/appliances. If they were common, I'm pretty sure code would add something about them.

Does code really not say anything about spa installations requiring GFCI? I've never seen a spa that didn't use 240V.

Brew on

oh yes, not at all surprising it doesn't address brewing system. there is way to much electrical 'stuff' out there to address every possible scenario.

and code definitely addresses spa installations and similar 240v systems it is just that the most common locations where folks use brewing systems is in/around the the home. there are separate gfci requirements listed in the code for vending machines, carnivals/circuses, mobile/manufactured homes, recreational vehicles, floating buildings, temporary installations, pools/spas, fountains/ponds, marinas/boatyards and natural/artificial bodies of water.

most of these are areas where folks don't do any brewing but instances where 240v receptacles explicitly get called out include areas around bodies of water (within certain heights/distances). this includes lakes, pools, fountains, etc. but even these areas are limited to 20 amp circuits. around pools and boat hoists, any 240v stuff is on gfci whether it is hard wired or plug connected (for the most part, within certain distances).

one of the main reasons most of the gfci rules apply to receptacles is because that is where someone with a wet hand could get exposed to live electrical parts as they plug in/out equipment. and limited to 15/20 amp since this is the most common type of receptacle around where stuff is routinely plugged in/out. there just isn't that much 240v or 30+ amp stuff in wet areas where equipment is routinely plugged in/out so code doesn't bother addressing it.

hard-wired is a different animal in that under normal use, you just can't come into contact with live parts. that's why your electric oven/stove in your kitchen doesn't need gfci protection, even though most near everything else does. sure, you could get exposed to live parts if it malfunctioned but it is so uncommon, there isn't a need to have additional gfci requirements.

now compare this to an electric brewing system. most of them are plug connected, especially for mobile systems. folks unplug heating elements and/or pumps during the brewing process, often with wet hands. how is unplugging these items in potentially wet environments any different than in a kitchen, where the same loads would need gfci protection by code?

just seems smart to me to have gfci...

 

[passedpawn]

I think you need to come back to "reality land"........ Remember what you've written here next time you are stirring a pot on your kitchen range, or loading wet clothes into your dryer. I'm imagining you running back and shutting off the circuit breaker every time you need to stir a pot, or touch the clothes drier. I sure hope you don't have copper pipe to your water heater!! Seems to me that you are dancing with death every single day....... or your wife and children are!!

Please explain to me the difference between stirring a pot on the stove...... which does not have a GFCI, and brewing.......... You depend entirely on good grounding on both the range and the drier...... How's that different from your brew stand?

H.W.

Those are good points. However, on those devices it's hard to find access to any electrical circuit. I guess if you took a lopper to the heating coil you could. On our homemade brewing systems, I think there are a lot of opportunities for hand/water/electricity contact (not to mention many/most of these things are being built completely unqualified people who are trying to copy some schematic they found on some online forum). Pumps and liquid tubing everyone make it that much more hazardous.

BTW, my hot water heater is absolutely connected by (flexible) copper pipe to the copper supply lines that run throughout my house. I sweat the fittings myself when I installed it

 

[augiedoggy]

I think you need to come back to "reality land"........ Remember what you've written here next time you are stirring a pot on your kitchen range, or loading wet clothes into your dryer. I'm imagining you running back and shutting off the circuit breaker every time you need to stir a pot, or touch the clothes drier. I sure hope you don't have copper pipe to your water heater!! Seems to me that you are dancing with death every single day....... or your wife and children are!!

Please explain to me the difference between stirring a pot on the stove...... which does not have a GFCI, and brewing.......... You depend entirely on good grounding on both the range and the drier...... How's that different from your brew stand?

H.W.

For one thing electric stoves and dryers are not usually a DIY project made at home more times than not by an electrical amateur. Comparing them as such is wrong... and we both know that most home brewing applications have more potential for spills and "wet accidents due to pumps , valves and boilovers... thats why so many still brew in basements garages or outdoors even with electric..

Give it a few years and dryers and stoves will require them too...

 

[itsnotrequired]

Give it a few years and dryers and stoves will require them too...

its already happening, at least in locations other than dwelling units. 2017 nec added this requirement:

"all single-phase receptacles rated 150 volts to ground or less, 50 amperes or less and three-phase receptacles rated 150 volts to ground or less, 100 amperes or less installed in the following locations shall have ground-fault circuit-interrupter protection for personnel."

this applies to kitchens, bathrooms, garages, locations within 6' of sinks, etc. locations other than dwelling units would be businesses, schools, churches, etc. not there yet for dwelling units but you can see the writing on the wall...

also note the phrase 'single-phase receptacles rated 150 volts to ground or less'. your typical 120/240v single-phase system is 240v between hot legs but only 120v hot-to-ground so 120/240v systems would fall under this requirement (e.g. plug-in electric clothes dryer). also note this applies to receptacles with cord/plug connections only, not hard-wired.

 

[thekraken]

many/most of these things are being built completely unqualified people who are trying to copy some schematic they found on some online forum

It ain't the way I wanted it! I can handle things! I'm qualified! Not like everybody says... like dumb... I'm qualified and I want respect!

 

[ajdelange]

As another poster wrote "touche"................ I've worked with electronics all my life, and am well aware of how networks of resistors work.

But not apparently how GFCI breakers or grounding systems do.

The reality in this case is that the path to ground has virtually no resistance, where your body has very high resistance.

The reality is that the impedance of the path from my kitchen floor to system ground is about 4.7 MΩ dry and about 2.9 MΩ wet. The path from my basement floor (slab) to system ground is about 2.4 MΩ dry and 1 KΩ wet.

I just now moistened my finger tips and measured my internal resistance at 229K ohms. That's wet finger tip to wet finger tip.............. do the math.

The reality is that the impedance between my left wet hand and my wet feet is 5 KΩ.

how much current is going to flow through your body??? Essentially none.

120/(1000 + 5000) = 20mA.

This assuming you have some sort of good ground. So you have your hand on the brewstand, and suddenly the element shorts out.......... Where is the path to ground?

There isn't any and of course this is not what the GFCI portion of a GFCI breaker is intended to protect against. There are magnetic and thermal trips in there too and this sort of fault is what they are for.

What the GFCI portion is there for is to protect against you touching a hot wire or terminal or touching the kettle or brewstand when there is phase to kettle leakage which is not adequately grounded by the grounding conductor because of a loose terminal screw, corrosion, a broken wire or improper grounding system installation.

You not only have a very high internal resistance, but you likely are not connected to any ground except the brew stand itself, but even if you are barefoot standing in a puddle of wort over a clogged floor drain made of iron, your relative resistance is so high compared to the grounded brew stand that there will be essentially no current flow through you...... You won't feel a thing.

You (and I coincidentally) have high body impedance (in my case doubtless because TOE has induced upon me a pretty thick skin). As noted above the resistance from my wet hand to my wet bare feet is 5K. IEC's median hand to hand, intact, dry skin impedance at 100V and 50 Hz is 1850 Ω. Even with my high Z I do feel the leakage when the impedance from the bottoms of my feet to system ground is low (basement wet, not basement dry or kitchen, wet or dry)

Again I give the analogy of the grounded pliers pulling off sparkplug wires with 40,000 volts running through them. I've done this literally hundreds of times. You can watch the spark jump to the pliers, but you don't even feel a tickle even though you are bare handed.

Again this probably reflects your incomplete understanding of grounding which probably stems from not being clear on what a 'voltage' is. It is a potential measured between two points. You cannot speak of voltage meaningfully unless you specify the two points between which is specified any more than you can specify alkalinity with out specifying the two defining pH's. In the case of a house the reference point is system ground (the point in the panel where the earth and neutral or bonded). In the automobile the reference is the car's frame. The fact that the coil voltage is 40 KV in the car's frame is immaterial. What counts here is the voltage measured between one end of you and the other. The car sits on rubber tires and that sits on the bitumen or cement or whatever. Let's say it is parked on a metal plate for simplicity. Thus the circuit is from coil (40 KV re frame) through the plasma to the terminal being pulled off, through the insulation on the wire, through the uninsulated (I assume) pliers, through you, through your shoes, through the metal plate, through the tires and back to the bottom of the coil tied to the frame. Your body's impedance is going to be pretty low compared to the series resistance of the tires, the insulation and your shoes and so only a tiny fraction of the voltage is going to present itself between the hand holding the pliers and the bottoms of your feet. Don't try this demo whilst leaning with the other hand on a metal part of the car. Source impedance of the coil will probably protect you from death but then again perhaps it won't.

This, of course, has nothing to do with a GFCI's intended function. Were there GFCI protection in the ignition circuit it would not protect you against pulling a sparkplug wire while standing on the same metal plate as the car is parked on as long as your other hand is in your back pocket. I would protect against the case where you touch hi voltage whilst the other hand is in contact with the frame.

How many of your large appliances are on GFCI?

Except for the stuff in the brewery, none.

I've NEVER seen a large appliance connected to GFCI, yet you don't cringe every time you touch your kitchen range, drier, water heater, etc.

That's because faults that a GFCI is intended to protect against aren't very likely to occur (assuming proper installation) relative to the liklihood of occurance with appliances that plug into outlets. Note that the code requires GFCI on outlets near water, damp floors etc. It does not demand them for an appliance installed in a garage because you don't as a matter of course, touch the metal on your air handler.

Even your refrigerator is usually not on GFCI, though 120 can kill you just as dead as 240.

Now my refrigerator has a stainless door and where it sits (floor impedance of 2.9M wet) one would be of little use. Now were I to move that fridge (for its retirement) to the basement where floor impedance is 1K to earth if the sump pump fails I would install a GFCI for the outlet into which it would plug as, in fact the 2017 code would require me to. Also with respect to 120/240 - there is no potential in a normal home in the US which is greater than 120Vrms with respect to reference.

I'm not against GFCI except in so far as it leads to the mindset that whatever I do GFCI will protect me. A person should always design something like a brew stand as if
GFCI didn't exist.

Yes he should! And the code requires it. It does not offer the the option of installing a proper grounding system or installing GFCI breakers. It requires both (for certain locations). GFCI has an important potentially life/injury protection function. You need to understand what this is (and isn't) and how building grounding systems work. Clearly you have some distance to go here but, if it is any comfort, not many people, including professionals, really understand grounding.

 

[ajdelange]

Unfortunately it is NOT cheap insurance, it's a false sense of security.

It's not intended to be. It (GFCI) is intended to be suspenders in addition to your belt. If the floor and your feet are dry and you are wearing your Crocs (which I do as a fashion statement, not for protection from spurious currents) you don't need GFCI. It is there for when things go wrong that shouldn't go wrong.

You should check your GFCI EVERY TIME.........

You should do it periodically. Doing it every time you use it cannot, of course hurt and were I brewing once a month checking it each time would indeed be good practice.

Checking grounding is as simple as having a push button that routes a significant load through the ground from one leg. If the ground carries the load (120 volt load), it works, and will protect you. There are a number of clever ways to do this.

It's much simpler than what you propose and does not lead to objectionable current in the system. Simply stick one probe of your ohm meter in the grounding conductor hole (round) of an outlet near (can be the same) the one into which the appliance or rig is plugged and touch the other to the brew kettle, stand, sheet metal of the appliance or whatever you are testing. If the impedance is less than 1 Ω clearly your appliance is properly grounded. If you want to get fancy stick one probe of the meter into the earth (round) and the other into the wide slot (after having first verified with the voltmeter or bug that the outlet is wired correctly) of the outlet. This measures the impedance of a round trip from the receptacle to the panel half of which is the impedance of the grounding wire. You can, then, deduct half of what you measure here from what you measure from your appliance.

If you measure (appliance to system ground) 1 Ω (don't correct as the fault current has to flow to the fault point through the phase as well as back to the panel through the grounding connector) then it is clear that a phase to grounding conductor (not phase to neutral) fault will draw 120/1 = 120 amperes which is plenty to trip a breaker up to 120 amps. If it is, conversely 4 Ω then the fault current will be 120/4 = 30 amps which will not trip a 50 amp breaker. The grounding circuit in such a case needs attention (remove corrosion, tighten terminal screws etc.). Now note that you are still safe from the POV of the wires in the walls as the phase and grounding conductor are both carrying currents below the level of the protecting breaker. But lots of power is being dissipated in that extra 3 or so ohms of fault. That point will get hot and as it is probably a screw terminal possibly hot enough to start a fire but in a box, not the walls.

As the discussion here is mainly on GFCI's it is pertinent to assume that the poverty in the grounding system might occur by a corroded or loosened grounding ring at the kettle electrode. In this case we might assume that the 3 Ω is across that ring and then suppose a phase to the kettle wall fault. As objectionable current of about 30 amps is flowing across that ring the voltage on the kettle wall will be 90 volts WRT house reference. If you touch the kettle in this case and you are an IEC standard bloke (without your Crocs and wet feet) on a wet slab floor then you might have 90/3000 = 30 mA or more, as in any of the cases which can reduce human impedance below the IEC measurements, leakage through you. This, in a nutshell, is what GFCI is for.

We note again the belt and suspenders aspect of it. We had to have
1)A problem with the grounding system and...
2)A phase to grounding system fault
in order for the GFCI to step in and save the day.

 

[Owly055]

Your VOM will tell you if you have a ground, but not if it's sufficient to carry a large load. A fuse for example will show virtually zero resistance, though it may be a 1/2 amp fuse. Hence the suggestion of having a significant load.

H.W.

It's not intended to be. It (GFCI) is intended to be suspenders in addition to your belt. If the floor and your feet are dry and you are wearing your Crocs (which I do as a fashion statement, not for protection from spurious currents) you don't need GFCI. It is there for when things go wrong that shouldn't go wrong.

You should do it periodically. Doing it every time you use it cannot, of course hurt and were I brewing once a month checking it each time would indeed be good practice.

It's much simpler than what you propose and does not lead to objectionable current in the system. Simply stick one probe of your ohm meter in the grounding conductor hole (round) of an outlet near (can be the same) the one into which the appliance or rig is plugged and touch the other to the brew kettle, stand, sheet metal of the appliance or whatever you are testing. If the impedance is less than 1 Ω clearly your appliance is properly grounded. If you want to get fancy stick one probe of the meter into the earth (round) and the other into the wide slot (after having first verified with the voltmeter or bug that the outlet is wired correctly) of the outlet. This measures the impedance of a round trip from the receptacle to the panel half of which is the impedance of the grounding wire. You can, then, deduct half of what you measure here from what you measure from your appliance.

If you measure (appliance to system ground) 1 Ω (don't correct as the fault current has to flow to the fault point through the phase as well as back to the panel through the grounding connector) then it is clear that a phase to grounding conductor (not phase to neutral) fault will draw 120/1 = 120 amperes which is plenty to trip a breaker up to 120 amps. If it is, conversely 4 Ω then the fault current will be 120/4 = 30 amps which will not trip a 50 amp breaker. The grounding circuit in such a case needs attention (remove corrosion, tighten terminal screws etc.). Now note that you are still safe from the POV of the wires in the walls as the phase and grounding conductor are both carrying currents below the level of the protecting breaker. But lots of power is being dissipated in that extra 3 or so ohms of fault. That point will get hot and as it is probably a screw terminal possibly hot enough to start a fire but in a box, not the walls.

As the discussion here is mainly on GFCI's it is pertinent to assume that the poverty in the grounding system might occur by a corroded or loosened grounding ring at the kettle electrode. In this case we might assume that the 3 Ω is across that ring and then suppose a phase to the kettle wall fault. As objectionable current of about 30 amps is flowing across that ring the voltage on the kettle wall will be 90 volts WRT house reference. If you touch the kettle in this case and you are an IEC standard bloke (without your Crocs and wet feet) on a wet slab floor then you might have 90/3000 = 30 mA or more, as in any of the cases which can reduce human impedance below the IEC measurements, leakage through you. This, in a nutshell, is what GFCI is for.

We note again the belt and suspenders aspect of it. We had to have
1)A problem with the grounding system and...
2)A phase to grounding system fault
in order for the GFCI to step in and save the day.

 

[ajdelange]

Just too interesting not to post a little more data. My fridge has stainless steel drawers and doors. The impedances from the doors to system ground are both about 4Ω each which is low enough to render a 15 amp breaker sufficient to protect against a phase to door fault. The drawers run on nylon wheels and have rubber gaskets to seal them so their impedance to ground is ∞. A phase to drawer fault would not be protected against. But is there likely to be a phase to drawer fault or phase to door fault. Not likely. The place where the fault would be likely to occur (though I hope it won't) would be in the compartment where the compressors and condensers are located and the impedance to ground for the metal parts of that compartment is 0.4 Ω.

Another interesting aspect of this is that if I stand on the kitchen floor in bare wet feet and touch the phase wire in an outlet close to the fridge I would not get a shock. If I did the same thing while reaching into one of the fridge drawers I would not get a shock either but if I did it while grabbing the handle of one of the doors I would. Were the adjacent receptacle GFCI (it isn't nor does it have to be as it is just, by inches, over 6 feet from the sink) it would trip in the cases where I would get a shock. That is what a GFCI is for.

 

[passedpawn]

Your VOM will tell you if you have a ground, but not if it's sufficient to carry a large load. A fuse for example will show virtually zero resistance, though it may be a 1/2 amp fuse. Hence the suggestion of having a significant load.

H.W.

That's right. The ability of the grounding system to carry current is referred to as bonding in regulatory parlance. In fact, machines I've designed were required to have ground bonding test performed on every one before they went out the door. We alligator-clipped the leads from he tester and ran 10A (something like that) through the grounding for some time to be sure all the green/yellow wires inside had properly grounded the metal panels, from one end to the other.

 

[ajdelange]

Your VOM will tell you if you have a ground, but not if it's sufficient to carry a large load.

Clearly you haven't much experience in these matters but when an electrical installation is done one of the checks an inspector wants to see is the ground fault impedance. It uses exactly the principles I laid out above but it is done for the service, not for each circuit. An ohm meter (but one designed especially for the application) is used to measure this impedance.

What does carry a large load mean? Whatever it means it is immaterial. What is required is that the grounding circuit can pass enough current to trip the breaker in the event of a phase to grounding system fault. The loop impedance is sufficient to tell you that and the Fluke in your toolbox will measure that impedance (or the resistive part of it anyway).

 

[ChocolateMaltyBalls]

It's not intended to be. It (GFCI) is intended to be suspenders in addition to your belt. If the floor and your feet are dry and you are wearing your Crocs (which I do as a fashion statement, not for protection from spurious currents) you don't need GFCI. It is there for when things go wrong that shouldn't go wrong.

This is the salient point for any discussion about the merits of GFCI in the home brewing context. It doesn't matter how many years you've been a professional electrician or if you never changed a light bulb. What matters is you build your system with proper gauge wire, good connections, good grounds, a good diagram, etc. You can do everything by the book or even better and still get fried because it's what's outside of your control that will kill you. GFCI is the last line of defense.

The point is to have a GFCI and never need it, but if you ever need it.... then you'll REALLY need it.

 

[ajdelange]

That's right. The ability of the grounding system to carry current is referred to as bonding in regulatory parlance. In fact, machines I've designed were required to have ground bonding test performed on every one before they went out the door. We alligator-clipped the leads from he tester and ran 10A (something like that) through the grounding for some time to be sure all the green/yellow wires inside had properly grounded the metal panels, from one end to the other.

No, I don't think that is right. What we need to be assured of is that the fault loop impedance is low enough to allow a fault to trip the breaker. If you use a generator to run 10 A of current from the end of the grounding system (the series parallel connection of the green wires) most distal to the point where this network is bonded to the system reference ground and the system reference ground then you want to know the voltage it took to push that 10 amps as the ratio of the two is the impedance which is what you are actually looking for. The supply system voltage divided by that impedance is the current that would flow in the grounding system if there were a fault. If that current is greater than the breaker's rating you are OK.

I may be misunderstanding what you said as you made no reference to measuring the voltage required to push the 10 amps but it sounds to me as if you implemented an ohm meter with a power supply and a voltmeter and if that's the case what you did makes sense.

Also I think we need to emphasize that we are talking about the adequacy of the internal wiring of the building and thus discussing fault loop impedance in the case of a fault between phase and the grounding system conductor. There is more to it than that (I said it's complicated) as there is also the possibility of a ground fault (where a feeder wire falls off the pole and lies in the muck of a farm yard. Here the fault path is though the earth back to the grounding rod and into the panel. If the feeder is on a 100 amp breaker and the impedance of the grounding rod is 2Ω then 120 V can only drive 60 amps through this loop and the 100 amp breaker for this service would not open. You would be pushing 60 amps into mother earth to warm her up.

Actually, I just remembered something a colleague told me years ago. He kept his boat at a marina year round and had an electric hookup to keep a small heater in the cabin to keep things from freezing. Ice moved in and displaced pilings supporting the docking to the point that the wiring beneath the docking went into the water. The grounding system was not adequate to carry enough fault current to trip the feeder breakers and they thus warmed the bay for the month or so before the operator figured he ought to do something about this. The point of my friends story was that the marina wanted the boat owners to foot the huge electrical bills caused by the marina's incompetence.

 

[passedpawn]

No, I don't think that is right. What we need to be assured of is that the fault loop impedance is low enough to allow a fault to trip the breaker. If you use a generator to run 10 A of current from the end of the grounding system (the series parallel connection of the green wires) most distal to the point where this network is bonded to the system reference ground and the system reference ground then you want to know the voltage it took to push that 10 amps as the ratio of the two is the impedance which is what you are actually looking for. The supply system voltage divided by that impedance is the current that would flow in the grounding system if there were a fault. If that current is greater than the breaker's rating you are OK.

I may be misunderstanding what you said as you made no reference to measuring the voltage required to push the 10 amps but it sounds to me as if you implemented an ohm meter with a power supply and a voltmeter and if that's the case what you did makes sense.

Well OK, I left out exactly what the meter was doing. It applied 264VAC (I think), limited to 10A, and ensured the ground system was (from memory) under 100mohms. Something like that. Whatever IEC601 required, but I think that's it.

 

[ajdelange]

There you go. You were looking for that 0.1 Ω ground loop impedance. Thus the loop fault current would be 10 amps/volt. For example, in a 120V system that would be 1200A and any system with breakers less than that would be protected.