Checking Your Ground Connection

[hannibalmdq]

I'm in the middle of a Kal style build for a 1500W e-kettle for 2.5 gallon batches. I built the element housing this weekend and was testing continuity/resistance for my ground connection at a number of different placing on the housing.

I read that a good ground connection per NEMA is at or less than 4 ohms. I'm well under 1 ohm. Does this sound correct/decent? The resistance never stays more that .1 ohm from the resistance on the ground wire (end-to-end) itself, so I'm thinking I've got good solid connections between all the points on the housing. The .1 ohm could easily be due to the accuracy of the meter itself.

Once my locknuts arrive I'm going to connect everything to the kettle and do a bunch of tests on the kettle/housing/fittings to ground. Everything will be on a GFCI that I've verified is functioning properly.

 

[processhead]

You should be fine with low resistance reading like you reported.

Sometimes just the resistance of the meter leads and the connections from the leads to your system wiring will account for most of the resistance that you will measure.

 

[hannibalmdq]

You should be fine with low resistance reading like you reported.

Sometimes just the resistance of the meter leads and the connections from the leads to your system wiring will account for most of the resistance that you will measure.

Thanks, the locknut actually arrived today so I hooked it all up and measured the resistance at several places. It goes just above 1 ohm at some points on the kettle (thick stainless steel). Again that could just be the meter and the connections itself. The resistance measure touching the meter nodes together is between .6 and .8 ohms. The housing is consistent with that. The kettle shows more resistance though, low 1 ohms.

If I'm reading the information correctly, that should still be plenty sufficient for a ground, I believe. If the kettle was hot and I grabbed it, a 1 ohm path to ground would probably be preferable to going through me.

I'm trying to think of a short safety checklist for brew day.

1) Use GFCI tester to verify outlet in working order.
2) Verify the path to ground is intact for the housing and kettle.
3) Verify I'm wearing shoes.

I think that 30 second checklist would be sufficient for me to be comfortable that the system is in good working order. Thoughts?

 

[processhead]

Thanks, the locknut actually arrived today so I hooked it all up and measured the resistance at several places. It goes just above 1 ohm at some points on the kettle (thick stainless steel). Again that could just be the meter and the connections itself. The resistance measure touching the meter nodes together is between .6 and .8 ohms. The housing is consistent with that. The kettle shows more resistance though, low 1 ohms.

Shorting the meter leads together is standard practice before measuring resistance. It instantly tests the condition and resistance of your meter and test leads before measuring the actual resistance of the equipment you wish to test.

I'm trying to think of a short safety checklist for brew day.

1) Use GFCI tester to verify outlet in working order.
2) Verify the path to ground is intact for the housing and kettle.
3) Verify I'm wearing shoes.

I think that 30 second checklist would be sufficient for me to be comfortable that the system is in good working order. Thoughts?

Your test sounds...thorough.

Think about this. If your home is reasonably new, all of your kitchen, laundry room, and bathroom appliances are most likely protected by a GFCI.

Would you subject all those appliances to the same level of scrutiny that you are proposing for your brewing equipment?

Personally, I wouldn't.

 

[hannibalmdq]

Your test sounds...thorough.

Think about this. If your home is reasonably new, all of your kitchen, laundry room, and bathroom appliances are most likely protected by a GFCI.

Would you subject all those appliances to the same level of scrutiny that you are proposing for your brewing equipment?

Personally, I wouldn't.

I'm a bit of a worry-wort. Anyway, I see you points. Electricity just scares me. I touched the kettle with two hands this afternoon while testing it's heating power and I swear I got a shock. Except I'm like 99% sure it was impossible to receive one. I think my brain just gave me a jolt and adrenaline surge because I was touching something hot for a little too long. I'd checked the kettle for voltage and touched it with one hand several times before that.

The kettle was grounded, I verified continuity across the kettle, to the ground nut, the the housing. Etc. The GFCI was functional and I was wearing shoes. Even if the kettle ran hot, the only way I could make a connection would be to ground, meaning the GFCI should trip, or from point to point, meaning that there was a differential between the two points of the kettle and my body was the more attractive path. I can't really come up scenario where that could be the case.

I just don't know. Every test I can think to run on the system seems to indicate that it's safe and I didn't receive a shock. Still, that was a bit unpleasant. Hrmpf.

 

[ajdelange]

You could do some tests looking for stray voltages. Get a high impedance meter and measure between the thing you touched and the ground wire of an extension cord plugged into an outlet. Do the same between various points on the kettle and a fairly large metal plate (pizza platter is perfect for this) on the floor or the room. You may see a couple of volts but don't worry yet. Now shunt the meter leads with about 500Ω and repeat the tests. If you still see a couple of volts you do have a potential problem (pun not intended but it works).

 

[hannibalmdq]

You could do some tests looking for stray voltages. Get a high impedance meter and measure between the thing you touched and the ground wire of an extension cord plugged into an outlet. Do the same between various points on the kettle and a fairly large metal plate (pizza platter is perfect for this) on the floor or the room. You may see a couple of volts but don't worry yet. Now shunt the meter leads with about 500Ω and repeat the tests. If you still see a couple of volts you do have a potential problem (pun not intended but it works).

I know most of these words except shunt the meter leads with about 500 ohms. When I tested the kettle housing to the ground of another outlet I saw 0.7V. That's a pretty small potential difference. I tried testing it to the oven or the ground but I didn't get anything. To the sink faucet gave me 0.7V.

I'm trying to convince myself this is save. Any help is appreciated. I really don't think I shocked myself but damn that felt funny.

 

[ajdelange]

This can get awfully tricky but you want to be conservative to insure your safety. There should be 0 volts between any two points connected to the building grounding system (the network of bare copper wires running around your house). That is because no current is to flow in that set of conductors unless there is a fault. This is insured by connecting the grounding conductor system and the grounded conductor system, the network of white (neutral) wires together only at one point (the service entrance). I mention this because there are many here who are quite cavalier about interconnecting elsewhere and you never what a previous owner may have done. This can cause the flow of 'objectionable current' in the grounding conductors which is the source of potential (voltage) differences between the ground pins of different outlets or your kettle, connected to the grounding system at one point and another point (outlet) on it.

"Shunt a 500Ω resistor across the meter" means connect the resistor between the red and black leads thus converting the high impedance meter to a low impedance meter. The 500Ω simulates you. If there is a potential difference stiff enough to put 5 volts across a 500Ω resistor the resistor will be carrying 10 ma and that potential difference can push 10 ma through you.

There should also be 0 volts between any point on the grounding system and true ground. Sometimes this is not the case and where it is not it is often nothing within the control of the homeowner. So if you get a tingle while touching the kettle while touching nothing else and standing on the floor it is more likely that you grounding system is carrying objectionable current responsible for raising the kettle potential above ground than that the earth under your feet is at different potential than the building grounding system because of something the utility needs to address (at least that's what they will tell you).

Repeat your tests with the low impedance meter and hope that the voltages you have seen without the resistor across it go away (or go way down).

 

[processhead]

It is a good practice to be cautious and thorough while building and testing a panel/system. You want to find any issues or wiring errors long before your first brew day.

Your test for stray voltage with your meter on the kettle with the meter referenced to a known ground is the right way to do it.

I would not worry about the .7 volts you measured. Inexpensive meters in particular are prone to picking up induced AC voltage when high power equipment is being used near by.

Relax and brew a batch after everything is up and running properly (with water).

 

[hannibalmdq]

It is a good practice to be cautious and thorough while building and testing a panel/system. You want to find any issues or wiring errors long before your first brew day.

Your test for stray voltage with your meter on the kettle with the meter referenced to a known ground is the right way to do it.

I would not worry about the .7 volts you measured. Inexpensive meters in particular are prone to picking up induced AC voltage when high power equipment is being used near by.

Relax and brew a batch after everything is up and running properly (with water).

Okay, I'm picking this back up now and trying to test some things out. I'm still not 100% I was or wasn't shocked. If I was shocked, it means I completed a circuit. The most common way would be to touch a live surface while grounded. If this was the case, I should've tripped the GFCI because current wouldn't have been leaving the system. So, I shouldn't have been shocked. I have a physical GFCI tester and the outlet was tests fine. This makes me believe that I didn't get shocked this way.

The second way would be the circuit. I didn't grab the hot wire at any point, just two sections of the kettle about 5 inches from one another. So, in order for me to complete the circuit, (a) the kettle would have had to be hot and (B) there would have had to be a voltage gap across the kettle with a resistance more than myself. As far as I know, the kettle wasn't hot. I've measured a 0.7 V difference between the kettle and another ground but that was probably just interference and my cheap meter. I've tested for continuity around different parts of the kettle and the resistance across the surface seems to be between .7 and 2 ohms. It normally settles just under 1.

All of this together leads my to believe that whatever I felt this afternoon had more to do with the heat than electricity.

Everything that I test seems to indicate that (a) the kettle isn't hot and (b) there's a path to ground less than say 5 ohms everywhere in the system.

Does that make sense? Did I just scare myself into a bunch of extra worry because I touched a hot (temperature) kettle for a bit too long. I swear I felt a hum and that's what has my worried I'm missing something.

 

[processhead]

If you have ever experienced an electrical shock before, you would recognize it.

 

[hannibalmdq]

If you have ever experienced an electrical shock before, you would recognize it.

I don't think I've shocked myself since before college and that was over a decade ago.

The only thing in this setup that I can see that I'm unsure about is that when I go to measure the resistance across the kettle to ground. It tends to start at about 10 ohms and then drop down to 0.9 to 1.9 ohms over a second or two(the meter shows 0.7 ohms from node to node). Is this likely just the cheap meter/not making a firm enough connection with the little probes?

 

[brew_ny]

If you have ever experienced an electrical shock before, you would recognize it.

I have but I do not remember it well

 

[hannibalmdq]

This all has to be in my head. I've got the kettle running now and I can find no voltage between the kettle and the ground of another outlet. All my concerns about ground and other things aside, this basically means that the kettle isn't hot, rendering all my other concerns mute. I'm kinda amped up about this whole thing though. I'll let it run for a little while, check the kettle against a known ground again and call it a night.

I think I'm just going to have to have someone look at it with me and arrive at the same conclusion before I'm comfortable. I can't shake the feeling that something is off, but I have no real reason to suspect that.

 

[orangehero]

Depending on how often you brew if you trip the GFCI every brewday you will wear it out. I don't know how quickly off the top of my head, but it's something to consider.

 

[ajdelange]

I would not worry about the .7 volts you measured. Inexpensive meters in particular are prone to picking up induced AC voltage when high power equipment is being used near by.

I would if the voltage is measured with a shunt in place. Expensive meters are prone to pickup via capacitative coupling as well as cheap ones. Any meter with a high input impedance is. That's why the shunt is used.
[/QUOTE]

 

[ajdelange]

It tends to start at about 10 ohms and then drop down to 0.9 to 1.9 ohms over a second or two(the meter shows 0.7 ohms from node to node). Is this likely just the cheap meter/not making a firm enough connection with the little probes?

More probably the meter has a built-in low pass filter for noise immunity. I just checked a Fluke 87V and it does not show that behavior on the ohms scale.

 

[hannibalmdq]

I would if the voltage is measured with a shunt in place. Expensive meters are prone to pickup via capacitative coupling as well as cheap ones. Any meter with a high input impedance is. That's why the shunt is used.

[/QUOTE]

Where could I pick up one of these shunts? I'm running a boo of test right now and I can't find any voltage between the kettle and ground or across the kettle itself.

 

[ajdelange]

If you don't see any voltage without the shunt you won't see any with but the answer to the question is that you go to Radio Shack (if there is still one open in your area) and buy a couple of resistors and a banana plug adapter like these http://www.ebay.com/itm/4-PCS-Dual-...003?pt=LH_DefaultDomain_0&hash=item20f8baf33b. You use the screw terminals on the adapter to connect the resistor, plug the adapter into the meter and the test leads into the adapter. Some meters have the banana plug on the test lead shrouded in such a way that it can't plug into the adapter. In that case you buy a couple of extra test leads and cut off the shroud so that it will plug into the adapter.

 

[hannibalmdq]

Thanks, I may pick some up just to have on hand. I just completed a 60 minute boil. I checked several times and several locations, but I couldn't find a voltage on the kettle to another ground or across the kettle itself. I even waited 40 minutes between checks to see if there was some sort of buildup of charge on the kettle over time.

I can't really think of anything else to verify. I've got continuity from kettle to ground and I know the kettle isn't hot anyway.

At this point, I'm inclined to think the kettle is safe. I really can't think of anything else to even check.

Whatever I felt early today must have been some combination of things that wasn't related to the electrical safety of the kettle. I'll keep my multimeter on hand for the first couple brew days just in case.

Thank you everyone. I appreciate all the input.

 

[jeffmeh]

You have likely by now tested your ground an order of magnitude more than most do. Brew. Lol