The NEC and the 80% rule and Homebrewing

[mattd2]

there is a lot of recomendation on here that the total current draw must be under 80% of the protecting circuit breakers rated limit to be compliant to the NEC, specifically because of derating for continuous loads. I have always wondered if the NEC continous load rules actually applies for homebrewing. Today I read an forum post that actually stated what is meant by continuos load as per the NEC interpritation.
Article 100 defines a continuous load as a load that operates for three hours or more.
I have never had my element on 100% for 3 hours during a brewday.
lets look at a typical 3 vessle brewery withh 5500 watt elements in the HLT/BK
The HLT probably runs 100% for 1/2 hour to heat strike/sparge water. The during the mash it is only keeping the HLT at mashout temp so running max 25% for 1 hour.
Then a bit of downtime while sparging, etc.
The the boil kettle is on 100% to get up to boil for about another 1/2 hour, then it is cut back to 50(ish)% for the remainder of the boil.

Throughout that the load is not continously on for more that 3 hours.

It just seems like people are being recommended to go larger when they are only sitting at 80-90% of their breaker rating during the peak usage, not continously for more than 3 hours.

So can anyone clear up when you would need to apply the 80% derating with regards to homebrewing?

 

[kenh]

Per my electrician brother in-law.

The NEC 80% derating applies to the wiring that's already in your walls, not to the fixtures you plug into that wiring.

The 14 gauge house wiring being protected by 15 amp breakers is already derated to 80% which is why its 15 amps. That same 14 gauge wire is perfectly acceptacle for up 20 amps in chassis & conduit wiring!

The 12 gauge house wiring being protected by your 20 amp breakers is already derated to 80% which is why its 20 amps. That same 12 gauge wire is perfectly acceptacle for up 25 amps in chassis & conduit wiring!

The 10 gauge copper wiring or 8 gauge aluminum wiring that runs to your dryer outlet follows the same derating rules as the other two gauges but 10 gauge copper is on the fence which is why you should do long 30 amp copper runs in 8 gauge, or just use aluminum for 30 amps.

http://www.usawire-cable.com/pdfs/NEC AMPACITIES.pdf

Or look at this another way - if the rule was true as you quoted then how would the average homeowner know that he has more than 16 amps plugged into his 20 amp kitchen outlets? The breaker won't trip until he passed 20 amps!

 

[skunkfunk]

One reason to derate is so that you don't get nuisance trips. Particularly true if you're using pumps, or any other kind of motor.

 

[augiedoggy]

One reason to derate is so that you don't get nuisance trips. Particularly true if you're using pumps, or any other kind of motor.

That doesn't normally apply here in a 220v setup unless your pumps are being wired to run off of the dedicated 220v line which they shouldn't be...
I understand why they did it but still thing it silly to rate something and then derate it lower.... why all the confusion? Look at dryer outlets in general? They are now 4 wire instead of 3.

Its like construction regulations.... I took building trades in boces and found out when I rebuilt my front porch that the specs for safe spans and loads have all changed in the last 15-20 years from what's in my books. What was safe then is now not considered safe even though the lumber specs have not changed in that time period..... people just need something to constantly change somewhere to justify their jobs..... I mean really how much load is my from porch going to see that a 10ft 3" 2x10 spaced 16" oc can't bear the weight of the people walking arcoss it?? They spec it for loads such as appliances and heavy furniture even though its just a front porch and the last one only used 2x8's for the same size porch that was there with no suuport issues for 95 years!! Is everyone really that much more obese!
The inspector made me double up every other floor joist.... which meant another delivery of 12ft 2x10s

 

[skunkfunk]

That doesn't normally apply here in a 220v setup unless your pumps are being wired to run off of the dedicated 220v line which they shouldn't be...
I understand why they did it but still thing it silly to rate something and then derate it lower.... why all the confusion? Look at dryer outlets in general? They are now 4 wire instead of 3.

Its like construction regulations.... I took building trades in boces and found out when I rebuilt my front porch that the specs for safe spans and loads have all changed in the last 15-20 years from what's in my books. What was safe then is now not considered safe even though the lumber specs have not changed in that time period..... people just need something to constantly change somewhere to justify their jobs..... I mean really how much load is my from porch going to see that a 10ft 3" 2x10 spaced 16" oc can't bear the weight of the people walking arcoss it?? They spec it for loads such as appliances and heavy furniture even though its just a front porch and the last one only used 2x8's for the same size porch that was there with no suuport issues for 95 years!! Is everyone really that much more obese!
The inspector made me double up every other floor joist.... which meant another delivery of 12ft 2x10s

It's true that much of the NEC is driven by the manufacturers in the industry trying to make a buck (see the ridiculous bit about arc fault breakers added in 2011.) But in this case, thermal-magnetic breakers have always only been rated to continuously carry 80% of their rated load. On a hot day, or without enough ventilation, they really can trip if you load them to the hilt for too long.

They do sell breakers that are rated to carry 100% of their rating continuously, and with customizable trip settings, but those utilize electronic trip relays and are generally much more expensive.

 

[augiedoggy]

I utilize a volt/amp meter that measures the draw on my 4500w two element setup and I have to say it rarely hits 18.2 amps for more than a second unless I heating my mash/sparge water and I do run my pumps off the same power since they are 12v and ran off a supply that also powers my relay coils and fan.. I ran 10/3 (which is actually 4 wires??) For my setup and only one element is ever active at a time but I bet 12 gauge wiring would have worked with no issues for a dedicated use such as this.... For peace of mind I spent the extra $100+ dollars on the 10/3 even though I have rolls of 12/2 laying around...
I don't ever want to have to be explaining something like this to the fire dept or my insurance rep if there was an issue.
I found it interesting that the125ft roll of 3 wire 8/2 was cheaper than the 100ft roll of 10/3 at home depot..... someone taking advantage of supply and demand with markups?

Like previously mentioned the only time my 30a system sees a continuous Load of 18.2 amps is when heating water in the hlt for maybe 30 mins max

 

[augiedoggy]

I will add that the house next store to me suffered a large fire from the use of an air conditioner on too small of an extension cord...
If your wires get warm to the touch your pulling too much power through them.

 

[ivegot2legs]

A lot of times it's the connections that can be troublesome. They may not be rated for heavy use at 100% load.

I always view the ratings as nominal. A 20A breaker is a nominal rating and it's only rated for 16A. Like how a 2x4 doesn't measure 2"x4".

And the insurance/fire thing is also valid. It'd be tough to lose everything to a fire because someone tried to save $50 on parts, and then be denied insurance because it wasn't code compliant.

 

[skunkfunk]

I will add that the house next store to me suffered a large fire from the use of an air conditioner on too small of an extension cord...
If your wires get warm to the touch your pulling too much power through them.

Yeah, it drives me crazy that you buy at the store a 100 ft, 16 gauge extension and plug it into a 20A outlet. Voltage drop is so bad it'll barely power yard tools, vacuum cleaner, etc.

 

[kenh]

A lot of times it's the connections that can be troublesome. They may not be rated for heavy use at 100% load.

I always view the ratings as nominal. A 20A breaker is a nominal rating and it's only rated for 16A. Like how a 2x4 doesn't measure 2"x4".

And the insurance/fire thing is also valid. It'd be tough to lose everything to a fire because someone tried to save $50 on parts, and then be denied insurance because it wasn't code compliant.

Hmm, I have a 20 Amp breaker in my hand and it is clearly marked 20 Amps, no-where on the breaker is 16 Amps mentioned.

 

[skunkfunk]

Hmm, I have a 20 Amp breaker in my hand and it is clearly marked 20 Amps, no-where on the breaker is 16 Amps mentioned.

That's the intermittent rating. The 16 amps is mentioned in other documentation.

 

[gtmaus]

There is a lot of misinterpretation and wrong info here about the NEC code book. That table 310.16 (the one linked above) is not as simple as everyone makes it out to be. There are numerous exceptions, exemptions and asterisks to be looked at. One asterisks stated at the bottom of the table in the NEC take you to article 240.4(D)
which states

Unless specifically permitted in 240.4(E) or 240.4(G) the overcurrent protection shall NOT exceed 15 amperes for 14 AWG, 20 amperes for 12 AWG and 30 amperes for 10 AWG copper, or 15 amperes for 12 AWG and 25 amperes for 10 AWG aluminum and copper-clad aluminum after any correction factors for ambient temperature and number of conductors have been applied.

I've been an electrician for over 20 yrs and have personally witnessed the aftermath of someone using the wrong size wire or overcurrent protection. It's not worth it to save a few buck on materials.

Just don't want to see someones house burn because they took some bad advice off an internet forum.
Sorry for the rant. I'm off my soapbox now. Continue

 

[skunkfunk]

There is a lot of misinterpretation and wrong info here about the NEC code book. That table 310.16 (the one linked above) is not as simple as everyone makes it out to be. There are numerous exceptions, exemptions and asterisks to be looked at. One asterisks stated at the bottom of the table in the NEC take you to article 240.4(D)
which states

Unless specifically permitted in 240.4(E) or 240.4(G) the overcurrent protection shall NOT exceed 15 amperes for 14 AWG, 20 amperes for 12 AWG and 30 amperes for 10 AWG copper, or 15 amperes for 12 AWG and 25 amperes for 10 AWG aluminum and copper-clad aluminum after any correction factors for ambient temperature and number of conductors have been applied.

I've been an electrician for over 20 yrs and have personally witnessed the aftermath of someone using the wrong size wire or overcurrent protection. It's not worth it to save a few buck on materials.

Just don't want to see someones house burn because they took some bad advice off an internet forum.
Sorry for the rant. I'm off my soapbox now. Continue

You are correct, however, it is very common to have 14 gauge wire going to 15 amp receptacles (and lighting, for that matter) in residential applications off of a 20 amp breaker. No-one ever got hurt running 30 feet of 14 gauge wire to a receptacle. I don't know if they still do that, but the houses I've lived in have had some of that.

For what it's worth, my firm never specifies anything smaller than #12, even on a 15 amp circuit, except for low voltage control wiring.

 

[augiedoggy]

There is a lot of misinterpretation and wrong info here about the NEC code book. That table 310.16 (the one linked above) is not as simple as everyone makes it out to be. There are numerous exceptions, exemptions and asterisks to be looked at. One asterisks stated at the bottom of the table in the NEC take you to article 240.4(D)
which states

Unless specifically permitted in 240.4(E) or 240.4(G) the overcurrent protection shall NOT exceed 15 amperes for 14 AWG, 20 amperes for 12 AWG and 30 amperes for 10 AWG copper, or 15 amperes for 12 AWG and 25 amperes for 10 AWG aluminum and copper-clad aluminum after any correction factors for ambient temperature and number of conductors have been applied.

I've been an electrician for over 20 yrs and have personally witnessed the aftermath of someone using the wrong size wire or overcurrent protection. It's not worth it to save a few buck on materials.

Just don't want to see someones house burn because they took some bad advice off an internet forum.
Sorry for the rant. I'm off my soapbox now. Continue

so all that being said shouldn't a line rated for 20 amps be able to handle a load of 18 amps safely?. Especially if its for no more than an hour at a time and a dedicated circuit? Why not just put a 16 instead of a 20 on 12 gauge circuits if that's all they are safe for in most cases? Why confuse the hell out of everyone with double standards that counterdict one another?
In layman's terms...please set us straight.
Btw I've been told all commercial wiring in NY state is at least 20a .... 15a is only allowed in residential applications

 

[skunkfunk]

so all that being said shouldn't a line rated for 20 amps be able to handle a load of 18 amps safely?. Especially if its for no more than an hour at a time and a dedicated circuit? Why not just put a 16 instead of a 20 on 12 gauge circuits if that's all they are safe for in most cases? Why confuse the hell out of everyone with double standards that counterdict one another?

There's a lot of rules. The rules for sizing service conductors are different, it's different if it's in open air or a cable tray, it's different if it's in an area with a different ambient temperature, for other wire sizes you can go to the next standard size breaker, etc. It's too complicated to explain in one post.

That all said, you're perfectly safe and code compliant having #12 wire on a 20A circuit.

Your example with the 5500 watt element, however, doesn't work. That's 23 amp load on a 240V circuit.

 

[gtmaus]

Common?? maybe on non inspected work. Any inspector worth a grain of salt should fail that installation. What people need to understand is that breakers are not installed for personal protection. They are for protecting the wire and that's all. 20A ran on 14 AWG wire, the wire and insulation will heat up, break down, burn up (however you like to describe it) before the breaker trips. You are correct, electrically it will work for some amount of time. Correct over current protection is more an electrical fire thing than a personal protection thing.

 

[augiedoggy]

You are correct, however, it is very common to have 14 gauge wire going to 15 amp receptacles (and lighting, for that matter) in residential applications off of a 20 amp breaker. No-one ever got hurt running 30 feet of 14 gauge wire to a receptacle. I don't know if they still do that, but the houses I've lived in have had some of that.

For what it's worth, my firm never specifies anything smaller than #12, even on a 15 amp circuit, except for low voltage control wiring.

14 gauge wire on a 20 amp breaker is a no no.... you see it because people either cut corners or didn't know what they were doing. 15 amp breakers are for the 14 gauge.

 

[gtmaus]

There's a lot of rules. The rules for sizing service conductors are different, it's different if it's in open air or a cable tray, it's different if it's in an area with a different ambient temperature, for other wire sizes you can go to the next standard size breaker, etc. It's too complicated to explain in one post.

I completely agree with this. It's way to complicated to explain since there are so many factors to contend with. When explaining electrical to DIYers I try to emphasize that over sized wire is just overkill while under sized wire is dangerous.

 

[augiedoggy]

There's a lot of rules. The rules for sizing service conductors are different, it's different if it's in open air or a cable tray, it's different if it's in an area with a different ambient temperature, for other wire sizes you can go to the next standard size breaker, etc. It's too complicated to explain in one post.

That all said, you're perfectly safe and code compliant having #12 wire on a 20A circuit.

Your example with the 5500 watt element, however, doesn't work. That's 23 amp load on a 240V circuit.

I use a 4500w element.... only draws 18.25 amps....that's all I ever mentioned. I ran 10/3 but I'm curious if I could have got away with using 12 gauge.

 

[gtmaus]

at least here in St. Louis 15A circuits are mainly for resi work. Almost all comm or industrial circuits are 20A.

 

[gtmaus]

I use a 4500w element.... only draws 18.25 amps....that's all I ever mentioned. I ran 10/3 but I'm curious if I could have got away with using 12 gauge.

You probably would've been alright with 12 AWG. It's not a motor load circuit so it won't have the initial current surge that motors have when they start up. I personally don't care for pushing the limits of breakers. IMO electrical equipment wears out considerably faster when it's taken to the max.

I ran 10/3 to power my control box, 12/2 for my exhaust fan and a 12/2 for my pumps. Overkill? Yes, but I shouldn't ever have any issues

 

[skunkfunk]

I use a 4500w element.... only draws 18.25 amps....that's all I ever mentioned. I ran 10/3 but I'm curious if I could have got away with using 12 gauge.

Well, there was this bit in your first post . . .

lets look at a typical 3 vessle brewery withh 5500 watt elements in the HLT/BK

But yes, you would have got away with it. I would have used #10 wire. If it makes you feel any better, you'll get a little bit better efficiency (and more heat) out of your 4500w element with #10 feeder than you would have with a #12, due to a tiny bit less voltage drop.

Oh, and you won't have to redo the wiring if you move up to 30A circuit.

gtmaus, do you not use the occasional 15A breaker? Small enough motor and the 250% short circuit protection rule still leaves you at 15A, and you see 15A MOCP marked on them sometimes.

Edit: Never mind gtmaus, missed the word "almost."

 

[LordUlrich]

What it comes down to is that breakers are there to prevent fire. The more amps you draw the hotter a wire will get.

The listed rating is for instantaneous load. A 20 amp breaker will take up to 20 amps for a instant. It will also take 80% of that load (or 16 amps) continuously. Between those 2 points is a curve which is somewhat more complex than more people what to think about, SO if you are looking at a load for any period of time is is easier to just derate to 80%.

Also many people run pumps off the same circuit as their heating elements, that is part of why you would want to bring the neutral into the control panel. If you have have a neutral you can run 240 and 120 circuits (although you probably should have breakers in your panel. That is also part of why dryer plugs have 4 wires, 2 for the high power, a neutral for the 120 circuits like the controls, and a ground for safety, many older appliances do not have as much computer circuitry inside so the neutral was not used.

 

[augiedoggy]

Well, there was this bit in your first post . . .

But yes, you would have got away with it. I would have used #10 wire. If it makes you feel any better, you'll get a little bit better efficiency (and more heat) out of your 4500w element with #10 feeder than you would have with a #12, due to a tiny bit less voltage drop.

Oh, and you won't have to redo the wiring if you move up to 30A circuit.

gtmaus, do you not use the occasional 15A breaker? Small enough motor and the 250% short circuit protection rule still leaves you at 15A, and you see 15A MOCP marked on them sometimes.

Look again at your second quote.... that wasn't from me..

I did run 10/3 and do use the neutral for my 12/24v DC power supply inside my panel which runs off 120v... The most my volt and amp meter ever show as draw is 18.2 amps but I have it set to just measure draw from the elements not the whole control panel... that being said I agree it was a better choice to run the correct 10/3 wire... plus it made it easy to wire the spa panel gfci next to my control panel.
I just wanted clarification for what's really safe and meets code and what doesn't. I'm not trying to discredit anyone or their comment just get the facts straight.

 

[skunkfunk]

Look again at your second quote.... that wasn't from me..

Oops. Thread went on long enough that I got all turned around

 

[gtmaus]

Very nicely put LordUlrich!!!

Skunkfunk - sure if the application call for it. I work solely in commercial and industrial so most of the motors I deal with have the addition of motor starter, freq drives and whatnot

 

[kenh]

so all that being said shouldn't a line rated for 20 amps be able to handle a load of 18 amps safely?. Especially if its for no more than an hour at a time and a dedicated circuit? Why not just put a 16 instead of a 20 on 12 gauge circuits if that's all they are safe for in most cases? Why confuse the hell out of everyone with double standards that counterdict one another?
In layman's terms...please set us straight.
Btw I've been told all commercial wiring in NY state is at least 20a .... 15a is only allowed in residential applications

Yes, that's the point I made in an earlier post. A 30 Amp circuit is good for 30 Amps just like a 20 Amp circuit is good for 20 Amps. The current capacity has already been de-rated 20% in your house wiring before the plug.

But a few "experts" on this list and others want to apply the de-rating AGAIN, making a 20 Amp circuit a 16 Amp circuit and a 30 Amp circuit a 24 Amp circuit!

 

[skunkfunk]

Yes, that's the point I made in an earlier post. A 30 Amp circuit is good for 30 Amps just like a 20 Amp circuit is good for 20 Amps. The current capacity has already been de-rated 20% in your house wiring before the plug.

But a few "experts" on this list and others want to apply the de-rating AGAIN, making a 20 Amp circuit a 16 Amp circuit and a 30 Amp circuit a 24 Amp circuit!

You are incorrect. I feel like we've just about beat this horse dead. Continuous vs. Non- continuous and whatnot.

 

[LordUlrich]

Yes, that's the point I made in an earlier post. A 30 Amp circuit is good for 30 Amps just like a 20 Amp circuit is good for 20 Amps. The current capacity has already been de-rated 20% in your house wiring before the plug.

But a few "experts" on this list and others want to apply the de-rating AGAIN, making a 20 Amp circuit a 16 Amp circuit and a 30 Amp circuit a 24 Amp circuit!

Nobody is saying a 20 amp circuit is not good for 20 amps, we are saying a 20 amp circuit is not good for 20 amps for an extend period of time.
The breaker will trip, it happens all the time with space heaters. I have, not paying attention to which plug is which circuit plugged 2 space heater into the same circuit, and after a half hour or so they both quit. Space heaters pull about 9 amps, so I am fine with one, but 18 amps for too long and the breaker will trip.

ALSO every part of the circuit must be able to take the current, as the current goes through every part of the circuit. If I setup a circuit with #8 wire and then spliced it with a piece of #18, I cant run 50 amps through that circuit, the #18 would burn up. You can't say that part of the circuit can take 20 amps, so this part can be rated to 10 amps and I am fine.

Now there is some room for discussion as to if the gauge of the cable needs to be the same as the gauge of the wire in the wall. I have no idea what code says on that issue.

 

[The10mmKid]

I use a 4500w element.... only draws 18.25 amps....that's all I ever mentioned. I ran 10/3 but I'm curious if I could have got away with using 12 gauge.

Yes
Use a good quality cord labeled for at least 60degC

SoapBox/ON:

It is called a code for a reason . . . it is not a law.

It is so everybody in the country can be on the same page, discussing and installing pretty much the same way. Eliminates surprises and keep us safer.

Some things will be discovered down the road and the 'code' will change once again to reflect the new insight.

Imagine all the 'Grandfathered' electrical systems in the US that the current code now deems outdated. Want to make it the law and have a certain amount of time to get in compliance? I don't.

Think also that the code as written years/decades ago has kept us safer thus far.

As been mentioned here and everywhere, adhere to the code or be damn close. Sleep well at night knowing you didn't put folks in danger taking shortcuts.

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'da Kid