Two 24 amp heaters, one 60amp breaker.

[cthulu]

I have a thread on the heating/ac forum below

https://www.garagejournal.com/forum/showthread.php?t=370389

Basic premise is I wired a 60amp breaker and 6awg thhn for one large 10000 watt heater but am now thinking two 5000 watt heaters is the more efficient route. (200$ for both 5000 watt heaters vs 7-800$ for one 10000 watt)

I was looking to wire both 24amp heaters with 8 gauge going back to the breakout box that has 6awg run to it from the panel which has a 60amp breaker.

I couldn't think of anything wrong with it as both heaters will be on at the same time using up roughly the same load as one large heater. Wanted to see what you guys thought though.

 

[mm08822]

I have a thread on the heating/ac forum below

https://www.garagejournal.com/forum/showthread.php?t=370389

Basic premise is I wired a 60amp breaker and 6awg thhn for one large 10000 watt heater but am now thinking two 5000 watt heaters is the more efficient route. (200$ for both 5000 watt heaters vs 7-800$ for one 10000 watt)

I was looking to wire both 24amp heaters with 8 gauge going back to the breakout box that has 6awg run to it from the panel which has a 60amp breaker.

I couldn't think of anything wrong with it as both heaters will be on at the same time using up roughly the same load as one large heater. Wanted to see what you guys thought though.

You will need to run #6 to each heater if you keep them both on the same single circuit with a 60A cb.

Otherwise run 2 ckts from the panel 30A/#10 each or add ocp at the location where you intend to transition from 6 to 8 - basically a subpanel.

 

[Bert_]

Regardless of the wire size you run to the heaters I would say no.

In article 242 the code says in your application multiple heaters can be fed from a 30 amp or less circuit. Anything larger would then need to have it's own circuit.

I had actually considered this approach a year or so ago, but did not pursue it for the reason above.

 

[sberry]

It has been a long time since I read it and don't know it all that well anyway but that may have something to do with receptacles, not exactly the same when hard wired?

 

[ForceFed70]

You need separate circuits for each heater. What happens if there's an internal short in your heater? 60A before it trips - plenty of chance for wiring designed for 30A to start a fire before the circuit is interrupted.

 

[theoldwizard1]

Tandem 30A 240V breakers.

 

[cthulu]

Tandem 30A 240V breakers.

I am leaning in the two heaters direction but now I'm in a bit of a pickle. The points brought up here are good ones regarding the internal wiring of the 24 amp heaters though.

Currently the 6awg coming from the subpanel with the 60amp breaker is in a 4 11/16th box and everything is EMT. What would be a good way to split off from that breaker box into two 30A breakers? I looked at small subpanels but they all seem pretty for just two 30A 240b breakers.

 

[wyliesdiesels]

What does the manu call for in the manual?

 

[mm08822]

Bert is correct....NEC 424.3 limits the branch circuit ocp to 30A for multiple heaters on a single ckt.

Replace the 4-11/16 sq box with a 6 space main lug panel ($20-$30) and add 2 2P30A cbs.

If the 6's aren't pulled yet consider running 4 - 10's instead if conduit fill and conductor derating permit.

 

[sberry]

It may limit them if they use recepticals. If the wire is big enough to supply the heater which the 10 is then the over current needs to be within its short circuit rating, which is 60. Think how a range is wired internally or a cooktop and oven wired on the same circuit. You can't do it thru recepts though.
I don't have a book here but I recall something about recepticals in there somewhere.
Like many specialized circuits when they are hard wired or have multiples on them the breaker doesn't provide thermal, only fault. What provides thermal is that the wire is 125 percent required for the load.

 

[mm08822]

It may limit them if they use recepticals. If the wire is big enough to supply the heater which the 10 is then the over current needs to be within its short circuit rating, which is 60. Think how a range is wired internally or a cooktop and oven wired on the same circuit. You can't do it thru recepts though.
I don't have a book here but I recall something about recepticals in there somewhere.
Like many specialized circuits when they are hard wired or have multiples on them the breaker doesn't provide thermal, only fault. What provides thermal is that the wire is 125 percent required for the load.

Nec 424.3 makes no distinction for hard-wired or receptical based connections. 30a is the max ocp for multiple connected heater ckts.

 

[sberry]

I just got to my office, for giggles I looked it up. Correct and I couldn't remember the language, it doesn't say recept but outlets. The limitation is for 2 or more.
(fwiw, it does mention that it doesn't apply to integral,,, hence the range I mention in another post.) You may be correct as it doesn't list feeds as tap conductors like in cooking equipment.

 

[sberry]

210 may also limit how welder outlets may be wired if there is 2 or more. In theory a wire that was thermal protected by the breaker could be tapped with multiples.

 

[wyliesdiesels]

Tandem 30A 240V breakers.

FYI tandem breakers aka twins are 2 pole 120v

 

[sberry]

It reads like if he took them from the same point it would be legal It then follows with infrared being limited to 50 in non occupancies.

 

[Aceman]

Tandem 30A 240V breakers.

That's called a quad 30/30.

 

[sberry]

Pictures of breakers are good but I thought maybe Ace, Alfred, maybe Norcal or Wlylie would jump in here with some clarification. It really was curiosity as it doesn't say a circuit larger than 30 cant power the heaters but only that it can't supply 2 or more outlets.
Outlet is described as a point where the power is taken, if it's taken from a single point then it may be allowed?

 

[mm08822]

Pictures of breakers are good but I thought maybe Ace, Alfred, maybe Norcal or Wlylie would jump in here with some clarification. It really was curiosity as it doesn't say a circuit larger than 30 cant power the heaters but only that it can't supply 2 or more outlets.
Outlet is described as a point where the power is taken, if it's taken from a single point then it may be allowed?

The difference is multiple heaters fed from one ocp device where that ckt is sized for 125% or more of the total connected loads. "One outlet" could be construed to be a single j-box where 2 heaters connect at that point, but it is 2 loads connecting to the ckt.

Heater wiring instructions typically list the max ocp permitted to protect the heater. So that right there creates a requirement to preserve the ul listing as the mfr has specified installation details that must complied with.

In a single heater installation 125% of its load alone is much closer to that single heaters needed available current. Heaters are assumed to be a contiuous load.

In the 2 heater circuit scenario (assume same size for this example), if only 1 heater were operating and it faulted with a bad heating element, it possible that that unit could draw a fault current of possibly 150% more than intended/expected draw. This could easily melt down the internal insulation within that unit before the ckt ocp even though of tripping on ol. This type of fault could easily make the original fault mode cascade into a much larger fault by decreasing the resistance of that fault as more insulation melts down.

The explanitory notes in the nec handbook explain these thinkings.

Even heaters greater have 50kw are expected to have internal ocp to sub-divide the overall heater banks into less than 48a again to limit available fault energy. Nec 424.22

Im assuming as heaters are high on the list of faulting devices due to their very nature of continually degrading the internal materials from high heat exposure, nec has partially addressed the ocp requirements both external and internal to the unit.
This is somewhat contradictory to other gp circuits where plugging in 18-2 zip cord fed device while that ckt has 20a ocp!

 

[sberry]

I believe the 125% was for the wire.

"One outlet" could be construed to be a single j-box where 2 heaters connect at that point, but it is 2 loads connecting to the ckt.

As we know the code isn't written so it could be construed and it didn't say 2 units couldn't be connected. There is a definition for it as the point it is taken, means it cant be taken from multiple points. Didn't say 2 loads, only 2 or more outlets.
It says that the ocpd shall not be less than 125%. It goes back to 240.4B,1 if its not cord and plug the ocpd may be larger than the conductors. The language says,,, shall be permitted.
424.3 says not less than 125%. and shall be according to 240

Even heaters greater have 50kw are expected to have internal ocp to sub-divide the overall heater banks into less than 48a again to limit available fault energy. Nec 424.22

But they aint 48A or greater. I will agree that's why they do it though.
422.22 B says equipment greater than 48A must be subdivided with ocpd and allows heating to be on 60A, these are 24A units. Don't require additional protection and farther down only describes branch circuit conductors if ahead of the ocpd.
Using words like less than, greater than and shall be are very specific in code.

 

[sberry]

I can certainly be wrong about this and there is a right answer but, it kind of looks like if the wire is large enough to make 125% and within the short circuit rating of the ocpd and is taken from a single point this is allowed as long as the elements themselves are not over 48 and the breaker not over 60.
There could be some point on over 50 depending on the definition of occupancy I spose.
I looked back in 210.19 to see some limitation and to see if these were considered tap conductors and not so sure they are.

Heater wiring instructions typically list the max ocp permitted to protect the heater. So that right there creates a requirement to preserve the ul listing as the mfr has specified installation details that must complied with.

I will agree with that,,, where is the listing and what does it say?

 

[mm08822]

Go on northerntool and find a heater and open up the installation manual. You wiil find max ocp requirements for the specific unit.

 

[sberry]

Feel free, its your argument. I looked up code sections for the case I am making. I will agree it probably does list it, which supersedes the code section, you get no argument from me there but on other basis the code sections do not prohibit it. I never claimed it didn't say that, only what the code says.

 

[mm08822]

Feel free, its your argument. I looked up code sections for the case I am making. I will agree it probably does list it, which supersedes the code section, you get no argument from me there but on other basis the code sections do not prohibit it. I never claimed it didn't say that, only what the code says.

Its not an argument at least for me. Ill get back to a few points later tonite.

 

[sberry]

I agree that there are aspects of those that require ocpd lower by design.

 

[JRC3]

When I did my heaters I had considered using a 60A that was already in the box doing nothing. I decided to do it right and got two 30As. Funny part is I got the heaters on sale for $70 each and each 30A breaker cost me $18, more than 25% of the cost of each heater. Lucky for me I have plenty of open panel spaces in the garage.

If you're going to wire these with a pigtail and outlet, Menards has the best prices.

https://www.menards.com/main/electr...451133441-c-9526.htm?tid=-2944619850317470699

https://www.menards.com/main/electr...25968688-c-13965.htm?tid=-4510523297945039756

 

[sberry]

There is no doubt that a closer breaker for each piece is ideal and you certainly need to do it if its listed that way. Some equipment is designed to allow larger breakers and some isn't and its in the manuals and also by plug design if it comes with it.
For example, 2 welders, both can go on 50, both come 12 cord with 50 end. A ****** buzzer draws 48 and a 200 mig low 20's. The buzzer doesn't have any internal protection but the little mig has it immediately following the switch. In the ****** it is simpler to simply upsize a little wire for the fan vs putting additional on it.

 

[wyliesdiesels]

I can certainly be wrong about this and there is a right answer but, it kind of looks like if the wire is large enough to make 125% and within the short circuit rating of the ocpd and is taken from a single point this is allowed as long as the elements themselves are not over 48 and the breaker not over 60.
There could be some point on over 50 depending on the definition of occupancy I spose.
I looked back in 210.19 to see some limitation and to see if these were considered tap conductors and not so sure they are.
I will agree with that,,, where is the listing and what does it say?

Short circuit ratings have nothing to do with wire ratings.

Breakers used in residential are typically rated for 10KAIC.

The breakers in my shop are required to be rated at least 22KAIC due to the way the MDP feeding the complex is designed and the size of the transformer feeding it.

You could use the same #10, in a house with 10KAIC rated breakers, and in my shop with 22KAIC rated breakers.

Plants with 480 delta(Wye may be the same) have even higher short circuit ratings.... this is why GFPE is required on services >1Ka. The fault current is so high that it can melt copper bus bars, busways and wire IF there is a fault.

 

[mm08822]

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It has been a long time since I read it and don't know it all that well anyway but that may have something to do with receptacles, not exactly the same when hard wired?

We are talking about fixed electric heating equipment – aka -no plug and recept connections. If we were, then Nec 210. 21 B2 would apply. Since we aren’t, no further need to discuss recepts.

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You need separate circuits for each heater. What happens if there's an internal short in your heater? 60A before it trips - plenty of chance for wiring designed for 30A to start a fire before the circuit is interrupted.

In this specific case for NEC compliance for the stated loads, yes. Canada, whatever your local codes dictate.
09-15-2017, 11:20 PM #9

mm08822
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Bert is correct....NEC 424.3 limits the branch circuit ocp to 30A for multiple heaters on a single ckt.

Replace the 4-11/16 sq box with a 6 space main lug panel ($20-$30) and add 2 2P30A cbs.

If the 6's aren't pulled yet consider running 4 - 10's instead if conduit fill and conductor derating permit.

An outlet is not simply an outlet box, but rather any time a circuit is tapped for a load from the ckt. That constitutes an outlet point. A receptacle is a special case of an outlet.
A single recept is 1 outlet,
a duplex recept is 2 outlets,
a “quad” recept is 4 outlets.
See what Hubbell thinks……. http://www.hubbell-wiring.com/press/pdfs/H4416R.pdf
To partially quote 2017 NEC 424.3A “ Branch circuits supplying 2 or more outlets for fixed electric-space heating equipment shall be rated not over 30 amperes.” So, 2 discrete heater units tapping into a single ckt is 2 outlets from the circuit.
Yesterday, 02:45 AM #10

sberry
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It may limit them if they use recepticals. If the wire is big enough to supply the heater which the 10 is then the over current needs to be within its short circuit rating, which is 60. Think how a range is wired internally or a cooktop and oven wired on the same circuit. You can't do it thru recepts though.
I don't have a book here but I recall something about recepticals in there somewhere.
Like many specialized circuits when they are hard wired or have multiples on them the breaker doesn't provide thermal, only fault. What provides thermal is that the wire is 125 percent required for the load.
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Last edited by sberry; Yesterday at 02:57 AM.



10 wire provides 125% load ampacity in this case - 24a x 125% = 30a. As Wylie corrected you, the AIC rating of cb has nothing to do with the ckt ocp value – 60a is the ocp value in this discussion. Start a new thread if you want to discuss AIC topics.
Heaters and ranges are 2 different animals. That is why NEC article 422 is different than 424 – no further distraction needed in that regard.

Yesterday, 06:54 AM #11

mm08822
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Quote:
Originally Posted by sberry
It may limit them if they use recepticals. If the wire is big enough to supply the heater which the 10 is then the over current needs to be within its short circuit rating, which is 60. Think how a range is wired internally or a cooktop and oven wired on the same circuit. You can't do it thru recepts though.
I don't have a book here but I recall something about recepticals in there somewhere.
Like many specialized circuits when they are hard wired or have multiples on them the breaker doesn't provide thermal, only fault. What provides thermal is that the wire is 125 percent required for the load.
Nec 424.3 makes no distinction for hard-wired or receptical based connections. 30a is the max ocp for multiple connected heater ckts.

It made no distinction b/c there are no recepts in fixed heating equipment.

sberry
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I just got to my office, for giggles I looked it up. Correct and I couldn't remember the language, it doesn't say recept but outlets. The limitation is for 2 or more.
(fwiw, it does mention that it doesn't apply to integral,,, hence the range I mention in another post.) You may be correct as it doesn't list feeds as tap conductors like in cooking equipment.
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Last edited by sberry; Yesterday at 08:10 AM.

Ranges and heaters are not treated the same – hence two nec articles.
Yesterday, 08:21 AM #13

sberry
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210 may also limit how welder outlets may be wired if there is 2 or more. In theory a wire that was thermal protected by the breaker could be tapped with multiples.
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Last edited by sberry; Yesterday at 11:13 AM.


A welder has what relevance to a heater? Unless you can state an article/exception, stay on topic. No further distraction needed. (I know welders are like kin to you, but every other electrical device isnt a buzz box in disguise.)

sberry
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It reads like if he took them from the same point it would be legal It then follows with infrared being limited to 50 in non occupancies.
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Last edited by sberry; Yesterday at 02:25 PM.


It is written poorly, agreed. This is where the true definition of an outlet becomes trouble. As far as the branch ckt is concerned, it doesn’t matter if two “locations” (j-boxes) are used inches or several/hundred feet apart to feed the heaters. It could even be 1 j-box with 2 connections from it to the heaters. The conductor ampacity and the ocp value don’t know the difference. Nor does the available fault current.


mm08822
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Quote:
Originally Posted by sberry
Pictures of breakers are good but I thought maybe Ace, Alfred, maybe Norcal or Wlylie would jump in here with some clarification. It really was curiosity as it doesn't say a circuit larger than 30 cant power the heaters but only that it can't supply 2 or more outlets.
Outlet is described as a point where the power is taken, if it's taken from a single point then it may be allowed?
Each heater unit is considered an outlet point. Read below again – slowly…..

The difference is multiple heaters fed from one ocp device where that ckt is sized for 125% or more of the total connected loads. "One outlet" could be construed to be a single j-box where 2 heaters connect at that point, but it is actually 2 loads (outlets) connecting to the ckt.

Heater wiring instructions typically list the max ocp permitted to protect the heater. So that right there creates a requirement to preserve the ul listing as the mfr has specified installation details that must complied with.

In a single heater installation 125% of its load alone is much closer to that single heaters needed available current. Heaters are assumed to be a continuous load.

In the 2 heater circuit (2 or more =multiple) scenario (assume same size for this example), if only 1 heater were operating and it faulted with a bad heating element, it possible that that unit could draw a fault current of possibly 150% more than intended/expected draw. This could easily melt down the internal insulation within that unit before the ckt ocp even though of tripping on ol. This type of fault could easily make the original fault mode cascade into a much larger fault by decreasing the resistance of that fault as more insulation melts down.

The explanatory notes in the nec handbook explain these thinking’s.

To even further illustrate the protection nec is trying provide:
Even heaters greater have 50kw are expected to have internal ocp to sub-divide the overall heaterbanks into less than 48a again to limit available fault energy. Nec 424.22

I’m assuming as heaters are high on the list of faulting devices due to their very nature of continually degrading the internal materials from high heat exposure, nec has partially addressed the ocp requirements both external and internal to the unit.
This is somewhat contradictory to other gp circuits where plugging in 18-2 zip cord fed device while that ckt has 20a ocp!


Today, 06:55 AM #19

sberry
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I believe the 125% was for the wire.
And the cb, b/c heaters are considered continuous loads.
Quote:
"One outlet" could be construed to be a single j-box where 2 heaters connect at that point, but it is 2 loads connecting to the ckt.
As we know the code isn't written so it could be construed and it didn't say 2 units couldn't be connected.
We know that is not the intention of the code but sometimes wording is poor and causes mis-interpretation – like for example the meaning of “outlets” .
It states 2 (or more) outlets for fixed electric-space heating equipment can’t be fed from a ckt larger than 30A. Stated differently - More than one heating unit can not be fed from a single ckt greater than 30a.
There is a definition for it as the point it is taken, means it cant be taken from multiple points. Didn't say 2 loads, only 2 or more outlets.
You are confusing physical “points” (locations) as something different than multiple utilization devices.

It says that the ocpd shall not be less than 125%. It goes back to 240.4B,1 if its not cord and plug the ocpd may be larger than the conductors. The language says,,, shall be permitted.
424.3 says not less than 125%. and shall be according to 240
Your version of nec reads very differently than mine. How about providing a screen shot??
Quote:
Even heaters greater have 50kw are expected to have internal ocp to sub-divide the overall heater banks into less than 48a again to limit available fault energy. Nec 424.22
But they aint 48A or greater. I will agree that's why they do it though.
422.22 B says equipment greater than 48A must be subdivided with ocpd and allows heating to be on 60A, these are 24A units. Don't require additional protection and farther down only describes branch circuit conductors if ahead of the ocpd.
Good so you understood the intent of 422.22B that I presented to you as the nec’s method of limiting fault current to heating units. If 2 units are combined on one ckt of greater than 30A, the intent of this article is defeated.

Using words like less than, greater than and shall be are very specific in code.

YUP.
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Today, 07:51 AM #20

sberry
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I can certainly be wrong about this and there is a right answer but, it kind of looks like if the wire is large enough to make 125% and within the short circuit rating of the ocpd and is taken from a single point this is allowed as long as the elements themselves are not over 48 and the breaker not over 60. For a single heating unit on a ckt – not multiple.
There could be some point on over 50 depending on the definition of occupancy I spose. Now you are introducing infrared heating units in a non-residential setting and it is limited to 50a – no more.
I looked back in 210.19 to see some limitation and to see if these were considered tap conductors and not so sure they are.
Quote:
Heater wiring instructions typically list the max ocp permitted to protect the heater. So that right there creates a requirement to preserve the ul listing as the mfr has specified installation details that must complied with.
I will agree with that,,, where is the listing and what does it say?

I don’t have it and am not wasting a penny purchasing it from UL for this circular discussion. However, it is common knowledge that if a listed component/product is not installed according to its mfr’s instructions, it is considered to be non-conforming to its UL listing.
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vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
Today, 07:51 AM #20

sberry
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I can certainly be wrong about this and there is a right answer but, it kind of looks like if the wire is large enough to make 125% and within the short circuit rating of the ocpd and is taken from a single point this is allowed as long as the elements themselves are not over 48 and the breaker not over 60.
There could be some point on over 50 depending on the definition of occupancy I spose.
I looked back in 210.19 to see some limitation and to see if these were considered tap conductors and not so sure they are.

Not at all – 424.3B requires 125% ampacity of full load as all heater loads are considered continuous.
Quote:
Heater wiring instructions typically list the max ocp permitted to protect the heater. So that right there creates a requirement to preserve the ul listing as the mfr has specified installation details that must complied with.
I will agree with that,,, where is the listing and what does it say?
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Today, 07:51 AM #20

sberry
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I can certainly be wrong about this and there is a right answer but, it kind of looks like if the wire is large enough to make 125% and within the short circuit rating of the ocpd and is taken from a single point this is allowed as long as the elements themselves are not over 48 and the breaker not over 60.
There could be some point on over 50 depending on the definition of occupancy I spose.
I looked back in 210.19 to see some limitation and to see if these were considered tap conductors and not so sure they are.
Quote:
Heater wiring instructions typically list the max ocp permitted to protect the heater. So that right there creates a requirement to preserve the ul listing as the mfr has specified installation details that must complied with.
I will agree with that,,, where is the listing and what does it say?
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Last edited by sberry; Today at 08:05 AM.

mm08822
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Go on northerntool and find a heater and open up the installation manual. You wiil find max ocp requirements for the specific unit.

sberry
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Feel free, its your argument. I looked up code sections for the case I am making. I will agree it probably does list it, which supersedes the code section, you get no argument from me there but on other basis the code sections do not prohibit it. I never claimed it didn't say that, only what the code says.
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Today, 09:02 AM #24

sberry
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I agree that there are aspects of those that require ocpd lower by design.
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Today, 10:47 AM #26

sberry
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There is no doubt that a closer breaker for each piece is ideal and you certainly need to do it if its listed that way. Some equipment is designed to allow larger breakers and some isn't and its in the manuals and also by plug design if it comes with it.
For example, 2 welders, both can go on 50, both come 12 cord with 50 end. A ****** buzzer draws 48 and a 200 mig low 20's. The buzzer doesn't have any internal protection but the little mig has it immediately following the switch. In the ****** it is simpler to simply upsize a little wire for the fan vs putting additional on it.
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Today, 05:09 PM #27

wyliesdiesels
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Quote:
Originally Posted by sberry
I can certainly be wrong about this and there is a right answer but, it kind of looks like if the wire is large enough to make 125% and within the short circuit rating of the ocpd and is taken from a single point this is allowed as long as the elements themselves are not over 48 and the breaker not over 60.
There could be some point on over 50 depending on the definition of occupancy I spose.
I looked back in 210.19 to see some limitation and to see if these were considered tap conductors and not so sure they are.
I will agree with that,,, where is the listing and what does it say?
Short circuit ratings have nothing to do with wire ratings.

Breakers used in residential are typically rated for 10KAIC.

The breakers in my shop are required to be rated at least 22KAIC due to the way the MDP feeding the complex is designed and the size of the transformer feeding it.

You could use the same #10, in a house with 10KAIC rated breakers, and in my shop with 22KAIC rated breakers.

Plants with 480 delta(Wye may be the same) have even higher short circuit ratings.... this is why GFPE is required on services >1Ka. The fault current is so high that it can melt copper bus bars, busways and wire IF there is a fault.