Electric central heater tripping off breaker

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Old 04-05-10, 12:54 PM
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Electric central heater tripping off breaker

I have a sub-panel (125amp) that is being fed from a MAIN panel (200amp), and the actual central heater is running off the sub-panel, the weird thing is that the breakers are tripping on the main panel and not the sub-panel, I have 4 awg underground aluminum wires on a 100amp breaker running between both panels and the breaker only trips with the heater not the AC, and only if I set the thermostat to 73 degrees, if I set it to 72 it will run fine without any problem, can it be a bad undergroud cable? I had problems with one of the cables before but I replaced it and it has been working fine, I also checked it with a volt meter and I get 123/124amps on each leg even when the heater is running. Like I said the breaker only trips if setting thermostat above 73?

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Old 04-05-10, 01:06 PM
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Originally Posted by jorge13morales View Post
I have 4 awg underground aluminum wires on a 100amp breaker
The #4 aluminum should be protected with a 70A breaker max. You could be having an overheating issue at the breaker if load is actually high. Is the breaker in good condition? Any signs of overheating, burning smells, crackling, etc?

and only if I set the thermostat to 73 degrees, if I set it to 72 it will run fine without any problem
What type of heater is this and what are its electrical specs? Perhaps at 73 degrees it switches on another heating element or fan? Any other appliances on at the same time as the heater?

can it be a bad undergroud cable?
It's possible, but that usually trips the breaker at random times and not necessarily under load.

I also checked it with a volt meter and I get 123/124amps on each leg even when the heater is running.
Did you mean volts? Do you have a clamp-on meter to measure amps?
 
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Old 04-05-10, 02:30 PM
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I have 4 awg underground aluminum wires on a 100amp breaker
Shouldn't a 100 amp service be #2 aluminum or #4 copper?
 
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Old 04-05-10, 02:48 PM
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Originally Posted by SilverTattoo View Post
Shouldn't a 100 amp service be #2 aluminum or #4 copper?
For a subpanel based on 2008 code it should be #1 aluminum or #3 copper if in conduit; or, #1/0 aluminum or #2 copper if in a cable assembly (table 310.16). The smaller sizes (#4 cu / #2 al) were common prior to 2008 code based on a looser application of table 310.15(B)(6) allowed in previous revisions. To my knowledge #4 al has never been correct for 100A.
 

Last edited by ibpooks; 04-05-10 at 03:08 PM. Reason: correct of AWGs
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Old 04-05-10, 04:38 PM
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Ok thanks for the clarity. Here it varies from county to county. My county is still 05 and some of the surrounding counties are 08.

I have a sub-panel (125amp)
So for this 125 amp service (2005 NEC my 08 book is not accessible at the moment). It read #2 cu and 1/0 aluminum..
It appears the service is highly undersized..

Also (of subject kinda). My neighbor has a 100 amp main service (wired in 1990 passed inspection!, Sticker in panel) and when his old lady uses the range and the drier at the same time it kicks the main 100amp breaker. After inspection I noticed the 100amp was feed to panel with #4 aluminum..(the panel on the inside of house is a 200amp panel also 30 stabs with a 100amp breaker on the outside main) Now I told him it was sized wrong that someone sized it for copper! He called the guy who wired it and they told him something like" we have been in business for 23 years, blah blah blah and its a bad breaker! Of course I disagreed but the home owner took his word for it and that was that! The sad thing is the house was burnt down in 1990 and this was a new service!! I hate to see the same thing happen again.. Is this contractor right? I dont see how he could be!
 
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Old 04-05-10, 07:04 PM
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Originally Posted by SilverTattoo View Post
Ok thanks for the clarity. Here it varies from county to county. My county is still 05 and some of the surrounding counties are 08.



So for this 125 amp service (2005 NEC my 08 book is not accessible at the moment). It read #2 cu and 1/0 aluminum..
It appears the service is highly undersized..

Also (of subject kinda). My neighbor has a 100 amp main service (wired in 1990 passed inspection!, Sticker in panel) and when his old lady uses the range and the drier at the same time it kicks the main 100amp breaker. After inspection I noticed the 100amp was feed to panel with #4 aluminum..(the panel on the inside of house is a 200amp panel also 30 stabs with a 100amp breaker on the outside main) Now I told him it was sized wrong that someone sized it for copper! He called the guy who wired it and they told him something like" we have been in business for 23 years, blah blah blah and its a bad breaker! Of course I disagreed but the home owner took his word for it and that was that! The sad thing is the house was burnt down in 1990 and this was a new service!! I hate to see the same thing happen again.. Is this contractor right? I dont see how he could be!
That contractor is dead wrong! It sounds as if inspections/inspectors aren't very strict in your area.
 
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Old 04-05-10, 07:32 PM
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Yea i doubt a inspector ever showed up!! I am gonna take a piece of #2 wire over to my neighbor so he can compare it and then from there its out of my hands.. Hopefully he will listen.
Thanks

After re-reading we are talking about a 100 amp service..
the weird thing is that the breakers are tripping on the main panel and not the sub-panel, I have 4 awg underground aluminum wires on a 100amp breaker running between both panels and the breaker only trips with the heater
Still the wire is under sized..
 
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Old 04-06-10, 07:51 PM
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the weird thing is that the breakers are tripping on the main panel and not the sub-panel, I have 4 awg underground aluminum wires on a 100amp breaker running between both panels and the breaker only trips with the heater
I don't see it as such a big mystery. The #4 aluminum is undersized for the 100 amp breaker and is overheating the 100 amp breaker with the load of the heater.
 
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Old 04-06-10, 09:22 PM
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Originally Posted by jorge13morales View Post
I have a sub-panel (125amp) that is being fed from a MAIN panel (200amp), and the actual central heater is running off the sub-panel, the weird thing is that the breakers are tripping on the main panel and not the sub-panel, I have 4 awg underground aluminum wires on a 100amp breaker running between both panels and the breaker only trips with the heater not the AC, and only if I set the thermostat to 73 degrees, if I set it to 72 it will run fine without any problem, can it be a bad undergroud cable? I had problems with one of the cables before but I replaced it and it has been working fine, I also checked it with a volt meter and I get 123/124amps on each leg even when the heater is running. Like I said the breaker only trips if setting thermostat above 73?

Thanks,
I will make it super simple and clear you have serious undersized conductors no question asked and few members just gave you the straght shot answer.

As other members pointed clear on this one.

The only way you can slove it is replace with correct conductor size you will need 50mm˛{ 1 AWG } being underground run.

Merci,Marc
 
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Old 04-07-10, 12:33 PM
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Well now that is getting hot in Texas and I don't have to turn on the heater I have no problems, I am not sure if I am actually having a heater problem instead of an electrical problem, I spoke with one of my AC friends and he believes is a bad furnace control board or a bad element, my heater is electric and by the way 95% of Texas old homes are wired this way, that shoulnd't be a problem, When the breaker trips the only thing that is running is the heater, I only have an electric central heater, 4 electrical outlets and 2 lights running off of the sub-panel.
 
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Old 04-07-10, 12:38 PM
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I forgot to mention that the house has been set up this way for 10 years, same wires and heater so I don't see why all of the sudden the heater is overheating the "undersized wires" and panel, I'll probably understand having a bad wire but not an undersized wire that has been doing its job for the last 10 years without any problems.
 
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Old 04-07-10, 12:53 PM
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It would be helpful to know the size of the heater, but if it's the only thing on I doubt it's maxing the feeder. Based on this information though I do believe the heater has a fault in it. Perhaps in the control system or a heating element. My bet is on a heating element that has grounded to the frame. That fits with the trip at a specific setting on the heater.

The undersized wire is also a problem, but I don't think it's contributing to the breaker tripping in this case. The breaker feeding the outbuilding should be reduced to 70A to prevent overheating the #4 aluminum wire in case that panel ever does get toward its limit. The problem with an overheated wire is that it bakes the plastic insulation until it cracks and falls off which causes a hazard over time. That would be a problem if the panel was up over 70A on a regular basis, which sounds unlikely based on the description of your loads.
 
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Old 04-07-10, 01:10 PM
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Thanks for all your help Ben, I really appreciate it....
 
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Old 04-07-10, 06:58 PM
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I'll probably understand having a bad wire but not an undersized wire that has been doing its job for the last 10 years without any problems.
I'm not really sure why you bothered to ask the question since you don't seem interested in fixing the problems. Do as you wish, but I'd also recommend checking the limits of your insurance.
 
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Old 04-07-10, 07:11 PM
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The tripping of the breaker could be a sagging element but you have another even more serious problem that needs to be addressed. It could even be a failing breaker perhaps due to the extra load of undersized wires.
 
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Old 04-07-10, 09:51 PM
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The other thing it did bring up to my attetion is some of the electrique furance do have multistage heating sections so they are switched in sequince when they come on so like example first 5KW come on then few minutes second 5 KW kick on the last stage kick on in few minutes later so it will designed to prevent overloaded when it kick on quick that above is example.

so If the case if one of the stages have bad sections that can cause trip the breaker as well.

Merci,Marc
 
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Old 04-08-10, 08:48 AM
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Well the AC/heater is a 1 1/2 ton 18,000 BTU small unit, and like I said before that is the only thing running off of the sub-panel, the distance between Main and Sub-panel is 75 feet, pretty short distance, I also believe I have a AC/heater problem. And remember that these wires were up to code when they were originally installed so I don't see how the cables started overheating just because the code was changed on 2008 if they weren't before.
 
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Old 04-08-10, 09:31 AM
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Those sound like the ratings for the AC unit only. Electric heater strips are typically rated in Kw.

I don't think that wire ampacities have changed that much since your house was built.
 
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Old 04-08-10, 11:21 AM
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I had problems with one of the cables before but I replaced it and it has been working
It could of slowly but surely been a problem..

The thing is, its not about Code or the year so to speak. Its about it was never installed right the 1st time. Unless I am wrong and #4 al is acceptable to a 100amp service(which I have never heard of).
 
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Old 04-08-10, 11:33 AM
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Just a side note in Texas you might as well just burn your money for heat if you use an electric heat. It costs almost three times as much per BTU as natural gas. Or did you get snookered in to buying a house in one of those all electric subdivisions with no natural gas.
 
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Old 04-08-10, 06:59 PM
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And remember that these wires were up to code when they were originally installed so I don't see how the cables started overheating just because the code was changed on 2008 if they weren't before.
I suppose it all depends on what code you are referring to. #4 aluminum hasn't been rated for 100 amps in the last 40 years by the NEC. I couldn't say about the 40 years before that.
 
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Old 04-08-10, 10:38 PM
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I have never worked on anything 100amp with #4al with the exception of my neighbors house ironically and it was wired in 1990.. And I do not know code from 1970 you are right like Joe is sayin. Though im sure if it was code back then, they changed it out for a pretty good reason in the studies done and performed in the last 40 years.. Im not a expert or a pro and dont claim to know what is wrong with this mans heater but, it it were me I would sure start there along with a new breaker.
 
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Old 04-09-10, 06:42 AM
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It sounds like your problem may be in your heater. Like French 277V explained your heater could be a 2 stage. This works like my Geo system. When my system can't keep up with the heat on very cold days the electric back kicks in. The first thing I would do is to have a furnance person check your furnance out unless you know how to do it. If everything checks good then you might what to start checking your feed wires to your furnance. What I see is your wires could be getting bad and you may want a electrican to meg out your wires. This should be a good starting point to get your system up and running correct. The concern about the #4 AL is a concern and I would look into this very closely. Myself I would install a 70 amp breaker on it and you should be safe with the wire. Hopefully it's big enough for your current system.

Jim
 
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Old 04-09-10, 08:54 PM
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The concern about the #4 AL is a concern and I would look into this very closely. Myself I would install a 70 amp breaker on it and you should be safe with the wire. Hopefully it's big enough for your current system.
And that depends on the KW rating of the electric heater which we have yet to be told.
 
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Old 04-10-10, 01:56 AM
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Originally Posted by CasualJoe View Post
And that depends on the KW rating of the electric heater which we have yet to be told.
You are correct in your staement and that's why I thought it would be a good idea to call in a furnance person. We all know that this has ran for 10 years without problems. I'm just trying to lead him in the correct direction to get this fixed. We all know there could be a undersize wire problem and all of use have also gave him ideas on this and I stated he should change the breaker out to a 70 amp.

Jim
Beer 4U2
 
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Old 04-13-10, 02:10 PM
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I really appreciate everyone's input, great knowledge.
 
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