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Loose connection at breaker?

How hot?
"Burned in 30 seconds by 54°C, 5 sec. @ 60°C, 1 second @ 71°C."
No burn in 8 hrs. at 43°C.
Less than 40°C probably feels cool to the touch.

Anyone know the rise-above-ambient for a breaker carrying rated current? I doubt it is 24°C.
Don't know right off hand. But I do know that any breaker carrying at or near its rated current will heat up significantly. Most breakers are 40 C, meaning they will maintain their thermal trip characteristics til that point, I think...

I have seen breakers in outdoor enclosures go way over their rated capacity because it was below freezing outside. There was a 20 A breaker with 32 A continuous, without tripping. I changed it for a new one, and almost the same thing. At any rate we had to reduce the load.
 

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any breaker carrying at or near its rated current will heat up significantly. Most breakers are 40 C, meaning they will maintain their thermal trip characteristics til that point, I think...

I have seen breakers in outdoor enclosures go way over their rated capacity because it was below freezing outside. There was a 20 A breaker with 32 A continuous, without tripping. I changed it for a new one, and almost the same thing. At any rate we had to reduce the load.
I'll have to e-mail Square D or Cutler Hammer and ask, if they'll talk to me at all.

20 A squared = 400, 32 A squared ~1000, so this breaker had 2.5x the normal temp-rise-above-ambient for the thermal part, without tripping.
The NEC must know about this (?) and probably takes it into account. I guess they figure the wire is also colder, so the insulation is still below max temp.

Maybe the local codes for Alaska tweak these numbers a little.

Another way to figure this is max 30mV across closed, good contacts at rated current. At 30A this would be about 1w, and that won't heat something as large as a breaker.
For the thermal trip part they may have a 10w resistor in there. I'll have to take one apart sometime.

And so I did take one apart and found a mysterious component in it, which measured "zero" ohms on my meter.
10w at 20A is 25 mΩ, so I'll have to find some other way to measure this supposed resistor.

Rev A
Below 36°C probably feels cool to the touch
no burn @42°C
burned in:
30 seconds @ 54°C,
5 sec. @ 60°C,
1 second @ 71°C.

With the aid of some rum & coke, the internal resistor of a Square D Q0 breaker comes in at 4.4 mΩ. 20A through this gives ~2w to heat up their bimetallic mechanism. 2w dissipated in a plastic case with a surface area as big as a breaker can't get very warm.

I don't know why the breaker you mentioned was hot at rated current, based on what I measured.
 

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4500 watts at 240 volts is 18.75 amps so if he had 12 awg copper on an individual circuit under your analysis he would be fine
That was not what I was saying.

I just said the wire size determines the maximum breaker size. If you disagree with this then we have bigger problems.
 

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That was not what I was saying.

I just said the wire size determines the maximum breaker size. If you disagree with this then we have bigger problems.
I certainly disagree if your saying this is always the case.
 

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I just said the wire size determines the maximum breaker size. If you disagree with this then we have bigger problems.
Your methodology is 100% backwards and in conflict with basic electrical system design practices. Wire size is determined by the breaker ampacity. The ampacity of the specific circuit is determined for you by code or by the appliance manufacturer's requirements, and you pull the correct size of wire accordingly.
 

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Wire size is determined by the breaker ampacity.
If you were pulling a new run then it might seem backward to say that the wire dictates the maximum breaker ampacity, but we are talking about an existing run in this thread.

It's just two different ways to say the same thing:

  • Breaker ampacity determines minimum wire size
  • (Smallest) wire size determines maximum breaker ampacity.
 

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I realize we are all bored here but wire size does not dictate breaker size in all cases. In this case we are serving a hot water tank...storage type.... so if the existing branch circuit breaker conductors are 12 awg copper then the maximum breaker is 20 amps. So I would agree that looking at an existing run of lets say 12/2 awg romax serving a hot water tank then 12 awg copper would dictate a maximum 20 amp circuit breaker.
What I am saying is that this is not always the case for maximum circuit breaker depending on what equipment or appliance the branch circuit serves exiting run or not. A 20 amp breaker on 12 awg copper romax is not necessarrily the maximum breaker size. I could put it on a 30 amp breaker.
 

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... A 20 amp breaker on 12 awg copper romax is not necessarrily the maximum breaker size. I could put it on a 30 amp breaker....
In some cases, yes. Like with an A/C unit or other motor load.

In the case of a water heater (which is the topic of this thread), then no you are not allowed to use a 30 Amp breaker on a #12 wire.

For those who are lurking here, let's point out that a 4500 watts for a water heater circuit is considered to be a continuous load and as such has to be figured with a 125% multiplier. 18.75Amps x 125% = 23.43 Amps.

This translates to:

Minimum Circuit Ampacity = 25 Amps.
-- and --

Maximum overcurrent protection = 30 Amps.

Many new manufactured homes come equipped with a #10 wire connected to a 25 Amp breaker for a 4500 watt water heater.





 

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In some cases, yes. Like with an A/C unit or other motor load.

In the case of a water heater (which is the topic of this thread), then no you are not allowed to use a 30 Amp breaker on a #12 wire.

For those who are lurking here, let's point out that a 4500 watts for a water heater circuit is considered to be a continuous load and as such has to be figured with a 125% multiplier. 18.75Amps x 125% = 23.43 Amps.

This translates to:

Minimum Circuit Ampacity = 25 Amps.
-- and --

Maximum overcurrent protection = 30 Amps.

Many new manufactured homes come equipped with a #10 wire connected to a 25 Amp breaker for a 4500 watt water heater.


Thanks for saving me the typing....that is exactly where I was going.
 

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Discussion Starter #30
Thanks All

Went and got me a new breaker and it is working great. Thanks for all the info. By the way it had a gas hot water heater and I ran a 220 from the main and put into a small breaker box and then put a 30 amp to the new Hot Water heater. But any how it is working OK now after two days.
 

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Went and got me a new breaker and it is working great.
So the hot breaker was actually bad,
or during installing the new breaker bad connections were tightened up in which case reinstalling the old breaker would have worked, also.

All's well that ends well.
 

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Went and got me a new breaker and it is working great. Thanks for all the info. By the way it had a gas hot water heater and I ran a 220 from the main and put into a small breaker box and then put a 30 amp to the new Hot Water heater. But any how it is working OK now after two days.
What size wire did you use?
 

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Breaker trips

Went and got me a new breaker and it is working great. Thanks for all the info. By the way it had a gas hot water heater and I ran a 220 from the main and put into a small breaker box and then put a 30 amp to the new Hot Water heater. But any how it is working OK now after two days.
Did you check if the lower Heat tube is good. Do you have soft water,or could you have a deposit on the lower unite grounding out?:eek:
 
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