Ambient temp. compensated?

[GG]

Source - Ray C. Mullin, Electrical Wiring Residential, 2005, page 559. Mr. Mullin states that "most circuit breakers are ambient temperature compensated. This means that the tripping point of the breaker is not affected by an increase in the surrounding temperature. An ambient-compensated breaker has 2 elements. One element heats up due to the current passing through it and the heat in the surrounding area. the other element heats up because of surrounding air only. The actions of these elements oppose each other. Thus, as the tripping element tends to lower its tripping point because of external heat, the 2nd element opposes the tripping element and stabilizes the tripping point. As a result, the current through the tripping element is the only factor that causes the element to open the circuit." Is this true, I have never heard of a ambient temperature compensated breaker

 

[LarryFine]

Re: Ambient temp. compensated?

I cant't disagree, except to say that "the current through the tripping element is the only factor that causes the element to open the circuit." may apply to that "element", but most breakers use magnetism to open the circuit for short-circuit and bolted faults.

Besides, I've seen plenty of breakers that open due to heat from nearby overheated breakers and/or high-impedance connections. Last week, we had a couple of breakers trip due to a hot main-lug terminal. (Loose and no anti-oxidant compound)

 

[iwire]

Re: Ambient temp. compensated?

The only thing I find in the UL white book about this so far is this.

Circuit breakers, the performance of which may be affected by a 40?C ambient temperature within the enclosure, and that have been investigated for this application, are marked ??40 C.?

 

[GG]

Re: Ambient temp. compensated?

Well I asked because I went to an apt complex where the handyman had installed a new panel and skipped a slot for every breaker in the panel. I asked him what in the world would possess him to do that, and he said it was so the other breakers wouldn't trip and air could flow through and keep all the breakers cooler. All I could say was "WOW".

[ August 13, 2005, 08:43 PM: Message edited by: GG ]

 

[iwire]

Re: Ambient temp. compensated?

I went on a night time service call to a large store that was open but also being remodeled during the day.

A lighting breaker had tripped, the 20 amp breaker was carrying about 24 amps of load on 10 AWG THHN.

At that point there was little I could do, I left the panel door open (panel cover was on) and aimed a fan at it.

It held fine until proper repairs where made the next day.

 

[hardworkingstiff]

Re: Ambient temp. compensated?

Originally posted by GG:
Well I asked because I went to an apt complex where the handyman had installed a new panel and skipped a slot for every breaker in the panel.

Did it work out that he had most of the ciruits on one phase?

 

[templdl]

Re: Ambient temp. compensated?

Ambient compensated breaker is calibrated with respect to a specific ambient temperature such a the UL489 listed breaker is calibrated a 40degC. Another standard ambient calibration is 50degC but it is not UL listed as it isn't recognized by UL.
All "critical tests" are performed at a 40degC ambient while others are performed at 25degC and some test both 25 and 40degC.
Yes there were what may be called a sort of double bimetallic thermal element breaker which does compensate for ambient temperatures where the trip curve shifts with the ambient temperature. However I'm not aware that any manufacturer provides this feature in a modern breaker today. If it is it is not UL489. It is also referred to as an ambient "compensating" breaker and not ambient compensated which was designated as an 'A' with the catalog number of Westinghouse breakers in the past.

 

[physis]

Re: Ambient temp. compensated?

By GG:

Well I asked because I went to an apt complex where the handyman had installed a new panel and skipped a slot for every breaker in the panel. I asked him what in the world would possess him to do that, and he said it was so the other breakers wouldn't trip and air could flow through and keep all the breakers cooler. All I could say was "WOW".

I don't know what to say either.

Except maybe that's why we have electricians.

I'm wondering if this was his solution to maybe an overloaded circuit that kept tripping a breaker. And if it was, I wonder if the circuit is still overloaded?

Cause I'm sure that wouldn't fix it.

 

[jim dungar]

Re: Ambient temp. compensated?

Mr. Mullin is wrong. Most circuit breakers are not ambient compensated.

I base my claim on the fact that Square D and Cutler Hammer are two of the largest circuit breaker manufacturers in the US, and neither one makes an ambient compensated residential breaker.

Also, the only commonly available ambient compensated breakers I can think of are "electronic" trip industrial devices.

 

[celtic]

Re: Ambient temp. compensated?

Originally posted by GG:
...he said it was so the other breakers wouldn't trip and air could flow through and keep all the breakers cooler.

LMAO.
So a maintenance guy has more insight than an entire corporation with a complete R&D department.

Give this to the maintenance guy for me, ok?

 

[templdl]

Re: Ambient temp. compensated?

FYI, A QO and CH breaker both which show 40degC which is part of the molding on the side of each breaker.

The following is a data sheet that may be older but really hasn't changed. Note the 40degC under Tripping characteristics.