What say ye?

about the elevated heat at these breakers…deal or no deal

At 135 degrees, I’d say “No deal”.

I definitely take the pretty lady holding the number though.

I would not necessarily say “no deal”

First, the panel cover should be removed if possible, so you can see if the conductor is warm throughout the circuit.

In order to really confirm whether or not this is a problem, you have to measure the load of the circuit with a true RMS ammeter. Compare the rated load to the measured load. Then compare your warm circuit to a similar circuit under similar load.

I would take these steps before saying that it is not a problem. It is impossible to predict failures based solely on temperature. You’ll need to confirm findings.

Great question, Barry!

Kevin

I agree with Kevin but, after the panel cover was removed and I saw nothing untoward, I would probably say no deal. Need more than temp.

Definitely starting to get up there…but something for discussion today (I won’t be around as I have 2 inspections):

***[FONT=Times New Roman]From University of Georgia College of Agriculture Extension Services:
[/FONT]***[FONT=Times New Roman]
[/FONT][FONT=Times New Roman]
[/FONT]

[FONT=Times New Roman]"Generally, the temperature of a circuit breaker should not exceed 140

[/FONT][FONT=Times New Roman]o[/FONT][FONT=Times New Roman]F. If it does, it means the circuit breaker is in danger of “tripping out” due to overloading or **maintenance related problems."[/FONT]

From a Square D catalogue:

[FONT=Helvetica-Bold]QOU Miniature Circuit Breaker Types

[/FONT][FONT=Helvetica]Miniature molded case circuit breakers are intended for use in residential and commercial applications.

[/FONT]

[FONT=Helvetica]Ambient Temperature Rating
*To meet the requirements of UL 489 and the Canadian Standards Association, thermal-magnetic **circuit breakers are designed, built and calibrated for use on 50/60 Hz ac systems in a 104° F (40° C) **ambient temperature. Time/current characteristic trip curves are drawn from actual test data that meets *UL 489 testing requirements.

*The ambient temperature is the temperature of the air surrounding the circuit breaker. Thermalmagnetic **circuit breakers are temperature-sensitive devices, and their rated continuous current **carrying capacity is based on a UL specified 104° F (40° C) calibration temperature. The ambient **temperature can affect the performance characteristics of the circuit breaker. Thus, when applying a **circuit breaker at temperatures other than 104° F (40° C), it is necessary to determine the circuit **breaker’s actual current carrying capacity under this condition. Further, it may be necessary to rerate *the circuit breaker to compensate for these ambient conditions. See Figure 3:

*Thermal-magnetic circuit breakers use bimetal strips that bend in response to temperature changes. **Current flowing through the circuit breaker creates most of the heat that causes the tripping action. The **ambient temperature surrounding the circuit breaker either adds to or subtracts from this available **heat. Conductors are sized using the ampacity rerating factors shown on the bottom of NEC Table *310-16 when designing systems for ambient temperatures other than 40° C.

[/FONT]

[FONT=Helvetica]Rerating of Thermal-magnetic Circuit Breakers for Ambient Conditions
*Square D thermal-magnetic circuit breakers are to be **applied in ambient temperatures within the range ******of 14° F to 140° F *(-10° C to 60° C). Use the following rerating guidelines:

[/FONT][FONT=Helvetica]
*• *

[/FONT][FONT=Helvetica]Ambient Temperatures Between 77° F and 104° F (25° C and 40° C):
— No rerating is necessary.[/FONT]

[FONT=Helvetica]

[/FONT][FONT=Helvetica]
*• *

[/FONT][FONT=Helvetica]Ambient Temperatures Between 14° F and 75° F (-10° C and 24° C):
*— Thermal-magnetic circuit breakers operating within this ambient temperature range will carry **more than their continuous current rating without tripping. Conductor and equipment damage *can result if they are not in the same low ambient environment as the circuit breaker.
— Nuisance tripping will not be a problem. However, if closer protection of the equipment and **conductor is required, the increased current carrying capacity of the circuit breaker at the lower **ambient temperature should be taken into consideration.[/FONT]

[FONT=Helvetica]

[/FONT][FONT=Helvetica]
*• *

[/FONT][FONT=Helvetica]Ambient Temperatures Between 106° F and 140° F (41° C and 60° C):
*— Thermal-magnetic circuit breakers operating within this ambient temperature range will carry **less than their continuous current rating and must be carefully selected to prevent nuisance *tripping

***SO what is the temperature at which “too hot” breakers should be called?***[/FONT]

[FONT=Helvetica][size=1]

[/size][/FONT]

[FONT=Times New Roman][size=3]
[/size][/FONT]

Here are a few good references on this topic:


http://www.flirthermography.com/media/2005-006%20Cronholm.pdf

It is wise to conduct Infrared Surveys using a set of standards:

https://secure.infraspection.com/comersus/store/comersus_viewItem.asp?idProduct=4103

Hope this is helpful…

Kevin

Here is an excerpt from an article that John Snell wrote in 2001.

He makes a very good point, which is we should not get hung up on temperature and take the time to investigate the potential problem.

Kevin

[quote=krichardson]
I would not necessarily say “no deal”

First, the panel cover should be removed if possible, so you can see if the conductor is warm throughout the circuit.

In order to really confirm whether or not this is a problem, you have to measure the load of the circuit with a true RMS ammeter. Compare the rated load to the measured load. Then compare your warm circuit to a similar circuit under similar load.

I would take these steps before saying that it is not a problem. It is impossible to predict failures based solely on temperature. You’ll need to confirm findings.

Great question, Barry!

Kevin/quote)

Well Stated Kevin your level 2 training is showing. Knowing BA he did pull the dead front will be interesting to know what he found and what that circuit was actually feeding

Something to consider. The temps are indirect. You are just measuring the surface of the black molded casing. It is safe to say that the temp at the connection is likely higher than what the camera is measuring on the surface of the casing. Every wire has a rating (60, 75 or 90 C). As the temp edges closer to this rating the condition becomes more suspect and potentially dangerous. My approach to HI electrical thermography is simple. If the measured temps are approaching the rating on the wire then I write it up as a suspect condition and refer it out for further investigation. I always tell my client the limitations of technology and that I am not specifically calling out a problem just a suspect condition that should be evaluated. Yes, there are more thorough approaches that will require more time and expertise (and you should command a higher fee) to deliver and I am certainly not suggesting that one should not go further with this. This is just a simple approach that is based on a standard UL rating. I do not call out a specific temp or suggest that the temp is more accurate than the limitations.

The problem with evaluating comparative samples in a residential panel is that you are not likely to get similar loads on certain circuits (i.e. there is only one oven circuit in the building).

[quote=sramos]
Something to consider. The temps are indirect. You are just measuring the surface of the black molded casing. It is safe to say that the temp at the connection is likely higher than what the camera is measuring on the surface of the casing. Every wire has a rating (60, 75 or 90 C). As the temp edges closer to this rating the condition becomes more suspect and potentially dangerous. My approach to HI electrical thermography is simple. If the measured temps are approaching the rating on the wire then I write it up as a suspect condition and refer it out for further investigation. I always tell my client the limitations of technology and that I am not specifically calling out a problem just a suspect condition that should be evaluated. Yes, there are more thorough approaches that will require more time and expertise (and you should command a higher fee) to deliver and I am certainly not suggesting that one should not go further with this. This is just a simple approach that is based on a standard UL rating. I do not call out a specific temp or suggest that the temp is more accurate than the limitations.

**The problem with evaluating comparative samples in a residential panel is that you are not likely to get similar loads on certain circuits (i.e. there is only one oven circuit in the building)./**quote]

Steve one does not need similar loads within the same panel to compare, an electrical oven is an electrical oven I use my images (library) of past normal operating components as comparisons

Hey Charlie-

Are you suggesting that all electric oven have breakers that have a normal operating temperature range? If so, where can I find that information.

If you are suggesting that you can compare a breaker from one building to another just becaus they both have electric ovens - can you please explain your methodology in a little more details and the theory/basis for how you set your standards and what your thresholds are?

If you are suggesting that you would compare the same electric oven over time such as in a PD procedure that makes more sense to me but that is not something we get the chance to do as home inspectors. I do understand that some in this group do straight up thermography not connected with HI.:smiley:

No Steve not comparing ovens to ovens but breakers to breakers as the standard operating temp defined by the MFG. Yes I am suggesting one can compare a 60 amp breaker under full load in one home to a 60 amp breaker under the same full load in another home. Example one with a loose lug and one not, watch the temp rise
</IMG>