What say ye?

[Barry Adair]

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

[David P. Valley]

At 135 degrees, I'd say "No deal".

I definitely take the pretty lady holding the number though.

[Kevin A. Richardson]

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

[Larry D. Kage]

Originally Posted by 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

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.

[Brian A. MacNeish]

Originally Posted by dvalley

At 135 degrees, I'd say "No deal".

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

From University of Georgia College of Agriculture Extension Services:

"Generally, the temperature of a circuit breaker should not exceed 140

oF. If it does, it means the circuit breaker is in danger of “tripping out” due to overloading or maintenance related problems."


From a Square D catalogue:

QOU Miniature Circuit Breaker Types

Miniature molded case circuit breakers are intended for use in residential and commercial applications.

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.

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:

•

Ambient Temperatures Between 77° F and 104° F (25° C and 40° C):
— No rerating is necessary.

•

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.

•

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?

[Kevin A. Richardson]

Here are a few good references on this topic:

http://irinfo.org/tip_of_week_2005.html#t01102005
http://www.flirthermography.com/medi...20Cronholm.pdf


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

https://secure.infraspection.com/com...idProduct=4103

Hope this is helpful...

Kevin

[Kevin A. Richardson]

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

How hot is too hot?

Many thermographers make the mistake of believing that only problems that are very hot are serious. Nothing could be further from the truth! Imagine a lightly-loaded, shiny connection outside on a windy, winter day. The probability of detecting such a problem is very low. However, when loads increase or winds drop on a hot summer afternoon, this same problem will probably be very warm. A key to locating problems is comparing similar components or phases. Honestly, much of the time we are not concerned with the “exact” temperature because it is often not possible to reliably measure them in the field on a repeatable basis. The real value of thermography is locating problems, not measuring temperatures! To prioritize findings, all relevant information must be accounted for. This includes not only the heat transfer relationships, but also such factors as the criticality of the component, the consequences of a failure, availability for repair, and the trend of change over time. Such an analysis is not always simple, but it is always worth spending time in the process.
-John Snell

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

[Charley L. Bottger]

[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

[Steven S. Ramos]

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).

[Charley L. Bottger]

[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

[Steven S. Ramos]

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.

[Charley L. Bottger]

Originally Posted by sramos

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.

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
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