Hello, I recently performed a mock inspection as part of my training on a friend’s subpanel. I used an infrared thermometer to detect the temperature of the breakers. Upon scanning the breakers, I noticed that one breaker was 7-8 degrees (88 degrees) hotter than the others in the 80-81 range. This breaker happened to be on an AFCI circuit which I tested and was functional. What difference in temperature would warrant a comment? The breakers in the subpanel are not labeled in the legend so I have no idea what part of the house this AFCI services. Is this difference drastic enough to call out and comment on? Thank you in advance.
Been a lot of discussion about this.
https://forum.nachi.org/search?q=afci%20breaker%20hotter%20order%3Alatest
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As David said, this has been discussed several times previously. However, for anyone new coming aboard and seeing this thread, AFCI breakers have active circuitry that consume electricity and produce heat. So, AFCI breakers being 7-8 degrees warmer than non-AFCI breakers is to be expected and perfectly normal.
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No.
There’s no need comment unless the temperature exceeds the temperature rating of the breaker.
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Even if the temperature is less than the breaker rating, if one breaker is 20 to 30 degrees warmer than the rest, that should be a clarion signal to evaluate further as to possible causes. Is the breaker currently under a heavy load? If yes, then it is likely fine. If not, why is it warm? There could be a damaged conductor, double-tap or loose connection, and so forth.
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Glad to meet you, Egal Shamash.
Best of luck with all your endeavors.
Save you temperature testing methods, and your liability, for boilers, radiators, furnaces, HVAC plenums, water heater supply temperature at faucets or pipes, around window frames, ect. But not breakers. Testing methods are more stringent and defined. Infrared is better equipped to pin point heat.
The acceptable operating temperature of a circuit breaker is defined by UL in the UL489 standard (June 2011), which is listed below.
- Terminations for standard rated breakers: UL 489 Paragraph 7.1.4.2.2 says the temperature rise on a wiring terminal at a point to which the insulation of a wire is brought up as in actual service shall not exceed 50°C (122°F).
- Terminations for 100% rated breakers: UL489 Paragraph 7.1.4.3.3 says the temperature rise on the termination shall not exceed 60°C (140°F).
- Handles, knobs, and other user surfaces: UL489 Paragraph 7.1.4.1.6 says the maximum temperature on handles, knobs, and other surfaces subject to user contact during normal operation shall not exceed 60°C (140°F) on metallic and 85°C (185°F) on nonmetallic surfaces.
Table 1: Summary of temperature rise and maximums for a standard rated breaker (breakers are calibrated in 40 deg. C ambient)
| Surface | Temp. Rise above ambient | Temp. Max at 40 deg. C ambient (104 F) |
|---|---|---|
| Termination on standard rated breaker | 50°C (122°F) | 90°C (194°F) |
| Termination on 100% rated breaker | 60°C (140°F) | 100°C (212°F) |
| Handles, knobs, other user contact surfaces - Metallic | N/A | 60°C (140°F) Maximum |
| Handles, knobs, other user contact surfaces - Nonmetallic | N/A | 85°C (185°F) Maximum |
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It is irrelevant what temperatures of the other breakers are.
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True. However, just trying to encourage good investigative skills.
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So what’s the protocol for your example? Take a current reading?
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I do not have a precise protocol. Around here, it is usually the HVAC circuit that is warm because the AC is running or the pool filter is running (i.e. there is a logical explanation for why that branch circuit would be warm). However, if there is no readily-apparent explanation, I do have an AMP meter and am not afraid to use it.
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@eshamash - good on you for looking at things and being curious and asking…as others have said, this is normal and not a concern - Scan any GFCI on the wall and it will also show as warmer than a normal receptacle. Looking at smoke detection or CO - both will be warmer…
I would encourage you to get very familiar and take some thermography classes if you plan on using what you refer to as an infrared thermometer. You need to know how to interpret results. It is not good if you see a colder spot in the corner and call it out as a concern - realizing later that it is simple thermal bridging where framing members join and no insulation is possible. Freshly applied paint that is drying, will rack your brain…there is a lot of potential good info to be gained with a thermal camera - but knowing how to interpret it and use it properly is a whole other ballgame…practice looking at homes and the world around you with it and more of it will click as things progress
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Did you check for loose connection(s)?
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not 100% sure but i think op is taking about a non contact thermometer, which is what i would call it, and not an thermal imager.
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Yeah, that’s what it appears to be to me.
To just add on to Brian’s comment, the temperature of the other breakers isn’t relevant to that circuit, but it is a data point. If you’re in BFE North Dakota in February in an unheated garage, a breaker sitting there at 80 degrees should at least make you look at the label. “Electric Baseboards”, all good. “Garage door opener” might be a red flag as long as the door isn’t banging up and down like it’s trying to kill someone.
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Yep…
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