Breakers tripping - heat related???

Greg Swartz

Greg Swartz

Senior Member
Location
Colorado Springs, Colorado
Hey all,
Been a while since I posted.

It's starting to get hot out, and we are getting more and more complaints about breakers tripping.
This has happened the last 2 years in June, July, and August. - and 2024 is no different.
Tesla EVs are tripping their NEMA 14-50 receptacle 50A breakers. (No - the customers are not changing the ampacity. They work fine the rest of the year.)
"Random" breakers trip - but only on hot days. - And no, not much of a load on them.
This happens with Square D Homeline, Cutler Hammer BR, and Siemens QP panels. - oddly enough... I CAN'T get FPEs to trip no matter what... but that's a different story! (Bad joke)
It happens with old breakers (>20 years old)... it happens with new breakers (<1 year old)... it happens with in-between breakers (1-20 years old)

I called my 3 major suppliers (Square D, Eaton, and Siemens) today to see if they have any knowledge on such items.
All 3 "I've never heard such a thing before!" - each with the incredulity that such a thing could ever happen with their product.

Sunday, a Siemens 100A Main breaker tripped with about 55A on it. It is about 24 years old.
I was there Monday, got everything up to about 86A, and she held fine for 15-20 minutes.
Today, Tuesday, it tripped with only about 45A on it.
The difference... Sunday it was about 95 degrees out, Monday about 82 degrees (rain helped a lot), Tuesday (Today) about 93 degrees.
Customer took an IR thermometer gun to his panel today... registered at 168 degrees.

Would swapping out his main with a new 100A main even help? (Procure material, pull permit, call POCO, building department inspection, and my time)

I know that the breakers are both thermal and magnetic...

Is this something you all experience?
Are there any white papers out there on this?
And if this is an issue in 95 degree weather... what about places like Phoenix at 120+?

Thanks,
Greg
 
H

hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
May also be poco voltage dropping due to higher line loads, which may increase the amperage on certain loads, combined with the higher ambient temperature might be the problem.
 
W

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
Yes, breakers respond to high ambient temperature.

But they also respond to any source of heating.

Based on the numbers, I suspect that the 100A main tripping at low current is experiencing heat generated by a bad connection in or near the breaker.

This could be supply wires loose, a bad connection to the panel bus bars, or a contact failure inside the breaker.

Jonathan
 
Fred B

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
Have you done thermal imaging or temperature testing on the breakers yet? See what temperature they are getting to as they trip. Seen tripping on AFCI/GFCI when stacked multiple side by side hot days and heavier loads but not overloaded.

Are these panels on exterior? Exposed to direct sun? Or in a conditioned space? It is common for extreme temperatures in either direction to effect the breaker trip. A chart related to SD breakers shows normal operating temperature not to exceed 104oF based on UL489. If temperature is exceeding or getting close you might consider some sort of cabinet cooling equipment.

 
ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
Breakers will get warmer as the load goes up. Adding a high ambient moves it closer to a thermal trip point.

A thermal scan with a $40 non contact from TSC is convenient.
A FOP test using a meter with a millivolt range will weed out poor internal and external connections.
 
Greg Swartz

Greg Swartz

Senior Member
Location
Colorado Springs, Colorado
To respond to several comments:
Thermal imaging - the customer has an IR thermometer (He's a firefighter.) - Yesterday (Tuesday), with a very LOW load, the temperature on the surface of the panel (read: The panel cover) was 168 degrees.
Side note: when it originally tripped on Sunday - it was hot as well.

On Monday, when I loaded the panel up to 86A for 15-20 minutes, I did touch the breaker, and the surrounding breakers... not even warm to the touch. It was fine... BUT it had also just rained out... so even though the temp reached 82 degrees, the rain cooled things down... a LOT.
(Also side note: Had the customer touch it as well, and he said that it was not nearly as warm as the previous day.)

I knew the loose connection comment was going to come up, and forgot to head it off at the pass: No loose connections I could find.

Also keep in mind, this is not only a "specific" problem (The Siemens panel from Monday), it is a "general" problem (the EVs, and others from all 3 of my "normal" manufacturers: Square D, Eaton, and Siemens) that happens during the summer months.
Usually when the interior panels on exterior walls have the sun beating on them for several hours.

So, mainly this is an interior panel on an exterior wall issue... because I don't have this issue on exterior panels.
And again, this is something that I have seen issues with even new breakers we have installed... all the way to older breakers.
 
W

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
Greg Swartz said:
To respond to several comments:
Thermal imaging - the customer has an IR thermometer (He's a firefighter.) - Yesterday (Tuesday), with a very LOW load, the temperature on the surface of the panel (read: The panel cover) was 168 degrees.
Side note: when it originally tripped on Sunday - it was hot as well.

On Monday, when I loaded the panel up to 86A for 15-20 minutes, I did touch the breaker, and the surrounding breakers... not even warm to the touch. It was fine... BUT it had also just rained out... so even though the temp reached 82 degrees, the rain cooled things down... a LOT.
(Also side note: Had the customer touch it as well, and he said that it was not nearly as warm as the previous day.)

I knew the loose connection comment was going to come up, and forgot to head it off at the pass: No loose connections I could find.
Click to expand...

IMHO with a low load and a panel at 168F, there has to be a specific source of heat causing problems. Yes, the 93F ambient will reduce the tripping threshold, but not enough to cause a 100A breaker loaded at 45A to self heat to an external surface temperature of 168F and trip.

If the problem isn't a loose connection, then there has to be some other source of heat, something hotter than 168F so that as the heat dissipates it shows up as a surface temperature of 168F. The loose connection might be the switch contact internal to the breaker, or it might be in an adjacent breaker. But my guess is that there is a loose connection somewhere, or some other source of heat directed at the breaker.

-Jonthan
 
Jraef

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Fred B said:
Have you done thermal imaging or temperature testing on the breakers yet? See what temperature they are getting to as they trip. Seen tripping on AFCI/GFCI when stacked multiple side by side hot days and heavier loads but not overloaded.

Are these panels on exterior? Exposed to direct sun? Or in a conditioned space? It is common for extreme temperatures in either direction to effect the breaker trip. A chart related to SD breakers shows normal operating temperature not to exceed 104oF based on UL489. If temperature is exceeding or getting close you might consider some sort of cabinet cooling equipment.

Click to expand...
But... that 40C max temperature is for the air around the BREAKER, not the outside air. t can be a lot less outside and the temperature IN the breaker panel can get really high, especially if you are running a car charger AND an couple of AC units AND someone took a shower so the water heater is pulling current, etc. etc.

As to the breaker suppliers telling you otherwise, they were just blowing you off out of laziness. EVERY breaker manufacturer has a de-rating curve for temperature. For example, here is Square D's. They don't show the HOM breakers, but I know that the trip curves are the same for QO, so I'm going to assume the de-rate curves will be as well. So as an example from page 5, the trip point of a QO 100A breaker from your example above gets de-rated to 80A if the temperature INSIDE THE BOX gets to 60C (140F). Tripping at 55A seems a little extreme, but who knows how hot it got inside that panel!
 
W

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
The OP's original line of questioning appears to be to determine if it made sense to swap the main breaker. If a normally functioning breaker (meaning a breaker with normal temperature sensitivity in normal tolerances) would be expected to trip at these low current levels (100A breaker tripping at 45A) because of the ambient temperatures. If the breaker is expected to trip given the measured conditions, then replacing the breaker won't fix the problem.

IMHO the 168F temperature measurement is strongly suggestive of a source of heat _inside_ the panel.

OP checked for loose connections. Question to the OP: did this check include pulling breakers off the bus to see if they were loose on the bus stabs? I think the Siemens main breaker bolts to the bus, but the other breakers snap on to the bus.

One plausible source of heat inside the panel would be breakers adjacent to the main breaker.

OP related the experience of EV charging circuits in hot ambient conditions. This is a closer case; a breaker likely loaded at 80% of trip rating for an extended period of time.

-Jonathan
 
readydave8

readydave8

re member
Location
Clarkesville, Georgia
Occupation
electrician
I have some experience with breakers tripping during heat waves

These were mobile homes, came with 3500 watt water heaters, wire size 12, breaker size 20

For several years I would get calls on exceptionally hot days that breaker tripping, they all had water heaters changed to standard with 4500w elements, so 18+ amps?

Maybe 6-8 instances in perhaps a 10 year span
 
G

greco

Member
Location
colorado
I had that problem also ( Ft. Collins here) sorry but I don't remember our solution. We were sure it was the temp and the panel was getting direct sunlight. I think we may have put something for shade. This was a pre manufactured building, movable, pre wired and well done. We had several of these and the only ones that tripped got direct sunlight.
Greco
 
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