Will a panel that is overloaded cause branch circuits to trip before the main breaker

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EEEC

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Benicia, CA, USA
I have a buddy who owns a bar/restaurant and when I did a load calc on his equipment, he is way over the 200A main capacity. I told him we need to do a service upgrade. Well, against my advice, he has chosen to plug in and run an electric grill and two induction plates. He called me and said after a few minutes, the grill breaker trips and he is asking me why.

If the circuit size is correct for the grill, the grill isn't overloading the circuit itself. And if it doesn't trip immediately, there isn't a direct short. Would the fact that the panel amperage is so close to the main breaker limit cause excessive heat and resistance and possibly cause the branch circuit breaker to trip instead of the main? I wouldn't think so, but just thought I'd ask.
 
If the local ambient temperature, inside the panel, is higher than 40*C, and/or adjacent breakers are running warm, the grill breaker's trip curve will be affected downward, that is it will trip at a lower current than what its indicated trip current is.

Are the grill and induction plates on the same circuit, or is there something else on the circuit with the grill?

An IR scan of the panel may be in order.

This topic has come up before, and a temporary fix to an overloaded/warm panel is aiming a floor fan at it.
 
When you say
I did a load calc on his equipment, he is way over the 200A main capacity
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do you mean you did the actual amp draw measurements or did calculation on paper?
 
JFletcher said:
If the local ambient temperature, inside the panel, is higher than 40*C, and/or adjacent breakers are running warm, the grill breaker's trip curve will be affected downward, that is it will trip at a lower current than what its indicated trip current is.

An IR scan of the panel may be in order.

This topic has come up before, and a temporary fix to an overloaded/warm panel is aiming a floor fan at it.
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Thank you JFletcher. Very good to know...


Are the grill and induction plates on the same circuit, or is there something else on the circuit with the grill?
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They appear to be dedicated.
 
edward said:
When you say do you mean you did the actual amp draw measurements or did calculation on paper?
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I did both; on paper and took a reading. On paper, it adds up to about 240A. When I did the reading, both legs were near 90A with existing items running. However, there was no guarantee that the cooler motors were active at the time and he didn't want me to leave all the doors open to kick them on. The blender, espresso machine, etc., were not active either.

For a 200A service, one could technically have up to 160A per leg safely, correct?
 
I went down there to pull another reading with the new equipment installed, and when I went to open the panel, I found that the "maintenance" guy used self-tappers to fasten the panel cover. Low and behold, he nicked the sheathing. There are two sets of burners with a dedicated circuit for each set. When he turned the first set on, no problem. When he turned the other on, well... BOOM :blink:
 
EEEC said:
I did both; on paper and took a reading. On paper, it adds up to about 240A. When I did the reading, both legs were near 90A with existing items running. However, there was no guarantee that the cooler motors were active at the time and he didn't want me to leave all the doors open to kick them on. The blender, espresso machine, etc., were not active either.

For a 200A service, one could technically have up to 160A per leg safely, correct?
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You could check with utility to get demand history data to see where things stand. It is very common to have a nec calc value 2.5 times the highest record actual demand.
 
Thank you for the update. I was going to suggest examining the element's mounting brackets for tightness.

I found a loose bracket in a heatstrip. Several minutes after energizing, thermal expansion pushed the (non-fastened) element's terminal end into the chassis causing the breaker to trip.
 
It sounds like what "Jfletcher" suggested is the way to go.

Does not sound the main is over loaded. So upgrading will not solve the issue.

Move the high performing breakers away from each other so the produced heat does not effect the trip curve. Any outside generated heat will effect the trip curve. Where is the panel located? Outside in the sun or inside in the hot kitchen?
 
The self-tapper was in contact with one of the induction plate hot legs when it pierced the coating, which created a direct short to ground via the panel cover. This was the issue with the breaker tripping.
 
Thanks for updating with the problem found and a solution to it. :thumbsup:

EEEC said:
The self-tapper was in contact with one of the induction plate hot legs when it pierced the coating, which created a direct short to ground via the panel cover. This was the issue with the breaker tripping.
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EEEC said:
I did both; on paper and took a reading. On paper, it adds up to about 240A. When I did the reading, both legs were near 90A with existing items running. However, there was no guarantee that the cooler motors were active at the time and he didn't want me to leave all the doors open to kick them on. The blender, espresso machine, etc., were not active either.

For a 200A service, one could technically have up to 160A per leg safely, correct?
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A 200A main is good for 200A per leg. The other loads that were off, arent likely to get you above 200A per leg, or all be run simultaneously.

The 200A main should hold 200A indefinitely w/o overheating, tho I wouldnt want more than 160A continuous.
 
A 200A main is good for 200A per leg. The other loads that were off, arent likely to get you above 200A per leg, or all be run simultaneously.

The 200A main should hold 200A indefinitely w/o overheating, tho I wouldnt want more than 160A continuous.
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Thanks for the clarification!
 
The 200 amp main is also "thermal magnetic", meaning both current level and time effect the trip curve.

If you had every possible load turned on and did reach say 250, maybe even 300 amps, it still will take some time before it trips. the higher the load the less time it will take. But you also have many loads that do not normally run for very long so the possibility of having it loaded to 250 or 300 amps for long enough to trip isn't necessarily that great. The loads that are more continuous like HVAC loads are the ones that you do need to pay closer attention to. Things like a blender typically only run for a minute or less, cooking appliances may have a heavy draw, but once they reach operating temp they only cycle elements on/off as needed to maintain temp so they aren't a constant draw either. Demand factors in the code for cooking equipment are there because of this type of operation.
 
If the grill breaker is tripping then it has nothing to do with the service size. My bet is that your calculation may not be correct esp. if the actual readings were only 90 amps. The 20 amp circuit may have other things on it that is causing it to trip.
 
Dennis Alwon said:
If the grill breaker is tripping then it has nothing to do with the service size. My bet is that your calculation may not be correct esp. if the actual readings were only 90 amps. The 20 amp circuit may have other things on it that is causing it to trip.
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The OP figured out why the breaker was tripping:

EEEC said:
The self-tapper was in contact with one of the induction plate hot legs when it pierced the coating, which created a direct short to ground via the panel cover. This was the issue with the breaker tripping.
Click to expand...
 
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