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Hi and thank you in advance for any comments or help you may have.

I'm new to the site and first time member of any forum, but this one looked like there were some really good electricians as members.

So on to my dilemma,

I have an excellent commercial customer that has a couple of high end French restaurants that I service. The restaurant with the main tripping is fed by a single phase 200A service. (I know its small for a kitchen but its not a big place maybe 1k sqft). Included in the load is a small walk in freezer, a 30A convection oven, a 45A oven, a hot plate, a sandwich press, a few coffee makers, 3 under the counter coolers, 3 ceiling fans, 12.5kw AC, 2 exhaust fans, ,2 microwaves and general lighting and receptacles. Now before you tell me i'm over my load, let me give you some background.

I installed a 50A circuit for the oven and a 30A circuit for the convection oven over 2 years ago. There have not been any issues until about 1 month ago. They have not added any new equipment since then.

The first time that the main tripped they were using both the oven and convection oven at the same time. Shut the bigger oven off and reset the main breaker and they had no issues for the rest of the day. The next time it tripped they were using the bigger oven only. I went out to evaluate the problem after hours and found that the circuit was ok, all the connections were tight, no issues up to the outlet feeding the oven. I advised them to have an appliance tech come out to service the oven. When the tech came out he said that there was a heating element that was bad and replaced it. The next day the main tripped again. I went back out after hours and put my amp probe on the feeders and had a stable reading of about 40-50A per phase. The panel is about 20 years old and I suggested that if it continued to be an issue that I would replace the main breaker, which may repair the issue. Of course over the new few weeks it tripped another 10-12 times. I ordered the new breaker and installed it. (While I was taking off the cover to replace the breaker I tapped the panel and the main tripped, I thought for sure that the breaker had been worn over time and became weak). The next day after I installed the breaker there were no issues, on the following day the main tripped while using the smaller oven, and not both ovens at the same time.

I went out again, this time during there busiest time of the day and put my amp probe on the main, Phase A was reading about 95A and Phase B was jumping from 80A to 175A within seconds without either oven on.

And to add another issue, the bigger oven was no longer working. There was power to the receptacle outlet, although it was not functioning.

Normally this is a no brainer, they are over there load cals and its tripping the main. But there were no issues for years and all of a sudden, its tripping.

My next thought, would be that there is obviously an issue with the larger oven, which should trip the 50A breaker not the 200A main unless its cross phasing (which I guess would be possible if there was a bad heating element) and now its stopped working. Definitively the problem right, well no because it tripped without the oven even on.

Maybe a faulty or worn main breaker, thats brand new now.

And these amp probe readings spiking all over the place without the ovens even on. I did shut down each 220v piece of equipment to see if there was one thing that was causing it, but I couldn't determine the issue. I checked the service lugs including the neutral all tight.

I'm out of ideas, I don't want to be a parts changer until I find the problem. It would be hard to talk the customer into upgrading the service since there were no issues for such a long time.

If you made it this far, thank you for caring and any advise or comments you may have would be greatly appreciated.
 

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felonious smile.
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Compressor or motor lock load while service is under heavy demand.
 

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Compressor or motor lock load while service is under heavy demand.
x2 You've either got a really hard starting or locked up compressor someplace, or you've got a really bad short you haven't found.

Go down through each branch breaker with the amprobe and see what's what. Your load spikes are coming from someplace. (hopefully the bus is not melting down behind the branch breakers- worth a look).
 

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animal lover /rat bastard
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I agree with all of the above. I don't understand why you didn't amp probe it the first time though, before you replaced the main.
 

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x2 You've either got a really hard starting or locked up compressor someplace, or you've got a really bad short you haven't found.

Go down through each branch breaker with the amprobe and see what's what. Your load spikes are coming from someplace. (hopefully the bus is not melting down behind the branch breakers- worth a look).
I would certainly look at the bus behind that oven circuit.
 

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RIP 1959-2015
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x2 You've either got a really hard starting or locked up compressor someplace, or you've got a really bad short you haven't found.

Go down through each branch breaker with the amprobe and see what's what. Your load spikes are coming from someplace. (hopefully the bus is not melting down behind the branch breakers- worth a look).
X3

An IR temperature reading will find that fast, I'll bet that panel is hot as hell.

Welcome to the forum 'Pendl Electric'..:thumbup::thumbup:
 

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1Ø or 3Ø ? and what style Main? TQD ? Some GE breakers have very low spike tolerance with motor loads, so, as other posters have noted, if you have a compressor or other motors (vent/ hood fans?) you may want to either install a small MMS between those units and the branch breakers... Also, as other have posted, check for hot spots in the panel.. and speaking of.. is this just a 240v? or 277/480? Shockingly there are alot of low end and resi panels being used in industrial/ commercial applications....
Keep me posted.....breakers and control is my specialty... I love to learn from issues like this as much as i like to help people..
 

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Did you perform a FOP TEST?
Have you checked the temperature of the CB?
Did you megger all components?
Defective CB, overload or short, this ain't magic.
 

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1Ø or 3Ø ? and what style Main? TQD ? Some GE breakers have very low spike tolerance with motor loads, so, as other posters have noted, if you have a compressor or other motors (vent/ hood fans?) you may want to either install a small MMS between those units and the branch breakers... Also, as other have posted, check for hot spots in the panel.. and speaking of.. is this just a 240v? or 277/480? Shockingly there are alot of low end and resi panels being used in industrial/ commercial applications....
Keep me posted.....breakers and control is my specialty... I love to learn from issues like this as much as i like to help people..

SPIKE TOLERANCE, do you mean current inrush, a spike is a voltage anomily.
 

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SPIKE TOLERANCE, do you mean current inrush, a spike is a voltage anomily.
yeah.. sorry...motor's current inrush... most small commercial panels (208 & 240v) dont have an option for branch breakers with high magnetic settings, and the circuit(s) with any motor load could really use something in line to "catch' the inrush..
 

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yeah.. sorry...motor's current inrush... most small commercial panels (208 & 240v) dont have an option for branch breakers with high magnetic settings, and the circuit(s) with any motor load could really use something in line to "catch' the inrush..
A starter isn't going to do diddly to "catch" any inrush, as far as the breaker is concerned. Not sure what you mean, exactly.
 

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A starter isn't going to do diddly to "catch" any inrush, as far as the breaker is concerned. Not sure what you mean, exactly.
A MMS or small line starter with a class 10 or even class 20 overload will hold the inrush load alot longer before tripping than a standard thermal/mag breaker alone will.. I am, however, more concerned why the branch breakers are NOT tripping before the main is.. I am curious as to the hearing the outcome.... I'm no sparky- so hearing all of your replies definitely helps me in the long run :)
 

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A MMS or small line starter with a class 10 or even class 20 overload will hold the inrush load alot longer before tripping than a standard thermal/mag breaker alone will.. I am, however, more concerned why the branch breakers are NOT tripping before the main is.. I am curious as to the hearing the outcome.... I'm no sparky- so hearing all of your replies definitely helps me in the long run :)
The main tripping first is an easy one. Plot it's load, compared to the load on the offending branch breaker, on their respective time-current trip curves, and the main is often closer to tripping on a hard fault. Happens all the time.

Your starter thing still confounds the hell out of me. The starter, on the load side of this breaker he's having trouble with, won't do a blessed thing for the breaker. It's not like he can tap the starter off the line side of this main.
 
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Would probably help if non-sparkies would say so before they post as to not mislead others.
Sorry, didn't mean to sound misleading.... MD is right and makes a valid point..and I thoroughly enjoy his knowledge, I'm here to learn as well ;) ....I was simply suggesting that if a circuit that has a motor on it, it would benefit to having some sort of MCP.... (I got a little off topic to the OP... my bad)... and as posted earlier.. distribution and control products is my specialty, and anything I can learn from electricians to help me build or sell a better product, will be a lesson WELL learned... even the constructive criticism to my posts... (and yep.. Im a newbie to the blog/ thread thing as well).. Yall be safe..
 

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Discussion Starter #16
Thanks

I really appreciate all the responses.

To address your comments and replays:

I did complete amp probe readings on the main and branch circuit breakers before replacing the main, I did not see the fluctuation until I went there while they were under full load. The first and second time I took readings it was after hours or they were getting ready to close. Any one who services restaurants knows they push the after hours thing.

Its a single phase 240v service. A separate meter can, the main GE 200A breaker is in a main breaker distribution panel and is below the meter, its also feeding two sub panels a 100A main lug and 125 main lug.

I have not completed a thermal scan, but I will.

I'm going to go back during business hours and check all the refrigeration equipment and bus bar. (I did check to see if any breakers were loose but I'll check again)

I will keep you posted... Thanks again.
 

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Any chance the 200A main has ground fault protection?
 
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