Main Trips

pat c

hi everybody im new here . Ive been having a problem with one of my customers plant. its about 60000 square feet theres a main distribution panel 347/600Volts 1200 amps has u can see this is canadian voltage, anyhow a few months ago theve been calling me cause the main would trip during the night and once during the day i get there all that is trip is the main which does not help me to find and correct the problem, so i close all the other swiths after the main to try an isolate the problem put them on 1 at the time and nothing, then one day i did that again 1 switch blew 300amp i followed the pipe broght me to find that the problme was an a/c unit so i close the power feeding the a/c unit told my customer call the ventilaation guy to check out his unit, so now im happy thinking i found the problem NO MORE 3 am wake up calls... Wrong 2 months later 3 am wake up call the main triped again now . the a/c unit was repaired and its not triping any other switchs take in consideration that this is an old plant over 60 years so theres alote of old stuff in there. i just bought a megger thinking i can find the problem wit this ... How does it work ive never used one before and wat am i suppose to be looking for when i use the megger is there a web site (megger for dummies) anyone.....

TxElectrician

I am not familiar working with Canadian voltages or codes. Is the MDP equiped with ground fault protection?

pat c

this is an old military base the main is new was redone id say about 10 years ago but most of the stuff most ppl in the trade never seen stuff like they have in these buildings. the main is a MCC from square D

Bubbles

Overload (set amprobe on peak hold overnight) see if it's overloading. Kicking 1/2 way or all the way?

Short (maybe since they happen at those time heating cooling expansion). Something is touching at those times. Meggar might pick up the culprit when you deengergize and check branch circuits.

Bad Main

Thats what I can think of for the moment. Or it could be the Boogieman. I'm staying tuned to hear what others think....

mdshunk

I think you're a world-class nutcase if you reset any of that without doing a megger check. Megger things out before you reset anything. It may save your life one day.

Magnettica

I'm thinking a short in one of the feeders to one of the panels.

I had this happen at a garbage disposal company truck storage/ repair shop once.

One of the ungrounded feeders got knicked on the original pull and it took a few years before it finally began to arc during a rainstorm, a portion of the run was on the exterior of the bldg.

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pat c

but its not normal that an a/c makes a 1200 main trip its feeding of a 30 amp. can the main be to sensetive. can something be done,

mdshunk

Oh yes it is!!!!!

Brother, you really need to bone up. You're seriously going to get yourself or someone else hurt bad one day.

Bkessler

I shorted out a 20 amp receptical circuit that tripped a 2000 amp main in a medical facility once. Before it was occupied.

Magnettica

I had the same thing happen once. Accidentally tripped a 20 amp branch circuit and the MLO panel's MB tripped. It had something to do with the short-circuit rating of the circuit breaker which I am still a little confused about.

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Magnettica

Correction.... not that I am totally confused about the short circuit ratings, just that the branch circuit circuit breaker had the same short circuit rating as the main did. the main had a 10k rating, as did the branch circuit circuit breaker. The main should have been whatever the transformer supplying it required, it did not. It was undersized and that's why the whole panel tripped and not just the branch circuit.

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pat c

ppl come here to talk electrical not to be insulted by you..ease up tough guy

Bkessler

People here are going to tell you the things you need to here as well as things you want to hear and also the things you don't want to here. Don't be so touchy.

TxElectrician

hear here