Tripping Main

[jerjwillelec]

First...I started a thread back in August of 2013 named "Tripping Main"...this is an extension of that thread.

Lengthy post...bare with me.

I am in the process (took the winter off because, well, who plays baseball in the winter) of troubleshooting a 400 amp Main Breaker that tripped twice last summer. This breaker feeds a baseball field consisting of field lighting (1500 watt MH...approx 10 - 13 years old), a press box and concessions stand.

Service is 400 amp and with the lights on, there is a 246 - 250 amp load.

The lighting is split up into two 175 amp branch circuits feeding through a lighting contactor, each with a 122 amp load.

The concessions consists of a couple of refrigerators, freezers, cookers, microwaves, etc...certainly no more than a 50 amp load (note: test was done without concessions stand load).

We had a HOT & DRY summer last year...one of the days this breaker tripped had a 104 deg heat index...the other was cooler but I don't recall how much. The Panelboard is in direct sunlight in a N3R enclosure. I don't recall for sure, but I don't think it had rained with in many days previous of the tripping (we were in a drout so I doubt it).

Just last week (ambient temp of 33 deg), I borrowed (because I don't have $5k - $10k to buy one myself) a thermal scanner from our fire department and did an infrared scan (keep in mind I have no experience with infrared scanning). I turned the lights on and let them run for a little over an hour and scanned throughout that time period. I did not notice anything abnormal around the main breaker...both line and load connections were hot but both equally so and they only reached around 91 deg or so. I am keeping in mind the ambient temperature difference and wonder if the heat index would be a factor.

I hope this works (because I've had issues in the past and I'm not much of a tech geek) but here is my Evernote page with notes and pictures.

https://www.evernote.com/shard/s89/...12789336003f/72b1532bdf6b1316707683c03cda0b08

So...what ya'll think? Please ask for more info if needed and I will do my best to oblige.

 

[just the cowboy]

Thermal Magnetic Molded Case Circuit Breaker

Thermal Magnetic Molded Case Circuit Breaker

You have a Thermal Magnetic Molded Case Circuit Breaker, They are tested at 40C they do make a magnetic only breaker for that enclosure. BUT I am not positive about it I could not find a temperature corrected curve for your breaker. Someone else will chime in.

 

[ATSman]

The concessions consists of a couple of refrigerators, freezers, cookers, microwaves, etc...certainly no more than a 50 amp load (note: test was done without concessions stand load).

This is a big assumption. I suggest you put a simple current recorder on the main cables. Since the notes state that a trip occurred during a night game, I would tend to rule out high ambient temp as the culprit.
If the breaker/ enclosure is 100% rated then an OC (thermal) trip would only occur if the phase current exceeded 400A. Otherwise the NEMA 80% rule would apply (320A) if I am not mistaken (someone correct me if I'm wrong.)
Then again the breaker could be faulty and be tripping under it's published rating.
You could have it OC tested by a NETA testing Co. but it may be cheaper in the long run to replace the breaker.
But FIRST you need to find out what the TOTAL load is when it trips and that comes from the recording AM.

 

[jerjwillelec]

But FIRST you need to find out what the TOTAL load is when it trips and that comes from the recording AM.

Any suggestions for a simple/affordable recording ammeter? I did a quick search and came up with:

http://www.amprobe.com/amprobe/usen...y-analyzers-/dm-iii-multitest-f.htm?PID=73223

and

http://en-us.fluke.com/products/pow...ree-phase-energy-logger.html#fbid=H1JmqmJuU98

but in my world...these aren't considered "affordable"