Tripped Mains

[mxslick]

Thanks for the pics..good news is IIRC that main lug assembly is replaceable, so it and the main breaker can be replaced without too much fuss.

As for one your last posts,

I am just not convinced this was an inrush problem because all the mains tripped.

I disagree that inrush wasn't the cause of the mains tripping, as in addition to the refrigerated loads there will be this factor:

Another reason can be a lot of thermostaticly controled water heaters, hot beverage machines and so on.
Under normal conditions the average load of such appliances can be suprisingly small, since they cycle on/off and only use power briefly once warmed up. After a shutdown though, all such appliances will draw full load current until the water/space/coffee is heated.
The load can easily exceed the service.

This lack of load diversity upon restoration of power can really add up the loads, and combined with the inrush from refrig loads, will easily trip the mains. I have seen this firsthand a few times.

Finally, if I were in your position I would go the extra mile and megger the panels and loads, as the reports of smoke and burning smells indicates that SOMETHING got too hot and will fail again at the worst possible time. I'm not convinced that the popping and smells have come from just this lug failure.

Oh, and did the customer say WHEN in this event they noticed the smoke and smells, and heard the pop? Was it BEFORE the power went out, during the restoration when the utility voltage was very likely unstable, or did they notice all that AFTER the power came back on? Was there a utility outage at all for other buildings served by the same transformers?

Still sounds like a potentially dangerous failure is imminent from here..

 

[charlietuna]

I agree with John Brian -- i am not downgrading anyone here--but as electrical contractors we need to KNOW what the problem is and not guess!
"High inrush" is a guess -- but to me "high inrush" should not cause a main breaker to trip--anywhere! Power company have outages from time to time--people hit utility poles, they blow transformers,etc.. but when the power is restored something is wrong when a customer's main or mains trip. To KNOW without doubt we need to KNOW the load over a period of time--the more time the better--maybe a data recorder. Spot infrared does not give you the full picture of what is happening in this panel--the main lugs might be hot--but to KNOW what the problem is you must determine the heat source ie: is it the wire termination or is it the lug fastening to the panel's bus. Now i know it is expensive to have this problem properly thermographed but does your customer have any idea on how much this problem has cost him over maybe (?) ten years. Consider that a poor connection on a simple 20 amp circuit can cost over $200. a year, then you can imagine what a 200 amp terminal can cost. If(?) this convienance store is a chain type someone needs to explain the advantage of maybe having their entire chain systematically thermographed??? And maybe you can team up with a thermographer on a contract---and end up with the repairs found. Infrared "pays" -- it does not "COST"! More contractors need to invest in data recording equipment -- you can get payed to set it up -- rent the data logger by the day or week --- and get payed to disconnect it and prepare the report papers. And again, get payed to do any necessary repairs. It's good work and can generate additional customers too.......

 

[charlie]

. . . The common link would be the primary but shouldn't the primary fuses or fuse trip before a service main? . .

There is a misconception that the primary fuses on electric utility transformers are there to protect the transformers; THIS IS NOT TRUE! Those fuses are there to protect all the other customers from having an outage. The primary fuses are often sized to only let go under fault conditions and will never open on overload. As an example, we use a 15T fuse on the primary of a 7.62 kV, 15 kVA transformer and the fuse will hold 150% indefinitely. That is 170 kVA to blow the fuse that is "protecting" a 15 kVA transformer! It is my understanding that most other electric utilities do the same thing to keep the lights on. :smile:

 

[HotConductor]

FYI, we service 140 of these regional stores and I've never seen tripped mains from an outage, NEVER! We respond to outages average of 2-3 times per week. If I thought there was an overload problem I would have set up our Fluke 434 but there is no overload problem.
Good news is GE still makes these Power Mark Gold panels so I'm replacing the entire guts, breakers and all. Also FYI to all who mentioned it I did use an infrared gun on my initial call to the store and there were no hot spots that I could find. Anyone have any suggestions on a reasonable TI gun?