Service disconnect issues?

[princeofpen]

I'll be the first to admit not being as savy as some on electrical issues but need a few comments on this one. Here's the situation.

1 2500 A 3ph 208 service disconnect approx 100yds (yes yards) away from sub service.

2 Sub service is 7 disconnects (I know the 6 rule but moving on) of 400A each

3 An unbalanced load is drawn that does not open any of the 400A disconnects but ends up opening the 2500A main in another building.

Would having a given unbalanced load somehow cause such a large breaker to open or is the breaker it'self an issue? Tripping too easily etc. :banghd

 

[Dennis]

This can happen if the service breaker has not been adjusted properly. I am not savvy on this but I blew a 400 amp fuse when I shorted a 20 amp breaker.

 

[gfretwell]

The unbalanced load could easily gang up on the main. 7x 400 is 2800

 

[Dennis]

The term unbalanced load is deceptive. If the amps on one phase is not greater than the breaker rating then it should not trip. I can certainly have three different loads on a 3 pole breaker- an unbalance - but that in itself should not trip the breaker.

 

[gfretwell]

I was thinking more along the lines that he had unbalanced phases on all or some of the separate panels and they all ended up on the same service phase. You may be able to just rebalance each panel or roll the phases on a couple to fix this. I would start with a survey using my clamp to see what was going on.

 

[chris kennedy]

2 Sub service is 7 disconnects (I know the 6 rule but moving on) of 400A each

The 2500A is the service disco so the 6 rule doesn't apply down stream.

3 An unbalanced load is drawn that does not open any of the 400A disconnects but ends up opening the 2500A main in another building.

How are you sure this is what happened? Most likely a situation as Dennis mentioned occured. A 3Ø breaker that size will come with one if not several trip adjustments. These breakers are shipped from the factory on their lowest settings. A line to line fault of short duration will easily open an improperly adjusted 2500A main before any HACR rated branch circuit or feeder breaker.

 

[princeofpen]

The 2500A is the service disco so the 6 rule doesn't apply down stream.6 rule does apply in that the 2500A overcurrent is 100yds away in another building. Reason I stated the distance is not knowing if distance from 7 breaker sub to main mattered or not. The problem of tripping the main seems to come with either a large draw of current from time to time or once with a short on a 30A circuit.

 

[steveray]

Are you thinking about 230.3? One building not supplied through another? But I still do not belive that the 6 rule applies to your situation...I do not believe there is anything that says you need a service disconnect at each stucture, just for each service...and if there is only one service, UR good to go....

The 2500A is the service disco so the 6 rule doesn't apply down stream.6 rule does apply in that the 2500A overcurrent is 100yds away in another building. Reason I stated the distance is not knowing if distance from 7 breaker sub to main mattered or not. The problem of tripping the main seems to come with either a large draw of current from time to time or once with a short on a 30A circuit.

Hunh....quotes are coming out wierd....