Sizing Main Disconnect

[girl]

Hello All,

Your help is appreciated!
Here is my question: The contractor installed 3 phase , 600 Volt disconnect at MCC. Disconnect has 3 fuses, 25 Amp each fuse, 600 volt.
It supplys power to a 100 Amp Panel.
On the panel there are some 15 Amp single pole breakers, three pole breakers for a water pump, some 40 Amp breakers, and or 20 Amp breakers.

My question is: is that 25 Amp Main Disconnect on MCC properly sized for this Panel?

Thank you everybody

 

[GoldDigger]

Is there a transformer involved?


Sent from my XT1080 using Tapatalk

 

[charlie b]

I really hope that the person who made those selections was not counting on the three 25 amp fuses to supply a total of 75 amps. :happysad:

Your question cannot be answered (not enough information given), though an answer of "no" would be a really good bet. :happyyes:

The breaker ratings downstream of the three 25 amp fuses mean nothing. All that matters is the total calculated load. You might have a 40 amp breaker serving a load that actually draws only a couple amps. But it is more likely that the total amount of load that all those breakers serve would exceed 25 amps, and that will be a problem.

 

[Fulthrotl]

Your question cannot be answered (not enough information given),
though an answer of "no" would be a really good bet. :happyyes:

i'll put $10 on your "no" bet... sounds good to me.

can we double down on a pair of no's?

 

[Fulthrotl]

Is there a transformer involved?

gotta be.... i've never seen a 480 volt 100 amp panel.
does anyone even make something like that?

and 1 pole 15 amp 480 volt breakers.....

sounds like someone fed a transformer out of a 30 amp bucket
in a MCC...... to a 100 amp panel.... so that would give you
roughly 50 amps at the panel.... it'll probably work if you don't
turn everything on at once....

 

[charlie b]

25 amp primary fuses would work for the primary protection of a 15KVA, 480-120/208V transformer. Putting a 100 amp 120/208V panel downstream of that transformer would also work. But it would need to have a main circuit breaker rated at 50 amps or less, or it would need a similarly rated overcurrent device upstream of the 100 amp panel. You didn't mention whether the 100 amp panel had a main breaker.

As I said at first, the question did not give us enough information to allow us to provide a useful answer. Can you tell us more?