Service fuses different sizes

Kiwimike

New member
Location
Seattle
Can you use different size fuses for a 120/240V service? 30 amp fused disco, A phase running some pole lights needs a 30A fuse and a 20A outlet on b phase. Can't find anything in 230 saying its not
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
I have seen a number of high leg services where the conductor size and the fuse for the high leg was smaller than the other two fuses. I don't know of anything that would prohibit that.
 

Ravenvalor

Senior Member
Can you use different size fuses for a 120/240V service? 30 amp fused disco, A phase running some pole lights needs a 30A fuse and a 20A outlet on b phase. Can't find anything in 230 saying its not
Is this a service being fed by the utility company? Is it a service being fed by another electrical panel? Will both fuses be disconnected at the same time?
 

kwired

Electron manager
Location
NE Nebraska
There is no general minimum overcurrent protection requirements in NEC, there is maximums.

With a circuit breaker you are typically stuck with same setting for all poles of a multipole unit, fuses you have the ability to select a different level of each pole of a circuit.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
...
With a circuit breaker you are typically stuck with same setting for all poles of a multipole unit, fuses you have the ability to select a different level of each pole of a circuit.
And with fuses and a high leg service, you can also select different conductor sizes. The high leg can be smaller than the other two hot legs.
 

kwired

Electron manager
Location
NE Nebraska
And with fuses and a high leg service, you can also select different conductor sizes. The high leg can be smaller than the other two hot legs.
Which I have seen before. Was kind of common to see in services constructed in 1960's and 70's in small retail spaces that had air conditioning as the only three phase load and rest of space supplied by 120/240 single phase.
 
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