125a breaker and 2/0 feeding 100a non fused safety switch.

[ctaylo360860]

We currently have an existing 125a breaker with 2/0 aluminum feeding 100a non fused safety switch. The diss then feeds 100a fuses in a pump panel with #4so chord… I know none of that is up to code. my question is for a multiple motor load can you have a non fused disconnect that is smaller than the ocpd?

 

[augie47]

Off the top of my head I would have thought not, but 430.110 requires the switch to have a rating at 115% of current and the breaker can be at 250% so it appears it would be permissible.

 

[Jraef]

Augie47 is correct. The conductors are protected by the feeder. The disconnect must be sized for the load. If the load is such that 100A fuses are appropriate for it, the disconnect is probably good too.

That said, you didn’t post any details about the load. Disconnects for motor loads MUST be rated for the HP of the motor, not the amps, because opening a disconnect while a motor is running is much tougher duty for the switch than just the amps. Then you mention “multiple motor load”, which brings in a different set of sizing rules on disconnects. Details are important here

 

[ctaylo360860]

Augie47 is correct. The conductors are protected by the feeder. The disconnect must be sized for the load. If the load is such that 100A fuses are appropriate for it, the disconnect is probably good too.

That said, you didn’t post any details about the load. Disconnects for motor loads MUST be rated for the HP of the motor, not the amps, because opening a disconnect while a motor is running is much tougher duty for the switch than just the amps. Then you mention “multiple motor load”, which brings in a different set of sizing rules on disconnects. Details are important here

Looks like I add up the values in 430.251 a and b and make if sure the disconnect is up rated for the added value of locked motors currents…I didn’t do the math test just went up to a 200a

 

[ctaylo360860]

Looks like I add up the values in 430.251 a and b and make if sure the disconnect is up rated for the added value of locked motors currents…I didn’t do the math test just went up to a 200a

Equipment on load side of disconnect has 7 motors . 1-30hp 3phase 480. 1-15hp 3phase 480. 3-2hp 3phase 480. 1-2hp 1ph 240v. 1-1/2hp 120v motor. Only the 30hp and the 15hp run at the same time. They might bump the 1/2 hp motor or the front axle motor to aim the product. they won’t run longer than 30 sec and they will go back to just 30hp and 15hp motors running.