rated amperage of 600V disconnect at 240V load

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comprev

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In order to save a buck the journeyman electrician I work with suggests using a 60A 600V rated fusible disconnect we have on hand to serve as the disconnect for a line supplying 100A at 240V to motor. He reasons that a 60A 600V disconnect should be sufficient to support 150A at 240V. Is this reasoning flawed, and is it consistent with what the NEC code requires? Thanks for your advice...
 
The amperage rating of the disconnect will dictate how much current can flow safely through the contacts of the switch. In this case it has nothing to do with the voltage rating.
 
I agree with Trevor, take a look at 430.110 for the ampere rating and interrupting capacity of the disconnecting means for a motor.

Chris
 
tell him to give back his journeyman's license....

do you use #18 for a 20A circuit at 277V? same principle...
 
Thanks for the quick responses.
I thought he must be mistaken, but he was so sure of himself. I guess certifications don't mean everything...
 
If the disconnect is rated at 60A, then it can only be used at 60A.

However _many_ devices have different ratings at different voltages. I've seen this on a contactor or molded case switch, for example. Perhaps this guy saw a device rated in this fashion and (incorrectly) generalized.

-Jon
 
He reasons that a 60A 600V disconnect should be sufficient to support 150A at 240V
Click to expand...
His reasoning is very flawed and at this point I would question his reasoning in other areas within the skilled trade. Confidenance overcomes ignorance?
While you can use a higher votlage rated OCPD in an application, the wire and fuse can only handle 60 amps. Additionally I would look within the label of the disconnect, which probably is only rated 10K (my quess) and you may have more fault current than the rating of the Disco.
Just my $.02
 
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