300v fuses

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Capital

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morris plains nj
I pulled a fuse disconnect 3ph, 200amp, 480v and found a A3T200 protecting each leg. Looking at the fuses it says they are rated with 300v. That cant be right, can it? Is it protecting only the 277 to ground.
 

infinity

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New Jersey
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Are you saying that those fuses were in a 200 amp, 600 volt disconnect switch?
 

Jraef

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San Francisco Bay Area, CA, USA
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Electrical Engineer
Nope. That fuse is only rated for 300VAC max, if you have 480V you need the A6T for 600VAC max. Doesn’t matter that the L-N is 277V, it’s based on the line volts.

The A6T is 1/2” longer, so either you have a 300V rated disconnect being used on 480V, or someone deliberately moved the lower fuse block. Either way it’s because someone didn’t know what they were doing. You cannot replicate their error and continue doing it wrong. You will be the last person to touch it so you now own the error if you fail to rectify it.
 
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