Fused Neutrals - Why? -

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C

CCCI

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I have found that all of the air conditioning units (six) and the computer room here at my work all have fused neutrals. They each have a fused disconnect with the hot (277 volts) and neutral condutors fused. I find this odd. I just want to see what people think of this practice.
 
To me, 277-volt refrigeration equipment is odd. Can't say I've ever seen it. First thing I would do is make sure the disconnects are rated 600v, not 250.
 
Fused Neutrals

Fused Neutrals

The only place I'm aware of where fusing the grounded (neutral) conductor is prohibited is in service equipment disconnects. Branch circuits are permitted to have the grounded conductor fused. Next question is....why? I've seen installations where a fuse is installed to protect the grounded conductor serving specific types of equipment based on maunfacturer requirements. In the case of a 277v equipment branch circuit that shares a "neutral", there exists a possibility of a lost neutral resulting in the potential of 480V to the equipment. The fused neutral will not limit the voltage, but may provide some protection depending on proper fuse sizing. Best to install dedicated neutrals to the equipment in your installation.
 
277 Volts

277 Volts

Yes it is 277 volts Liebert Units. I looked at the panel and tested the voltage. I also looked at the nameplate. It is 277 volts. My question is why someone would fuse the neutral.
 
CCCI said:
My question is why someone would fuse the neutral.
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I bet they fused the neutral because someone didn't realize that 277 volts has a neutral. When I first heard about 277 Volts I remember not understanding how 220 volts was 2 hot conductors and 277 only had one.
 
In certain maritime applications, oil tankers is one example, fusing the neutral of 120 volt circuits (or more commonly switching the neutral and the hot conductor with the same 2-pole breaker) is a legal requirement.
 
CCCI said:
I have found that all of the air conditioning units (six) and the computer room here at my work all have fused neutrals. They each have a fused disconnect with the hot (277 volts) and neutral condutors fused. I find this odd. I just want to see what people think of this practice.
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It is a violation of 240.22 to install a fuse in series with the grounded conductor in this situation.

My thoughts are that the installer used a 2 pole fused disconnect and just decided to install the grounded conductor in series with one of the fuse sections.

Chris
 
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