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wireperson

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I was looking at a building where I have to feed HVAC , there is a old square D MD 400 A. what got my attention was that the fuses on each phase of the 3 phase were different , one was 125A other 100A and another 150A its 120/240 .Is this legal ? what could be the consecuences of having this.
they eventually willl be installing cubicles , the wiring on this building doesn't have grounding in the outlets , do I need to run ground wires for the regular outlets and the ground for the isolated ground outlets?
thank you
 
wireperson said:
I was looking at a building where I have to feed HVAC , there is a old square D MD 400 A. what got my attention was that the fuses on each phase of the 3 phase were different , one was 125A other 100A and another 150A its 120/240 .Is this legal ? what could be the consecuences of having this.
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Unorthodox, but not illegal as long as each fuse is not larger than it need to be to protect its condcutor.

they eventually willl be installing cubicles , the wiring on this building doesn't have grounding in the outlets , do I need to run ground wires for the regular outlets and the ground for the isolated ground outlets?
thank you
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For the IG's, definitely. For the others, yes if there's no intact metallic conduit.
 
wireperson said:
I ... , one was 125A other 100A and another 150A its 120/240 .Is this legal ? what could be the consecuences of having this.

thank you
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trying to think of catastrophic failures, but only thing that comes to mind is maybe a large motor killing one phase (the lowest rated fuse) and then burning up. conditions would have to be right tho.
 
One fuse blowing is normally what happens if they're all the same size too. I really don't see a problem, as long as none of them are oversized. Just a case of "what's on hand" and not wanting to take the system out of service to replace them with the right one's later.
 
wireperson said:
there is a old square D MD 400 A. what got my attention was that the fuses on each phase of the 3 phase were different , one was 125A other 100A and another 150A its 120/240 .Is this legal ? what could be the consecuences of having this.
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Being an old delta system, I would bet the conductor for the wild leg is smaller than the other two. If that's true, than the fuse would naturally be smaller. As far as the other odd fuse, like Marc said, it's what was available.
 
Minuteman said:
Being an old delta system, I would bet the conductor for the wild leg is smaller than the other two. If that's true, than the fuse would naturally be smaller. As far as the other odd fuse, like Marc said, it's what was available.
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Why would the conductor be smaller?
 
paul said:
Why would the conductor be smaller?
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If it is a 120/240V, 3?, 4w service, the high leg (B?) will have less load on it and could be fused at a lower value for better or closer protection. However, with three different sizes of fuses, that doesn't seem to be the case. :)
 
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