Tap conductor

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mgtack

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I recently ran across a situation and need some help. I recently found a panel (3 phase 4 wire 277/480volt) that has a 70 amp 3 pole breaker that feeds numerous pull boxes in a building. Each pull box is approximately 100 feet from the next one. The wire feeding the pull boxes is #4 awg throughout. At each pull box, the previous installer has tapped into one leg of the (i'm assuming they alternate legs)feeder with a #10 that is then run approximately 30 feet to a 30 amp 3 phase disconnect and the single leg is fused with a 30 amp fuse. The load side runs to the fan coil which is rated at 30 amps.

My question: I think the breaker can only 30 amps due to the #10 tap that is run from the pull box to the disconnect. Is this correct?

If it can only be 30 amps, what would be the least expensive way to correct the problem. Can a fused disconnect be mounted at the pole box and fused at 30 amps?

Can you give me a specific code I can reference?

Thanks for you help
 
Not supposed to be over 25' (but I'd let it go for 30') If its in a highbay area its fine under 100'. see 240.21B4
 
I think it is fine except in a very technical sense the maximum tap length might well be 25' and not 30', as another poster mentioned.

I would not be getting a tape measure out and worrying too much if the tap conductor is really 28' or 25'.
 
mgtack said:
So does the 70 amp breaker have to be replaced with a 30 amp?
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As long as the tap conductors are not over 25', the 70 amp breaker is ok.

If the tap conductors are in a cable or in a raceway that has an equipment ground, the equipment ground wire size would have to be the same size as the feeder ground.See 250.122(G) for article.

Rick
 
RUWired said:
As long as the tap conductors are not over 25', the 70 amp breaker is ok.

If the tap conductors are in a cable or in a raceway that has an equipment ground, the equipment ground wire size would have to be the same size as the feeder ground.See 250.122(G) for article.

Rick
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Are you saying the EGC would need to be larger than the #10 tap conductors? A 70 amp circuit would require a minimum of a #8 EGC.
 
infinity said:
Are you saying the EGC would need to be larger than the #10 tap conductors? A 70 amp circuit would require a minimum of a #8 EGC.
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No , i mispoke, the egc would have to be as large the tap conductors, up to the size of the feeder egc.

Rick
 
Imo, The egc never needs to be larger than the tap conductors. If there is a line to line fault the #10 will trip the 70 amp breaker so a line to ground fault would trip it also with a #10 EGC-- under these tap conditions.
 
Dennis Alwon said:
Imo, The egc never needs to be larger than the tap conductors. .
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Right, what i was thinking to say is as the tap conductors are increased, the egc also needs to be increased to the same size as the tap conductors even if the OCPD for the tap is in this case is 30 amps.

Rick
 
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