Tap Rule question

[sesomkb]

Hello,

I'm looking over NEC 240.21(B)(5) for a tap rule. I have the following situation and want to know if it's permissible?

Situation: Incoming feeder from transformer to outside fused 800A disconnect is 480V. Secondary of this 480V fused disconnect will feed two 400A 480V panels inside of a building, cables will be protected in conduit. then from the 480V panels on to step down transformers, 208V panels, etc. length of feeder conductors to 480V panel will be greater than 25 feet.

Am I allowed to tap both feeds to the 480V panels from the secondary of the 800A fused disconnect and be code compliant or will I have to install one disconnect for each panel?

I'm still reviewing the NEC but appreciate any input here.

Thanks,

 

[david luchini]

If the feeders run outside the building from the exterior disconnect and terminate at the panelboards as soon as the enter the building, then the outside feeders (taps) can be any length.

 

[sesomkb]

If the feeders run outside the building from the exterior disconnect and terminate at the panelboards as soon as the enter the building, then the outside feeders (taps) can be any length.

Thank you. That's how I was reading it could be any length just wanted to make sure it was allowable to tap in this scenario.

 

[augie47]

The following might be worth noting:
"The provisions of 240.4(B) shall not be permitted for tap conductors."

 

[sesomkb]

The following might be worth noting:
"The provisions of 240.4(B) shall not be permitted for tap conductors."

I'm a little confused by 240.4(b). Are you saying with a tap I cannot size the fuse to the next standard size based on the cable's ampacity rating? Thank you for the thought I enjoy researching.

 

[david luchini]

I'm a little confused by 240.4(b). Are you saying with a tap I cannot size the fuse to the next standard size based on the cable's ampacity rating? Thank you for the thought I enjoy researching.

That's correct. For your 400A MCB panels, the conductor ampacity will have to be at least 400A.

 

[sesomkb]

That's correct. For your 400A MCB panels, the conductor ampacity will have to be at least 400A.

ok that's what I was thinking you were talking about. I'd have to size the conductor for 400A for each panel from the disconnect and fuse accordingly.