25 foot tap rule

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Grouch

Grouch

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New York, NY
Hi all,
in a 10 story building there's an existing 1200 amp riser that feeds multiple floors (riser fused at 1200 amps). on the 4th floor, we have a 100 amp disc. sw (fused at 100 amps) that taps off this main riser. however, due to architectural revisions, the 100 amp disc. sw. has to be relocated, and it will be about 20 feet away from the riser. In which case i follow the 25 foot tap rule. So my tap conductors now have to be sized at 1/3 of the feeder fuses, which would make it 400 amps, so i would use 600MCM tap conductors. my question is:

1) can the 600 MCM conductors terminate in the 100 amp disc. sw. that is 20 feet away? would there be an issue with the 600mcm not fitting in the lugs of the 100 amp disc. sw.? should i be specifying a 400 amp disc. sw. instead, and use fuse reducer clips to keep the fuses at 100 amps? a 400 amp switch is pretty big. is there another way around this?

thanks!
 
The 25' tap needs to be sized 1/3 all the way to the line side of the OCPD. The Lugs that the feeder tap land on need to be fully rated to the ampacity of that tap. I think that you're stuck with a 400 amp with the 25' rule. With the 10' rule, you would me good. Can I build a case with code sections? Not without a lot of time digging.


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Grouch1980 said:
Hi all,
in a 10 story building there's an existing 1200 amp riser that feeds multiple floors (riser fused at 1200 amps). on the 4th floor, we have a 100 amp disc. sw (fused at 100 amps) that taps off this main riser. however, due to architectural revisions, the 100 amp disc. sw. has to be relocated, and it will be about 20 feet away from the riser. In which case i follow the 25 foot tap rule. So my tap conductors now have to be sized at 1/3 of the feeder fuses, which would make it 400 amps, so i would use 600MCM tap conductors. my question is:

1) can the 600 MCM conductors terminate in the 100 amp disc. sw. that is 20 feet away? would there be an issue with the 600mcm not fitting in the lugs of the 100 amp disc. sw.? should i be specifying a 400 amp disc. sw. instead, and use fuse reducer clips to keep the fuses at 100 amps? a 400 amp switch is pretty big. is there another way around this?

thanks!
Click to expand...
You may not like this either, but you could extend the 1200 amp conductors to within 10 feet and then use the 10 foot tap rule.

If you can find a way to run the tap conductors outside the building there is no minimum size or length.
 
thanks everyone for the feedback. yeah, the taps originate inside, so I wouldn't be able to use 240.21.b.5. I'm stuck with the 400 amp switches. we'll just have to build a larger closet!
 
ron said:
Unless you can get a 100A disc with the ability to field replace lugs that accept 600's.
Click to expand...

I'm not so sure that the NEC is very clear on this, why wouldn't the switch need to be rated for 400 amps? Do the tap conductors end at the terminals on the switch or at the fuse?
 
Yetibiker said:
The 25' tap needs to be sized 1/3 all the way to the line side of the OCPD. The Lugs that the feeder tap land on need to be fully rated to the ampacity of that tap. I think that you're stuck with a 400 amp with the 25' rule. With the 10' rule, you would me good. Can I build a case with code sections? Not without a lot of time digging.


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Click to expand...

Where does it say that in the code?

It might be impractical to do it otherwise, but I don't recall any code requirement for this.
 
petersonra said:
Where does it say that in the code?

It might be impractical to do it otherwise, but I don't recall any code requirement for this.
Click to expand...

I think that it was discussed here years ago that the conductor ends at the fuse clip, it's at that point the tap conductors end not at the terminals.
 
infinity said:
I think that it was discussed here years ago that the conductor ends at the fuse clip, it's at that point the tap conductors end not at the terminals.
Click to expand...

the lug is not a conductor IMO. it is a terminal, since UL lists them that way.
interesting that the code does not define conductor.
 
Until they start putting ameperage ratings on lugs,nuts and bolts I'd have to say the tap conductor ends a the lug.

JAP>
 
I would be concerned that even if you found lugs large enough the wire bending at the switch termination would be a problem.
 
kwired said:
Extend 1200 amp feeder to outside, make the tap outside then.
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All of the tap conductors except at the point of load termination is required to be outside. Installation per 230.6 (2" concrete or brick encasement) qualifies.


How are the taps being made to the 1200A riser? In a riser vault? Is there a splice box being used? Seems odd that a 100A fused disconnect can't be squeezed in right there somewhere.
 
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Smart $ said:
All of the tap conductors except at the point of load termination is required to be outside. Installation per 230.6 (2" concrete or brick encasement) qualifies.
Click to expand...
Extending the 1200 amp feeder to the outside does not involve a tap conductor. Then you make the tap outside and could run the feeder tap around the perimeter (on the outside) of the building several times if you wanted to, but could enter the building a short (but not specified) distance to end the feeder tap at an appropriate overcurrent device.
 
I would hope this is a bussway riser, is it not?

Otherwise it paints a very ugly picture for me to begin with.

JAP>
 
ron said:
Unless you can get a 100A disc with the ability to field replace lugs that accept 600's.
Click to expand...

You're not going to get 600's crammed into a 100 amp disconnect, there simply isn't the room.

This is a job for a 400 amp disconnect and fuse reducers.
 
Cow said:
You're not going to get 600's crammed into a 100 amp disconnect, there simply isn't the room.

This is a job for a 400 amp disconnect and fuse reducers.
Click to expand...
I tried to not be so blunt, but yes normally there simply isn't room, 1/0 or 2/0 is usually the largest conductor they are designed to accept.
 
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