I have a question about the application of the 10 foot tap rule (240.21 (B) (1)). I have two RTU's I need to power, one requiring 150 A, the other 40 A at 208V 3 phase. There is an existing 2500 Amp switchgear that is full up (capacity wise, not ampacity wise) that I would like to tap off from to a couple of fusible disconnect switches within 10 feet. My confusion stems from part (4) of the article referenced above that states that if the tap conductors leave the enclosure from where they are tapped, they have to be no less than a tenth of the ampacity of the OCPD of the line side (in this case, 2500 Amps). Does this mean I have to have conductors sized for 250 A, since the conductors leave the switchgear, go a few feet in conduit, to disconnect switches?
10 Foot Tap Rule Question
- Thread starter darren71
- Start date
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- Location
- Massachusetts
Re: 10 Foot Tap Rule Question
Yes that is correct.
Also if you run an EGC it will need to be 350 CU or 600 AL from the service gear to the disconnects.
Yes that is correct.
Also if you run an EGC it will need to be 350 CU or 600 AL from the service gear to the disconnects.
- Location
- Massachusetts
Re: 10 Foot Tap Rule Question
Thinking about this more I would say you better plan on two 200 amp disconnects one with fuse reducers in it to get the 40 amp fuses in.
I doubt you can get a 60 amp disconnect with lugs large enough and space to bend 250 amp conductors.
Thinking about this more I would say you better plan on two 200 amp disconnects one with fuse reducers in it to get the 40 amp fuses in.
I doubt you can get a 60 amp disconnect with lugs large enough and space to bend 250 amp conductors.
lady sparks lover
Senior Member
Re: 10 Foot Tap Rule Question
Lady
Equipment Grounding Conductor
Lady
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: 10 Foot Tap Rule Question
Do you have the alternative of taping off one of the existing feeders? In other words, instead of connecting directly to the switchgear (with its 2500 amp Main), can you tap off downstream of one of the existing breakers? If an existing breaker is listed for double lugs, that could solve your problem. Or perhaps you have an existing breaker that feeds a conveniently located panel that, in turn, has feed-through lugs that you can use. There are other possibilities for tap points.
Finally, can you install a new sub-panel, disconnect an existing circuit from its breaker (thus creating a spare breaker on the switchgear), reconnect that circuit to the new sub-panel, and then power the sub-panel from the (newly created) spare?
Do you have the alternative of taping off one of the existing feeders? In other words, instead of connecting directly to the switchgear (with its 2500 amp Main), can you tap off downstream of one of the existing breakers? If an existing breaker is listed for double lugs, that could solve your problem. Or perhaps you have an existing breaker that feeds a conveniently located panel that, in turn, has feed-through lugs that you can use. There are other possibilities for tap points.
Finally, can you install a new sub-panel, disconnect an existing circuit from its breaker (thus creating a spare breaker on the switchgear), reconnect that circuit to the new sub-panel, and then power the sub-panel from the (newly created) spare?
- Location
- Massachusetts
Re: 10 Foot Tap Rule Question
Good point, I did not really think about the size of the ungrounded conductors he would be running.
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