Taps and 310.15(b)(6)

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mark32

mark32

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Currently in NJ
Hello,

Let's say you need to feed a 100amp disconnect that in turn feeds a 100 amp load center in a multi family dwelling (120/240) by tapping off the service, which is being fed with 350 copper. Initially I purchased #4 cu because this panel is only feeding a single unit, soon thereafter, I noticed that such a tap (Less than 10') needs to have an ampacity equal to or greater than the overcurrent device it supplies, which #4 cu does not. However, 310.15(b)(6) says you can use #4 cu to feed a 100amp panel in this dwelling circumstance. I had little time to make up my mind and my inspector buddy was on vacation (So I couldn't call him) so I purchased #3 cu and did the job with it. So the job is done, just wondering if I could have used the #4 cu and be compliant. To take this a step further, considering I went up a size on the grounded and ungrounded conductors, would I have to go up a size on the EGC? (From the disconnect to the panel)
 
The tap rules do not apply when your connection is ahead of the service disconnecting means. Your "tap" conductors are actually service entrance conductors.
 
mark32 said:
Doh! So I could have used #4.

Thank you Infinity, you learn something every day.
Click to expand...
You mentioned that the wires are feeding only one dwelling unit. The other requirement is that it supply all of the power to that unit.
If you meet the full requirement, then you can use the 86% ampacity allowance for either a service conductor or a feeder.
To be a tap, there has to be OCPD upstream of the wire that does not adequately protect that wire.

Sent from my XT1585 using Tapatalk
 
GoldDigger said:
You mentioned that the wires are feeding only one dwelling unit. The other requirement is that it supply all of the power to that unit.
If you meet the full requirement, then you can use the 86% ampacity allowance for either a service conductor or a feeder.
To be a tap, there has to be OCPD upstream of the wire that does not adequately protect that wire.
Click to expand...


Digger I believe that you meant 83%.

BTW did you get my PM?
 
electrofelon said:
Ok, so say we have a feeder of 300mcm copper and are making a 25' 240.21 tap to supply a dwelling unit. Could we use #4 cu for the tap to supply a 100 amp MB in the dwelling unit? My answer is no.
Click to expand...

In that case you're correct because you have a feeder tap. In the case of the OP there is no feeder tap because you have SEC's.
 
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