10' tap rule

[busboy]

I have an existing installation with a 250a main feeding 500MCM for voltage drop in the risers in a dorm. Off of the 500mcm conductors are 100a 3' taps feeding a sub panel in each dorm apartment. The panels are full. Can we tap the 100a conductor with 25 amp conductors (240-21-B-4) based on the 250a main to feed a 20 breaker for AC in the dorm?.

 

[steve66]

Re: 10' tap rule

You can't tap a tap. So the answer is no. See 240.21 of the 2002 NEC.

Steve

 

[benaround]

Re: 10' tap rule

busboy,

You could tap the 500mcm agian within 10',but f

frirst has there been a load calc. done by anyone?

frank

[ August 09, 2005, 06:41 PM: Message edited by: benaround ]

 

[benaround]

Re: 10' tap rule

busboy,

You could tap the 500mcm agian within 10',but first of all,has there been a load calc done on the system yet? I was just thinking (3) 100a panels full,250a main, I don't know what kind of load a dorm would pull.

frank

 

[redfish]

Re: 10' tap rule

Why can't you check the load on the 100A panel, if there is room for more load just add a four circuit sub panel and feed it from the 100A panel. Move two circuits from the 100A panel to the four circuit panel, add your A/C circuit, figure the load on the four circuit panel and install an OCPD sized accordingly, to the 100A panel.