outside feeder / tap

R

rlqdot

Member
Location
St. Louis, MO - USA
Occupation
Professional Engineer (multiple states) - building design
is it permissible under NEC 240.21(B)(5) to extend a 70 amp 208/3 volt feeder from a circuit breaker inside a building underground to an outdoor wireway, then tap that feeder with two 20 amp taps and one 30 amp tap which each terminate in its own circuit breaker. feeding a septic treatment "plant" with three controllers - two 20 amp, 2-pole (208/1 volt) controllers and one 30 amp (208/3 volt) controller. feeder would be #4 (or #3 depending on voltage drop), taps would be #12 and #10 conductors. i can't tell if 240.1(B)(5) dictates the location of the line-end circuit breaker or the load-end circuit breaker.
 
Yes, and load-end circuit breaker.

If a conductor is protected at its ampacity at its supply end, then it complies with the first sentence of 240.21, and it is not a tap and there's no need to look at 240.21(B).

Cheers, Wayne
 
THANKS Wayne - maybe i'm over thinking this, but my only reason for considering 240.21(B) are the three taps at the load end of the feeder (the two 20 and one 30 amp taps) ... each of those taps terminate on their own circuit breaker of matching ampacity located in an outdoor control panel at the septic treatment "plant". my confusion was since the feeder gets its supply inside the building, whether the installation complied with 240.21(B)(5) "where the conductors are located outside of a building" and 240(B)(5)(4) "where the disonnecting means for the tap conductors is installed ... a. Outside of a building or structure ... b. Inside, nearest the point of entrance ... ". do those statements apply to the FEEDER (the 70 amp conductor) or to the three taps (2 x 20 & 1 x 30 amp conductors)? does the fact that the feeder originates inside the building violate the requirements of the main code section 240.21(B)(5)?
 
Since 240.21(B)(5)(3) refers to the overcurrent device for the tap (which is at the load end, not the line end, that's why it's a tap) being integral to or adjacent to the disconnecting means, we know the disconnecting means under discussion in 240.21(B)(5)(4) is at the load end of the tap conductors.

Basically in evaluating whether a tap conductor complies with 240.21(B), you only have to look at the tap conductor itself. And the tap conductor(s) start at the load end of your 70A feeder (which I presume is protected at 70A at its supply end, i.e. is not a tap). Nothing else about that 70A feeder is relevant for 240.21(B).

Cheers, Wayne
 
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