tap conductors

[electro7]

Hi,

I have a situation where there is an old meter main combo panel. From the meter it feeds 2 100 amp breakers and there is no more room to add any breakers. I was wondering if it is okay to tap onto the load side conductors of one of the 100 amp feeder breakers according to 705.12? I would then go to a fused disconnect for the PV. The fused disconnect will be rated for 30 amps. I think I would still need to use #3 wire from the tap to the fused disconnect, is that correct?

Thanks for your help

 

[Zee]

Load side taps with fused discos for PV are permitted by the NEC. Under certain conditions that apply to all load side connections (breakers in panels)

HOWEVER, many local authorities will not allow them ever! So check with them.

1. You do have to consider the 120% rule though....and i cannot remember if the latest code would allow 30 A of PV on a 100 amp circuit............
(someone else here can comment.)
2. the tap location is problematic also..... as it is not opposite feed.
i.e. your 30 A PV "supply" is between the loads in the s.p. and the 100A brkr. in the Main Service Panel.


FWIW: load side taps are so problematic here...i have the whole MSP replaced and then pop in a breaker at the bottom.

 

[ggunn]

Hi,

I have a situation where there is an old meter main combo panel. From the meter it feeds 2 100 amp breakers and there is no more room to add any breakers. I was wondering if it is okay to tap onto the load side conductors of one of the 100 amp feeder breakers according to 705.12? I would then go to a fused disconnect for the PV. The fused disconnect will be rated for 30 amps. I think I would still need to use #3 wire from the tap to the fused disconnect, is that correct?

Thanks for your help

Could you possibly install two-wire lugs on the busbars of the panel where it is fed from the meter and tap there for a supply side tap?

 

[electro7]

Yeah was also thinking that. If I remember correctly it has a busbar feeding from meter to 2 100 amp breakers. So maybe there is a lug kit?
Thanks

 

[jaggedben]

The 2014 code is the first code to explicitly address feeder taps. See 705.12(D)(2)(1). You are allowed to tap a feeder if the feeder is rated for the sum of the utility source breaker and 125% of the inverter output. You are also allowed to tap the feeder if the load end of the feeder is protected by a OCPD that doesn't exceed the feeder's ampacity.

Under previous codes you could argue that you can connect sources with breakers adding up to 120% of the feeder conductors' rating. E.g. if the feeder is rated 100A and has a 100A breaker, you could tap to a 20A solar breaker. As Zee says though, sometimes the code doesn't matter with AHJs.

Sometimes feeder conductors happen to be large enough that the rating exceeds the sum of all breakers, in which case you ought to be fine under any code. (Under the 2014 code it can be the sum of the utility feed breaker plus 125% of inverter output. That is, possibly slightly lower than the breaker sum.)

Depending on your situation, another option besides a tap or service upgrade could be to break out one of the 100A feeds to a new subpanel with distribution for the solar and the existing feed. Sometimes this is simpler and cheaper, sometimes not.

 

[ggunn]

Yeah was also thinking that. If I remember correctly it has a busbar feeding from meter to 2 100 amp breakers. So maybe there is a lug kit?
Thanks

Something like these, maybe?

http://mechanicallugs.com/index.php/two-wire-lugs.html