If you are running extra parallel sets for voltage drop, can you get to a point (maybe 500 feet away let's say) where you decide to decrease the quantity of parallel sets and also decrease the feeder size - just as long this smaller feeder is still protected by the OCPD upstream??
Increasing feeders for voltage drop then decreasing feeder size
- Thread starter cppoly
- Start date
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Yes that's correct. As long as the smaller conductors are still large enough to be protected by the feeder OCPD you're good. If your smaller conductors are smaller than the OCPD then you may need to apply a tap rule.
Elect117
Senior Member
- Location
- California
- Occupation
- Engineer E.E. P.E.
That actually raises a good follow up question.
Then would the EGC be sized based on the increased size (250.122(B))? Would it apply only for the portion where the size is increased?
Or would you increase it the whole way?
I lean towards increase it the whole way.
Then would the EGC be sized based on the increased size (250.122(B))? Would it apply only for the portion where the size is increased?
Or would you increase it the whole way?
I lean towards increase it the whole way.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
The 2017 NEC made this clear, it started off "Where ungrounded conductors are increased in size . . ." Where is a spatial term and limits the requirement to the portion of the circuit with the larger size ungrounded conductors.
The 2020 NEC makes this slightly less clear, as it now starts "If ungrounded conductors are increased in size . . ." Still, how do we determine the size increase required for the EGC? It's based on the size increase in the ungrounded conductors. So it still makes sense to me that where the size increase factor in the ungrounded conductors is 100%, i.e. no increase, the same applies to the EGC.
If you think of 250.122(B) as requiring a fixed minimum impedance ratio between the EGC and the ungrounded conductors, this approach make sense.
Cheers, Wayne
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Good question. The NEC is clear as mud on this one.
Elect117
Senior Member
- Location
- California
- Occupation
- Engineer E.E. P.E.
If I am understanding you correctly, you are saying increase it for the portion where the feeder/branch circuit size is increased?
That makes sense.
The size of the EGC size stays proportional to the circuit size is a good way of thinking about it.
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
Maybe you have increased them too much if you can reduce them 500' away (number of paralleled sets need to match to make the transition easier). Most people reduce them close to the termination to be able to terminate in standard equipment lugs.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
Say your run is 700', and you calculate that #6 AWG has a little too much voltage drop, but #4 AWG is totally fine. Your equipment takes #6 AWG as the largest size conductor, so you're going to have to splice at least once because of that. And it's convenient to get 500 ft rolls of wire/cable, so you're going to set a junction box at 500' anyway.
Why not check the voltage drop with 500' of #4 and 200' of #6? If that suffices, it lets you economize a little on wire, and avoid an extra splice.
Cheers, Wayne
Why not check the voltage drop with 500' of #4 and 200' of #6? If that suffices, it lets you economize a little on wire, and avoid an extra splice.
Cheers, Wayne