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Ampacity and wiring question

1020 Views 6 Replies 3 Participants Last post by  Arrow3030
Hi all and thanks for help in checking my work and calculations.

I want to replace an old electrical subpanel with a junction box, install a new panel in an NEC compliant location and run 10 hot wires, one neutral and one ground through a 1 1/2" EMT to the new location. The old wiring is mostly AWG 14 and the old breakers are 15 amp. Some of the receptacles are ungrounded and I will either run new wire or, where more convenient, install GFCI with labels. I will upgrade the power to 50 amps for this sub-panel from 30 currently feeding it.

My conduit ampacity and size calculations for 10 circuits at 15 amps protection are 12 AWG hots, a 4AWG neutral and a 10 AWG ground through 1-1/2" EMT (oversized in case I want to add another circuit at a later time.

A few details:

I have an old Zinsco sub-panel feeding three small bedrooms and a bathroom. When a visitor tripped a circuit breaker I put on my investigation hat and made some awful discoveries (realize that an electrical subcontractor last worked on this panel 25 years ago when we did some remodeling):

1. Ground is bonded to neutral, several breakers have two wires under one screw, feeding power is 10AWG romex run through 3/4" EMT on a 30 amp breaker
2. All three bedrooms have receptacles and lights on a single circuit.
3. Bathroom gfci outlet is on the bedroom circuit
4. The sub-panel is in a linen closet between two shelves and I had to move a pile of cotton towels and remove a shelf to get access
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You need a separate neutral for each circuit. You can't use #4 common neutral.
Thanks for the reply. In that case I am probably much better off running multiple 1/2" conduits with 3 pairs of 12 AWG THNN-2 and one ground each and run an extra empty conduit for unexpected growth.
If you're using 12 gauge for 15 amp circuits it may be better to run two 3/4" with 11 conductors, counting a ground, in each.
Two important questions are; is the conduit going to be longer than two feet and will the new wire be over ten feet?
Regarding expansion. Does it make sense to connect the new location to the old or is it better to stub from the new location to an accessible area such as a crawl space or attic? Keep in mind that if conduit is under two feet long you granted major advantages over longer runs. Specifically, 20% more conductor fill and no ampacity adjustments.
Thanks so much for your interest in my problem.

In a world ruled by engineers I would just put the new panel in the hallway adjacent to the linen closet, find a distracting picture to put over the panel door and be done with it.

In the world as it is, ruled by spouses, I have to move the panel about 20 feet to a utility room and I either run conduit almost all of that distance or drill multiple holes through joists in a crawlspace and end up running conduit about 4 feet.

I can certainly gain access to the attic for any needed expansion, so that is an excellent strategy.
Since you're extending existing circuits for bedrooms more than ten feet the circuits now are required to be arc fault protected. The cost difference is HUGE. 500% more than a regular breaker plus all the existing issues associated with old wiring and poorly executed modifications.
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