My New House & Workshop

[franklin2]

The only 2-2-4-6 MHF I can find is aluminum and I need 1 AWG for 100 amps.

The only wire I can find that O can go pick up is Southwire 1/0-1/0-1/0-2 aluminum wire for $551 + tax

If I want copper I'd have to order it online from a wire distributor.

3-3-3-5 is $885
2-2-2-4 is $1063

Huge difference in price from the aluminum.

Where are you coming up with these wire sizes? In special cases, as in very long runs, you need different sizes. But if you are close to 100 ft give or take, the 2-2-4-6 aluminum should be good enough, and more easy to find since that is what everyone mostly uses.

The only reason you would need a #2 neutral, is if you had a 100 amp single pole breaker with something on the other end that would pull 100 amps or near it. That would be very very odd.

It's easy to think how this works. The power is A/C, so it goes one direction, turns around, and goes the other direction in the circuit 60 times a second. The two #2 wires will have 240v between them. But from each one of the #2's to neutral will be 120v. But these two "sides" , A phase and B phase of the 120v are out of phase. When one 120v circuit is pulling, the other 120v side is pushing.

If you have two 20 amp 120v circuit breakers, one on A phase to neutral, and the other on B phase to neutral, and both circuits perfectly draw 15 amps each, there will be zero amps on the neutral. One phase will be pushing 15 amps while at the same time the other phase will be pulling 15 amps. This cancels the current flow in the neutral.

If you have a circuit on A phase that draws 15amps, and another circuit on B phase that draws 10 amps, the current in the neutral will be 5 amps if these are the only two circuits in the panel.

This is why the neutral can be undersized. It will never see 100 amps in normal conditions.

 

[franklin2]

P.S. You can buy individual aluminum wires and make your own quadraplex setup. The reason I use it is because I am lazy, they cut it to length and I stick it in the conduit.

 

[Jim Oaks]

Where are you coming up with these wire sizes? In special cases, as in very long runs, you need different sizes. But if you are close to 100 ft give or take, the 2-2-4-6 aluminum should be good enough, and more easy to find since that is what everyone mostly uses.

The only reason you would need a #2 neutral, is if you had a 100 amp single pole breaker with something on the other end that would pull 100 amps or near it. That would be very very odd.

It's easy to think how this works. The power is A/C, so it goes one direction, turns around, and goes the other direction in the circuit 60 times a second. The two #2 wires will have 240v between them. But from each one of the #2's to neutral will be 120v. But these two "sides" , A phase and B phase of the 120v are out of phase. When one 120v circuit is pulling, the other 120v side is pushing.

If you have two 20 amp 120v circuit breakers, one on A phase to neutral, and the other on B phase to neutral, and both circuits perfectly draw 15 amps each, there will be zero amps on the neutral. One phase will be pushing 15 amps while at the same time the other phase will be pulling 15 amps. This cancels the current flow in the neutral.

If you have a circuit on A phase that draws 15amps, and another circuit on B phase that draws 10 amps, the current in the neutral will be 5 amps if these are the only two circuits in the panel.

This is why the neutral can be undersized. It will never see 100 amps in normal conditions.

I have a book for doing electrical and it will tell me how to wire up a subpanel, but it doesn't tell me what size wire to run to it. The only example I found was for a 40 amp subpanel.

I asked Google what size wire to use for a 100 amp subpanel 100 feet from the main panel and thats where I got the 3 AWG copper or 1 AWG aluminum.

I asked ChatGPT the same question and it said:

Short answer — two common, safe options:

• Copper (recommended): 3 AWG copper THHN/THWN-2 for the two hot legs and the neutral (in conduit), with a #8 AWG copper equipment ground. Lori's Web+1
• Aluminum (budget option): 1 AWG aluminum (XHHW-2 / AA-8000) for the two hots and neutral, with a #6 AWG aluminum equipment ground (or #8 Cu equivalent). BLUETTI-US+1

Why those sizes?

• NEC ampacity tables show 3 AWG copper (75°C column) is commonly used for a 100-amp feeder; aluminum alternative is typically 1 AWG. (Terminals must be rated for the conductor temperature used.) Lori's Web+1
• The equipment grounding conductor is sized from NEC Table 250.122 — for a 100 A breaker that’s #8 Cu or #6 Al minimum. TEP Docs

Voltage-drop check (practical point)

• At 100 ft one-way (200 ft round trip) carrying 100 A, #3 Cu yields roughly ~4.0 V drop on a 240 V feeder — about 1.7%, well under the usual 3% guideline. So you typically do not need to upsize for voltage drop at that distance. (If you expect continuous 100 A loads or much longer runs, you might upsize.) FM Systems+1

Installation / wiring type notes

• Use four conductors to a subpanel: two hots, one neutral, one equipment ground. In the subpanel do not bond neutral to ground (neutral must be isolated). TEP Docs
• Common conductor types: individual THHN/THWN-2 conductors in conduit, XHHW-2, or a 4-conductor SER/SEU or direct-burial cable (where code permits). Choose the cable type rated for how you’ll install it (in conduit, buried, exposed, etc.). BLUETTI-US+1
• Make sure terminations (breaker and lugs) are rated for the conductor temperature column you’re using (75°C vs 90°C) — that affects ampacity choices. Lori's Web

Safety & code reminder

• Local code and AHJ (inspector) rules vary. Always pull the required permit and either confirm these choices with your local inspector or hire a licensed electrician to install/verify. If you want, tell me whether you’ll use copper vs aluminum and whether the run is buried or in conduit and I’ll give a precise parts list (conduit size, cable lengths, pull socks, recommended breakers, and a voltage-drop calculation shown step-by-step).

As far as the 2-2-4-6 aluminum, Home Depot, Lowes and Ace Hardware doesn't stock it anywhere within a couple hours from me. Home Depot has it in a 500' roll, and it's out of stock.

I want to make sure I'm using the right wire and not 'should be good enough' wire.

 

[Jim Oaks]

This guy did a great video on installing a subpanel.

 

[Curious Hound]

This guy did a great video on installing a subpanel.

That's a good video. Also, I double checked the chart in the code book. Yoir wire size info os correct.

 

[franklin2]

I looked at this a little more, and found out there is something in the code which allows the 2 awg for a 100 amp "service" conductor, but they call for the larger size to feed a "subpanel". So the 1 awg should work like the AI said.

If you can find it, you still should be able to run this in individual aluminum wire. And it's never against the code to put a larger wire than you need in there, as long as it fits the lugs in the panel and fits in the conduit you use.

 

[Curious Hound]

I looked at this a little more, and found out there is something in the code which allows the 2 awg for a 100 amp "service" conductor, but they call for the larger size to feed a "subpanel". So the 1 awg should work like the AI said.

If you can find it, you still should be able to run this in individual aluminum wire. And it's never against the code to put a larger wire than you need in there, as long as it fits the lugs in the panel and fits in the conduit you use.

That's correct. For a typical subpanel, the conductors and overcurrent protection are sized like a normal load, not as they might be for service entrance conductors.

 

[Rick W]

When you’re talking to suppliers, don’t forget to ask for the military/police discount. It’s as common as coffee these days, a good thing. But don’t ask until after you get a firm quote to make sure that it’s a real discount, and they don’t run up the price so they can just lower the price for a smile.