Sub-panel

[greg Forster]

I want to run 40 amp to an outbuilding subpanel from my main workshop sub-panel
(2) light circuits;
(3) recpt. circuits;
(1) small mini-split

I don't need 240v here- hand tool workshop

Do I still need to run 4 wire from main panel; the 40 amp breaker is at the main panel, not in the outbuilding

Also, the run is 100', what wires should I run?; underground conduit (1-1/4" is already buried)

[William Chain]

I think you're looking at #8 4-wire.

I want to run 40 amp to an outbuilding subpanel from my main workshop sub-panel
(2) light circuits;
(3) recpt. circuits;
(1) small mini-split

I don't need 240v here- hand tool workshop

Do I still need to run 4 wire from main panel; the 40 amp breaker is at the main panel, not in the outbuilding

Also, the run is 100', what wires should I run?; underground conduit (1-1/4" is already buried)

[roger wiegand]

I don't think you're required to to pull a 240 V circuit, but for the cost of one piece of wire that will be a pain to install later you will have future-proofed your installation to some degree, You can also service your needs with smaller gauge wire and save some money, despite the extra wire. (the 8 ga wire cited above will be a lot more expensive than the 12 ga required by an equivalent 240v/20A circuit) You will need to install a grounding rod at your outbuilding in either event. If you google outbuilding electrical service you'll find the code requirements.

[Mike Cutler]

Greg

You will get many different answers. In the end though the NEC and the inspector will determine your inspection requirements.
If your conduit is already buried, You'll be running THWN wiring through it #8 sounds right for 40 amps,, but there are many online calculators that can be referenced.
Yes, you should run 4 conductors, and you should run 240 to the panel, especially with that mini split. You need to runt he 240 just to be able to balance the neutral return. You don't need 240 through the shop, but you do want to balance the loads.

My advice would be to run the maximum sized wiring that meets the conduit fill requirements right off the bat. You may never need it, but you will never need to run it again. You could easily install a 100 amp sub panel, and #2 wiring for not much more than the 40 amp service you're planning to run. You'll also find that rated, approved, 100 amp panel disconnect breakers are cheaper and easier to find than a 40 amp model. This is assuming that your current sub panel can meet the requirements.
Do it once. So many people don't, and regret it 10 years later.

[Frank Pratt]

By running 120/240V out there you will better be able to maintain a balanced load between the 2 lines on your service, which is a desired thing. I would do some voltage drop calculations to ensure that you have sufficient voltage at full load. You may need to up size the wire.

Since you already have an 1 1/4" conduit, then you don't need to pull cable. It will be easier & cheaper to pull individual wires; 2 hots, 1 neutral, 1 ground.

[Jim Becker]

Four wire required. Run 240V for the reasons stated. It makes for more options with your small mini-split, too.

[greg Forster]

Thanks for the information; 4 wires it is

[John K Jordan]

Thanks for the information; 4 wires it is

I just did the same thing, but dug a trench and ran 650' of underground in conduit. I needed just 110v but it was more flexible to run 220v with four wires My thinking was although I currently plan to use only 110v circuits someday I might want to use 220 in the equipment shed I'm building there (air compressor, welder, AC?) and a 220 panel can let you divide the 110v load between the two sides.

There are on-line calculators that will let you decide what wire size to use based on the length, the load, and the voltage drop you are willing to tolerate. I used #2 copper with THWN-2 insulation. Check with your local electrical inspector - for common and ground you might be able to use smaller gauge wires than for the two load carrying conductors.

trackhoe_trench_long.jpg

JKJ

[Mike Henderson]

If I were you, I'd go for more than 40 amps. You always wind up needing more and pulling new wire is a pain. If you decide to go with 40 amps, I'd pull bigger wire so I could upgrade later. Maybe spec the wire for 60 or 70 amps.

I have 50 amps to my shop and wish I had done more. One day I'll get an electric vehicle and will want a 50 amp outlet in the garage for charging it. I could get by by only charging in the middle of the night but I'd prefer not to be limited to that.

Mike

[Bill Dufour]

50 amps is what a stick welder should have. Can the ground wire be smaller?
Bill D

[Mike Cutler]

50 amps is what a stick welder should have. Can the ground wire be smaller?
Bill D

The charts start at #10, up to 60 amps.

[Jim Becker]

The OP's stated purpose for the small, auxiliary shop structure should be reasonably served by a 40-50 amp subpanel, IMHO. He stated it would be for hand-tool woodworking and already has a larger shop setup.

[Bill Dufour]

Check C-list for wire/cable. I bought 100+amp wire to supply my shop cheaper then new 60 amp would have been. I lucked out and bought only about 3 feet extra.
Bill D.

[Charlie Velasquez]

I will throw my 2¢ in here.
2-2-2-4 Mobile Home Feeder is cheaper to buy and gives greater ampacity than #6 or #4 copper thwn.
The mhf counts as one cable allowing a 53% fill, which in 1&1/4” conduit is only 41%.

Not sure if your work will be permitted and inspected, but in the upcoming 2020 NEC they are doing away with the 6-throw rule. If your locale uses the newest code your sub will need a main disconnect on the exterior of the building. An air-conditioner disconnect would work. Probably be a while before municipalities go through the mechanics of a new adoption, but some people like to work to code anyway.

The NEC is available online for free from the National Fire Prevention Association’s website. You have to register, but registration is free.

[John K Jordan]

I will throw my 2¢ in here.
2-2-2-4 Mobile Home Feeder is cheaper to buy and gives greater ampacity than #6 or #4 copper thwn.
...

I'm sticking with copper even though the cost is higher.

On the advice of the utility company and two electricians I installed 650' of 2-2-2-4 mobile home feeder underground to a future barn site but used it only for a couple of low amperage circuits (lights at the sub panel and from there another 400' of #10 copper underground to the electric gate opener). I was wary of using aluminum underground because I had heard horror anecdotes but was assured it would be fine.

After about 8 years it failed. dropping voltage drastically over a few days, eventually killing three of the four conductors.

I replaced the run with #2 copper thwn in conduit. The initial cost benefit of the aluminum vs copper was negated by the cost of doing the job twice.

For my shop I ran 250' of #1 copper underground in conduit and fed with a 100amp breaker. That wire provides more capacity than I need in the shop but who knows what other sub-panels I might decide to run from there or what the next owner of the property might do with the building when I kick off.

JKJ