Wire size for sub-panel

[Bob Deroeck]

Hi Aaron,

The 2-2-2-4 cable I was referring to was 4 individual THHN cables, two hots, a neutral and a ground with the ground the 4 AWG cable. The reason I went with 2 AWG copper for the 100 amp subpanel service was for voltage drop considerations for the larger machine motors over the long 170' run to the workshop. With this cable I should be able to run 8-10 HP worth of motors simultaneously. That may sound like a lot but it's only a 5 HP dust collector plus a 3-5 HP table saw. I could have tried to squeeze the amps through 2 AWG aluminum conductors or 4 AWG copper, but I just know that if I did, I'd regret it later when some beautiful old 5 HP machine was being sold on Craigslist for small money, but I couldn't tolerate the amps.

Bob

[Dennis McCullen]

Getting all the correct jargon down..... wires are individual, some stranded and some solid. "Cables" are things, such as Romex where 3 or 4 "wires" are encased in a common sheath. Refer to cables as 2-2-2-4 and refer to "wires" and three #2s plus a #4 ground. Trying to learn all this before I start wiring to new shop.

[Tom M King]

Ok thanks for the info guys!!! A couple more questions. should I be using stranded thhn cable? Home depot dosent carry the aluminum cable. Some one told me (who has electrical knowledge) that i dont need a ground from the main panel to the sub panel if i use conduit, because the conduit bonds it. Is this true? He said I only need 2 hots and 1 Neutral, He also told me to use #2 guage thhn cable, (Is that overkill?)The home depot guy said (which I take with a grain of salt) That I need to put a grounding rod outside and tie to that, I have not heard that before. He also said I could get away with #4 Thhn cable. Hiring a electrition is out of the question ($), I have no problem adding new circuts and outlets and switches. But I just want to make sure I go big enough so to speak with the sub panel. I have read alot of information on installing a sub-panel, But it seems everyone has a different opinion. I plan on having 5 220 outlets and a couple 110 outlets and some shop lights. It seems to me that I need a 100 amp breaker in the main panel, 2 hot cables a neutral cable and a ground going to the sub-panel? Or is the ground optional with conduit? Once again thanks for your time and your knowledge!!!

I'd run the ground wire too, rather than rely on the conduit. You can run into all sorts of weird trouble if for some reason you end up with separate grounds at the main and sub panel. No problem with a ground rod at both places (some inspectors even require it), but the whole ground system needs to have every part of it bonded together.

Wire at dedicated electrical supply stores costs about half what it does at the big box stores. Around here, the cheapest wire you would get for this run is commonly called "mobile home service entry wire"- comes in a few different gauges, and has four separate conductors including one with a yellow stripe and one with a green stripe (or maybe a white instead of one of those depending on wire manufacturer), and is okay for direct burial, so you really only need conduit where it is exposed above ground. You can buy it by the foot in electrical supply stores too.

Dig any trench first, and THEN measure for the wire. Get enough to make sure you have a few feet to throw away, rather than running short.

A box end wrench over the wire can help for tight bends, but sometimes you still end up having to hit it with a hammer.

Make sure to get plastic bushings for anywhere the wire enters or exits a metal opening. Use some De-Ox coating on any aluminum wire before inserting it into the connector.

2-2-2-4 would be the size, and the name also lists the sizes of the conductors. It looks like this: http://www.southwire.com/ProductCata...prodcatsheet15

All connections damtite. I use a 1/4" drive breaker bar with a short extension, and an Allen socket.

Here's a pdf for the latest Electrical Code: https://archive.org/details/nfpa.nec.2014

[James Tibbetts]

I'm in the same boat to run a sub panel. I found this site for wire: http://www.paigewire.com/products.aspx
Looked like good prices compared to HD and Lowe's.

[Rollie Meyers]

To any posters saying that 4 AWG is OK for 100A this is in error, the ONLY way this is allowed is the service entrance conductors that carry the entire load of a residence, a subfeed does not meet the criteria allowing undersizing the conductors to comply w/ code & use 4 AWG a 90A breaker is the maximum allowed, for 100A 3 AWG is minimum, this assuming copper conductors.