A Few Questions On Installing A New Subpanel.

Hdoilcan · Dec 25, 2015

I just purchased a new Miller 211 mig welder and I have a small inverter stick welder that calls for a 20 amp line. I plan on purchasing a Hobart Stickmate LX ac/dc. Right now I have a 200 amp panel and I'd like to add subpanel about 55' away (all indoors). If possible I was planning on using the subpanel with a 50 amp breaker (Hobart stick welder), a 30 amp breaker (Miller mig welder), and a 20 breaker ( small inverter stick welder). Obviously I won't ever use these three welders at the same time so my question is what size subpanel should I install? If I could I'd like to also run one or two more 20 amp circuits for mabe 12 shop lights (that WOULD be on at the same time as using the welder) providing it not going to put me where I have to install a much larger wire. I was hoping to go no larger than a 6/3 wire if possible but if I have to then of course. Can I use aluminum wire that Lowes sells? Or should I stick with copper? Going larger than 6/3 is where the aluminum/copper issue would come in as they didn't have anything larger than 6/3 in copper. I want to do this the right way and cut no corners. Any help would be appreciated.

truckdiagnostics · Dec 25, 2015

This much I can tell you, i think you need to run 4 wire if you are going to break off the 110. the two hots, the neutral and the ground has to go back to the main panel. Thinking you will want 100 amp sub panel, it will give you the breaker space, then if you want to put 50 amp in the main so be it. As long as whatever you put in main protects the 55' of wire. Then if I remember correctly you can't put the neutrals and grounds together in the sub(check that) then you need to find a wire gauge chart for amps you want and run length, and they are different for aluminium if you go that way. I'm doing the same thing here shortly, however I'm at 250', looking at aluminium direct buried, at 04,04,04,02.(don't quote me) It will be next weeks purchase before the end of the year. It will be 100 amp panel with 100 amps. Now I need to check the reasons/code, if I can get away with driving a ground rod and run 3 wire with it being that far away. Somebody explained the deal with the 4 wires and not driving a grounding rods but don't remember. If i would just stop adding on, I could learn it then forget it. You might be able to get away with it too, Don't know it there is min max distance for separate ground rods on sub panel. Didn't tell you much, but I raised a bunch of questions.

arlen4720 · Dec 25, 2015

I agree a 100 amp panel s probably the best. You wouldn't need a main breaker in it, since it will be protected at the source. You do need 4 wires. You would need #2 copper for 100 amps by code. Your ground wire could be #10 but I would go #8. a number 6 neutral would be plenty big as well.

Mysfyt · Dec 25, 2015

I run my man cave off of a 60 amp breaker from the main to a 100 amp sub using #6 copper. The only issue I've had was when tig welding aluminum I popped the breaker. Don't do too much of that so I'll live with it. If your the only person in the shop, you can manage it quite well. I ran my feed through 2" PVC conduit so if I need too, I can pull some larger wire through in the future if I want to up the amperage. I actually run the 20hp lathe motor with no issues so far, but I run the motor with a VFD that stretches the start time over ten seconds to manage the amp draw. My run from the main to the sub is about 80 feet.
Truckdiagnostics covered most of the code issues. There are some very good electricians on this forum that will be along shortly to set any code issues straight. Good luck and enjoy!

muddstopper · Dec 25, 2015

I had to run my shop wire about 100ft. I installed a 100amp breaker in my panel and my shop panel is actually a fuse box. It has 2 60amp fuses for 220 and 2 30amp fuses. 110v each. Which makes things pretty aggravating in the shop. The shop was wired that way when I bought the place. Anyways, I didnt like the way the wire was ran overhead to the shop, so I decided to change it out. Having buddies that work for the power company, I was able to obtain some of the overhead wire they string between power poles. Dont know the gauge, but its big. To bury the wire, I bought electrical conduit and ran the wire thru it. I keep telling myself that one of these days I am going to rewire the shop. Only having One 220v outlet gets old when you have to share it with the welders, plasma cutter and the Lathe.

ttriff · Dec 25, 2015

Just installed a pair of 100 amp subpanels.

Surprising to me was that Siemens offers the best prices on panels and breakers. Their 8 space/16 circuit surface mount load center panels (E0816ML1125S) were $36/ea @ Lowes.

Not wanting to break the bank with Cu wire, I used the Alu 4 wire main panel wire from Home Depot. It's $1.49/ft locally (written with a Sharpie on the top of the huge wooden spool), and much easier to work with compared to copper

IIRC, when the subpanel is in the same structure as the main panel (with a ground rod) you don't need another ground rod. If you're wiring a separate structure a ground rod is needed.