Wiring in a welder


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Old 08-09-17, 11:00 AM
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Wiring in a welder

Hi All,

I have an older home built in 1911

Probably 30-40-50 years ago it's main fusebox was replaced by a Murray 200 amp panel. (long before I bought it)

At some period beyond that a detached garage was built, and the homeowner ran what looks like #4 aluminum underground from a 50amp breaker in the main panel to a Federal Pacific subpanel (using stab-lok) in the garage. There are 3 individual conductors, 2 hots and a neutral.

The subpanel has NO busbar in it for a separate earth ground. It just has the 2 hots and a busbar for the neutral connections. All of the outlets in the garage have both white and greens connected to the neutral busbar

My son went out and bought an old Lincoln 225v/125v ac/dc welder. This has a 50 amp plug that is 2 hots and a green.

I have connected this to the subpanel but I am wondering now about grounding. Let's assume that City of Portland code permitted subpanels without the separate safety ground back in 1970 or whenever the subpanel was installed and ignore that argument for now.

As long as I was just running lighting and 15amp loads in the garage I didn't care. But with the welder I am a bit nervous with this setup. Should I run a separate ground to the neutral busbar in the subpanel to a copper rod? I don't know what the city codes are on this but let's be honest this house still has a mix of old knob-and-tube to some of the lighting and it has the infamous "glow-in-the-dark" bright red Murray main breaker cutoff, and the "burn down the house" FPE stab-lock subpanel in the garage - and pulling the garage subpanel and replacing it would really be like putting lipstick on the pig.

I'm more concerned with the welder shorting out and the ground between the subpanel failing in this setup.
 
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Old 08-09-17, 12:13 PM
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It was allowed up until about 15 years ago to feed an outbuilding with two hots and a shared ground/neutral. That configuration is expected in an older house.

I would replace the FPE panel even if you leave the feeder from the house as-is. The subpanel is by far the biggest risk of anything you listed in your post. It will be $100 in parts and a couple hours work to do a simple panel swap. FPE is a known fire hazard because the breakers fail in the ON position -- no sense adding the load of a welder to that. Further it doesn't matter how good your ground or neutral is if the breaker is jammed on. On the new subpanel, leave the ground-neutral bonding screw in place to ensure a connection between neutral and ground. I would also add a ground rod bonded back to the subpanel ground-neutral bus using #6 copper (although this is for lightning protection -- nor related to the breaker issue).
 
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Old 08-10-17, 02:43 AM
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The panel is an 8 circuit panel, probably a 125amp panel, it looks a lot like the modern Eaton 8 space 16 circuit flush mount panel at home depot, although it does not have a door. It can feed 2 225v circuits plus some 125v circuits or 8 125v circuits.

The garage has 7 electrical outlets all home run to this panel all on separate 15a breakers. It is fed by #6 AL. (I looked more closely at the wire) coming in from the bottom. In the house and in the garage these cables are bare (not in insulation) The breaker box is actually mounted upside down.

I changed it around a bit years ago to feed a 30amp 225v garage heater (which is hardly ever used) and a 20a 225v air compressor.

I understand your advice on the panel and indeed, subpanels are a lot cheaper than last time I looked. Unfortunately the "deals" seem to mainly be the "kits" where they sell the panel plus a bunch of breakers, you get soaked for the most part if you buy the bare panel and the breakers all separately. The one nice thing is that the layout in the Eaton panel allows for more than 2 220v circuits so that there is a strong motivator.

When I had the driveway re-poured a decade ago I had them put in an underground pipe to the garage for future cabling. Right now, the existing feed is just rubber-coated laid in dirt. The detached garage is only separated from the house by about 10 feet so why they didn't swag it over or put it inside underground conduit is beyond me. What I'd really like to do is run a new feed using 1/0 aluminum.
 
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Old 08-10-17, 04:16 AM
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Note: Nominal voltages are 120v and 240v (residential), no 220v or 225 v. The new panel should be a main breaker panel*. A100 amp main breaker panel should be okay. You can bury one inch PVC conduit at 18". With only 10 feet cost of copper over aluminum isn't as real factor so I would suggest copper THWN. For 60 amps two #6 black, one # #6 white and one #10 green. For 100 amp increase conduit size to 1¼" and use H//3-H/3-N/3-G/6** copper THWN.

*The main breaker in a subpanel is used only as the required disconnect switch if more than six breakers so it can be larger than the supplying breaker.

**#3 will probably be available in black only so the neutral needs to be marked with bands of white tape. #6 for ground should be green (or bare).
 

Last edited by ray2047; 08-10-17 at 07:16 AM.
 

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