electrical question

I have a 200 amp service panel that I left two spaces empty for a 100 amp breaker for a welder. A few years back I added a 100 amp sub panel wired with #3 THN wire, and maybe a #6 ground wire. I still have the two empty spaces. The 200 amp panel is very crowded with wire. Question is, would it be a bad idea to wire the welder from the sub panel? The sub panel is wired from the 200 amp panel from a 100 amp breaker. The welder draws maximum of 60 amps, but the manual with the welder said to fuse it at 100 amps. The idea was to come from the panel with #4 copper to a disconnect then to the welder. I already have the disconnect with 100 amp fuses in it. One more question, would I need to run a ground wire from the disconnect to the panel if I used plastic pipe to run the wire in?

The welder is a Miller Dialarc 250 amp with high frequency that I bought new back in the early 1980's. It might have one hour of running time on the machine. The warranty ran off the machine sitting on the pallet it was shipped on. When I did wire it up the cooling fans bearings started making a noise so I always used another welder. I need a TIG machine now so I want to get it wired up. Any help would be appreciated, thanks.

That sounds fine . How far is the sub panel from the main service? The welder calls for 100 probably to prevent nuisance tripping when tigging alum or larger pieces. I don't think there is any violations in your plan. The 100 from a 100 is odd but should be do-able .

You should have no problem off the sub. As long as you do not have any big currant draws off that panel examples such as electric heat, electric range, pool heater ect. Plus that spec is for Max currant draw off that welder. I dought you will run that welder at full power all the time.
Thanks
Steve

The sub might have three feet of wire between panels. Maximum draw on the welder is 60 amps, I don't know why they want it fused at 100.

I don't really want to wire from the sub, but the 200 amp is very crowded and the neutral bar doesn't look like there is room to put the adapter on it to wire in a #4 neutral wire. Thanks

Off that panel so far is just a couple of lighting circuits and receptacle circuits. I don't see anything big in the future, and if there is I doubt they will be used at the same time as the welder. Thanks

Job, FIRST of all does that 100 amp Sub Panel have a 100 Amp Main Breaker or not????

It was never my normal design practice to use a 100 Amp Branch Breaker inside a 100 Amp Panel (perhaps a 60 or 70 but NOT a 100 amp branch breaker inside a 100 amp panel) so you might want to check to see the maximum size of branch breaker that Sub Panel will accommodate. Of course, if it fits yes it will "work" My practice would be to feed a load that required a 100 amp branch breaker out of the 200 amp panel.

If that 100 amp sub panel is I assume a 120/240 volt single phase three wire, it would require 2 Hot Ungrounded Conductors (L1 & L2), 1 Grounded Neutral Conductor, 1 Equipment Grounding Conductor, and it requires the Neutral Buss and the Equipment Ground Buss be separate and electrically isolated and insulated.

"Question is, would it be a bad idea to wire the welder from the sub panel?"

It can be made to "work" if you can use a 100 amp branch breaker inside that 100 amp sub panel?????????????????????????? Its NOT how I would do it, see above.

"One more question, would I need to run a ground wire from the disconnect to the panel if I used plastic pipe to run the wire in?"

YESSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS

All non current carrying conductive (metal) enclosures such as a disconnect switch etc. or junction box etc need bonded to the Equipment Grounding Conductor.

ALSO assuming the Welder has an outer metal case/frame, you for sure want that bonded to the Equipment Grounding Conductor

AGAIN YES you need to carry an Equipment Grounding Conductor from the panel or sub to BOTH the disconnect as well as the welders metal frame WELL DUHHHHHHHHHHHHH

Hope this helps

John T

John T, The sub panel is fed from a 100 amp breaker in the main. The sub has no main breaker in it. A 100 amp breaker will fit in the sub panel. I wanted to feed the welder from the main panel also, the neutral bar is full and there is no room for an adapter to fit on to wire in the #4 neutral wire. I think I could use a #6 neutral.

The sub is 120/240 volt single phase and does have a neutral and grounding buss that is separate. It is a square D panel and I would assume the two bars are electrically isolated and insulated. If they are not why would square D separate them? In the main they are not separate, that panel was put in, in 1983 or so.

I thought I would need too ground the panels if I used plastic but wanted to make sure. The panels are inside the stud walls and the disconnect is on the outside of the wall so I will need an offset to get the wire out of the wall and into the disconnect. I doubt that a plastic offset would have that much offset so I will probably go with steel. It will be fun using steel inside the stud wall though, (smile) but the panels and disconnect are close together.

When I wired it in years ago I used flexible metal conduit from the welder to the disconnect, so if I use metal pipe from the disconnect to the panel I should be good. The years ago wiring was not done right because I came off a 40 amp sub in the garage. When I built this house I made sure I had enough service to run the welder. But that main panel is really crowded.

I would really like to run the welder from the main also.

John T you really go into detail, Thanks.

Thanks for the kind words.

"A 100 amp breaker will fit in the sub panel"

If that's the case I don't see a problem using the sub then


"The sub is 120/240 volt single phase and does have a neutral and grounding buss that is separate. It is a square D panel and I would assume the two bars are electrically isolated and insulated. If they are not why would square D separate them?"

If a Panel is labeled suitable for service entrance, that means a TIE CROSS BAR can be used to bond the Neutral and Ground Busses. Some service entrance panels don't even have separate Neutral and Ground busses, just one big common buss where Neutrals and Grounds all connect. If they are separate and electrically isolated and insulated that's fine for a SUB PANEL but then if you connect the cross tie bar they are bonded together as required in the first main service entrance. PS there can be green bonding screws maybe near bottom of the buss that go through the buss and screw down into the panels metal frame.


"When I wired it in years ago I used flexible metal conduit from the welder to the disconnect, so if I use metal pipe from the disconnect to the panel I should be good."


I'm NOT a fan of using metal conduit as the Equipment Grounding Conductor, I prefer a separate stand alone wire, however if the correct bonding connections are used at all junctions, it can be NEC compliant, but its NOT for amateurs to install in my opinion.

"John T you really go into detail,"

I was an Electrical AC Distribution Design Engineer for years, just an old habit going into detail I guess lol, but Im rusty on latest coders so no warranty.