Sub panel questions

[600SL]

Since I will be adding a new plasma cutter and a new MIG welder to my existing TIG welder I have decided to replace my welder outlet with a sub-panel and add multiple outlets. I currently have a 1.25" EMT conduit with a about a 55' run to my welder. Since I already have the 1.25" conduit I would like to max it out with #1 AGW wire to get 125 amp capacity to the sub panel.

Technically 4 #1' really don't fit in a 1.25" conduit depending on how you round. but 3#1 and a #2 will fit. Also I'm I correct in assuming that I could reduce both the ground and neutral 2 wire sizes and use 2 #1 and 2 #3? That would save alot of money and ease the pull.

As far as the sub panel goes do I need to get one with a main breaker or do they make them without and if the main breaker is required is there a sub panel available with a 125 amp main breaker.

 

[sberry]

2 number 1, a 2 and a 6 and you do not need a main. But what size is the tig?

 

[600SL]

2 number 1, a 2 and a 6 and you do not need a main. But what size is the tig?

A 2 for the Neutral an a 6 for ground?

The TIG is a Lincoln Square wave 175. It has a recommended CB size of 125 amps with #8 wire, but I ran it many years on a 70 AMP. Max current draw is 62 Amps. I have no idea why Lincoln recommends a 125, but then again I haven't done too much AC TIG at 175 amps.

 

[Cmreschke]

Pipe ground eases the pull too, fyi.

 

[600SL]

Pipe ground eases the pull too, fyi.

Do you mean that there will be less jamb ratio issues with 4 wires. My intent is to run a ground.

 

[sberry]

I think the guys at Lincoln sniif the glue before they come up with some of those, other machines are rated wonky too. You don't need 125 for that and over 100 should be on a 6 with 6 ground. But one of the benefits to pipe is it is a ground. Personally would use 3 number 2 and 100 to a 100 a main lug.

 

[Cmreschke]

Do you mean that there will be less jamb ratio issues with 4 wires. My intent is to run a ground.

Its gonna be a tough pull if your filling to max conduit size. I'm just suggesting using your pipe as a ground instead of an actual conductor ground.

 

[rockwithjason]

when making these calculations you always round up, never down. i would have to look but i believe that you are not allowed to reduce the neutrals. at one time they allowed that but there were issues with harmonics in some appliances overheating the neutral wire and terminals. also be aware that many local jurisdictions do not allow the pipe to be used as the equipment ground at all because of issues with improper installation and in some cases the use is limited to 60a circuits or less.

 

[sberry]

Also you not really trying to "get the most out" but what it needs. There are 1000's of those running from 60, I know a couple guys got them.

 

[600SL]

I think the guys at Lincoln sniif the glue before they come up with some of those, other machines are rated wonky too. You don't need 125 for that and over 100 should be on a 6 with 6 ground. But one of the benefits to pipe is it is a ground. Personally would use 3 number 2 and 100 to a 100 a main lug.

The Lincoln is currently wired with a 100 amp on #6. It works just fine and it worked fine with a 70 amp previously. There is also a possibility I may opt for an AC unit off the same sub panel so I have the conduit to handle 125 its about $50 more in wire, I'm leaning to the 125 AMP.

The possibility of me running the TIG at max while the AC comes on is likely. Still probably wouldn't trip a 100AMP but leaves no margin. The possibility of me running the TIG with the AC on and my son running the MIG or Plasma is fairly remote. But then again the possibility of me getting my son to do anything is fairly remote.

 

[bjcouche]

If you are looking to get the full 125A out of a 125A load center, then I would have to concur with Sberry.

Use copper THHN/THWN 1-1-2-6, or even 1-1-4-6.

Yes, you CAN undersize your neutral to a subpanel, and still pass code legally, but you might be required to show an actual load calculation.
Generally you're load calculation would go something like this:
Plasma cutter: 240V, no neutral current.
MIG welder: 240V, no neutral current.
TIG welder: 240V, no neutral current.
Air Conditioner, 240V, neutral current only for the blower (<8A@120V)

maybe you add a 120V outlet or lighting circuit, or a 120V coolant pump for your welder.. But basically nearly all your significant loads in that subpanel will be 240V. Reading through article 220 of the NEC is a chore at best. In laymans terms, think of a panel with 8 20A 120V breakers. IF they are installed with 4 on L1 and 4 on L2, then the maximum possible neutral current would be with 4 breakers off on one of the hot legs, 20*4=80A. Now add several 240V 30A, 40A and 50A breakers to that panel, and your overall L1 and L2 current go up but your maximum worst case neutral current is still 80A. Article 220 goes into more detail by calculating the actual load current instead of just adding up breaker ratings.

1-1-2-6 THHN would be .1562+.1562+.1158+.0507 = 0.4789in2.
1.25" EMT for > 2 wires is 40% max fill = 0.598
0.598>0.4789 thus it will fit.

I think I provided too much info, but it was a good exercise for me.

Brian

 

[600SL]

If you are looking to get the full 125A out of a 125A load center, then I would have to concur with Sberry.

Use copper THHN/THWN 1-1-2-6, or even 1-1-4-6.

Yes, you CAN undersize your neutral to a subpanel, and still pass code legally, but you might be required to show an actual load calculation.
Generally you're load calculation would go something like this:
Plasma cutter: 240V, no neutral current.
MIG welder: 240V, no neutral current.
TIG welder: 240V, no neutral current.
Air Conditioner, 240V, neutral current only for the blower (<8A@120V)

maybe you add a 120V outlet or lighting circuit, or a 120V coolant pump for your welder.. But basically nearly all your significant loads in that subpanel will be 240V. Reading through article 220 of the NEC is a chore at best. In laymans terms, think of a panel with 8 20A 120V breakers. IF they are installed with 4 on L1 and 4 on L2, then the maximum possible neutral current would be with 4 breakers off on one of the hot legs, 20*4=80A. Now add several 240V 30A, 40A and 50A breakers to that panel, and your overall L1 and L2 current go up but your maximum worst case neutral current is still 80A. Article 220 goes into more detail by calculating the actual load current instead of just adding up breaker ratings.

1-1-2-6 THHN would be .1562+.1562+.1158+.0507 = 0.4789in2.
1.25" EMT for > 2 wires is 40% max fill = 0.598
0.598>0.4789 thus it will fit.

I think I provided too much info, but it was a good exercise for me.

Brian

I thing your spot on.

I was actually thinking of a 240 only sub-panel and use a separate run for the AC blower. But that would be limiting me for any unforeseen future expansions.

 

[600SL]

Well I went with the 1-1-2-6 solution. I am a fan of grounds.

$400 for wire, sub panel and a 100 amp breaker for the welder. I will still need a 125 amp breaker for the main panel but the 100 will do fine for the moment. I will also need two more breakers for the welder and plasma cutter, but I wont know what size until they get here. Looks like they will be about 60 and 30 amps.

The Plasma is a Hypertherm 65. The welder will be a Lincoln Power Mig 210.

 

[600SL]

Some bad news for me.

I purchased the sub-panel and wire. Went to do the job and just realized I do not have 1-1/4 EMT. I have 1 inch. In desperation I actually tried to pull 2 AGW1 1 AGW2 and 1 AGW6. Not a hope in hell. I got all of about 6 inches. in the conduit.

So the plan is reduce to 100 Amps using 2 #3 1 #6 neutral and a #6 ground. That was almost $300 in wire. Out of all that I get to use the #6 ground. If there is any good news to this I will probably be able to sell the #1 and #2 conductors for about the same as I can buy the #3 and #6 replacements.

So at 100 Amps that puts this panel on the hairy edge when using the Hypertherm 65 and AC at the same time. The Hypertherm 65 runs at about 45 amps but can pull ~75 when pulling the torch away from the work. So if I actually do that just when the AC compressor kicks on I would say I may or may not blow it. I actually am finding that the plasma cutters are worse than the TIG welders because you typically run at max nearly all the time and that pulling away really cranks the current. But the odds of those two events occurring simultaneously are slim and brief, probably to quick to trip the breaker.

So any one interested in sub panel wire send me a PM.

 

[600SL]

Finally completed the job today. After rewiring to #2 gauge CU. I was also able to find a 110 Amp breaker for the main box so I should have reasonable margin for just about anything I do.

The three welders have all the same plugs so I'm considering cutting the wire on my Mig 210 and seeing what else I can find in the 40 AMP range. I have already found a different 50 AMP outlet for the Plasma cutter.