Grounding 240v metal box using 8awg

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Old 02-20-14, 02:20 PM
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Grounding 240v metal box using 8awg

What is the correct (i.e safest) way to ground a 4x4x2 metal box? Cable is 8/3 SOOW (green, white, black). It's being used in a 240v welder whip/extension and is going to get dragged around on the floor so even though the receptacle is technically self-grounding I'd like to directly ground the box also for maximum safety.

Is it same as 110v? Pigtail&wire-nut? Wrap wire around ground nut or use some form of crimp-terminal?

If a pigtail is required, I believe 10awg is fine to the ground nut but I'm not sure if it has to be solid? I have some stranded.
 
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Old 02-20-14, 02:28 PM
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Personal choice pigtail to solid for box ground. Easier to wrap around the screw.
 
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Old 02-20-14, 02:44 PM
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Originally Posted by ray2047
Personal choice pigtail to solid for box ground. Easier to wrap around the screw.
Personal choice on solid vs ground? Or personal choice on a pigtail vs ???? I've read comments where people just stripped last 6" of insulation from green 8ga stranded, wrapped around grounding screw and then onto the receptacle terminal.

I've never worked with wire this thick before, seems hard to wrap 8ga stranded around a 10-32 grounding screw.
 
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Old 02-20-14, 03:01 PM
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I would use a crimp type ring terminal on the number 8 an and bolt it to the box the less splices the better.
 
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Old 02-20-14, 03:10 PM
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Originally Posted by Geochurchi
I would use a crimp type ring terminal on the number 8 an and bolt it to the box the less splices the better.
Are you saying crimp a ring terminal 6" in from the end of the green wire and then continue the same wire to the ground terminal on the receptacle?

If so, something like this would work better than a standard ring terminal to allow the cable to route past the screw head.

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Old 02-20-14, 06:11 PM
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I use something like this for my 6/4 cords:
[ATTACH=CONFIG]27079[/ATTACH]



Image Source: Ground Straps & Terminal Lugs
 
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Old 02-22-14, 04:00 PM
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Justin's lug is a good solution.
 
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Old 04-21-14, 12:23 PM
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I couldn't find what Justin posted locally. So I ended up using a TE 321051 flag terminal. Removed insulation, crimped and soldered it to the cable and reinstalled the insulation.

Hopefully it's a safe way of doing it.

Put a NEMA 10-50 plug on the other end. I don't believe there is any orientation to the two HOT terminals with 240v. The existing basement 10-50 dryer outlet just has 2 red wires to each hot running back to the breaker (plus obviously the white ground).
 
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Old 04-21-14, 07:07 PM
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Put a NEMA 10-50 plug on the other end. I don't believe there is any orientation to the two HOT terminals with 240v. The existing basement 10-50 dryer outlet just has 2 red wires to each hot running back to the breaker (plus obviously the white ground).
A 10-50 receptacle is a 125/250 volt device with no ground connection and requires 2 hot wires and 1 neutral wire. You have wired yours using a white conductor as a hot wire and a green conductor as a neutral wire. You need to change it, it is wrong. I would have used either 2 blacks or 1 black and 1 red for the hot conductors and 1 white for the neutral. A 10-50 device has nowhere to terminate a green grounding conductor.
 
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Old 04-21-14, 07:18 PM
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A 10-50 receptacle is a 125/250 volt device with no ground connection and requires 2 hot wires and 1 neutral wire.
The 10-50 receptacle is 2 reds (going to the 30A breaker) and white going to the ground bar. It's running to the main panel (not a sub) so ground/neutral are bonded in the panel. I talked to the head city electrical inspector and was told a) there is no need for me to change to a 4-pin outlet b) it was fine to connect a welder to the existing 10-50 receptacle c) I don't need to change the breaker -- all grandfathered.

You have wired yours using a white conductor as a hot wire and a green conductor as a neutral wire. You need to change it, it is wrong. I would have used either 2 blacks or 1 black and 1 red for the hot conductors and 1 white for the neutral. A 10-50 device has nowhere to terminate a green grounding conductor.
I understand that by the letter of the code the wire colors are not correct but it's just a 3' extension cord. The 8/3 SOOW cable was available with black, white and green wires. There was no cable available that was 2 blacks or black and red. I suppose I can put some white and red shrink tubing onto the wires.

Wire colors not withstanding, is there an actual safety problem? I don't believe so.
 

Last edited by dorkshoei; 04-21-14 at 07:38 PM.
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Old 04-21-14, 07:38 PM
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Change it why? It's just a 3' extension cord. The 8/3 SOOW cable was available with black, white and green wires. There was no cable available that was 2 blacks or black and red.
I didn't realize it was an extension cord and assumed it was conduit with individual wires.

Wire colors not withstanding, is there an actual problem?
2 code violations. Extension cords cannot be used for permanent wiring and the green conductor cannot be used as a neutral.
 
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Old 04-21-14, 07:42 PM
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Extension cords cannot be used for permanent wiring and the green conductor cannot be used as a neutral.
It's not permanent wiring. The dryer is normally plugged into that receptacle.

The green connector is not being used as a neutral. It's being used as a ground.
 
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Old 04-21-14, 07:55 PM
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It's not permanent wiring. The dryer is normally plugged into that receptacle.

The green connector is not being used as a neutral. It's being used as a ground.
Do what you want, I'm just saying it isn't right. If you have a typical 120/240 volt electric dryer, the 3rd wire is a neutral and should not be green (although the grounding is done through the neutral conductor). If you have some other type of 240 volt only dryer, you are using the neutral terminal as a ground. Both are wrong.
 
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Old 04-21-14, 08:08 PM
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Dunno what to say. I talked at length to the head electrical inspector at the city and he said it was fine to do what I'm doing (color of wires in the extension cord not withstanding). Electrician who recently upgraded main panel said it was fine also. There is a code exception for running dryer ground+neutral over one wire. Electrically that single wire is connected to the ground bus inside the panel where ground and neutral are bonded.

Would it be "better" if I removed the dryer 10-50r, installed a 4-pin 14-30r, bought a new dryer cord, jumpered the dryer accordingly. Probably for the dryer yes, as it's safer for the dryer to have ground/neutral separate but as far as the welder extension cord is concerned it would be electrically identical.

Eventually when I free up some space in the panel I'll run a dedicated circuit for the welder to an external NEMA 10-30r. I think most electric cars use this connector so long term it may have usefulness beyond plugging a welder in.
 
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Old 04-22-14, 07:27 AM
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Assumuing an existing 3-wire dryer circuit, the dryer receptacle should be a NEMA 10-30R (30 amp, 125/250 volt). The welder should be on either a NEMA 6-30R (30 amp, 250 volt) or 6-50R (50 amp, 250 volt).
 
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Old 04-22-14, 07:50 AM
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The dryer is on a NEMA 6-50R range outlet. It was there when I moved in. Breaker is 30A. Should it be something else, yes but it isn't. End of story as far as I'm concerned. Neither the inspector who inspected the panel upgrade or the head inspector I talked to on the phone (when I verified it was ok to connect the welder to the dryer circuit) said it needs to be changed.


You're obviously correct on the welder. I'm not sure why I wrote 10-30 as clearly the ThermalArc I have uses a 6-50r since that's what put into the metal box.

That said, this thread was intended to be about how to ground a metal box for 240v. It's sadly gone way off-topic

I would greatly appreciate it if any further replies could be about the topic at hand. Thanks
 

Last edited by dorkshoei; 04-22-14 at 08:09 AM.
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