Yet another ground/neutral 220v question

Reply

  #1  
Old 02-12-14, 12:47 PM
Member
Thread Starter
Join Date: Dec 2012
Location: USA
Posts: 161
Yet another ground/neutral 220v question

I had my panel upgraded recently (eliminated old 1960 split bus). At the time the electrician told me he was required by code to replace the existing 3-wire running 4' to the basement dryer outlet with 4-wire but that he wasn't required to change the existing NEMA 10-50 receptacle, so the new ground wire would just be left disconnected inside the box. Strikes me as odd now as I'd have at least connected it to the box.

Obviously my (old 1990s) dryer still has the ground/neutral jumper in place.

I just bought a TIG welder (30A) which I'm going to have to run off the dryer outlet. The house only has 100A service (upgrade to 250A is not cost effective as it forces $$$ mast relo and it's only a 900 sq/ft house that we don't plan to live in much longer) so I'm not going to run a new dedicated circuit for it but it did remind me of the above conversation.

I checked and it turns out he never ran new 4-wire so it's still the old 2 red + white. I know NEC code (250.140) has a specific exemption for dryers to allow bonded ground/neutral.

If the dryer outlet was running off a subpanel I'd definitely be rewiring it for 4-wire but since it's running to the main panel inside of which ground/neutral are all bonded, is there any reason to run 4-wire? Clearly a welder is not a dryer but ignoring the NEC dryer exemption I can't see any reason to change to 4-wire. I called the owner of the electrical company (not the guy who did the work) and he said "he must have forgot, it's not needed"). I think he's right but wanted to check.
 
Sponsored Links
  #2  
Old 02-12-14, 12:55 PM
Member
Thread Starter
Join Date: Dec 2012
Location: USA
Posts: 161
The only other thing is that the welder has a NEMA 6-50p plug on the end so I need to make a short adapter. I bought 8' of 8/3 soow, a 10-50p and a 6-50r but noone makes an inexpensive 6-50r inline so I was forced to use a Leviton 5374 plus a standard metal box.

Clearly the metal box needs to be grounded. I'm pretty sure it's safe to so this with the previous (bonded) scenario. Going back and forth about the metal box being more durable vs plastic not having any grounding issues.
 
  #3  
Old 02-12-14, 05:13 PM
Member
Join Date: Mar 2010
Location: USA
Posts: 3,093
The dryer circuit can stay as-is but if you add to it or change it such as put in a different receptacle, then you must upgrade it to 4 wire cable or conduit including ground (equipment grounding conductor).
 
  #4  
Old 02-12-14, 06:29 PM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: USA
Posts: 9,385
The only other thing is that the welder has a NEMA 6-50p plug on the end so I need to make a short adapter.
The dryer circuit can remain as a 3-wire circuit, but the welder needs a 50 amp circuit. Since the dryer receptacle is only 4 feet from the panel, you wouldn't be saving much to try to use the dryer receptacle for the welder anyway. I'd install the proper welder 50 amp circuit and receptacle near the panel for the welder.
 
  #5  
Old 02-17-14, 07:51 PM
Member
Thread Starter
Join Date: Dec 2012
Location: USA
Posts: 161
1. The maximum draw of the welder (ThermalArc 186) is 32.4A @230VAC (20% duty cycle). I asked the senior tech support person at ThermalArc if it would be compatible with a "clothes dryer circuit" and he said "Yes you can run that unit on a dryer circuit, that should be fine". I didn't specify to him that it was a 30A breaker but I thought this was the norm. My assumption was that they said it was OK as I would rarely ever draw the max current.

2. The dryer currently has a 50A range outlet but the breaker is only 30A. I am not sure on gauge of cable but can find out.

3. The panel is currently full so I don't have room to add a new circuit. Eventually I plan to have room as circuits need consolidating but right now I don't. Frustrating as it's a brand new panel but the house has been wired by a series of electricians and not much of the wiring makes sense. If I add a new 50A welder circuits it creates the possibility of both welder and dryer being used at the same time. Is that a smart idea given that I only have 100A service?

Also the specs for the welder state that I can use 50ft of 12 AWG for an extension cord which I assume says something about the current draw?
 

Last edited by dorkshoei; 02-17-14 at 08:41 PM.
  #6  
Old 02-17-14, 08:29 PM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 33,047
but that he wasn't required to change the existing NEMA 10-50 receptacle, so the new ground wire would just be left disconnected inside the box. Strikes me as odd now as I'd have at least connected it to the box.
Did he have a license. You can't use a 50 amp receptacle on a 30 amp breaker and if you replace the wiring the whole circuit must be brought up to code.
Also the specs for the welder state that I can use 50ft of 12 AWG for an extension cord which I assume says something about the current draw
No duty cycle. The NEC bases wire size on amps and duty cycle. The multiplier for 20% is .45.
 

Last edited by ray2047; 02-17-14 at 08:46 PM.
  #7  
Old 02-17-14, 08:34 PM
Member
Thread Starter
Join Date: Dec 2012
Location: USA
Posts: 161
Did he have a license
Yes. It was also inspected.

No duty cycle. The NEC bases wire size on amps and duty cycle.
Welder specs:
200A 18V -- 20% duty cycle
116A 14.6V -- 60% duty cycle
[email protected] 13.6V -- 100% duty cycle

Effective Input Current (I1eff) (See Note 1)
TIG @ 230V
14.1A

Maximum Input Current (I1max)
TIG @ 230V
32.4A

Note 1: The Effective Input Current should be used for the determination of cable size & supply requirements.
 
Attached Images  

Last edited by dorkshoei; 02-17-14 at 08:53 PM.
  #8  
Old 02-17-14, 09:07 PM
Member
Thread Starter
Join Date: Dec 2012
Location: USA
Posts: 161
So my reading of "Note 1" is that the Tech Support at Thermal Arc was correct and it will work perfectly fine on a 30A dryer circuit.

I still need to make up a short extension cord adapter. 10-50p, 8' 8-AWG, 6-50r. I bought a metal box and this 6-50r receptacle

What is the correct way to ground the box containing this receptacle? I've only ever grounded narrower gauge wire using the little green sheet metal screws.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes