Got Welder need wiring Advice ASAP!

[uhmgawa]

</font><font color="blue" class="small">(
The welder circuit breaker should be 50 amps, and smallest wire size (copper) should be 8 awg. Do you have 8 or 6 awg wire off of that 60 amp circuit breaker? If you are using 8 awg the breaker will have to be changed to a 50.)</font>

My copy of the NEC requires #6CU for a general 50A branch circuit.
There are some exceptions which might allow an #8 conductor
to be used but they are special cases a of single conductor
in free air, alone in a conduit, buried, etc..

The issues are minimizing the temperature elevation of the
conductor's insulation and minimizing voltage drop. The
former is to prevent breakdown/melting of the insulation and
the later is to minimize the voltage reduction seen by the
load which should be within 5% of nominal from all sources
combined.

That said the NEC is assuming continuous worst case full
draw off the branch circuit where an AC buzz box maxes out
to 20-40% duty cycle drawing its full load of 45-50A. So
you could 'get by' with a lighter gauge particularly for
short cable lengths and/or for newer inverter welders which
can compensate for excessive voltage drop. But if you are
making it part of a structure, it would be wise to follow
code.

 

[bnixon]

My feed to the switch box is #6 off of a 60 amp breaker. So what I am hearing is that I need to switch this out with a 50 amp?

I am also going to look into what it would take to replace the main service box with a new one.

What do you guys think is a fare price to do this? Ballpark.

thanks for all of the feed back.

 

[bnixon]

It is all starting to become clear now! /forums/images/graemlins/smile.gif

Great explination DaveL.

So I have one more question to get straight in my head.

If I understand this correctly when you have a subpanel it should not have a grounding rod. The subpanel should have a ground running back to the main service box grounding bar.

Is this correct?

If so it sound like I need to pull a new wire 3 and a ground from my switch panel back to my main service. I also need to ground the actual switch panel housing to the main ground and then my outlet gound to the panel housing and not the common (white) wire.

Is this starting to sink into my very simple brain or am I still a couple of pepperoni's shy of a full pizza? /forums/images/graemlins/grin.gif

 

[Anonymous Poster]

uhmgawa,
I've had this discussion in the field a few times, and in some cases 6 awg is correct. I may be wrong here, like I said power isn't my forte', but I don't really see a run for a welder as a general branch circuit , actually it is a dedicated circuit supplying the welder. I don't have a code book at home, but I do have my handy dandy Square D slide rule wire size calculator. Based on article 310-16, appendix "C", tables C1 and C1A, THHN 75 degree c copper wire is good for 50 amps using 75 degree c connectors. You may be right in saying that 6 awg is correct in this application. I will check my code book tomorrow.

In regard to voltage drop, you are correct. If the run is long, the wire size will need to be increased.
Line to line voltage drop (single phase) of 8 awg is .15 volts per amp per 100 ft based on 95% power factor. Drop in 6 awg is .095 volts. Some equipment will tolerate some drop, but inductive loads (motors and transformers) have high inrush currents and will cause a voltage sag in the line during startup.
DaveL

 

[Anonymous Poster]

yooperdave,
Sounds ok to me. Anybody else?
DaveL

 

[Anonymous Poster]

bnixon,
The subpanel should have a ground rod if it is in a seperate structure, not attached to the building where the service panel is located. In your case you do not have a subpanel, you have a single circuit supplying a welder. They are different in that you do not have a neutral so having a segregated neutral bar is not needed. You should have a ground wire running from the service panel in the house to the welder disconnect and it should be attached so that it grounds the frame of the welder disconnect and continues out through the welder plug to ground the welder itself. The white wire in your picture is essentially the ground for the circuit, and I assume you could tape mark it green to properly identify it as a grounding conductor.
Hope this helps.
DaveL

 

[bnixon]

Thanks DaveL,

That does help. How do you recommend I tie the ground wire to the box frame?

The bar that is in there now is isolated fromt the box.

thanks,

 

[Anonymous Poster]

I thought that was a neutral kit in the disconnect. They make a grounding kit (preferred), or I guess you could connect a wire from a lug on the neutral bar to a screw into the box itself. Don't use a self tap or sheetmetal screw, it should be a machine screw. You can use ground lugs screwed to the box as well, just remember not to put more than 1 wire per lug. If we don't have the grounding kit, thats what we usually do.
DaveL

 

[bnixon]

Thanks,

I guess I'll run to Home Depot and pick up a grounding lug.

 

[uhmgawa]

</font><font color="blue" class="small">( Based on article 310-16, appendix "C", tables C1 and C1A, THHN 75 degree c copper wire is good for 50 amps using 75 degree c connectors. You may be right in saying that 6 awg is correct in this application. I will check my code book tomorrow.)</font>

I believe I'm looking at the same table which lists two/three
conductor cable of #8CU will carry 50A within a 75C/167F
temperature elevation, but this assumes the cable is in
free-air. If so and the voltage drop is within reason #8CU
would be an economical choice. And as I stated before it is
unlikely the cable will be carrying full load at full duty
cycle.

Still 167F is getting rather warm and the closest you may
find to free-air in a residential environment would be
running the cable under/over uninsulated joists. Here it
gets even more complicated as the NEC (336-12) disallows
running a cable as small as #8-2 directly on top/bottom of
a joist. You would need to drill holes in the joists
(thermally preferable) or add running boards to which the
cable is fastened. [Note: #6-2, #8-3, and larger are not
restricted as such.]

My comment of a "general" branch circuit may have been
misleading. Likely the 50A feed would terminate in an
appropriate receptacle and the welder would connect via
plug to such. Hard-wiring a welder has additional code
complications as well as becoming an unintended leash.
At some point one will need to roll the anchor outside/
elsewhere for remote use via temporary extension. Also
having a general 240V/50A supply can prove useful for
other welders/cutters/etc..

Another thought concerning the use of an extension cord
is to plan ahead via including it in the voltage drop
calculation of the branch feed. If you consume an excess
of the voltage drop budget in the hard-wired portion of the
feed, not much may be left for the extension portion. In
which case only the options of oversized conductors or
short length may exist.