sub-panel yet again


Old 12-11-04, 09:45 PM
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sub-panel yet again

Hi, I need to run power to my garage for welding... the welder has these specs: input volts: 230 - input amps: 52.

I've spent hours looking at old threads, but I still haven't answered all of my questions.

My hope was to create a 60 amp sub-panel in my garage by running 3 6ga wires through 3/4" conduit - and to put three circuit breakers in this panel (one 50 amp circuit for the welder and one 20 amp circuit for other tools and one 15 amp circuit for lighting). I do not expect to be using the welder at the same time I use other tools.

The total length from my main service panel (100amp) to the garage is 80 to 90 feet. I have a grounding rod, and understand these issues. The underground conduit crosses an area that will receive vehicular traffic - I plan to use plastic conduit and bury it 30" deep.

Does this proposed sound sufficient?

Many thanks! Chris
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Old 12-11-04, 10:18 PM
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No, probably not.

Give us all the information on the welder's rating plate. Might as well give us the make and model of the welder too.
Old 12-11-04, 11:13 PM
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Thanks for responding. Here is info on the welder:

Miller Econotig... I haven't bought it yet, but here is the info in the ad:

Rated amps: 150
Duty cycle: 20 percent
input amps: 52
OCV: 78
Old 12-12-04, 10:19 AM
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I beleive you are going to need 4 wires to run to your subpanel, not three. (Hot, Hot, Neutral, Gnd). 60 amps off of a 100 amp main panel might be a bit much, but it depends on household load.

I would suggest running #4 or even #2 to your garage.

Are you running new light circuits as well? Is this cirucit new or is it an addition to power that is already in your garage?

If you are using your welder, lights, say a radio, maybe a tv, etc.. etc.. you are not going to have enough juice for the load. But I'm not sure your 100 amp service is sufficient to serve your needs for your garage. Could you have the power company put in a second service to your garage? The cost might actually be comparable to what you are trying to do now.
Old 12-12-04, 04:41 PM
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I'm hoping somebody with more welder experience will come help out with this question. Welders have unique rules about wire ampacity and overcurrent protection, and I'm not sure what this particular welder wants for breaker size. The code allows breakers up to 100 amps on this welder on wire size as small as #10. But I would see what the manufacturer recommends.

But Sky makes a good point about the fourth wire. It is not always required (i.e., the no metallic path rule), but it is always recommended.

Sky also makes a good point about whether your house and the breaker will be able to run at the same time.

Welder expert anywhere?
Old 12-12-04, 05:10 PM
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I don't know much about welding machines...but this is the link for the machine in question.
Old 12-12-04, 07:43 PM
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Single phase you will need an 80 amp breaker. All of this information is in your owner's manual by the way... (when you buy it)....

Here is the link I'm referencing:

It is on page 14 in section 5-4. For 230 volts "Max Circuit breaker" is 80 amp and use 6 AWG wire. (I would use something more substantial). If you have different voltage, there are other specs for them.

I'm no welder expert but that was your answer. I wondered that too. I'm going to buy the MillerMatic 251 or 210 soon! Now that I upgraded to 200 amps I will anyway.

The thing you should notice about the electrical service chart is an important concept in welding. As you gain more voltage you need (draw) less amperage. I like the analogy: "Electricity is like a river, Voltage is how fast the water is moving, Amperage is how much water is moving".

Happy welding! It should be a fine addition to anyone's shop. After all, there is absolutely no such thing as too many tools!
Old 12-16-04, 09:18 PM
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Thank you all so much for your advice... I've just downloaded the welder documentation. As for the comments about the fourth wire, I was under the impression that the fourth wire was the "equipment ground" wire that was connected to the grounding rod outside of the garage (rather than running all of the way back to the main panel). Am I missing something?

Thanks, Chris
Old 12-16-04, 09:37 PM
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If you make the garage a sub panel off the main panel in the house you will need to run all four wires back. There should be only a single ground wire to a ground rod in the system and that's at the main panel. All sub panels should connect to that and have the neutral separated from the ground. They should be connected together at only one spot and that's in the main panel.
Old 12-16-04, 09:41 PM
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Equipment grounding conductors do not connect to grounding rods. Grounding electrode conductors connect to grounding rods. The two grounding systems server completely different purposes. It is critical that you understand the fact that grounding is two systems. Don't get them mixed up. The EGCs are primarily for fault protection. The GEC is primarily for lightning protection. They work off different principles.

But contrary to what jughead just said, each building needs its own grounding rod(s).
Old 12-16-04, 09:48 PM
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Originally Posted by John Nelson
But contrary to what jughead just said, each building needs its own grounding rod(s).

OK, so for a sub-panel to an attached garage, ground wire goes back to main panel.

For a sub-panel to a detached garage, ground wire goes just to a grounding rod, or does it go to a grounding rod *and* back to main as well to tie all grounds together?
Old 12-16-04, 10:02 PM
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The two grounding systems serve separate purposes. Neither system can do the job of the other, and hence both are necessary.

Here are the salient points of the grounding electrode system:
  • Each building always needs its own grounding rod(s).
  • Subpanels within the same building must not have their own grounding rod(s).
  • Grounding rods serve primarily to protect against faults outside the building.
Here are the salient points of the other grounding system, the equipment grounding system:
  • A grounding wire (EGC) must be run between the main panel and a subpanel in the same building.
  • A grounding wire (EGC) may be run between panels in separate buildings, in some conditions must be run between panels in separate buildings, and is always recommended even if not required.
  • EGCs serve primarily to protect against faults inside the building.
  • This system does not depend on a connection to dirt. The EGC must be an excellent conductor to function properly, and dirt is not an excellent conductor.

Last edited by John Nelson; 12-16-04 at 10:20 PM.

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