wire size for shop 240V circuits?

Hello, all,
I'm still waiting for my electrician to come out and install a 6-circuit subpanel in my barn workshop for 240V. Since I'm having so
much trouble getting a crew out here, I'm thinking of running all the boxes and stapling up all the wire myself, so that all the electrician has to do is install the sub-panel and hook my wires into the subpanel buss bars.(I already have one 6-circuit subpanel in the barn for 120V so I guess the subsequent sub-panel would come off of that.)
Can anyone tell me what sizes of ROMEX wire I should run for the following circuits?
A. 240V, 20A (table saw OR compressor but never both) with a run of maybe 18' from the subpanel
B. 240V, 20A (18" bandsaw or 12" planer/molder) with a run of maybe 20' from the subpanel.
C. 240V, 50A (arc welder) with a run of maybe 1 foot from the subpanel.
For the purposes of what I want to know here, we can ignore the issue of whether I have enough amperage service to the barn, since my electrician already said I have enough, and if he's wrong, I'll add more capacity. My concern here is buying the right wire to install the runs and boxes.
Thank you for any info.
Jones.
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Wait for the electrician.
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| Can anyone tell me what sizes of ROMEX wire I should run for the | following circuits?
I'll assume the listed amperages are the circuit specifications, and the actual load of the equipment is 80% of that. If this is wrong, please post an update. All wiring is copper only.
| A. 240V, 20A (table saw OR compressor but never both) with a run of | maybe 18' from the subpanel
AWG 12. Use a single NEMA 6-20R receptacle.
| B. 240V, 20A (18" bandsaw or 12" planer/molder) with a run of maybe 20' | from the subpanel.
AWG 12. Use a single NEMA 6-20R receptacle.
| C. 240V, 50A (arc welder) with a run of maybe 1 foot from the subpanel.
Some will say you can use AWG 8 and you probably can, if it has a high enough temperature rating (75C or more). Personally I'd run AWG 6 to this. For just one foot, you're not saving all that much to go with AWG 8.
An arc welder will not need a neutral. However, some may come with a NEMA 14-50P plug instead of a NEMA 6-50P plug. Check what yours has and choose the matching receptacle. If you do install a 14-50R outlet you must run the neutral wire to it and connect it correctly. However, if you can use a 6-50R outlet, you can omit the neutral as described.
As close to the panel that the arc welder will be, the choice does not really matter. On one hand you save a few pennies without a neutral. But if you later need a combination 120/240 for some reason at that location, you can just run another circuit.
All 240 volt circuits that do not need a neutral can be wired without one, as long as a NEMA 6-XXR outlet is involved. Or you can choose to go ahead and wire the circuit with a neutral in case you might ever decide it may need 120 volts in the future.
To wire the circuit for 240 with a neutral for 120 volts, you would use a 4 wire cable that has a ground wire, a white wire (neutral), a black wire (one hot), and a red wire (other hot). Your electrician should connect the neutral at the panel and leave it long and capped off at the outlet.
To wire the circuit for 240 without a neutral, you would use a 3 wire cable that has a ground wire, a white wire (normally used as neutral but we'll change that), and a black wire. Buy some red electrical tape (black can be used, but red is better) appropriate for marking (most is). The white wire will be wrapped several times around for 2 to 4 inches of its length at each end with the red tape to re-designate it as a hot wire. If there are any junctions, mark the wire at those junctions, too.
If you insert a switch in a 240 volt circuit, use a TWO POLE switch so it breaks the circuit on BOTH hot wires. If you use a neutral, do not switch the neutral.
If this is a wet environment, you may need to use UF cable instead of NM cable. Be sure the wiring is placed where it will avoid any possible damage from mechanical accidents. If the wiring is in conduit, you can use singles wires, THHN, or if a wet environment, THWN.
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| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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snipped-for-privacy@ipal.net wrote:

You can not use #8 for 50A, regardless of the temperature rating. You must use the 60c ampacity.
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Benjamin D Miller, PE
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wrote:

I don't suppose we want to kick the article 630 tar baby (welder rules) here. The flame war could go on for months ;-)
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snipped-for-privacy@aol.com wrote:

OK, if it is dedicated to the welder then 200% of the welder rating or conductor ampacity is fine for the ocpd.. And yes, the duty cycle is probably less than 100%.
More important, however, was the statement that implied that you can use 75 or 90C ratings when sizing the conductors (assuming we don't know the terminal temperature ratings at both ends).
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wrote:

Sincwe he specifically saod Romex (or UF or MC) the 75c column is out anyway. You are going to be in the 60c column
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| snipped-for-privacy@ipal.net wrote: |> |> Some will say you can use AWG 8 and you probably can, if it has a high |> enough temperature rating (75C or more). Personally I'd run AWG 6 to |> this. For just one foot, you're not saving all that much to go with |> AWG 8. | | You can not use #8 for 50A, regardless of the temperature rating. You must | use the 60c ampacity.
Were you in on previous threads that argued for #8 vs. for #6?
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snipped-for-privacy@ipal.net wrote:

Apparently not. In what context? What kind of circuit?
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| snipped-for-privacy@ipal.net wrote:
|>>> |>>> Some will say you can use AWG 8 and you probably can, if it has a |>>> high enough temperature rating (75C or more). Personally I'd run |>>> AWG 6 to this. For just one foot, you're not saving all that much |>>> to go with AWG 8. |>> |>> You can not use #8 for 50A, regardless of the temperature rating. |>> You must use the 60c ampacity. |> |> Were you in on previous threads that argued for #8 vs. for #6? |> |>> ---------------------------------------/----------------------------------| |>> Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address |>> below | first name lower case at ipal.net /
|>> ------------------------------------/-------------------------------------| | | Apparently not. In what context? What kind of circuit?
I'd have to go back and find it and read it again. I'm too lazy to do that (e.g. I have some RTFM-ing to do tonight on an unrelated project). I was just wondering if you had been there. So I guess not. It does seem to be an occaisionally debated issue that, when it comes up, not everyone who might really know weighs in on. But it is generally in the back of my mind that at times some people do suggest using #8 AWG on 50 amp circuits. I would not do that, myself. But I have not seen a solid detailed explanation of why not, for whatever circumstances not to, yet, from someone that clearly knows (the level of detail and how well written it is might further that perception).
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| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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On 2008-02-19 11:31:32 -0500, snipped-for-privacy@ipal.net said:

Great reply, Phil! Thanks very much for taking the time and trouble!
Jones.
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