Will an existing 10-3 w/ground electrical wire handle a 50 amp 240 volt welder?

Question

I am wondering if my current electric service wiring can handle a welder. The welder documentation recommends a 50 amp breaker on a 240v line.

Currently I have a 60 amp breaker on a 240 line going to a separate garage. I presume this was installed by the electrician who wired the house 10 years ago but I am the third owner so this is not for certain. The 10-3 w/ ground wiring (not in conduit) to the garage is approximately 60 feet long or less. It doesn't seem right that this has a 60 amp breaker but I'm not familiar with 240 v lines. On 120v I believe this should be a 30 amp breaker max.

There are 2 unused 20 amp 110v circuits in the garage. I have two configurations that I can run after removing the unused circuits. One is to run another 40 feet to get to a double garage door and the other is to put a 240 outlet right by the current box which would be a bit restrictive. I haven't found the NEC code that specifies what size wire I need for a 240v 50 amp draw.

Answer 1

Wiring from garage panel to welder

NEC 630.11(A) may be of interest.

National Electric Code 2008

ARTICLE 630 Electric Welders

II. Arc Welders

630.11 Ampacity of Supply Conductors.

(A) Individual Welders. The ampacity of the supply conductors shall be not less than the I1eff value on the rating plate. Alternatively, if the I1eff is not given, the ampacity of the supply conductors shall not be less than the current value determined by multiplying the rated primary current in amperes given on the welder rating plate by the factor shown in Table 630.11(A) based on the duty cycle of the welder.

Also take a look at 630.12 Overcurrent Protection.

The Owners manual (PDF) seems to contain the answer.

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Wiring from service panel to sub panel

If we look at 110.14(C) in 2008 NEC, it says:

National Electrical Code 2008

ARTICLE 110 Requirements for Electrical Installations

I. General

110.14 Electrical Connections.

(C) Temperature Limitations. The temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor, or device. Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both.

Which means we'll have to check the breakers temperature rating, and the subpanel terminals temperature rating. Then we'll have to look at table 310.16 (Table 310.15(B)(16) NEC 2011), so we can determine the wire size we should use.

In this example image you can see if we're using copper, we'll use 60°C. Once we look at the table, we'll see that for 50A @ 60°C we need 6 AWG copper wire. (50A @ 75°C = 8 AWG).

110.14(C)(1)(a) basically says that if the temperature is not listed, use 60°C for circuits less than 100A. 110.14(C)(1)(b) says if the temperature is not listed, use 75°C for circuits over 100A. However, in the real world 75°C is often used for both.

Answer 2

Here's your answer. I don't know how the cable is run but I used the choice of overhead to get this answer.

1 conductors per phase utilizing a #8 Copper conductor will limit the voltage drop to 1.89% or less when supplying 50.0 amps for 60 feet on a 220 volt system.

For Engineering Information Only:
60.0 Amps Rated ampacity of selected conductor
0.7421 Ohms Resistance (Ohms per 1000 feet)
0.052 Ohms Reactance (Ohms per 1000 feet)
6.6000000000000005 volts maximum allowable voltage drop at 3%
4.143. Actual voltage drop loss at 1.89% for the circuit
0.9 Power Factor

This is from Southwire's Voltage Drop Calculator

Answer 3

No you can't use it. !0 awg wire is good for a 30A breaker, and if you are going 60' I recommend you up the size to allow for the lost resistance in that long wire.

Referring to the popular UGLY's Electrical Reference: "In Raceway, Cable, or Earth for copper wire; Type UF or TW 4AWG for 70A of current. "6AWG; Type UF or TW for 55A of current".

What you need for 60A service @ 60' would be at least #4 AWG.

Answer 4

I can't say conclusively; Prelimary web searches seem to indicate you need #6 wire or better for that many volts/amps.

It looks like the answer may be in a book like: http://www.worldcat.org/title/wiring-a-house/oclc/48951042 where the above is a link to where you might find it, at a local library. That's probably your best bet, short of an electrician answering the question. Simply-put, though, your city and county will have guides, and you may be able to contact a building inspector with your questions if-needed.

Answer 5

If the rated primary current is 47 amps and the duty cycle is 20% you can use #12 thhn or #10 Romex with a 50 amp breaker.