Ask Me Help Desk - Wiring a 60 amp welder

Good evening,

This type of wiring will require work to be done inside the main service panel. If you do not know what you are doing, please contact a licensed electrician. You can get dead very fast if you make a mistake! I'll respond to your questions in sequence.

1. what advantages/disadvantage to using 6ga #2 over thhn (vise versa)

1) THHN is a thermoplastic insulator with a nylon jacket. The "HH" stand for "High Heat". The insulation of the conductor is independent of the gauge of the conductor.
The "2" refers to the number of current carrying conductors within the cable. Usually you will see it written a 6/2 with ground. This is acceptable for a 240 Volt connection, because the Neutral is not needed. In this connection scheme, you would connect Black to one blade and White to another blade. Then on both ends of the white conductor you would permanently change the color of the white conductor by either using red, black or blue tape or a sharpie. This is to let anyone following know that this conductor is not being used as a Neutral conductor it is a hot conductor.

2. the wires will not be inside the wall

2) If the conductors are not inside the wall, then they must be protected from damage.

3. why is thhn #6 rated for 65 amps when the #6 sheathed wire rated for 55 (at least by a Menard's chart)

3) Again "THHN" is describing the insulation covering the wire. What the Menards chart is showing you is two different "Temperature Columns" The three available columns are given in the 2008 NEC code Table 310.16. There are three temperature columns.

60c - 75c - 90c. You will not find 90c in general use in a residence.
You would use the 60c column if you do not have any idea what the operating temperature of the conductors would be. In order to use the 75c column, the temp of the connections and cable must match. So, if you are planning to use the THHN insulated conductors to connect to the welder to the breaker and the welder connections are listed at 75c then the conductors and connection points match. The table is telling you that a 75c copper conductor can safely carry 65 amps.

If however, the connection points on the welder do not list the temperature, then you must use the 60c column and even if you were using THHN insulated conductors you would be limited to 55 amps.

4. is 6ga the proper size for this load and distance ?

#6 is fine for 30'. Again, this based on the insulating and operating temp of all the listed components of the circuit. Table 310.16 allows 65 amps for a THHN insulated copper conductor at 6 gauge. If however, you are using the 60c column, than you would need to go to 4 gauge conductors. Use the 75c THHN conductors!!

5. would it be smart to put a 60amp sub panel where I want the outlet and then connect the outlet to the sub panel or is that not needed

5) This is a totally different question than you think.

First, does your panel box have room for a double pole 60 Amp breaker? That's the question you have to answer.

If it does not, than you have to decide how you are going to make room for the circuit. Sometimes you can use "tandem" or "Slim-line" breaker in a slot. So you would place two slim-lines in one breaker slot, if allowed. Possibly you would have to do that to a total of four breakers to make two full breaker slots available.

If you cannot do that, than you can create sup panel feeder and move at least two full breakers to connect the ones you removed for the panel in the sup panel. Then you would need at least two more positions in the sub for the welder.

Sub panels have very specific codes and there is no waffle room. If you need to do a sub panel, then let me know.