ECN Forum Forums Code Related Discussion NEC & other Code issues Welding Cable as branch circuit and feeders

Message from reader:

I am reviewing a reseach laboratory design for an owner in which Schedule 80 PVC conduit, and up to 4/0 AWG welding cables are being specified for feeders and branch circuits to maintain power quality.

The "clean power" source is a 180 kVA rotary UPS on the sixth floor of a lab building serving sensitive equipment on the 4th, and 5th floors. The lab professor is requesting the PVC conduit and welding cabling stating that these wiring methods are European standard and required for maximum power quality in his lab.

I question the wiring methods.

To refute the PVC conduit, I can refer to the IEEE Emerald Book, Chapter 9, "Recommended Materials".

I am unable to locate any Code limitation or other authority that prohibits, or even
discourages welding cable as a grounding conductor.

Can someone offer me any advice?

Best Regards,

Jeffrey M. Leavenworth, P.E.

This is a listing violation (110-3(b)). 310-13 might also apply since welding cable does not appear in any of the tables mentiond.

From UL's white book "Welding Cable (ZMAY),
"Welding cable...intended for use in accordance with National Electrical Code Article 630, Part E in the secondary circuits of electric welders." Since this laboratory application doesn't involve welders, this cable would not be allowed.

The finer stranding of welding cables may have something to do with lowering their impedance to high frequency currents, but I've never heard of a welding cable actually being applied in this manner.

Tom

[This message has been edited by Tom (edited 11-20-2001).]

Even though it is not code compliant, welding cable is often used for temporary power applications. There are types "W" and "P" listed power cables that have very similar construction as welding cables that can be used on power circuits and be code compliant. I looked into one brand of welding cable and Type "W" power cable a few years ago and found that they we identical in every way except that the welding cable had 25% thicker insulation of the same material as used on the Type "W" power cable. The type "W" power cable was suitable for 600 volt power circuits and the welding cable wasn't according to the listing.
Don(resqcapt19)

Don,

Did you happen to remember how much more type W would cost versus THHN? Just curious.

Tom

[This message has been edited by Tom (edited 11-21-2001).]

This is not an answer to your question but I would like to comment on the welding cable usage. When doing maintenance type work, this cable is great. The high ampacity, the heavy duty rubberized insulation and the flexibility make this a real asset during temp set ups and emergencies.

Tom,
I don't know what the welding cable costs, but diesel locomotive cable which is also very flexible but has a 2000 volt rated insulation costs about 3 times THWN. I have used diesel locomotive cable a number of times on large DC motors that have 700 volt armatures. The last one I did was 1500 hp and took 16 535.3kcmil diesel locomotive cables. 8 for the plus side and 8 for the negative side. This stuff is almost as flexible as welding cable and is great to work with. While I don't find this cable in the NEC, the manufacturers cut sheets say that it is suitable for 90°C wet or dry, in conduits, ducts, or cable tray.
Don(resqcapt19)

Type “W” cable is roughly twice the cost of thhn copper. I bought a lot of it last summer for a job and our special “big contractor” discount cost was about $1800 per 1000ft. tack on 10-20% for a non-discounted rate and it’s about double the local home center cost on #4/0 thhn. If I remember correctly it was also 2000V rated.