Are shore power cables legal to use for temporary power connections, like to connect portable generators to a switchboard while the main building generators are undergoing mainenance/upgrade? NEC seems silent on the matter- would it rely completely on the UL listing? They're perfectly suited for this, though- flexible, tough, watertight, weathertight, etc.

By the same token, could other UL listed cable (like welding cable) be used in permanant installations? I've seen it done and been told it was legal, but never pressed the issue.

Steve,
You can't use welding cable unless it has a dual listing as building type wire. Some welding cable is also listed as RHH and you can use that. There is also type W power cable that is very much like welding cable and it can be used per the rules in Article 400.

Speaking of "temporary" installations, what is the time period that temporary is good for? Specifically, when I worked on a movie set, welding cables were used to hook up portable distribution centers to installed building wiring. These cables were left installed for about 9 months. The facility was not a theater but a former manufacturing / warehouse structure.

Larry, the NEC defines temporary as 90 days or less.

Don, I agree with your answer, but not the reasoning.
When an issue comes up, I check the UL "White Book" for a little more clarification as to what the listing means.

In the case of welding cable, UL states that it is only rated for 100 volts, unless marked differently.

Then there is the issue of connectors. Most lugs and connectors are only evaluated for use with "ordinary" stranded wire. Very finely stranded wire ... welding cable, locomotive cable, whatever ... require connectors that are designed for use with them. In 'practical' terms, the approved connectors will have two set screws, bouble length barrels, etc.

[This message has been edited by renosteinke (edited 02-26-2007).]

One other thing about welding cable is it is destroyed by U/V. I found this out on my boat

John I do not understand.

Welding cable is not (generally) listed as building wire.

If it is not listed in article 400 we can not use it.

The portable power cables we can use are listed in 400 and I think it goes without saying that you must use the proper terminals.

As far as I know the proper terminals are compression terminals, I don't think any lug that the set screw contacts the fine strands is listed for that use.

Type W cable is listed in article 400 as going up to 1000kcmil, which is the size shore power cable I'm talking about, not just some #10 extention cord for a portable generator. 400.7 (B) which requires plugs does give an exception, "as permitted in 368.56" which allows direct bus connections for hard-usage.

If welding cable is cross-rated as class W, then 400.7 does appear to permit the uses I've seen it in, which is good news for me!

I believe the shore power cable I have availible is THOF/MIL-915. I've found a couple references to UL 44, RHH & RHW-2 in the catalog entries for these cables, but I don't know if those are universal throughout the industry or just happen to be what those particular manufacturers have done.

Follow-up question: if "Shore Power Cable" is RHW-2, is it exempt from cableway requirements for temporary installations? I don't see RHW-2 listed in Article 400. Where is RHH/RHW discussed? (Curse my non-searchable paper copy of NEC!)

John,
Most of the welding cable used around here is rated for 600 volts, but the UL listing says that the cable is only listed for use on the secondary side of electric welding machines. That being said I think that this is another bogus issue. I looked into using some Type "W" power cable for a temporaty installation a few years ago and found that in the case of one manufacturer the only difference between their Type W power cable and their welding cable, other than the listing and price, was that the welding cable had an insulation that was 25% thicker than the power cable. The stranding, strand count, and insulation type was identical. After finding that information, I went ahead and used the welding cable. Note this may not be true for all brands of cable, but it was true for the brand that I used.

Don

Larry,
I think that would not be an Article 590 installation. It would be covered by 530. In a quick look, I did not see a time limit for the portable wiring on a movie set. However, listed cables and cords are required and welding cable would not be permitted.
Don

[This message has been edited by resqcapt19 (edited 02-27-2007).]

Steve,
RHW is a building wire. See Table 310.13.
Don

Don, yes, I saw it in 310.13, but didn't see any articles like 320-340, which I'd expect to see if RHW were allowed to be used in the way I've seen shore power cable used, EG, laid on the ground temporarily connecting large commercial power loads. As I do not intend to run this in strict accordance with article 300 methods, I was hoping to find a clause allowing some relaxation of techniques. Specifically, that this cable should be installed in raceways. I know extension cords are not required to be run in raceways, but I couldn't find anything in articles 400 or 590 permitting it for type W, letalone 300 permitting it for RHW...


400.4 might give an easy out, as it allows for other cables used, if a special investigation deeps it acceptable. As mil-spec marine shore power cables are clearly legal to lay on the ground, span long distances without support and carry high levels of current, the investigation would be short and positive, I'd expect.

Steve,
The RHW rating alone would not permit that use for applications covered by the NEC.
Don

Using cables not listed in the table are "subject to special investigation" according to 400.4. This is one of those times that engineers, and others, get to make their case for varying from standard practices.

I don't mean to say that this is a 'blank permit' to use any old wire that might be about; rather, there is absolutely no way for the code to list every possible type of cable (especially ones not yet invented).
There are numerous specialty cables that may turn up, whose use may (or may not) be appropriate. Buss Drop cable, Stage and lighting cable, Boat cable, Shipboard cable .... the list goes on. I, for one, have no idea how "boat" cable differs from "shipboard" cable, but they are two different listings.
A more common situation where unusual cables might appear is with the assembly of imported production equipment. It is very possible that machine sections might be interconnected using cables that are not identified according to NEC classifications.

All this supposes the correct use of terms by everyone. The term 'welding cable' seems to be applied indiscriminately to any fat, supple cable.

I consult the UL "White Book" for additional information as to what a type designation may mean. For example, I am told that if welding cable has ratings different than 60 degree and 100 volts, it will be marked on the cable. Since there is no mention of testing for outdoor, wet, or sunlight exposure, I cannot assume that the cable is rated for those uses.

As for the connectors and lugs used, this was discussed in IAEI News. ("Do You Know Where Your Cables Are Tonight" , Jan/Feb 2005). It appears that there are actually industry standards for stranding; "normal" stranding is called 'Class B.' Much of the specialty cables have class K or M stranding.
UL standards require that terminals, lugs, and connectors be marked if they are suitable for use with other than "normal" wire. While the article also discusses longer-barrel crimp connectors, I have also seen terminations where multiple set screws pressed against a plate that, in turn, gripped the wire. The article refers to instances where a set screw, in direct contact with the wire, may break off strands as it is tightened.

So, in answer to the original question (Are these cables suitable?) I have to look more closely at the cable, and it's connections. I'd then have to research exactly what the cable has been listed for.

Granted my ship board experience was on warships built to defeat the axis powers but the shipboard cable I remember was covered in a galvanized steel braid about as heavy as a Kellems grip but very tightly woven.
I have never seen that on a "boat".

Thanks John I understand more what you where trying to convey.

That said why would I want to choose a cable that I would have to jump through hoops to use when portable power cable is readily available that is listed in Table 400.4?

I used to have a job that required hooking up power to traveling bands and if they had cable that was simply welding cable I would not hook up. They would usually end up renting the right cable or if I had enough on hand I would loan it to them.