welding cable -vs- thhn/thwn

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vango

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1/0 flex-a-prene -50C to +105C heavy duty welding cable
-vs-
1/0 THWN/THHN 90C

75' feeder to 225A 3ph panel

1/0 welding cable (according to manufacture) is good for 250A
1/0 THWN/THHN (according to Table 310.16) is good for 170 A
1/0 THWN/THHN would require parallel, welding cable would not.
Welding cable is much easier to manipulate than thwn/thhn, esp
with the larger gauges.

I guess my question is, is it a prohibited procedure to utilize welding cable in lieu of THWN/THHN as a feeder?
 
The first issue is you must use a conductor type that is listed in 300.13 if you want to install it in a raceway or a flexible cable type that is listed in 400.4. However flexible cables listed in 400.4 are very limited when it comes to installing them in raceways.

Next comes ampacity.

The manufacturer can rate it any ampacity they see fit, we have to ignore that rating and use the NECs ratings which will likely result in the 75 C column of table 310.16 or 150 amps for 1/0.

While we are at it, yes, table 310.16 shows 1/0 THHN as 170 amp rated in the 90 C column however none of your equipment terminations will be rated higher than 75 C so 1/0 THHN will be effectively good for only 150 amps.

So....

1/0 THWN/THHN 90C allowable ampacity is 150 amps and will need over current protection at 150 amps.

and

1/0 flex-a-prene -50C to +105C heavy duty welding cable if it is listed in 310.13 also has an allowable ampacity of 150 amps and will need over current protection at 150 amps.

There is no good reason to use welding cable for this, it will pull hard in the raceway and the termination on your equipment are not designed for the fine stranding which means you will have to use a compression tool and connector.

I install 225 amp panels quite often and at a minimum we use 4/0 copper with a 75 C rating of 230 amps this allows the use of 225 amp overcurrent protection

3/0 copper is rated 190 and the largest allowable over current protection will be 200 amps.

Bottom line is 1/0 of any type does not come close to providing 225 amps.
 
Bob did you mean that 3/0 copper was rated at 225 amps, with a usable ampacity at 75 degrees C of 200 amps.
 
infinity said:
Bob did you mean that 3/0 copper was rated at 225 amps, with a usable ampacity at 75 degrees C of 200 amps.
Click to expand...

No, that was not really what I meant but I did goof up in saying 3/0 was rated 190.

What I was trying to get across was that if you want to use a 225 amp OCPD even 3/0 CU is to small.

Its 4/0 copper or 250 AL minimum for a 225 amp breaker.
 
iwire said:
No, that was not really what I meant but I did goof up in saying 3/0 was rated 190.

What I was trying to get across was that if you want to use a 225 amp OCPD even 3/0 CU is to small.

Its 4/0 copper or 250 AL minimum for a 225 amp breaker.
Click to expand...

I figured that. A standard for us is a 225 amp panel with #4/0 Cu feeders also. A 200 amp panel would get #3/0 Cu feeders.
 
There is welding cable that is dual listed as RHH and can be used for electrical systems, but you have to use the NEC ampacities. The manufacturers use the 90?C rating from Table 310.17. In most cases you are limited to the 75?C rating from Table 310.16. Also as Bob pointed out, you have to use a connector that is listed for use with the fine strands in the welding cable.
The listing of welding cable does bring up an issue to me. A few years ago, I was doing an emergency feed to an industrial building and we used welding cable as many do for this purpose. I did some reaseach on the welding cable and Type W power cable and found that the only difference was that the insulation on the Type W power cable was thinner than that on the welding cable. Every thing else from the stranding to the type of material used for the insulation was identical except the use of the welding cable with the better insulation was a code violation. Note that both the welding calbe and the Type W cable were made by the same company and I don't not know if this is true in general for all welding cable.
Don
 
iwire said:
1/0 flex-a-prene -50C to +105C heavy duty welding cable if it is listed in 310.13 ..will likely (be limited by equip.-termination listings or) the 75 C column of table 310.16. ..There is no good reason to use welding cable for this, it will pull hard in the raceway and the termination on your equipment are not designed for the fine stranding which means you will have to use a compression tool and connector.
Click to expand...

Nice work on clearing up the use of these exotic cables.

Perhaps switch-gear terminations are rare exceptions, but how much ampacity of such hi-temps in conduit is lost to ambient derating, unless fed from open-air or expensive trays? 310.16 say remove 60% at 80c ambient.

Should also add, impedance-altering shielding is common to many of these welding cables, which makes more confusion trying to standardize line Z, with different bonding methods employed across these shields.
 
Last edited:
Good points!

110.14(C)(1)
300.14
400.4
Just to mention a few.
However not be cavil, and please correct me if I miss this, but wouldnt
310.4 (and related articles) get me the ampacity required with 1/0 THWN copper, notwithstanding 310.15(B)(2)(a), ambient corrections, and etc...?

I questioned the welding cable because I ran into a situation where is was used "as a feeder" as prescribed by an EE and approved by the AHJ. I didnt ask why it was done this way (didnt have time to open the can of worms), I was there to do an unrelated job. I thought maybe I was missing out on something, obviously not. Didnt mean to muddy up the water with the hypothetical numbers. It was just "welding cable"???
 
vango said:
wouldnt
310.4 (and related articles) get me the ampacity required with 1/0 THWN copper, notwithstanding 310.15(B)(2)(a), ambient corrections, and etc...?
Click to expand...

Sure, more than enough.

If you keep the runs in separate raceways you would have 300 amps of capacity.

If you run them all in one raceway you will likely have an ampacity of 272 amps.

170 * 2 * .8 = 272.

That is certainly a large enough feeder for a 225 amp panel.

I don't see many prices but it will surprise me if two sets of 1/0 are not a lot more money than one set of 4/0s.

Don't forget to order the equipment with lugs for parallel feeds, a 225 amp equipment does not usually come with double barrel lugs unless specified that way.

Good luck. :)
 
vango said:
I guess my question is, is it a prohibited procedure to utilize welding cable in lieu of THWN/THHN as a feeder?
Click to expand...

Based on 400.7(A) I would answer yes, unless you can show where it is "specifically permitted elsewhere in this Code" [400.7(A)(10)].

Based on 400.8(1) I would asnwer yes.

I believe both of these code references prohibit the use as I understand you to describe.
 
I guess my question is, is it a prohibited procedure to utilize welding cable in lieu of THWN/THHN as a feeder?
Click to expand...
Yes, the listing for welding cable says that it cannot be used for power circuits. This changes if the cable is the dual listed cable and if it is Article 400 does not apply. The dual listed cable is used like anyother cable shown in Article 310.
Don
 
Doesn't welding cable have a given duty cycle that limits it use?

I had a "engineer", spec this out, for motor controls once. Once I looked around on the net, and I think asking this question somewhere(forget which site), the welding cable was rated for ampacities, based on it's length.

Then it was also rated by it's duty cycle of use. For a given amperage, you could only use it for a 50% duty cycle.

Can any confirm this?
 
Dnkldorf said:
Doesn't welding cable have a given duty cycle that limits it use?
Click to expand...

I have never heard of this and would be interested also.

The term ?welding cable? can get confusing. Some tend to call all flexible cord or cable welding cable.

We use type G-GC and W in cable trays a lot for 200hp and 450hp pumps, 400.7(6) and 400.7(11). Some years ago, someone purchased 500+ft of single conductor ?Cable DLO 313 kcmil (UL) 2kV RHH RHW-2 for CT USE? cable. I could never find the term DLO in the code, although I have read an IAEI article that discusses using the proper (crimp) lugs for these cables.

One web site specifically warns of using welding cable as a feeder.
http://store.weldingdepot.com/pdf/weldingcable.pdf
 
Plate, on that link you posted, under the chart, it talks about 50% duty cycles.

I don't know if it apllies to using cables as feeders, and don't remmember where I have seen it in the past.

One of the problems of getting old.....
 
Dnkldorf,

Thanks, I have to actually start to read the fine print. Where did I put my reading glasses... Dollar store glasses do the job, so far.
 
More thoughts- "welding cable" is rather generic. Flexaprene doesn't appear to be listed, OTOH Suprt VuTron (General Cable) is listed as RHH/RHW.

From http://www.generalcable.com/NR/rdon...6-E527283DB631/0/Pg27_SVTrnWldgTy_RHH_RHW.pdf

1/0 - 4/0 AWG: CAROL SUPER VU-TRON WELDING CABLE (SIZE) EXTRA FLEXIBLE (UL) 600 VOLT (-50 to +90C) OIL RESISTANT P-123-141 MSHA --- CSA 90C ARC WELDING CABLE FT-1 --- TYPE RHH OR RHW (UL) 600V FOR CT USE

Compare with:
http://www.generalcable.com/NR/rdon...B31024F5173F/0/Pg23_SVTrnSngCndTyW_RHHRHW.pdf
#1/0 AWG - 500MCM ? CAROL SUPER VU-TRON TYPE W PORTABLE POWER
CABLE (UL) DRY 90C WET 75C 2000V SUNLIGHT RESISTANT P-7K-123049-
MSHA (SIZE) TYPE RHH OR RHW (UL) 600V FOR CT

Either way, I can't see how using any sort of super-flexible cable will be that useful when pulled into conduit. As others have observed, it'll be harder to pull in, and is going to be more expensive.

(Just about all stage lighting companies swtched from generic welding cable to "entertainment" cable 10-15 years ago. They also switched from welding tweeco connectors to camloks.)
 
i would not say its the exact same type wires.

welding cable is made of allot more thin strands compared to stranded.

I could see it having a hard time staying under lugs in a panel board or anything for our line of work.
 
Dnkldorf said:
Doesn't welding cable have a given duty cycle that limits it use?

I had a "engineer", spec this out, for motor controls once. Once I looked around on the net, and I think asking this question somewhere(forget which site), the welding cable was rated for ampacities, based on it's length.

Then it was also rated by it's duty cycle of use. For a given amperage, you could only use it for a 50% duty cycle.

Can any confirm this?
Click to expand...


The welder machine has the duty cycle, not the wire going from the stinger to the machine.

I have gone though a few welding classes and do a few projects with my equipment...i have never heard of a Duty Cycle for the cable.

I can see a voltage drop if the cable is too long undersized but that's about it.
 
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