310.13(a)

[TwinCitySparky]

I have a heat trace -roof application- question. Manufacturers info shows me that my 170' long cable is to be protected with 30A @ 120 volts. The cable consumes a fairly large inrush current at start-up. The application was pre-wired with a dedicated circuit, 12G THWN wire, 20 amp breaker and 20A GFCI.

Per instructions if cable length was 130' I would be fine with 20 amp capacity. But the extra 40' of cable pushes me into the 30A category. So I tentatively approach my NEC book...

The vast portion of the circuit is ran in PVC conduit outside where ambient temp will always be below freezing. (Wintertime) 5' of the circuit is ran inside the heated garage which is kept at about 55 Fahrenheit.

Using the 90C table for THWN (obviously far below my app. temp) I think I'm OK using a 30 breaker with my 12G wire. Am I compliant or confused.

 

[augie47]

You would have found a possible solution were it not for 240.4(D) which limits #12 to 20 amps (unless overd by 240.4(E)or(G), which do not seem to exempt your application)

 

[iwire]

In addition to 240.4 you would have problems with 110.14.

None of the equipment you are terminating the 12 AWG to will be rated for 90C and some may actually hold you back to the 60 C column.

 

[TwinCitySparky]

You would have found a possible solution were it not for 240.4(D) which limits #12 to 20 amps (unless overd by 240.4(E)or(G), which do not seem to exempt your application)

No it doesn't.

You would think it would... Freezing conditions and all. Guess I'm chopping 40' off this cable.

Anyone need 40' of Icestop cable?:roll:

Thanks guys.

 

[TwinCitySparky]

In addition to 240.4 you would have problems with 110.14.

None of the equipment you are terminating the 12 AWG to will be rated for 90C and some may actually hold you back to the 60 C column.

Those durn terminations. and I've read that here so many time before...

It's funny sometimes how things dont stick in the brain - unless they are thrown directly at it!

 

[LarryFine]

TC, any chance of converting the installation to 240v (or 208v), which would reduce the current demand?

A 2p GFCI breaker (or faceless GFCI device) might cost quite a bit less than repulling the wire.

 

[TwinCitySparky]

Hi Larry

I appreciate the suggestion but the cable I am stuck with is only rated for 120 volts. They do of course make the 208, 240, and 277 versions. I could have ran 270' with the 240V version.

Scritching away more hairs now...

I am actually wiring for two separate heat traces in my one 1/2" PVC sched. 80 - So now I think I need to max my pipe fill to four 10's (2 hots, neutral, grnd) and place a 120/240 volt 30 amp GFCI to power both of my 120V circuits - then I should be OK.

Or chop my cables...

 

[LarryFine]

TC, what about running a single feeder in that conduit, and placing a small panel on the roof, or wherever the cables and conduit meet.

1/2" sched. 80??? That stuff definitely does not have a 1/2" ID. I don't think four 10's (plus an EGC) will even fit.

 

[TwinCitySparky]

Hey Larry

Sub is out of question also. These cables are going on top of a Frank Loyd Wright house. These homes have huge odd sized soffits that hang far out from the house and use flat rubber membranes of top. No place to hide panel.

But now I'm confused regarding my four 10's :-?

Annex C Table C.9

10G THWN with 1/2 sched 80 - table shows four 10's will squeeze in. (That's including my EGC - using shared neutral and changing my GFCI plan to a single 120/240 30 amp 2 pole GFCI) What did I miss??

 

[augie47]

If I correctly understand your heat cable, According to 426.28 GF protection is required.
You might check availability of a two pole GF breaker. if you need to reduce conductor fill.
(The GF protection for these cables is not the same a GFCI protection)

 

[TwinCitySparky]

If I correctly understand your heat cable, According to 426.28 GF protection is required.
You might check availability of a two pole GF breaker. if you need to reduce conductor fill.
(The GF protection for these cables is not the same a GFCI protection)

I can source a 30A GFCI 2 pole breaker for this.

Will that meet GF requirements?

If seeing C.9 correctly, then four 10's (using EGC) is OK.

 

[benaround]

I can source a 30A GFCI 2 pole breaker for this.

Will that meet GF requirements?

If seeing C.9 correctly, then four 10's (using EGC) is OK.

The GFEP that Gus mentions is 6-50 miliamps.

 

[augie47]

TwinCity, I can't speak for your particular type cable, I know those that I have inspected have called for the GFPE protection.
GFCI might not work well for your application if this is the case. Hopefully the instructions with you install will specify what type ground fault is needed.

 

[Cavie]

I can source a 30A GFCI 2 pole breaker for this.

Will that meet GF requirements?

If seeing C.9 correctly, then four 10's (using EGC) is OK.

Yes it will. you can also drop the EGC to 12.

 

[benaround]

Yes it will. you can also drop the EGC to 12.

Cavie, # 12 egc on a 30a ocpd ?

 

[Cavie]

Cavie, # 12 egc on a 30a ocpd ?

Opps! my mistake. I have problems moving back and forth between the NEC world and the road building world. The road building world is supposed to adhere to the NEC and the local maintaining agency. They local maintaining agency and the Egineer of record often overide the NEC. I have a project going where they did just that with the ground wires and 30 amp ckts. Most of the time we we use #6 for all EGC between light poles with 15 and 20 ckts. I got yelled at because my company installed #8 and #10 for grounds as shown on the prints. I directed the problem to the EOR and he said leave it. My 58 year old brain has trouble remembering which book to read.

 

[TwinCitySparky]

GFEP


Equipment Protection.

I'll be returning my 150.00 GFIC now...

Any clues where a guy can find a cutler hammer CH GFEP 2 pole 30 amp breaker? Or am I setting a small sub for another brand.

 

[TwinCitySparky]

Found online only $450.00! -

Hey, I'm getting extras for stock!

 

[TwinCitySparky]

Plan B

Set sub for different brand.

Any suggestions out there what brand to use to save $$$

(Trying to find a reasonably priced 30A 2 pole GFEP of any brand)

???

 

[TwinCitySparky]

Guess I'm the only guy on this site running industrial roof heat trace. :roll:

To the poor sap electrician trying to install heat trace who stumbles across this thread: Plan on the ETI SST-2 control for your heat cables. It has the GFEP built in with set controls and costs less than regular GFEP breaker. If you have 2 cables/circuits, use separate neutrals. Read all manufacturers info first.

Finally, try really hard to sell and complete the job in July.