Conductor Sizing | Individual Branch Circuit

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Conductor Sizing | Individual Branch Circuit

  • Yes

    Votes: 2 40.0%

  • No

    Votes: 3 60.0%
  • Total voters
    5
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DTL

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We are working on a heat tape system (WinterGard Wet H622 240 V) which is specified, by the manufacturer, to be on 30A branch circuit with 30-mA trip level overcurrent protection device such as Square D QOEPD.

As I understand it, (Unless specifically permitted in Section 240-3) the conductor sizing for 30 amperes over current protection should be No 10 copper, however, since this is not a multi-outlet branch circuit, could 240-3(b) apply as a suitable exception to this conductor sizing rule?

Since this heat tape is the only device on the circuit, does this qualify as an individual branch circuit? And then if so, as an individual branch circuit, does the code permit for smaller conductor to be used in the circuit (i.e. No 12 in 30A)?
 
Having conflicting information coming for two electricians. Would like to satisfy home-owner, put their mind at ease.
 
By the way, though you might be interested to know that the #10 guy is an apprentice and the #12 guy is a master. Owner thought the master electrician might have known something the apprentice did not...
 
I don't. As I understand it, the load current varies significantly between the 0f to 40f ranges, mainly at start-up. Because we have not yet had sub 32f temps, the site conditions are unknown. Raychem tells us (we've all called them, including home-owner) that power output @ 32F (in snow or ice) is 8W continuous. So many variables. Home-owner wants it to work. Electrican(s) want it to work and not have service calls. I want both electrician and HO to rest well at night and not do-over...
 
One other thing we heard was that the steady state amps is dependent upon heating cable temperature. Would have been good to obtain a graph showing this temp vs. start and temp vs operating so that limits could be understood but was not able to get this info...
 
Yeah that is self regulating heat tape, very common but the manufacturer should provide a max current.

Gus, I was just wondering if the electrician was considering the load, I see no way around 10 AWG for this circuit.:)
 
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That's a relief..... I was waiting for you to show me something I have overlooked (not unusual). I could find nothing that exempted Art 424 installs from 240.4
DTL, from your comment "Electrican(s) want it to work and not have service calls. I want both electrician and HO to rest well at night and not do-over... ", the conservative route would win in any event.
Also, I don't find a 240.3-b to which you made reference. For curiosity, I'd ask electrician #2 on what Code Article he based his #12 comment.
 
Thanks Gus, I will ask him to clarify. I guess in the end section 426 is the most applicable section and specifically "...continuous load". If apprentice comes back with something really good, I'll let you know. Thanks for all of your input.
 
Apprentice says that NEC calculations for Branch Circuits and Individual Circuits are different. He suggested that most people that have not recently been to school default to the rule of #10 for 30 or #12 for 20 because they are considering residential "branch circuits", not "Individual Branch Circuits". He suggested that historic thinking defaults to this because in most residential applications "Individual Branch Circuits", will have a duplex receptical nullifying it as "Individual" and making it "Branch". He says the calculation for "branch circuit" allows for more cushion for overloading, where the "individual branch circuit" calculation has a smaller tolerances allowance since the calculation for the circuit can be done just on the dedicated load.

He is pretty convincing.

He then said, changing to #10 is fine but the other guy wants to do that just to up the $ to the home-owner and it is not necessary. He would do it either way, whichever is chosen, but #12 is cheaper (no changing of wire) and meets code...
 
When he has time off from attending his classes on used car sales (sounds like he's getting "A"s :)), ask him to look closely at 240 (General) and 240(G) in particular.
 
DTL said:
Apprentice says that NEC calculations for Branch Circuits and Individual Circuits are different. He suggested that most people that have not recently been to school default to the rule of #10 for 30 or #12 for 20 because they are considering residential "branch circuits", not "Individual Branch Circuits". He suggested that historic thinking defaults to this because in most residential applications "Individual Branch Circuits", will have a duplex receptical nullifying it as "Individual" and making it "Branch". He says the calculation for "branch circuit" allows for more cushion for overloading, where the "individual branch circuit" calculation has a smaller tolerances allowance since the calculation for the circuit can be done just on the dedicated load.

He is pretty convincing.

He then said, changing to #10 is fine but the other guy wants to do that just to up the $ to the home-owner and it is not necessary. He would do it either way, whichever is chosen, but #12 is cheaper (no changing of wire) and meets code...
Click to expand...

DTL,

Maybe the apprentice has been to school more recent than a lot of us, but the NEC definition of a Branch Circuit by him needs to be looked at a little differently. First up, there are four different Categories of Branch Circuits...Appliance, General Purpose, Individual and Multi-wire Branch Circuits. The Master would agree.

I do not believe that having a single receptacle on any one of those BC's would change my view defining any particular Category. I could venture to designate an adapter powered heat tape as an Appliance BC on a basis of the manufacturer's listed product instruction sheet if there is one. The length variables can change the conductor "branch feeder" AWG size to support the interface requirement stipulated OCPD by the manufacturer. Linking to the specific manufacturer spec sheet would help answer a lot of unknowns. Tx, rbj
 
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Simple answer to this, is @ 8 watts per foot, anything over 480' of this cable will require a 30 amp circuit, 426.4 which will be 10AWG conductor on a 30 amp breaker, if you can get a 25 amp breaker the above increases to any thing over 600' will require a 30 amp circuit, so from 480' to 600 feet a 25 amp circuit could be used, but the wire would still be 10 awg, so its kind of mute.

and because of 426.28 Ground fault protection (30ma) will be required, this is not for over load as stated in the OP but for faults to ground to protect against shorts of the resistive heating element which in some cases will not trip a regular type breaker and can cause the portion of shorted cable to achieve a much higher temperature causing a fire. so a GFP is a must.

A GFP is much like a GFCI breaker we use for bathroom/kitchen circuits
the difference is the fault to ground is limited to 30ma's instead of 5ma's in a GFCI. they will instantly open any grounded circuit conductor that applies more then 30 ma's to the ground fault.
 
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