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#78815 - 10/25/01 08:26 AM NEC 300-3(b)  
Bill Addiss  Offline
Member
Joined: Oct 2000
Posts: 3,875
NY, USA
Does ('99) NEC 300-3(b) prohibit wiring to Multi-function units like Heater-Fan-Light combo units from being run in more than 1 cable (or raceway) from switches to unit?

Bill


2017 / 2014 NEC & Related Books and Study Guides

#78816 - 10/25/01 08:54 AM Re: NEC 300-3(b)  
Tom  Offline
Member
Joined: Jan 2001
Posts: 1,044
Shinnston, WV USA
In my opinion, no. The installer will need to pay attention to how he makes the connections in the unit to make sure that the correct wires are used.

For example, a 2 wire cable could handle the heat part, making sure that the white wire from the heater is connected only to this cable. The rest of the functions could be done with a 3 wire, making sure none of the connectons share a wire with the heater.

I've always hated this product because of this. Seems you never have a piece of Greenfield on the truck when you need it.

Life would be simpler if you could buy 4 wire Romex, but, according to my supplier, no such thing.


Few things are harder to put up with than the annoyance of a good example.

#78817 - 10/25/01 10:28 AM Re: NEC 300-3(b)  
ElectricAL  Offline
Member
Joined: Oct 2001
Posts: 597
Minneapolis, MN USA
The key word in 300-3 (b), to me, is "circuit". Not to be confused with "branch circuit", which is defined in Art. 100. Rather, the current path to and from a load.

The multi-function unit is built with individual loads each with their own neutral and hot. The installer is one who has to make sense of the multiple neutrals.

When I'm installing an unfamiliar multi-function device that I'm running more than one cable to, the image I work with is that the net magnetic field about any individual cable must sum to zero under all normal load conditions. Any switch leg current in a cable must return only in the neutral in that same cable for their individual magnetic fields to cancel.

It's interesting to me that "circuit" by itself is not defined.

Tom, I've ordered in NM-B 4 wG. Got a spool of 14 & 12 that I keep in the shop for special occasions. Crescent Electric brought it in from Montana or Wyoming, I forget which.

Al


Al Hildenbrand

#78818 - 10/25/01 11:09 AM Re: NEC 300-3(b)  
resqcapt19  Offline
Member
Joined: Nov 2000
Posts: 2,148
IL
Doesn't the rule in 300-3(b)(3) permit you to use multiple NM cables for this application?
Don(resqcapt19)


Don(resqcapt19)

#78819 - 10/27/01 01:09 PM Re: NEC 300-3(b)  
bordew  Offline
Member
Joined: Aug 2001
Posts: 142
Vienna,Ohio, USA
Bill;
you mentioned that you saw no problem splitting up the H/v/L/NL , my question is why ?
To me that would mean more work.
First, on the Nu-tone unit I looked at yesterday it said a 20 amp circuit is required. Assume for a moment that is a non-issue,the one I saw was a 1400 w heater, two 60 watt bulbs and a 7 w night-light and about 50VA for the motor, almost 1600 watts total. A 20 amp ccircuit resi can draw 2400 watts as long as it is not a continuous load, this is not considered a continuous load. But if it was 80 % of 2400 is 1920 watts, which neans this unit could run all day, no-problem. Which is why these units require their own breaker.(20 amps)
I guess from what I have read that it is common to run a 3/c and a two conductor, ok now you have 4 switches, the 3/c R,B,W and bare, the 2/c B,W and bare, which switch gets the white wire to return to the load ?
I did go to home depot to find a h/v/l unit they didnt have the 4-switch combos, but still recomomended running two cables. On the switching that would have all legal colors but again another circuit and breaker, or two spaces used in the panel instead of one, unless you are going to tie that into the Bathroom lighting circuit, providing there is a vanity light.


#78820 - 10/27/01 01:50 PM Re: NEC 300-3(b)  
ElectricAL  Offline
Member
Joined: Oct 2001
Posts: 597
Minneapolis, MN USA
The heater alone is more than 50% of the bathroom circuit's capacity, so it can't be added to that circuit, right?

Al


Al Hildenbrand

#78821 - 10/27/01 02:23 PM Re: NEC 300-3(b)  
Bill Addiss  Offline
Member
Joined: Oct 2000
Posts: 3,875
NY, USA
bordew,

Yes, running separate cables to it would be more work for sure! I hope that you don't think I meant from the Panel? (I'm just talking about how to get from the switches to the unit.)
I wouldn't recommend it, I was just trying to get behind the meaning of 300-3(b) and verify that it is not a violation to do so. I like the idea of 1 cable and would recommend that method first. One point I was trying to make was that if 2 cables are used the installer has to make sure that there is a neutral in each cable that returns only the current from the loads supplied on that cable. A 3 function could use a 3 wire w/Gr and a 2 wire w/Gr and a 4 function unit would need (2) 3 wire w/Gr cables. There wouldn't be a need for 2 breakers though, they could still be on the same 20A circuit, couldn't they?

Al,

I, personally, do not agree with adding anything to that Bathroom Receptacle circuit.

Bill

[This message has been edited by Bill Addiss (edited 10-27-2001).]


#78822 - 10/27/01 02:36 PM Re: NEC 300-3(b)  
ElectricAL  Offline
Member
Joined: Oct 2001
Posts: 597
Minneapolis, MN USA
I'm thinking of 210-23(a).

Al


Al Hildenbrand

#78823 - 10/27/01 02:43 PM Re: NEC 300-3(b)  
Bill Addiss  Offline
Member
Joined: Oct 2000
Posts: 3,875
NY, USA
Gotcha!

I thought that you meant the 20A receptacle circuit.

Bill


#78824 - 10/28/01 09:36 PM Re: NEC 300-3(b)  
bordew  Offline
Member
Joined: Aug 2001
Posts: 142
Vienna,Ohio, USA
Al:
As far as I know a H/V/L/NL unit requires its own circuit, a 20 amp circcuit. this would be in addition to the one 20 amp required in art. 210.
To tell you the truth I think there should be two gfci circuits in a large bathroom, How many times have you gone into a residence and hanging in the bathroom are two .44 magnum-1850 watt hair dryers. Do these manufaccturers every think before they put out such units ? I mean you could use one of those ' Babies ' for a heat-shrink gun.


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