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NEC 300-3(b) #78815 10/25/01 08:26 AM
Joined: Oct 2000
Posts: 3,961
Bill Addiss Offline OP
Member
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


Bill
2017 / 2014 NEC & Related Books and Study Guides
Re: NEC 300-3(b) #78816 10/25/01 08:54 AM
Joined: Jan 2001
Posts: 1,044
Tom Offline
Member
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.
Re: NEC 300-3(b) #78817 10/25/01 10:28 AM
Joined: Oct 2001
Posts: 597
E
ElectricAL Offline
Member
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
Re: NEC 300-3(b) #78818 10/25/01 11:09 AM
Joined: Nov 2000
Posts: 2,148
R
resqcapt19 Offline
Member
Doesn't the rule in 300-3(b)(3) permit you to use multiple NM cables for this application?
Don(resqcapt19)


Don(resqcapt19)
Re: NEC 300-3(b) #78819 10/27/01 01:09 PM
Joined: Aug 2001
Posts: 142
B
bordew Offline
Member
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.

Re: NEC 300-3(b) #78820 10/27/01 01:50 PM
Joined: Oct 2001
Posts: 597
E
ElectricAL Offline
Member
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
Re: NEC 300-3(b) #78821 10/27/01 02:23 PM
Joined: Oct 2000
Posts: 3,961
Bill Addiss Offline OP
Member
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).]


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

Al


Al Hildenbrand
Re: NEC 300-3(b) #78823 10/27/01 02:43 PM
Joined: Oct 2000
Posts: 3,961
Bill Addiss Offline OP
Member
Gotcha!

I thought that you meant the 20A receptacle circuit.

Bill


Bill
Re: NEC 300-3(b) #78824 10/28/01 09:36 PM
Joined: Aug 2001
Posts: 142
B
bordew Offline
Member
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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