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Posted By: Bill Addiss NEC 300-3(b) - 10/25/01 12:26 PM
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
Posted By: Tom Re: NEC 300-3(b) - 10/25/01 12:54 PM
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.
Posted By: ElectricAL Re: NEC 300-3(b) - 10/25/01 02:28 PM
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
Posted By: resqcapt19 Re: NEC 300-3(b) - 10/25/01 03:09 PM
Doesn't the rule in 300-3(b)(3) permit you to use multiple NM cables for this application?
Don(resqcapt19)
Posted By: bordew Re: NEC 300-3(b) - 10/27/01 05:09 PM
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.
Posted By: ElectricAL Re: NEC 300-3(b) - 10/27/01 05:50 PM
The heater alone is more than 50% of the bathroom circuit's capacity, so it can't be added to that circuit, right?

Al
Posted By: Bill Addiss Re: NEC 300-3(b) - 10/27/01 06:23 PM
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).]
Posted By: ElectricAL Re: NEC 300-3(b) - 10/27/01 06:36 PM
I'm thinking of 210-23(a).

Al
Posted By: Bill Addiss Re: NEC 300-3(b) - 10/27/01 06:43 PM
Gotcha!

I thought that you meant the 20A receptacle circuit.

Bill
Posted By: bordew Re: NEC 300-3(b) - 10/29/01 01:36 AM
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.
Posted By: frodo Re: NEC 300-3(b) - 10/29/01 01:53 AM
hi,
try using a 4/C #10
Posted By: ElectricAL Re: NEC 300-3(b) - 10/29/01 03:58 PM
Bordew,

I agree with you that these combination units are required to be on a 20 amp circuit, by virtue of the 1500 watt heater. 1440 watts is the 80% limit for a single load on a 15 amp circuit. And 1000 watts is the limit for any fastened in place load that could be added to the bath circuit, if the circuit is used for that one bath only (outlet, and including lights, etc.). The installation cost (a 20 amp circuit) of the heater in this combo unit is dictated by the size of the heater. No way around it.

But if I wire only the bath outlet on the 210 required bath outlet circuit (as is my option), and have the bath lighting tagged onto a general lighting circuit, what's to keep me from putting the combo unit fan/light/nitelite on the gen ltg ckt?...instead of the heater 20 amp circuit. The internal construction of the combo unit results in multiple neutrals being in its j-box for connection to the field installed wiring, so the manufacturer is making it possible for the field installer to hookup the neutrals in any grouping. It's up to the field installer to do it to code.

I understand that your AHJ wants to see one cable or conduit cause that simplifies his inspection. . .doesn't have to question the installer as to his/her understanding of 300-3(b), or open the combo's j-box to look for separated neutrals. . .but I think that's the AHJ's local spin.

Now, for the sake of discussion, in this hypothetical big bath (no jacuzzi) with two blow dryers (and maybe two bath outlet circuits. . .but that's another story. . .) what's to keep me from feeding the night light continuously (say I put in a LED bulb, less energy loss), switching the light at the door, switching the fart fan at the WC, and putting a spring wound timer for the heater at a location convenient to where one drys off? The extra work really isn't a problem cause the client is buying a really BIG bath and can afford my contract and I saw this on the prints so I included it in the contract. I feed the heater at the timer off its own 20 amp circuit, and tap the feed for the night light off the general lighting circuit and drop two switch loops to the WC and the door to the bath. By my count, I get to shoehorn one 12-2 and three 14-2s into the combo's j-box. The heater neutral is connected to the 12-2 and the rest on the neutrals are connected to the 14-2 feed.

That's what I call a version of a designer install. What do you think?

Al
Posted By: bordew Re: NEC 300-3(b) - 10/30/01 12:18 AM
Al:
As far as I can tell with the rating of this thing approx. 1400 w, I would think that would by itself require a seperate circuit, and I would think would severely limit the General lighting circuit that it was taken from.
I think it was you that mentioned the 50 % rule on the bathroom gfci circuit, that is a 10 amp load for a ceiling vent or whatever would come out in that ballpark.
You are right about the multiple neutrals in the circuit but they are confined to that box, the thing that bothers me is if one circuit is taken from the gen'l lighting circuit and another brought in from the panel, the heater, now you could inadvertantly shut off the one circuit and still have the heater hot. Also if the second circuit is taken froom the second buss now there is a possibility of 240 volts there unbeknownst to the electrician and two neutrals sort of belying that fact that there could be a higher voltage there than believed.
thats the way I look at it. Because when we go on a service call we are never really sure who did the work and the home-owner seldom owns up to especially if he screwed it up and now has a real problem. You know you get there and he suddenly develops a problem on a multi-wire circuit and one breakers is now back-fed, and you know he did something which would be a great place to start looking for the problem, but of course, he hasnt done anything to the wiring in years.
anyway just my opinion.
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