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Hickory
12-15-2005, 09:45 AM
I'd like to install a radiant floor for a small (7x9') bathroom. I figure after subtracting for shower, vanity, w/c, on max. 35 sq. ft. of radiant floor area.

I have read in the forum and elsewhere that I should install a dedicated circuit. I'm maxed out on circuit breakers, though I have several 20 amp circuits with only a few outlets on them.

Why the dedicated circuit, for something that should only require a 15 amp circuit? & is this a rule that can be broken? I understand it has something to do with the GFCI, but I don't know why that would require a dedicated circuit.

And, somewhat off-topic: is there any advantage at all to running a 12 gauge wire, rather than a 14 gauge, in my situation?

-- Hickory

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RAEIKEN
12-15-2005, 10:16 AM
I am installing a Warm Wire radiant floor. They suggest a dedicated circuit which I am doing, but as long as your small floor and anything else on the circuit stays within the circuit limits, you should be fine.

-Ron

geniescience
12-15-2005, 10:27 AM
....Why the dedicated circuit, for something that should only require a 15 amp circuit? & is this a rule that can be broken? I understand it has something to do with the GFCI, but I don't know why that would require a dedicated circuit.

And, somewhat off-topic: is there any advantage at all to running a 12 gauge wire, rather than a 14 gauge, in my situation?

Hickory,

The electricity needed to power this is actually only about one-tenth of a 15 amp circuit. I.e. 1 or 2 amperes.

Do you know why all heaters are always on dedicated circuits? This has to do with Code and Heating, not just radiant heaters or electric cable heating or in-floor heating.

If you do otherwise, it is your choice, and you do so without anyone's explicit blessing or approval, so it is a good idea to know a lot first so your decision is based on understanding the situation and not just on having read or heard that you could indeed do what you are hoping to. Have you consulted an electrician? Have you read a bit about how electricity works, how the Code applies, and why the Code is as it is?.

MarcusEngley
12-15-2005, 10:56 AM
Hi Hickory,

I agree with David -- ultimately, it's your call, if you're not getting your work inspected. I'm sure a heating system could function adequately on a circuit with other things, but the manufacturers want a dedicated circuit, so that's what I gave them with mine. Peace of mind -- that's the biggest reason for me, especially with electricity.

And I wouldn't bother with anything other than 12 gauge. It may not apply for the heat circuit (which should certainly be 12), but for lights and outlets you never know what someone's going to plug in down the road. 12 can't hurt.

NOT an electrician, just trying to keep my house from burning down.

cx
12-15-2005, 11:16 AM
The minimum wire size is dictated by by the circuit protection, Hick. If you're connecting anything to a circuit on a 20amp breaker, you must use #12 or larger wire. [There are a couple exceptions, but you ain't got one.]

Depending upon the brand and style of breaker box you have, you may be able to replace one of your single-pole breakers with a tandem-style breaker to provide another, independent circuit.

My opinion; worth price charged.

RLeVan
12-15-2005, 11:32 AM
I was just doing a little looking around at different floor heating companies. From the one's that actually gave specs. it appears that the 1-2 amp draw is per 10 sqft. So, if your room was 35 sqft. you would draw anywhere from 3.5 to 7 amps on that circuit while the system was on. It would give you plenty of headroom on a 15 or 20 amp breaker.

However, if this heater is cyclic which I imagine it is, if you have lights on the same circuit you may notice the lights dim or get brighter as it cycles on/off. If it's on the same circuit as a receptacle/GFCI, expect to possibly reset the breaker if you plug in a hair dryer.

As far as gauge, I agree with the everyone else, go for 12. It's a little bit harder to wire up since it's thicker but you'll have no problems with the distance from the breaker box. The only time you wouldn't use 12 was if you were hooking into an existing circuit that was wired with 14.

Hopefully this helped a bit.

Rick

Hickory
12-15-2005, 01:20 PM
Depending upon the brand and style of breaker box you have, you may be able to replace one of your single-pole breakers with a tandem-style breaker to provide another, independent circuit.


I already did that, and I'm outta options.

I appreciate the responses.

I don't know what I don't know... but I've looked for an Electricity Forum, and I don't think there is one -- at least not one that is as helpful for electrons as this forum is for mud and ceramic. So your answers are doubly helpful.

Thanks.

-- Hick

Electrician Al
12-15-2005, 01:44 PM
Put it on an existing 15A or 20a circuit other than a kitchen or bathroom one that does not have much load. It is not a code violation unless the manufacturers instructions require you to do so, then you must use a dedicated circuit.

Al

bbcamp
12-15-2005, 02:08 PM
It may be time to consider a sub-panel.

Star
12-15-2005, 03:03 PM
Bob the engineer wins! (in my opinion)

Really easy to do, take out one double breaker and add a 60A, from there, use a #6awg and feed a 60A subpanel located real close to the main panel. The new sub will have enough space to replace the one you took out and will allow you to add that 20A dedicated circuit (which I strongly recomend).

Be carefull,

_peter (master electrician)

Tool Guy - Kg
12-15-2005, 03:23 PM
I don't know what I don't know... A sub-panel should be put in by a qualified person. Time to call an electrician. No disrespect meant in any way. Electricity is too unforgiving to be learning it on your first go-round. :)

Electrician Al
12-15-2005, 03:30 PM
You guys are going for overkill. Would you put in a sub panel if you iaddad a 400watt light fixture? Probably not. Its the same thing.

Al

MarcusEngley
12-15-2005, 04:02 PM
As a DIY fella I'd say it's pretty good practice to go for overkill if you're doing the work yourself. The mat's I looked at all required a dedicated circuit anyway, so if you're looking to stick with code and you're out of space in the box, what can you do?

Hickory
12-15-2005, 07:23 PM
I appreciate the responses, really (and a sub-panel sounds neat, especially for some future projects a year down the line.) But nobody has answered my main question. WHY do the mat manufacturers require a dedicated circuit, when the amperage is so far below the capacity of a single 15A or 20A circuit?

In case this helps: One rep told me it had something to do with a GFCI. Another advised me that having two GFCI devices on one circuit can cause problems. But when I asked, Can I put it on a circuit with no other GFCI devices, he said, No.

I respect electricity a lot. Also, natural gas, lightning, and blondes. But I'd like to know whether the mat makers are simply protecting themselves against lawsuits, or whether there is a legit reason for the dedicated circuit.

The circuits I have in mind for this have exactly one wall outlet apiece on them right now. The outlets power nothing in one case, and a 60 watt bulb and alarm clock in the other. I realize that there's nothing to prevent my plugging in a hotplate.

That was a good quote of my "I don't know" line. And True That. But what I was talking about was the non-existence, apparently, of a good electrical DIY forum. I guess the theory is that nobody DIYs electricity. A walk through Homers would put that idea to rest.

-- Hickory

Kevster
12-15-2005, 08:05 PM
Hey Hickory, Check out this forum...http://ths.gardenweb.com/forums/wiring/

They were really helpfull for me when I was rewiring a range.

Have you considered rewiring the single outlet to another breaker?

I think it is important to always run 12 gauge wire for any type of electrical heater. I had some baseboard heaters wired off of a 14 gauge when I bought my home and my electrician was supprised the wires were not melted out.

Good Luck!

NVC
12-15-2005, 09:44 PM
I agree with Al here,

Some of the under floor radiant heat systems don't require a dedicated circuit. eg. 'sun touch'. Under floor heating is much different than electric strip/coil heaters.

What I would do is figure out the square footage of radiant heat (it doesn't have to go next to the walls) and calculate the wattage. Take the wattage and divide it by 120 (volts) and see how many amps it will actually draw. Odds are it will be fine on an existing circuit, unless it's a massive bathroom.

What CX said re: a 20 amp. circuit has to be on #12 (unless it's a 'hellasious' length of a run, and then might be stepped up to #10 to account for voltage drop. (not many houses fall into the latter)

<ching, ching> my two cents dropped into the bucket. ;)

Mark

Electrician Al
12-16-2005, 05:12 AM
Hickory, Which mfg's require a dedicated branch circuit?
The Nuheat company does not require a dedicated branch circuit.

In reference to the NEC:

The maximum load for utilization equipment fastened in place (floor mat) on the same circuit with luminares or cord and plug equipment is 50% of the branch circuit rating. Thus 7.5A for 15A branch circuit and 10A for a 20A branch circuit. At 12watts/sqft this relates to a 75 sqft and 100 sqft of mat.

Al

Dinahpinah
12-16-2005, 01:27 PM
I wonder if the manufacturer's requirement could be related to the section in the code NEC 424-99 (5) and the FPN (fine print note) following it. It's in the section dealing with heating panel sets installed under the floor. It reads:
"Fault protection: A device to open all ungrounded conductors supplying the heating panels..., provided by the manufacturer, shall function when a low- or high-resistance line-to-line, line-to-grounded conductor, or line-to-ground fault occurs, such as the result of a penetration of the element or element assembly.
FPN: An integral grounding shield may be required to provide this protection."

If that's the case, wouldn't it have to be on a dedicated circuit to function properly? Dinah

Mike2
12-16-2005, 02:20 PM
Another guess, this alleged dedicated 20 amp circuit requirement could also be UL Listing thing.

Hickory, I'm with Al. Who's telling you this is a requirement? Lets go to the source. ;)

cx
12-16-2005, 04:34 PM
If that's the case, wouldn't it have to be on a dedicated circuit to function properly? In his situation, would seem to me that could be covered easily by connecting the heating system to the load side of a GFI receptacle.

Do those heating mats use a shielded conductor?

No electrician here, Hick (although I frequently play one on my job sites), but I don't think I'd hesitate to connect the heater to that available circuit you described.

As for requiring an in-floor heating system to be GFI protected? Sometimes they just get a little crazy with their regulation authority, thinks moi. Why is there not a similar requirement for any circuit you can plug a floor lamp into? Like, in case you break the bulb and stick your hand in there?

Rant Off.

My opinion; worth price charged.

Hickory
12-16-2005, 04:47 PM
Thanks a megawatt, folks. I guess I shouldn't be shocked to see so much electrical expertise on this forum. So erudite, so ... current!

Seriously... I appreciate your thoughtful and persuasive comments.

I'm all charged up to start this project. If I could only come up with a pun for "volt" I'd be ready to go.... As it is, I'm definitely amped.

-- Hickory

skydivr
12-16-2005, 04:48 PM
From my own experience, in my own house, a dedicated circuit was not neccessary. I just ran it off an existing 20 amp light circuit and it has worked fine.
I've installed about 18 of these mats for other customers before and never had problems. Most were on dedicated circuits but some were just run off of an existing light switch.

Dave

ameyer
12-16-2005, 04:59 PM
Try this for an electrical forum http://searcht.netscape.com/ns/boomframe.jsp?query=herb+porter&page=1&offset=0&result_url=redir%3Fsrc%3Dwebsearch%26requestId%3Dc563814f51950d2c%26clickedItemRank%3D7%26userQuery% 3Dherb%2Bporter%26clickedItemURN%3Dhttp%253A%252F%252Fwww.hdpelectricalconnection.com%252F%26invocat ionType%3D-%26fromPage%3DNSBoom%26amp%3BampTest%3D1&remove_url=http%3A%2F%2Fwww.hdpelectricalconnection.com%2F

Dinahpinah
12-16-2005, 05:09 PM
A GFCI works like this: "If a ground fault exists with some of the current flowing to ground and not returning on the neutral through the transformer, then the sum of the current flowing on the hot and neutral will not be zero and differential current will be detected.... If it reaches a predetermmined level (the GFCI trip threshold) for a given duration, it will trip." [from www.ecmweb.com/mag/electric_think_gfci/] So it can't detect everything, e.g., the "high-resistance fault" mentioned in the code section I cited above. I think.
I'm wondering if the manufacturer of the heat panels in question hasn't included in it some kind of sensing device that, for its proper function, requires a dedicated circuit.

Dinahpinah
12-16-2005, 05:12 PM
Mind you, by "proper function" I don't mean it won't work, I just mean it may not have all the protection the manufacturer wants it to have. For the UL listing maybe.

RLeVan
12-16-2005, 05:17 PM
The circuits I have in mind for this have exactly one wall outlet apiece on them right now. The outlets power nothing in one case, and a 60 watt bulb and alarm clock in the other. I realize that there's nothing to prevent my plugging in a hotplate.

-- Hickory

Would it be feasible to wire the existing outlets together so they're daisy chained on one 15amp breaker? Then use the existing run of wire from the receptacle you just removed and use that for the floor replacing the old breaker with a 15/20amp GFCI breaker.

I may have the wrong idea but it sounds like you have two circuits on two seperate breakers that only power one outlet apiece. Sounds like an awful waste of breaker space in your panel.

http://www.cornerhardware.com/howto/ht067.html

Dinahpinah
12-16-2005, 05:18 PM
Sorry, I messed up that link: try www.ecmweb.com/mag/electric_think_gfci

cx
12-16-2005, 05:23 PM
So it can't detect everything, e.g., the "high-resistance fault" mentioned in the code section I cited above. I think. Well, nor would a GFI breaker on a dedicated circuit, then, eh? Not sure exactly what they mean by "high-resistance fault" in their description when they go on to suggest it would be caused by a penetration of the wiring. If the "fault" between the current-carrying conductors were of high enough resistance not to trip the overcurrent feature of the protection device, wouldn't anything in the circuit - GFI sensing/protection - give a rat's patooti, either. That would just appear to be more heating mat or similar load, so far as the circuit was concerned.

And if the same "high resistance fault" were of low enough resistance to exceed the capacity of the overcurrent protection, that would trip and open the circuit.

Anybody 'splain me what they have in mind there? :scratch:

My opinion; worth price charged.

Dinahpinah
12-16-2005, 06:02 PM
Exactly, CX. I don't think GFCI protection is what the manufacturer is after here, or else they'd just say "put it on a GFCI". A GFCI is really a personnel protection device. A "high-resistance fault" is damage to the wire that doesn't open the circuit completely, but merely removes some copper (or whatever the conducting material is) so the resistance is increased. Which, of course, creates heat. As you say, as if there's "more heating mat". Maybe there's a limit to how hot they want this thing to get!

jadnashua
12-16-2005, 06:04 PM
A gfi compares the incoming vs return current (i.e., the whole shebang - a complete circuit). If the current going into the circuit does not match the outcoming current, (i.e., a leak to ground or through somebody to ground), then it trips. This typically is only a few milliamps threshold. That is one reason you can put a gfi on an old 2-wire circuit that doesn't have a ground and still achieve some increase in safety.

cx
12-16-2005, 06:31 PM
Don't see how having a dedicated circuit would have any effect on that either, Dinah.


Jim:

How are you applying that to the question at hand? :scratch:

jadnashua
12-16-2005, 06:53 PM
CX, not sure it does....but with gfi being bandied around, interesting, if nothing else!

The only good reason I can see for putting the heat mat on a dedicated circuit is that it is less likely to cause the lights to flicker, and inadvertent use of something else isn't likely to cause the breaker to trip.

pitterpat
12-16-2005, 07:26 PM
I have read in the forum and elsewhere that I should install a dedicated circuit. I'm maxed out on circuit breakers, though I have several 20 amp circuits with only a few outlets on them.
Hickory

Hey folks read the above. :loaded:

Hickory doesn't say that the manufacturer says to put it on a dedicated circuit.... he says that it "read it somewhere in the forum" sooooo all this banter back and forth about whether he needs a dedicated circuit is moot until he reads the instructions for whichever floor system he puts in.

I did one last year (Suntouch) and had an electrician hook it up for me. He did not put it on a dedicated circuit but he did put it on a circuit that you could not tell if it was powering on or not (flicker). He attached it to a circuit that was the light in a walk-in closet.

So until he buys the one he's using and reads the instruction :deal: or reads the instructions on the internet (probably better) he doesn't have to worry about a dedicated circuit.

My .02

NVC
12-16-2005, 07:30 PM
A dedicated circuit is only necessary because of the amperage it draws (or harmonics, but not in residential). Someone mentioned that might be a manuf.'s way of protecting themselves, I wouldn't be surprised

. The NEC quote basically says it's the manuf. burden. If they spec. it as a dedicated then so saith the manuf. Same goes if they require GFCI

Ground fault and arc fault devices can work on either dedicated or shared circuits. You just can't use a 3 wire romex as the load coming back on the neutral will trip the devices.(i.e. two hots and one shared neut.)

hope this helps,
Mark

Dinahpinah
12-17-2005, 07:29 AM
Pat's point might negate my argument which is that the manufacturer had included in the unit some protective device which required a dedicated circuit for its proper function. If not, then there's no reason for it. The load requirement for the heating unit is, then, the only factor involved (plus any code requirements). Again, my point about a dedicated circuit perhaps being necessary was predicated on there being some mysterious and unknown (to me) protective device included by the manufacturer that would malfunction if other loads are on the same circuit. I've never seen a manufacturer require a dedicated circuit just for the sake of the load requirement. In my experience it's usually been related to power quality issues, as Mark mentions.
Sometimes we run dedicated circuits for things that underload the circuit just to make it convenient for service (like a furnace) and to ensure that the equipment isn't shut down unnecessarily to work on other parts of the circuit.

Hickory
12-17-2005, 08:45 AM
Hickory doesn't say that the manufacturer says to put it on a dedicated circuit.... he says that it "read it somewhere in the forum" sooooo all this banter back and forth about whether he needs a dedicated circuit is moot until he reads the instructions for whichever floor system he puts in.

Pat, since I made that initial post I checked with two of the manufacturers by phone (one of them Sun Touch), and both adamantly said, "Dedicated circuit required."

Given the fact that this requirement would tend to reduce the market for their product somewhat, I thought it was a fairly significant statement.

But having read this thorough discussion, I think the manufacturers may be in CYA mode. I just wonder whether it was their engineers -- or their law firm -- that told them to require a dedicated circuit.

-- Hickory

Electrician Al
12-17-2005, 09:23 AM
Hickory,

Did they give any reasons for this?

Al,
Master of the obvious

NVC
12-17-2005, 09:49 AM
I'm surprised Hickory (re: Suntouch) and dedicated as I was told differently via a rep (rather then calling) so I'd like to know why as well. I don't remember anything in their brochure re: dedicated either, but I could be wrong. Did they ask for the sq.ft. of the heated matt?

NEC limits underfloor heating to 15watts/sq.ft. and times 35(heated floor sq.ft.) = 525 watts. 525 divided by 120 (volts) = 4.375 amps which is fine on a general purpose circuit, unless the circ. was already loaded to the max.

Suntouch and others may even be less than 15 watts/sq.ft. and the amperage would go down accordingly. The dedicated doesn't make any sense to me, excluding a huge floor, where the wattage and/or (amperage) would call for it.

Usually electrical device companies CYA by printing something about a 'licensed electrician' installing/wiring it. I'll be installing one in a month or so, so I'll get to see what the deal is first hand. (oh joy) :)

Mark

Dinahpinah
12-17-2005, 11:38 AM
I just looked at the installation instructions for the Suntouch mat (D12 Series) and it says it can be wired from an existing branch circuit but that is "not recommended" and to consult an electrician. That's in Step 1.1 of the Electrical Rough-In section. It IS starting to sound like a CYA.

NVC
12-17-2005, 12:35 PM
Thanks Dinah,

I think so too. My guess it's to avoid complaints (or worse) if someone hooks it to an already overloaded circuit and it causes nusiance tripping (or worse)

That's a relief, as bring up a dedicated to this upstairs bath from the downstairs sub-panel (that doesn't have a wall above it) would be like shoving a wet noodle up a tiger's hiney. (attics and crawlspaces and floor/wall patching, oh my) Not to mention the added expense to the homeowners.

Mark

geniescience
12-17-2005, 05:34 PM
Many good points. Dinah especially.

I'd like to add another idea, for which I have no specific proof. Think of the lighting fixtures you can buy at thousands of stores. When they connect into a wall socket, the only warning they give is about the maximum bulb wattage. When they get connected to the 110 Volt current-carrying wires in the wall, they ALWAYS say that these must be installed by a qualified electrician, and that local codes may vary and that you must verify your local code. They never say you can install these light fixtures yourself.

One exception I have found is IKEA, a private-capital (not publicly listed capital) foreign firm run by 'humorous' Swedish eccentrics who might easily admit that you can do what you want. Although the packaging never says you can do it yourself, it also does not attempt to utter dire warnings and other scary wordings. In fact, at IKEA, even the furniture can be dangerous -- I mean that some of it needs to be bolted into the ceiling, and you better know what you are doing or else you risk a serious accident some day down the line. A sudden, unexpected and out of control situation. Other stores sell only furntiure that sits on the floor and uses gravity to hold itself in place. No bolting into celings, no not even into walls.

So the idea is about being ultra-careful, and also not going against code and Law, since electricians do have a monopoly profession -- there are exceptions made for homeowners, but manufacturers don't want to start getting into the never-ending saga of whether you feel qualified or not. Same thing for plumbing I think. They always say, "your plumber" when they mean 'you'.

Getting back to the heating cables, have you asked them if there is a technical reason why it might 'hurt' regular fixtures like light bulbs and other such stuff? Example: when it starts (turns itself on), is there a surge and a peak and a little resulting brown-out? Example 2: is the thermostat a problem? Before you go giving them ideas they can say yes to, just ask if the only reason is that all heating things (like for example electric baseboard heaters) are always on separate circuits is that typical Codes allow either large loads on dedicated cicuits or else only wall outlets and light bulbs ?

I think there may be an excellent technical reason, that you should know about, that ehlps you figure out why dedicated circuits are 'required'. I know I looked into this too, five years ago when I installed mine. And I remember it was not 100% merely CYA. There was a reason. But not serious enough to worry me. And not serious enough to remember five years later. In my case. Your case may be different. In fact, so many things are different that I know it is different. :)