Bathroom remodel - electrical circuit question

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Old 01-22-10, 03:51 PM
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Bathroom remodel - electrical circuit question

I'm planning a master bathroom remodel and have a question about electrical circuit requirements. The two current circuits involved are:

1) a 20A circuit feeding just the GFCI protected receptacles in three bathrooms (two upstairs including the bathroom I'm going to remodel and one downstairs)
2) a 15A circuit feeding the lights/fans in the two upstairs bathrooms and the hallway light upstairs

As part of the remodel, I want to add an infloor electric heating mat which will add a load of about 3 amps. The question is which circuit do I tap into to power the heating mat?

If I recall correctly, code (in this case it's the NEC2008 that my city uses) prohibits putting anything other than receptacles on the 20A circuit (#1 above). Am I recalling that correctly?

If so that means I have to put the infloor heating on the 15A circuit (#2 above) since I can't pull a new circuit (at least not easily) just for the infloor heating.

The current loads on the 15A circuit are:
- 320 watts for the master bathroom vanity light bar
- 100 watts for the light above the master shower
- 40 watts (estimated--I can't find the spec) for the master bathroom fan
- 200 watts for the 2nd bathroom vanity light bar
- 40 watts (estimated) for the 2nd bathroom fan
- 60 watts for the hallway can light
- 60 watts for the stairway sconce

So, that's a total of 820 watts on the circuit as compared to the "desired" max of 1440 watts on a 15A circuit. If I add a 3 amp load from the heating mat, that gets me to 1180 watts, which still gives me a bit of room on circuit #2 after tapping in for the infloor heating.

Does that all make sense and is that kosher according to the NEC?

Thanks!

-Chris
 
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Old 01-22-10, 04:40 PM
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As long as the manufacturer's instructions for the floor heating pad don't state that it needs to be on its own circuit, you should be good to go running it off the 15A circuit. At 3A, you're probably right that it won't need to be on its own circuit. As you suspected, it can't pull from the 20A bathroom receptacle circuit.

It sounds like you're planning on running three bathroom receptacle circuits off one 20A GFI circuit. While this is permitted by the NEC, you may want to reconsider. Most hairdryers are 1000-1500w, and you'll find quickly if two people try to use a hairdryer, curling iron, etc. at once, you'll have a tripped circuit. This goes double or triple if you have more than one woman/girl in your house
 
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Old 01-22-10, 07:48 PM
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Zorfdt, thanks for the quick reply. I can't find anything indicating that the heating mat needs to be on its own circuit but will confirm that with the manufacturer.

As far as the three receptacle circuits on one 20A circuit, that's an existing circuit in the house that was put there by the original builder. I agree with you--I would have created separate circuits for each bathroom rather than having a single 20A circuit handle the receptacles in three separate bathrooms, but clearly they were thinking about a low budget rather than keeping multiple women happy ;-)

Thankfully one of the bathrooms is just a powder room and the other is a guest bathroom that (at least for now) won't see a lot of use by hairdryer/curler toting women!
 
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Old 01-22-10, 08:51 PM
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Originally Posted by co_diy View Post
Zorfdt, thanks for the quick reply. I can't find anything indicating that the heating mat needs to be on its own circuit but will confirm that with the manufacturer.
Also verify the specs of the thermostat/controller for your heating mat. What you are looking for is the SPECIFIC info on ground fault protection built in.

There are two kinds:
--One might say something like "ground fault protection", use the word "equipment", or mention 30mA.
--The other might say something like "GFCI", "ground fault protection for personnel", or mention 5mA.

Since you are installing it in a bathroom, you must use the second type. If yours is the second type, you're good to go. If it is the first type, you need to feed it from a GFCI.

What is the mfg and model of the thermostat/controller and heating mat?
 
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Old 01-22-10, 10:36 PM
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The controller is the SunStat Pro; the specs claim it's GFCI protected (see below for their specific language), but thanks for pointing out the difference between 30mA and 5mA!

"Built-In Class A GFCI protection with GFCI test Light and button - 5 milliAmp trip"
 
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Old 01-23-10, 06:29 AM
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Please be sure to make ALL the resistance checks on your heating mat. You certainly do not want to install the floor or install a broken mat.
 
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