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I'm wiring a 2-story addition to my house, each floor of the addition is a bathroom and closet.

I will be running two receptacle circuits, one for each bathroom, each protected by a GFCI receptacle, with all other receptacles in the room on the LOAD side. This will include the exhaust fan/light combo (with associated switches wired via a short section of 12/3).

I was planning on running an individual lighting circuit to each bathroom and an additional lighting/receptacle circuit to be shared by both closets.

This would get me a total of 5 circuits:

  1. Downstairs bath receptacles (including vent fan/light combo)
  2. Downstairs bath lights
  3. Upstairs bath receptacles (including vent fan/light combo)
  4. Upstairs bath lights
  5. Upstairs & downstairs receptacles & lights

Is there any distinct advantage to having the bathroom lighting (circuits 2 & 4) separated I had planned, or would I be just as well served by combining those into a single lighting circuit?

A GFCI trip would only kill the outlets, leaving lights on. A lighting circuit breaker trip would, potentially leave both rooms in the dark, however, all wiring will be 12/2 on 20A breakers and all lights (a total of about 15 bulbs) will be LED. Something would have to go seriously wrong for us to ever come close to overloading a single lighting circuit for both bathrooms.

I do have a brand new, 40-space panel with about 35 spaces free, so circuits are not at a premium at the moment. I'm just trying to determine if I need to use an extra circuit in this case. Of course, if NEC (we're currently on 2008) says that each room must be on its own lighting circuit, I'll stick with the current (pun intended) plan.


Note:

This could easily devolve into opinion-based territory. I'm looking to avoid that by looking for A) code reasons for having two circuits, and/or B) practical reasons for keeping them separated. At this point in time, saving the extra copper by not having to make an extra home run is very appealing.

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  • A con of having two circuits is probably needing more cable to go to the panel, unless you have a weird house design. A pro would be having at least one room with lights if there was a problem/work on the circuit, that took much longer to fix than planned on.
    – crip659
    Commented Feb 15, 2023 at 18:06
  • The panel is definitely not close, especially if you have to go in the morning before you're legally dressed. ;) There will be lighting into both bathrooms (from a closet or outside) if the lights have to be off because of work in the other bathroom. And, there's a 3rd bathroom if necessary, too. Another con is using more wire for the extra home run.
    – FreeMan
    Commented Feb 15, 2023 at 18:15
  • For lighting in the modern (LED) era, I prefer the "Lighting shares with Zero Receptacles" opinion, which makes the odds of a lighting trip negligible, and 15A on 14 AWG plenty. If you have Heater/Fan schemes in your head, that's a heater circuit, not a lighting circuit. Two lighting circuits for extra backup, if you like.
    – Ecnerwal
    Commented Feb 15, 2023 at 18:50
  • @Ecnerwal Important detail just edited in: The fan/light combo will be on the protected side of the receptacle circuit.
    – FreeMan
    Commented Feb 15, 2023 at 19:04
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    My preference when I am getting my house wired is to have a separate circuit for each room. The logic being two rooms could have an electric heater each and could end up on the same circuit thus overloading it. But one room will not have two heaters in it. Commented Feb 16, 2023 at 0:53

4 Answers 4

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It is incredibly easy to add extra circuits during construction. It is harder (sometimes a little, sometimes a lot) to add circuits later.

One thing that people sometimes don't think about for bathrooms is heat and fans.

Every bathroom is required (it is part of the usual building code) to have either a window that can be opened or an exhaust fan. Many people prefer an exhaust fan, particularly when it is very hot or very cold outside.

Heat is not a requirement, but a heat fan/heat lamp feels great after a bath or shower.

The easiest way to handle all of this is to run a separate lighting circuit for each bathroom. A 20A circuit can handle heat, light and fan without a problem, but can't handle heat for two bathrooms.

If you don't plan on installing fan and/or heat at this time, I recommend running appropriate cables (e.g., 1 12/3 + 1 12/2 or 1 12/4) in advance and terminate in a ceiling junction box with a blank plate.

If you run (per latest question edit) any fan or light from the receptacle circuit, that's OK. But consider two key things:

  • Lighting, fan. etc. in the ceiling (i.e., out of reach) do not need to be GFCI protected unless above a tub or shower. While I think GFCI is an incredible, life-saving, invention, I would not use it for lighting (fan doesn't matter) unless required. What if (as in my house) some people prefer the light that goes with the fan to the light that is above the sink and do something that trips the GFCI? Then they're in the dark.
  • Lighting and exhaust fans are all very small loads and can be combined with receptacles without a problem. But a heat fan is a large hard-wired load so if it is more than 10A then it can't share with receptacles (it can share with lighting).
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  • Thanks. Both bathrooms have a window and will also have a fan/light combo. The fan/light will be on the Load side of the GFCI receptacle (12/2 from LOAD to the box, then 12/3 from the switches to the device). The other lights will be on their own circuit. (I always leave out critical details. Dang it!)
    – FreeMan
    Commented Feb 15, 2023 at 19:02
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    Thanks. The switches for the fan & light will be just outside the shower where they're reachable from inside (on purpose), therefore they will be GFCI protected for safety. (Also, the fan will be above the tub.) She wants the light for showering, I don't, so this light will be independent of the other lights. There will be other lighting in both bathrooms precisely so a GFCI trip doesn't leave us in the dark. The current unit does not provide heat. If someone in the future puts a heat feature in, that's on them...
    – FreeMan
    Commented Feb 15, 2023 at 19:32
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IMHO You don't need 2 circuits for lighting if you are going all LED. LED is a total game changer.

Bathrooms require a dedicated 20 amp circuit for receptacles, but it can be shared between multiple bathrooms per code. If it were me, I'd put in an individual, dedicated 20 amp circuit for EACH bathroom. Clearly that's not required by code, but I think it's "best practice". When I wired my son's house (4 bathrooms) I put in an individual 20 amp circuit for each one...probably over-kill! The inspector asked why? what are you going to do with all that power!?

Bottom line: If it were me, I'd combine all the lighting circuits and NOT share the lighting with receptacles, you don't want the lights going out if you trip a breaker. OK: one more thing: Don't do the lighting wiring using the "switch leg design", if you ever want, or planning now to install smart switches, they don't work on switch legs. Power to the switch, then switched power to the fixture(s).

EDIT: I missed that switch loops (legs?) are still OK as long as you run /3 cable . Thanks to ChrisO for pointing that out.

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    I used to agree with your inspector, but the rise in popularity of the bidet in the US has changed my opinion and now I completely agree that 20A for each bathroom makes sense. Bidets and bidet additions sometimes draw up to 1 kW for heat. Add that to the plug-in hairstyling tools and 20A doesn't seem overkill at all.
    – Chris O
    Commented Feb 15, 2023 at 19:14
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    Yeah, we're still on 2008 here, @Ecnerwal. Just a smidge behind the times... :/
    – FreeMan
    Commented Feb 15, 2023 at 19:22
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    I'd have to check (I don't have a code book newer than 2014) but I've been told by inspectors that if you wire the switch loop with a /3 then it is still OK because you have your neutral present. I will try to verify that.
    – Chris O
    Commented Feb 15, 2023 at 19:24
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    That is the way it's been done since 2011 code cycle, yes, @ChrisO
    – Ecnerwal
    Commented Feb 15, 2023 at 19:25
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    @ChrisO you are correct. As long as you run /3 it's currently (pun intended) OK. Just not everyone knows a switch leg (loop) now requires /3. It's mostly personal preference on my part, it seems cleaner just to supply power to the switch, then switched power to the fixture(s) . It's like I like to wire 3-way switches with power into the first one, travelers to the other one and then to the fixtures. No having to code tape any wires, very straightforward. Commented Feb 15, 2023 at 22:25
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For Office occupancies, NEC 2020 lowered the lighting load from 3.5VA/ft2 to 1.3VA/ft2.

Residential appears to be still at 3 VA/ft2 but that also appears to be still the "general purpose outlet and lighting" approach, rather than anything lighting specific.

That means "lighting" load (including general purpose receptacles) for 1000 square feet is taken to be 3000VA, or 25A at 120V. So, if you have 800 square feet in the addition, one 20A circuit is required, while for 600 square feet or less that could be one 15A circuit.

Obviously the required circuits for bathrooms are additional, and you probably want more circuits in general than the minimum required.

I see nothing in there specifying a required number of circuits for lighting if the total lighting and receptacle load is provided for to code minimum (or more.)

That said, as commented, For lighting in the modern (LED) era, I prefer the "Lighting shares with Zero Receptacles" opinion, which makes the odds of a lighting trip negligible, and 15A on 14 AWG plenty unless your house is huge, or lit to "wear welding goggles" levels. There's no code requiring that, nor even suggesting it. It is merely an opinion.

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Having two separate lighting circuits for bathrooms, yet only one circuit for ALL the other living space, is bonkers.

If you are trying to clip to Code bare minimums, then one 20A circuit for both bathrooms' receptacles, and then one 15A circuit for everything else will comply. Two circuits and it sucks to be your buyer or tenant.

However, most people wire in electrical so they can actually use it for stuff functionally.

A separate receptacle circuit per bathroom is a good idea. There is no requirement whatsoever that bathroom lights and fans be in a bathroom circuit - they can be on any other lighting and receptacle circuit, and they should be - if someone trips the breaker on a receptacle circuit, it is better not to plunge the bathroom into darkness.

And as for the living-space rooms, here's a knowledge bomb for you: absolutely nothing in code requires that all outlets in a room be on the same circuit! Many people have that idea in their head, but it's a phantom. Actually, somebody may want to use a room for a home office or craft space. Having more than 1 circuit reaching that room can be a significant boon! I prefer to think of circuits as belonging to "walls" so I can minimize cable length. This tends to result in multiple circuits per room.

The panel is definitely not close,

If the panel is far away, think about a good location for a subpanel (hallways are winners, since the Working Space will be naturally kept clear). The typically aluminum feeder wire to a subpanel is a much better bargain than a bunch of parallel Romex runs, and it avoids the thermal problems of grouping too many Romex cables. . It is also more convenient for residents.

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  • All comments valid and noted. These are, however small closets, so there's no reasonable possibility of ever using them for much of anything but. While one could bring a laptop into one of the rooms, there wouldn't be space for a desk or chair, so home office is right out, and any crafting would, likewise, need to be done while standing. Honestly, not even sure why we're putting outlets in beyond simple code requirements, but there are a ton (2 on each wall, none of which is > 6' in length) in each closet. And, as an old farm house, there aren't any hallways in which to install a 3rd panel.
    – FreeMan
    Commented Feb 16, 2023 at 11:55
  • @FreeMan: Outlets in closets are great for charging ports for battery-powered vacuum cleaners. For this reason alone they should be standard. Commented Feb 16, 2023 at 15:16
  • Fair enough, @R..GitHubSTOPHELPINGICE. Might put a spare charger in there!
    – FreeMan
    Commented Feb 16, 2023 at 15:52
  • Harp: regarding the lighting circuits, I was only referring to the additions Freeman was working on, not the entire house. 1 circuit for bathroom lighting and incidental lighting is NOT BONKERS assuming LED lighting. Let's do the math: LEDs take about 7-14 watts each. Lets pick the middle at 10 watts, 100 LED bulbs at 120 v would take a bit less than 10 amps (10*100) = 1,000 watts , 1,000 watts divided by 120v is less than 10 amps (8.33 to be precise...thank you Mr. Spock). It's a waste of wire and breaker space to over subscribe lighting circuits these days. Commented Feb 16, 2023 at 16:46
  • ...continued: I sincerely doubt the OPs addition / remodel will involve 100 LED fixtures, but even if so, they could easily be serviced by a 15 amp circuit. Harp: Unless you are still old school and want to use incandescent, then yes, more circuits for lighting are needed. Commented Feb 16, 2023 at 16:51

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