Are there advantages to running separate lighting circuits to my addition?

Question

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.

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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.

Answer 1

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).

Answer 2

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.

Answer 3

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.

Answer 4

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.