I’m in the process of remodeling my basement bathroom and have hit a road-block with the wiring. Here are my questions.
• Before I started my basement bathroom remodel, the only thing that was wired in the bathroom was a vanity light from a 15A circuit. This circuit is shared with the upstairs bathroom, 1.5 bedrooms and a hallway for a total of (10 lights & 7 outlets). I’m guessing this circuit is probably overloaded (not sure by how much?).
• How many total outlets and light fixtures can be on a 15A circuit (rule of thumb)?
• How many for a 20A?
• With my circuit most likely being overloaded, and me eventually going to be adding some more inputs to the circuit, I’m guessing the bathroom should be on its own circuit?
• If that’s the case, then I would move the vanity light (x3 lights) off its current circuit and add it to the new basement bath circuit, which will now include a (GFI outlet & ceiling fan/light). Would a 15A circuit support all the bathroom items I listed? How about a 20A?
• If I didn’t create a new circuit and wanted to tap into an existing lower utilized 15A circuit (or 14g wire) where the circuit is running from the fuse box to a junction box. Can I tap into the junction box with 12g wire to add a light fixture, outlet, and/or ceiling fan? Or is there a problem with connecting two different gauges of wires?
• I’m trying to add up all the items on my circuit and wasn’t sure about a few items and how many watts they use.
o Bathroom ceiling fan = ?
o Sump-pump=?
o Refrig =?
o Furnace =?
o Microwave =?
o Hair Dryer=?
o Computer=?
o TV/Stereo=?

Bathrooms now require a 20 amp circuit for the receptacle that must be at the sink. If the circuit is only for that one bathroom, the lights and fan in the bathroom may be on the same circuit. The outlet must be GFI, the lights and fan, unless over the tub or shower, does not need to be GFI protected.

There is no maximum limit to the quantity of general purpose receptacles or lighting outlets on circuits in a residential application. The rule of thumb that is popular comes from the code for commercial requirements. 8 receptacles on a 15 amp circuit, and 10 on a 20 amp circuit. This can be used in residential as a guide.

Each one of your appliances has a nameplate that lists the load in amps or watts. I can tell you that a microwave needs it's own circuit. A furnace may not need it's own but every furnace I wire gets it's own circuit. Same with a refrigerator.

There is no problem extending a 15 amp circuit that's uses #14 wire with #12 wire, the circuit is still only rated for 15 amp.