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I am in the process of wiring my basement. 1. Main area 2. Hallway 3. Small Bath 4. Small Bedroom with egress window.

I have a single 15-amp and 20-amp wire coming in from the electrical panel located in the garage.

Based on my reading I should use 12-2 Romex for all the outlets (even though the builder only use 15-amp for the new construction ). Then use 14-2 Romex for any lighting? Is this true?

So, I guess my real question is do I actually need a single circuit for the bathroom or can I share the circuit with bathroom and bedroom.

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    The bathroom receptacle must be on a 20-A circuit, and maybe it's allowed to power the entire bathroom (receptacle, lights, heat lamp, exhaust fan) on one 20-A circuit. But the circuit powering the bathroom receptacle cannot power anything outside the bathroom. So if you have one 15-A circuit and one 20-circuit going to the basement (and you don't want to add another circuit), then the 15-A circuit would have to power all the receptacles and lights in the bedroom. It is not against code to have bedroom receptacles on a 15-A circuit, but don't if you know that high draw appliances will be used. – Jim Stewart Dec 22 '18 at 16:03
  • @JimStewart a 20A outlet is required in Kitchens, but I don't beleive the NEC requires 20A for a bathroom? 15 is the minimum. – noybman Dec 22 '18 at 16:32
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    @noybman -- see NEC 210.11(C)(3) -- the branch circuit must be 20A even if the receptacles aren't. – ThreePhaseEel Dec 22 '18 at 16:34
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    Bathroom, laundry, kitchen all require 20 amp, Jim that comment should be an answer. – Ed Beal Dec 22 '18 at 16:41
  • Got it, I misread – noybman Dec 23 '18 at 0:54
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Nope, you'll need 2 circuits for this

Bathroom receptacles must be on a 20A branch circuit that is either dedicated to bathroom receptacles (and no other loads), or to the loads in a single bathroom (and no other rooms), as per NEC 210.11(C)(3):

(3) Bathroom Branch Circuits. In addition to the number of branch circuits required by other parts of this section, at least one 120-volt, 20-ampere branch circuit shall be provided to supply the bathroom(s) receptacle outlet(s). Such circuits shall have no other outlets.

Exception: Where the 20-ampere circuit supplies a single bathroom, outlets for other equipment within the same bathroom shall be permitted to be supplied in accordance with 210.23(A)(1) and (A)(2).

As a result, the 20A circuit will need to feed the bathroom receptacles (and possibly the rest of the bathroom's loads as well), while all other loads (general receptacles outside the bathroom, and lighting loads) will go on the remaining 15A circuit. All wiring on the 20A circuit will need to be 12AWG, as well.

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    Do you have any knowledge about the motivation for this rule? Obviously stating motivations has the downside that people think they can ignore a rule if it "doesn't apply", but assuming there is a good motivation, it would also create better understanding about safety aspects that might not be widely understood. – R.. GitHub STOP HELPING ICE Dec 22 '18 at 17:29
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    @R.. -- primary reason is hairdryers, curlers, and other heavy-load heating appliances that are used in bathrooms :) – ThreePhaseEel Dec 22 '18 at 17:39
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    There is often more than one motivation, very common for a person to be told "the" motivation, go "hup, I don't care about that one" and ignore the other motivations which do in fact create a threat to their family. – Harper - Reinstate Monica Dec 22 '18 at 17:43
  • @ThreePhaseEel: Right, but I'm wondering if there's some reason I'm missing why this is a safety matter rather than a convenience one. Maybe it's that if other stuff was on the circuit, use of hairdryers etc. tripping the breaker might prompt someone to plug in an extension cord from another circuit to power the hairdryer (creating risk of overloading the extension cord and risks from using in in a bathroom on a non-GFCI circuit)? – R.. GitHub STOP HELPING ICE Dec 22 '18 at 18:54
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    Indeed. It's not a big deal, but I find it useful to think about these things for understanding the intended safety properties. This line of discussion has reminded me that some safety rules are simply about not creating incentives for people to do stupid things. – R.. GitHub STOP HELPING ICE Dec 22 '18 at 18:58

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