Smart light switch wiring

Question

I'm replacing a light switch with a smart switch and after some reading here I think I have things straight but wanted to get a second opinion before starting in on it.

There are 2 decora switches in the box on the same circuit; one is a 3-way but I'm not replacing that one. The existing wiring looks like this (ground is omitted, it's just connected to the box.)

    ┌────┐      ┌────┐      ┌────┐      
    │Wire│      │Wire│      │Wire│      
    │ A  │      │ B  │      │ C  │      
    │    │      │    │      │    │      
    │lite│      │feed│      │lite│      
    └─┬─┬┘      └┬──┬┘      ├─┬─┬┘      
      │B│W       │B │W      │W│R│B      
      │ └────────┼──O───────┘ │ │       
      └────────┐ │            │ └──────┐
               │ │    ┌───────┘        │
 ┌──────────┐  │ │    │  ┌──────────┐  │
 │          │  │ │    │  │          │  │
 │          │O─┘ │    │  │          │O─┘
 │          │    │    │  │          │   
 │ Switch 1 │    │    │  │ Switch 2 │   
 │          │    │    │  │ (3-way)  │   
 │          │    │    │  │          │   
 │          │┌───┘    │  │          │   
 │          ││        │  │          │   
O│          │O        └─O│          │O─┐
 │          ││           │          │  │
 └──────────┘│           └──────────┘  │
             │ B                       │
             └─────────────────────────┘

So my plan is:

make a pigtail with the black wire B and the 2 switches' black wires
add the switch's white wire to the existing neutral bundle

    ┌────┐      ┌────┐      ┌────┐      
    │Wire│      │Wire│      │Wire│      
    │ A  │      │ B  │      │ C  │      
    │    │      │    │      │    │      
    │lite│      │feed│      │lite│      
    └─┬─┬┘      └┬──┬┘      ├─┬─┬┘      
      │B│W       │B │W      │W│R│B      
      │ └────────┼──O───────┘ │ │       
      └────────┐ │  │         │ └──────┐
               │ │  │ ┌───────┘        │
 ┌──────────┐  │ │  │ │  ┌──────────┐  │
 │          │  │ │  │ │  │          │  │
 │          ├──O │  │ │  │          │O─┘
 │          │    │  │ │  │          │   
 │ Switch 1 │    │  │ │  │ Switch 2 │   
 │          │    │  │ │  │ (3-way)  │   
 │          ├────┼──┘ │  │          │   
 │          │    │    │  │          │   
 │          │    │    │  │          │   
 │          ├────O    └─O│          │O─┐
 │          │    │       │          │  │
 └──────────┘    │       └──────────┘  │
                 │ B                   │
                 └─────────────────────┘

The neutral wiring is what I'm not 100% sure on, and looking for confirmation that adding the white wire to the existing bundle is the right thing to do. The other option is to remove the white wire from B and put it into another pigtail with just the switch's wire but pretty sure that's wrong since it would break the circuit?

Ken Carlson · Accepted Answer · 2024-05-16T21:36:44.773

Yes, that's the correct thing to do, adding a pigtail for the neutral to connect to the neutral for the smart switch. All you should need is a 6 inch pigtail of sufficient size (e.g at least #14 for a 15 amp circuit or #12 for a 20 amp circuit) and white in color. Or actually you don't even need to supply your own pigtail if the smart switch comes with pigtails instead of terminals.

And one of the finer points is that make sure you have a wire nut of sufficient size since you now have 4 neutrals twisted together instead of three. Typically the Ideal yellow wire nuts are listed for up to three #14 or #12 I think, so if you currently have a yellow wire nut, you would need to change it to a red wire nut listed for at least 4 wires. (At least that's how Ideal color-codes their wire nuts, not sure about other manufacturers.)

You inferred correctly that your other option would be wrong because it would break the circuit: the lights still need to have the neutral also.

Smart light switch wiring

1 Answers1