How can I replace circuit breakers with GFCI breakers when it is a multiwire branch circuit?

Question

We have 2 carriage lights on our patio and 3 flood lights on our eves. The carriage lights are controlled by two 3-way switches and the yard lights are controlled by another set of two 3-way light switches (one in the bedroom, one in the living room). We are expanding our patio and are adding two more carriage lights which we want controlled on the same switches as the existing carriage lights and we are moving the flood lights to the eves of the expanded patio cover. The new lights and the moved lights will all be within 10 feet of the pool which is a code violation unless we change the circuit breaker to a GFCI breaker.

They are all on the same circuit breaker. The circuit breaker they are on has a BLACK wire going to it from a 12 gauge 3-wire. The RED wire from the same 3-wire goes to the circuit breaker next to it and controls our security system and some outdoor outlets. They are not tied together, they can be tripped separately.

My question is, can we replace just the one circuit breaker that the lights are on with a GFCI breaker or do we also need to replace the other breaker that the RED wire goes to that is next to it? If we have to replace both breakers, do we need to replace both of them with GFCI and then what do we connect the two neutral white wires from the two GFCI breakers to since the 3-wire only has the one white neutral wire coming off it? Or can we just replace the one breaker with a GFCI breaker and leave the other breaker which has the red wire to it as-is?

It is a single pole, 15 AMP Square D circuit breaker. And the current wiring and breakers in the panel are all original to the house when it was built 11 years ago and therefore passed inspection back then.

Answer 1

You'll need a double-pole GFCI breaker, wired like so:

What you have described is a multiwire branch circuit. Because the neutral is shared, the overcurrent protection device(s) (in your case the two separate breakers) must be able to trip together.

This can be remedied by installing a double-pole breaker, or by handle-tying two individual breakers. However, since you already have a need for GFCI protection, go ahead and install a double pole GFCI breaker.

However, existing lights might not need GFCI protection if they are 5 ft or more away from the pool (horizontally) and 5 ft or more above the maximum water level of the pool. Within 5 ft and below 5 ft above the maximum water level is not allowed. See (B)(3) and (4).

If you move or install new lights, they are subject to new installation requirements. See (B)(1).

2014 NEC

680.22 Lighting, Receptacles, and Equipment.

(B) Luminaires, Lighting Outlets, and Ceiling-Suspended (Paddle) Fans.

(1) New Outdoor Installation Clearances. In outdoor pool areas, luminaires, lighting outlets, and ceiling-suspended (paddle) fans installed above the pool or the area extending 1.5 m (5 ft) horizontally from the inside walls of the pool shall be installed at a height not less than 3.7 m (12 ft) above the maximum water level of the pool.

(3) Existing Installations. Existing luminaires and lighting outlets located less than 1.5 m (5 ft) measured horizontally from the inside walls of a pool shall be not less than 1.5 m (5 ft) above the surface of the maximum water level, shall be rigidly attached to the existing structure, and shall be protected by a ground-fault circuit interrupter.

(4) GFCI Protection in Adjacent Areas. Luminaries, lighting outlets, and ceiling -suspended (paddle) fans installed in the area extending between 1.5 m (5 ft) and 3.0 m (10 ft) horizontally from the inside walls of a pool shall be protected by a ground-fault circuit interrupter unless installed not less than 1.5 m (5 ft) above the maximum water level and rigidly attached to the structure adjacent to or enclosing the pool.