Arc-Fault Circuit Interrupter (AFCI)
An arc-fault circuit interruption device is designed to detect dangerous arcing within the protected circuit, and open (turn off) the circuit to prevent damage caused by the arcing. It does this using special circuitry to analyse the electrical characteristics of the circuit, looking for characteristics that match specific pre-programmed values. If the AFCI detects suspicious goings on, it opens the circuit.
AFCI breakers are typically combination devices, meaning they also provide similar overcurrent and short-circuit protection to a standard breaker.
Installing a combination AFCI breaker on a circuit containing knob and tube wiring would be a great idea, and could potentially prevent a fire.
Ground-Fault Circuit Interrupter (GFCI)
Ground-fault circuit interruption devices are designed to detect ground-faults, and open (turn off) the circuit when a ground-fault is detected. They work by using a current transformer (CT) to detect current imbalances between the ungrounded (hot), and grounded (neutral) conductors of a circuit. This blog entry might help you understand how GFCI devices work.
GFCI breakers are typically combination devices, meaning they also provide similar overcurrent and short-circuit protection to a standard breaker.
Installing a GFCI breaker on a circuit containing knob and tube wiring, probably won't provide any benefit. GFCI devices are designed to prevent electrocution, not to protect the wiring.
Combination AFCI GFCI Circuit Breakers
Circuit breakers that provide AFCI, GFCI, overload, and overcurrent protection are becoming more widely available. If you can find them for your panel (and afford therm), these would be the best option.
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.
Best Answer
Assuming the wires are all 12 AWG, this meets Code.
However, current Code requires dedicated circuits to certain rooms and loads, e.g. bathroom receptacles must serve only bathrooms; two kitchen countertop circuits; dedicated washing machine circuit; yadayada. Your setup as it was, with six circuits was Grandfathered, not obliged to be brought to current Code, however, you cannot make things worse. So for instance if one circuit once served a bathroom receptacle and 2 others, and now serves a bathroom receptacle and 5 others, that qualifies as "worse" and is not allowed.
You'll be able to charge a cell phone from any outlet. You'll be able to run a heater from any outlet. Two heaters.. good luck LOL. This is the problem with this setup. Why would the electrician really cheap out on this deal?
I can think of two possibilities. Some people worry about "old" Knob-n-Tube having arcing faults or ground faults. I think Knob-n-Tube is awesome, but discretion being the better part of fandom, I would still put K&T circuits on an AFCI breaker because that will detect most potential K&T problems (as well as most potential Romex problems), and GFCI also because that rounds up the last of potential problems, and allows 3-prong plugs on ungrounded circuits. I suspect the electrician did in fact put them on AFCI, and at $50 each, there wasn't budget for 6 of them. (possibly because you set the budget? ;)
Second, speaking of multi-wire branch circuits, back in the K&T day they positively loved multi-wire branch circuits. That's where 2 hots share a neutral, and this works if the hots are on opposite poles. I presume the electrician did attempt AFCI and/or GFCI. Those require a 2-pole AFCI/GFCI breaker, and the installer may not have been able to figure out the intended MWBC topology, or there may have been illicit neutral-sharing that would prevent an AFCI/GFCI from working. The easy fix is to put all hots which share neutrals (properly or not) on the same single breaker.
Absolutely, if I had done the job, it would have been six circuits, possibly three multi-wire branch circuits and a spare /3 to avoid hitting NEC 310.15b3a limits whilst giving me some expansion room. I'm not even thinking of MWBC because the Knob-n-Tube might have that; I just like how it lets you get 8 circuits within 310.15b3a limits.
I have no idea where you got the notion of a 15A breaker. Breaker size has nothing to do with circuit function. It has to do with
Not counting wires built into lamps, switches or other appliances... If your wires downline contain any wires which are #14, then the breaker must be 15A. If all wires are #12 or larger, 20A is correct. Any circuit which serves common NEMA 5-15 sockets (you know the one) must be 15A or 20A.