interesting re: pool pump wire guage

i have a 3/4 hp older starite and everything i've seen basically says use a 12 guage for the 3/4-120 volt pump..14 guage for a 1/2 hp..i'm guessing there must be a safe in between as i was doing some re-wiring and going to a timer and i thought i better buy some 12 (i have 14 at home already) to my surprise the current wiring to pump was all 14 guage so i stuck with that. and yes, i do have a good amount of "wire run" to the breaker box. some may say i'm asking for trouble running 14..i would say..that starite pump has been in service for 7 years without any problems at all.

if interested in other specs:

large pool shed fairly well ventilated but it can get pretty warm when the ngas furnace is no (i have a power roof ventilator but it still gets warm)

15 guage breaker devoted to the pool pump

and a spare, thankfully small, roll of unopened 12 guage wire:)

The question I have is how much of the wire are you replacing? Although you have not had a problem with the 14 gauge wire, it might be worth upping to 12 gauge and you won't have to think about it again. Since you say that the pump is older, suppose you ever wanted to go with a bigger pump? Do it once - do it right.

Peter

Your pump won't have a problem, BUT your wire will, the reason you put in a heavier guage wire over longer runs or for higher loads is because the 14 guage will heat up, won't be an issue the first year or two or three, but the insulation will become brittle due to the heat that's created in the wire - less heat will be created in the 12 guage in comparison and the insulation will therefore last way longer.
Brittle insulation will lead to a short, a short can lead to a fire, a fire can lead to a homeless family or God forbid, something even worse.
Don't mess with your families safety!

Oh, BTW - if the existing wire is 7 years old allready and was possibly overloaded, it could already be brittle or very close to being a hazzard.

interesting stuff guys..if i ever do replace the motor, i will stick with max 3/4 hp as that is adequate. the run from the panel box i would say is maximum 30 ft. is that maybe why i've been able to get away with 14 guage? i can replace the 14 guage starting at the pool shed to the timer to the pump with the 12 guage, but not easy to replace the wire from the panel in my basement to the shed..would it be of benefit even if i only replace the 14 guage from where it comes in shed>timer>pump with 12 guage and leave the other 14?

Some facts:

From copper wire tables #14 is 2.58 ohm / 1000', #12 is 1.62

That's .00258 / .00162 ohm per foot respectively.

For a 30' run (60' of wire) that's .155 / .097 total ohms respv.

I'm assuming a 120 V circuit with a 1/2 HP pump that draws 10 amps. Rough WAG here but erring on the conservative high side.

That's a voltage drop of 1.55 / .97 V respv.

Power loss is E**2 / R or I**2 * R or 15.5W / 9.7W respv.

That power loss works out to be .52 / .32 Watts per foot of heating.

Conclusions:
With #14 you're wasting 5.8 watts of power.
I don't feel the additional heating is significant.
Cost delta of #12 vs #14 is small.
Go with #12. Even on the partial run.
If this is underground use UFB for underground direct burial, or a conduit.

Hope I did all the math right.
Al



.

For 30ft of wire, 14 AWG is fine for a 3/4 hp motor. If you're running it at 110V it's still file. If you want a bigger pump you should consider running them off of 230V. If you're already running 230V then 14 AWG will handle all the way up to a 2hp pump at a distance of 30'.

I have 10 AWG running from my breaker to my pool equipment for 230V plus a 14 AWG neutral if I need 110V over there.

thanks again guys..i think i'm good..the run is actually 25 ft..it's on 120 w/ a 15amp breaker that powers the pump exclusively. i have no intention to get it to share with anything else. i have 3 other 120 volt lines available to the shed so no need. the one speed motor draws 8.6 amps at full load and 120 volts.

about a month ago I helped a friend drain and refill his pool (due to too high of CYA and CH.) About an hour into the draining, we started hearing a popping sound from over by the pump. After a couple of more pops, the motor shut down. After shutting down the power at the main panel, we discovered that the pump had been wired with 14 gauge solid wire (in 1988.) Over the years, the combination of current and vibration cause the wire to blow itself in two about 2 inches from the motor.