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Home Wiring Question
- Thread starter olds
- Start date
shortylickens
No Lifer
220 volts at 20 amps? And its running outside?
I'd say 10 gauge. And it should have some thick insulation too.
I'd say 10 gauge. And it should have some thick insulation too.
dullard
Elite Member
Electronics textbooks recommend no more than 20 A on 12 AWG and no more than 12 A on 14 AWG. That minimizes temperature rise in the wire (<10°C). However, those numbers are for constant current use. I doubt your well is operating at 20A 24 hours a day. In fact, it is probably not even the full 20A. Thus 14 AWG should be just fine.
drnickriviera
Platinum Member
Also need to consider the distance of the run because of voltage drop. You may need to go larger than 12
DrPizza
Administrator Elite Member Goat Whisperer
Agreed, but most pumps are at least close to 15Amps.
12 gauge is safest, but if all has gone well so far, and that's the only thing on the circuit, then it's probably not something to be dreadfully worried about. Nonetheless, and I may be mistaken, (I'm not going to think too long about this), but you could be:
a) shortening the life of the pump
b) drawing more power than is needed
Reason: you have to deal with the resistance in the wire when you use smaller than recommended wire. The biggest issue related to this though is probably, "how far is it from the breaker box to the pump?" If the distance isn't that great, it's not much of a problem.
HomeBrewerDude
Lifer
Doesn't the length of the run matter?
There are 4 issues that you need to consider:
1 - short circuit handling (e.g. you accidentally drive a nail through the cable)
If a short circuit develops, will the breaker trip before the wire starts to melt. Smaller wires will generate more heat under SC conditions, and will heat up more quickly. Higher rated breakers will trip more slowly.
2 - Overload handling
If a fault develops with the pump causing it to draw 40A (definitely a possiblity if the motor jams), a 20A breaker may not trip for 30 minutes (depends on the breaker, but many breakers will handle 2x rating for 30 mins before tripping). Will the heat generated in the wire cause the wire to overheat? What happens if a short circuit occurs while the wire is already warmed up from an overload fault? (I had exactly this happen to a faulty freezer - the motor was stalled, so it produced a big overload, before a short circuit finally finished it off)
3. Heat removal
If a wire runs through a conduit, then the conduit can trap air around the wire and act as a thermal insulator. This will increase the temperature rise. If you have more than one wire in the conduit, this also needs to be taken into account.
4. Voltage drop
You need to ensure that the pump will receive an adequate voltage to ensure correct operation. If the wire is too thin, or too long, then the voltage will be inadequate. It's not uncommon to have to specify a higher wire size, if the cable length is longer than about 100 feet.
I'm not familiar with US code, but I do know UK code:
It would *not* be acceptable to connect 14 AWG to a 20A breaker. The smallest size acceptable for a 20A breaker in the UK is 2.5 mm^2 which is pretty much 13 AWG.
Voltage drop has to be maintained below 5% in a circuit. Assuming the pump takes 15A - this would mean you need 10 AWG if the length of the cable exceeds 150 feet.
There are other problems with long cable runs - namely ground loop impedance. A short circuit live-ground fault has to produce a big enough current to trip the breaker instantly. If the cable is very long, the SC current might not cause instantaneous trip. In which case you need to install a residual current circuit breaker or GFI on the circuit in question.
1 - short circuit handling (e.g. you accidentally drive a nail through the cable)
If a short circuit develops, will the breaker trip before the wire starts to melt. Smaller wires will generate more heat under SC conditions, and will heat up more quickly. Higher rated breakers will trip more slowly.
2 - Overload handling
If a fault develops with the pump causing it to draw 40A (definitely a possiblity if the motor jams), a 20A breaker may not trip for 30 minutes (depends on the breaker, but many breakers will handle 2x rating for 30 mins before tripping). Will the heat generated in the wire cause the wire to overheat? What happens if a short circuit occurs while the wire is already warmed up from an overload fault? (I had exactly this happen to a faulty freezer - the motor was stalled, so it produced a big overload, before a short circuit finally finished it off)
3. Heat removal
If a wire runs through a conduit, then the conduit can trap air around the wire and act as a thermal insulator. This will increase the temperature rise. If you have more than one wire in the conduit, this also needs to be taken into account.
4. Voltage drop
You need to ensure that the pump will receive an adequate voltage to ensure correct operation. If the wire is too thin, or too long, then the voltage will be inadequate. It's not uncommon to have to specify a higher wire size, if the cable length is longer than about 100 feet.
I'm not familiar with US code, but I do know UK code:
It would *not* be acceptable to connect 14 AWG to a 20A breaker. The smallest size acceptable for a 20A breaker in the UK is 2.5 mm^2 which is pretty much 13 AWG.
Voltage drop has to be maintained below 5% in a circuit. Assuming the pump takes 15A - this would mean you need 10 AWG if the length of the cable exceeds 150 feet.
There are other problems with long cable runs - namely ground loop impedance. A short circuit live-ground fault has to produce a big enough current to trip the breaker instantly. If the cable is very long, the SC current might not cause instantaneous trip. In which case you need to install a residual current circuit breaker or GFI on the circuit in question.
olds
Elite Member
Here's what I decided to do:
I was running 6 awg to the pump house (60' away) anyway in 1.5" conduit. I was going to run a 110v/50 amp circuit.
I bought some green 8 awg and I will run 220v/60 amp instead. This way I can run the 220v/20 amp I need for the 15 amp pump. I have some 10 awg which I will run to the pump, about 15' from the sub panel.
The 6 awg awg was big for 110v/50 amp so I believe it will be fine for the new leg.
Sound right?
I was running 6 awg to the pump house (60' away) anyway in 1.5" conduit. I was going to run a 110v/50 amp circuit.
I bought some green 8 awg and I will run 220v/60 amp instead. This way I can run the 220v/20 amp I need for the 15 amp pump. I have some 10 awg which I will run to the pump, about 15' from the sub panel.
The 6 awg awg was big for 110v/50 amp so I believe it will be fine for the new leg.
Sound right?
Demon-Xanth
Lifer
20A needs 12 guage, 14 guage can be used for 15A breakers attached to fixed lighting (and appropriately laid out), but not outlets.
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