12AWG to 15A breaker... Allowed?

[hurk27]

You can't backstab with a 12 anyway. 10 for sure ain't gonna fit.

But the pressure plates on P&S are probably rated for 10s.

Never seen any GFCI receptacles you can back stab, the holes are for pressure plate connections, any time we had to up size 12 for voltage drop, we just pigtailed 12 to the 10 at the receptcle, made it easier to get into the box also.

 

[LarryFine]

How do I get the wire into those holes in the back of the GFI receptacle?

Use pigtails.

 

[jaylectricity]

Never seen any GFCI receptacles you can back stab, the holes are for pressure plate connections, any time we had to up size 12 for voltage drop, we just pigtailed 12 to the 10 at the receptcle, made it easier to get into the box also.

So the wire only needs to be #10 until it gets close to the receptacle? Then it doesn't matter any more? That doesn't sound right. Either you need larger wire or you don't.

 

[480sparky]

So the wire only needs to be #10 until it gets close to the receptacle? Then it doesn't matter any more? That doesn't sound right. Either you need larger wire or you don't.

You're saying that running #10 for 99.999% of the circuit is negated by the 0.001% of the circuit that's #12?

Dropping wire sizes for pigtails is common practice. Shoot, I've even done it for lot lighting.... run something on the order of #4 or #2 out the all the bases, then #10 up the poles... all on 20a circuits.

 

[Jim W in Tampa]

That 6 inches in #12 will never be noticed. But a 300 foot run of #12 will likely show problems.

 

[jaylectricity]

Six inches won't be noticed? If it melts away under heavy load, I'm sure it will be noticed. Isn't that how fuses work?

 

[hurk27]

Jay because you have increased your wire size to over come voltage drop, you don't increase your breaker because of the wire size, you would still protect the circuit at 20 amps, and the #12 will be protected.

 

[jaylectricity]

I mean, sure...if you're talking about a lighting fixture that has a relatively fixed load. But this receptacle should be able to use the full load. What if it's the only receptacle on the circuit?

 

[jaylectricity]

Jay because you have increased your wire size to over come voltage drop, you don't increase your breaker because of the wire size, you would still protect the circuit at 20 amps, and the #12 will be protected.

Does the increased size mean that the voltage won't drop? Or does it mean that the added intensity required to power the appliance won't burn up the wire?

 

[hurk27]

look at it this way:

I have a circuit that requires a 20 amp breaker, the load is 16 amps, the run is about 80', well the voltage drop will be too high so I up size the wire to a #10, but since the load is still 16 amps I keep the 20 amp breaker, and since #12 won't fit in the holes at the pool pump GFCI, I pig-tail back to #12, the #12 is still protected on a 20 amp breaker.

 

[480sparky]

Six inches won't be noticed? If it melts away under heavy load, I'm sure it will be noticed. Isn't that how fuses work?

Why would six inches of #12 melt if it's on a 15 or 20a breaker?

 

[jaylectricity]

Why would six inches of #12 melt if it's on a 15 or 20a breaker?

I guess I don't understand the principles of voltage drop very well.

If I upsize the wire does it prevent the voltage from dropping or does it account for it?

 

[hurk27]

Does the increased size mean that the voltage won't drop? Or does it mean that the added intensity required to power the appliance won't burn up the wire?

You increase the wire size to lower the resistance of the circuit thus lowering the voltage drop, the load determins the smallest wire size in the circuit and the OCPD size,

 

[hurk27]

voltage drop is a function of current(load) and resistance (wire size x length x 2)

 

[Jim W in Tampa]

Look at it like 2 resisters in series. 100 Feet of # 10 + 6 inches of numer 12. There is no way that the #12 will even get hot if it has full 20 amp load. This does assume you make a good splice. You could run 250 mcm copper and put pig tails on it and same results.

 

[480sparky]

I guess I don't understand the principles of voltage drop very well.

If I upsize the wire does it prevent the voltage from dropping or does it account for it?

It reduces it.

The difference between a 100-foot run with #10 and one with 99'-6" of #10 and 6" of #12 is insignificant.

 

[jaylectricity]

It reduces it.

Thank you...that explains my lack of understanding. Thanks to all of you for helping me figure this out.

 

[LarryFine]

Little more: You could have one foot of #2 copper wire from a 20a breaker to a receptacle, and there's still 20a worth of protection.

Aside from reducing power delivered to the load, too much voltage drop can extend trip time and increase wire heating and damage.

Understand that voltage drop does nothing to improve the function of anything in an electrical supply system. It's only detrimental.

 

[hurk27]

Voltage drop is a must learn for any person in the electrical field, even though it is an FPN in the NEC and not enforceable, learning on how to overcome voltage drop can save a lot of embarrassing moments with customers when they ask why does my lights dim in the garage when the air compressor kicks on, and also you will be able to keep from burning up motor loads because they cant start because of voltage drops (common with 5 hp air compressors ran on a 100' 16/3 extension cord)

Look in the directory under free stuff on here, and I think there is a voltage drop calculator, and play around with it to see how longer runs will have a higher voltage drop, then you can substitute larger wires to see how to bring it back down.

 

[jaylectricity]

Look in the directory under free stuff on here, and I think there is a voltage drop calculator, and play around with it to see how longer runs will have a higher voltage drop, then you can substitute larger wires to see how to bring it back down.

Thanks, I'll check that out.