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PaulGray 05-11-2006 08:59 PM

Replacing a circuit breaker
 
I am installing a new sump/sewage pump. The pump requires a
20 amp circuit breaker. The current breaker is 15 amps.
My question is, can I simply replace the existing circuit with
a 20 amp one?
I believe that this circuit is direct wired to a GFCI outlet?
I have not removed the service panel yet, so I am not sure what
it looks like inside.
I have a Square D QO Load Center, Series G1.

Speedy Petey 05-11-2006 09:32 PM

99.99% of the time NO, you cannot simply change the breaker for a larger one. Chances are very slim that someone undersized the breaker, or oversized the wire, allowing your intended upgrade.

I would run a new dedicated circuit to the pump. This way you are also completely sure nothing else is on that circuit.

IvoryRing 05-12-2006 09:59 AM

Just to spell out what Speedy is talking about when he says 99.99%...

There are three factors involved in a circuit, and it's easy to get them mixed up until you've worked through it.

1.) How much current your circuit will be asked to carry
2.) How much current your circuit can safely carry
3.) How much current your circuit will turn itself off when asked to carry

I'm going simplify things a lot, and gloss over a few technical details, but at the same time spell out more detail than just 'don't do it'...

#1 is determined by what device you connect. In your case, you want the sump pump and only the sump pump on a circuit. The documentation that came with your sump pump is saying that it won't request more than 20A during normal use. Since the next smaller standard size breaker is 15A, it is reasonable to assume that there will be at least some times during normal use where the pump will need between 15 and 20 amps.

#2 is determined by the size (gauge) of the wires going between the breaker and the device you are connecting. Note that there is more than just the wires in the wall, any outlets, switches, plugs along the circuit between the breaker and the final device also have to be able to handle the current the circuit will be asked to carry. For your purposes this means 12 AWG copper wire (or larger - AWG sizes are physically larger when the number gets smaller, so 14 AWG is physically smaller than 12 AWG and not suitable for your application, 10 AWG is physically bigger than 12 AWG and would work fine) and plugs/switches/outlets/etc rated for 20A or more (Unlike AWG sizes, 'A' for amps is bigger when the number is larger - amps can be added, so a 10A and a 5A device both plugged into one line will take 15A. AWG sizes can not be added, so an 8 AWG wire and a 10 AWG wire together are VERY different from an 18 AWG wire).

#3 is determined by the rating of the breaker. This is pretty straightforward, it's printed on the breaker itself.

Now, how does the all tie together, and why did Speedy say '99.99% of the time NO'?

Your device will pull whatever current it wants to pull from the circuit. The wires in the circuit have to be able to safely carry that current. How do you keep the wires from overheating and creating a fire? By putting a circuit breaker ahead of them that will trip at a slightly lower current than the maximum safe current for your wires. Most of the time, when a house is wired up, the rating of the wires and the rating of the circuit breaker are co-ordinated so the circuit breaker is rated for as much current as the wires can safely handle - if this is not done (i.e., as Speedy mentioned 'oversizing the wires' or 'undersizing the breaker'), then the cost of the wire will be higher than it needs to be. Because of this it is almost always dangerous to replace a circuit breaker with a larger rated breaker without also replacing the circuit wires at the same time.

PaulGray 05-13-2006 09:17 PM

Quote:

Originally Posted by IvoryRing
Just to spell out what Speedy is talking about when he says 99.99%...

There are three factors involved in a circuit, and it's easy to get them mixed up until you've worked through it.

1.) How much current your circuit will be asked to carry
2.) How much current your circuit can safely carry
3.) How much current your circuit will turn itself off when asked to carry

I'm going simplify things a lot, and gloss over a few technical details, but at the same time spell out more detail than just 'don't do it'...

#1 is determined by what device you connect. In your case, you want the sump pump and only the sump pump on a circuit. The documentation that came with your sump pump is saying that it won't request more than 20A during normal use. Since the next smaller standard size breaker is 15A, it is reasonable to assume that there will be at least some times during normal use where the pump will need between 15 and 20 amps.

#2 is determined by the size (gauge) of the wires going between the breaker and the device you are connecting. Note that there is more than just the wires in the wall, any outlets, switches, plugs along the circuit between the breaker and the final device also have to be able to handle the current the circuit will be asked to carry. For your purposes this means 12 AWG copper wire (or larger - AWG sizes are physically larger when the number gets smaller, so 14 AWG is physically smaller than 12 AWG and not suitable for your application, 10 AWG is physically bigger than 12 AWG and would work fine) and plugs/switches/outlets/etc rated for 20A or more (Unlike AWG sizes, 'A' for amps is bigger when the number is larger - amps can be added, so a 10A and a 5A device both plugged into one line will take 15A. AWG sizes can not be added, so an 8 AWG wire and a 10 AWG wire together are VERY different from an 18 AWG wire).

#3 is determined by the rating of the breaker. This is pretty straightforward, it's printed on the breaker itself.

Now, how does the all tie together, and why did Speedy say '99.99% of the time NO'?

Your device will pull whatever current it wants to pull from the circuit. The wires in the circuit have to be able to safely carry that current. How do you keep the wires from overheating and creating a fire? By putting a circuit breaker ahead of them that will trip at a slightly lower current than the maximum safe current for your wires. Most of the time, when a house is wired up, the rating of the wires and the rating of the circuit breaker are co-ordinated so the circuit breaker is rated for as much current as the wires can safely handle - if this is not done (i.e., as Speedy mentioned 'oversizing the wires' or 'undersizing the breaker'), then the cost of the wire will be higher than it needs to be. Because of this it is almost always dangerous to replace a circuit breaker with a larger rated breaker without also replacing the circuit wires at the same time.

Thanks for your detailed response. I really appreciate it.


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