30 amp breaker protecting #12

[Mule]

Here is an easy picture to follow...

View attachment 2856

So in that illistration...what would the branch circuit breaker be sized at?

 

[Jim W in Tampa]

So in that illistration...what would the branch circuit breaker be sized at?

you read the plate and provite the min breaker or max. That #12 was good for 30

 

[JohnJ0906]

So in that illistration...what would the branch circuit breaker be sized at?

I would size it the same as the max fuse - 40 amps.

 

[stickboy1375]

So in that illistration...what would the branch circuit breaker be sized at?

The MAX. fuse size.

 

[stickboy1375]

I would size it the same as the max fuse - 40 amps.

Why? When you can just run # 12 to the unit... .........

 

[Mule]

you read the plate and provite the min breaker or max. That #12 was good for 30

Just so I understand the "intent" correctly....

So the overcurrent device in the compressor is protecting the branch circuit conductors from overload?

 

[peter d]

So the overcurrent device in the compressor is protecting the branch circuit conductors from overload?

There ya go!

 

[JohnJ0906]

Why? When you can just run # 12 to the unit... .........

If I size the fuses to allow for startup current, why would I then install a smaller breaker, so that it trips on startup?

 

[stickboy1375]

Just so I understand the "intent" correctly....

So the overcurrent device in the compressor is protecting the branch circuit conductors from overload?

Yes, the motor is thermally protected, pretty hard to burn the wires up without the motor spinning.

 

[stickboy1375]

If I size the fuses to allow for startup current, why would I then install a smaller breaker, so that it trips on startup?

Sorry John, I misread what you were responding too... my fault.

 

[Rewire]

Here is an easy picture to follow...

View attachment 2856

I know you are allowed 175% of the circuit amps I was just saying what I see in the field alot

 

[stickboy1375]

I know you are allowed 175% of the circuit amps I was just saying what I see in the field alot

Thats fine, but I was just telling it how it really is.

 

[Mule]

I alway had it in my thick skull that a hacr rated breaker allowed for start up current, and then everything was normal #10/30amps etc......or whatever the unit called for....

 

[peter d]

I alway had it in my thick skull that a hacr rated breaker allowed for start up current, and then everything was normal #10/30amps etc......or whatever the unit called for....

I generally use this rule of thumb. Wire size to minimum circuit ampacity, OCPD size to maximum size listed.

 

[stickboy1375]

I alway had it in my thick skull that a hacr rated breaker allowed for start up current, and then everything was normal #10/30amps etc......or whatever the unit called for....

Never wondered why AC units had Minimum Circuit Ampacity AND Maximum Breaker Size?



Let me ask you this, how would you size a 1HP motor for a well pump?

 

[Mule]

I generally use this rule of thumb. Wire size to minimum circuit ampacity, OCPD size to maximum size listed.

I've always sized both the wire and the branch circuit device to the min circuit ampacity on the nameplate, and never had a issue.:-?

 

[JohnJ0906]

Well, Ive seen it again. Where someone had done a remodle and they rerouted some circuits and they had put some #12 on a 30 amp breaker!! there were some outlets out of power and I traced it back to a panel, (that was mislabled) and the 30 amp had tripped!! thank goodness that the #12 never over heated. How often do you run into this??

Did a service upgrade from an old fused service (after one of the fuse holders caught fire).

EVERY circuit had a 30 amp fuse. All were #14, except 1 #12.

After the tenants then complained about the kitchen circuit tripping, we gave the landlord a price to add some circuits. The (1) #14 circuit had: kitchen and dining room lights, dishwasher, disposeall, all kitchen receptacles, including fridge and microwave, and the detached garage.

Still haven't heard back on that one. :roll:

 

[Mule]

Never wondered why AC units had Minimum Circuit Ampacity AND Maximum Breaker Size?

That's where I went wrong as I thought the hacr rated breaker allowed for the additional current...

thanks guys...see there you can "teach a ole Mule new tricks"......

 

[stickboy1375]

I've always sized both the wire and the branch circuit device to the min circuit ampacity on the nameplate, and never had a issue.:-?

You wont when they are brand new units, but over time there could be.

 

[peter d]

You wont when they are brand new units, but over time there could be.

I think he meant minimum OCPD size, not MCA. In other words, if the min. OCPD is 40, #8 wire. Is this correct Mule?

In any event you haven't done any harm - you just have an oversized wire which is good for voltage drop, but not necessary.