AC Circuits

[jap]

I've heard talk on this forum that you may see a #12 wire on a 50 amp breaker feeding an Air Conditioner.
Most Residential Air Conditioners that I have hooked up just have a 2 or 3p contactor on them and the Overload if any is a Thermal overload that is laying against the face of the Compressor Motor. Not A full blown Starter with Heaters. I would think that this Thermal Overload is just a last line of Defense to take the compressor off line before destruction of the Compressor.I dont consider this like a set of overloads on a starter where there is a set amperage at which the contactor will drop out and protect the wire. I dont agree that a Thermal Overload that doesnt have a set trip point to Open,is an acceptable means of protecting the wire that feeds the unit.
Therefore I would think you would have to be very careful where you applied
the wire being protected for the simple fact that it has a Thermal Overload on it.

 

[raider1]

The motor overloads just provide overload protection for the motor and the branch circuit wiring.

The branch circuit conductors are protected from a short circuit or ground fault by the branch circuit overcurrent protection.

The fact that the branch circuit OCPD does not have to provide overload protection in addition to short circuit and ground fault protection means that the OCPD can be sized larger than is typical for other circuits.

Chris

 

[don_resqcapt19]

I've heard talk on this forum that you may see a #12 wire on a 50 amp breaker feeding an Air Conditioner.
Most Residential Air Conditioners that I have hooked up just have a 2 or 3p contactor on them and the Overload if any is a Thermal overload that is laying against the face of the Compressor Motor. Not A full blown Starter with Heaters. I would think that this Thermal Overload is just a last line of Defense to take the compressor off line before destruction of the Compressor.I dont consider this like a set of overloads on a starter where there is a set amperage at which the contactor will drop out and protect the wire. I dont agree that a Thermal Overload that doesnt have a set trip point to Open,is an acceptable means of protecting the wire that feeds the unit.
Therefore I would think you would have to be very careful where you applied
the wire being protected for the simple fact that it has a Thermal Overload on it.

You apply it per the rules in Article 440. The common installation is that the conductors are sized for the minimum circuit ampacity and the breaker is sized to the maximum OCPD as shown on the nameplate.

 

[charlie]

. . . I don't agree that a Thermal Overload that doesn't have a set trip point to Open,is an acceptable means of protecting the wire that feeds the unit. . .

Sometimes you just have to accept the technology. Besides, the 12 AWG, 60? C or 75? C wire is good for 25 amperes for this application.

 

[ceb58]

You apply it per the rules in Article 440. The common installation is that the conductors are sized for the minimum circuit ampacity and the breaker is sized to the maximum OCPD as shown on the nameplate.

What it comes down too is the mfg. has engineered there equipment and it meets there standard along with other testing agencies. They know their equipment and place the info that we follow on the plate. As Don stated we follow the minimum for circ. amp. and max. on ocpd. In your scenario you could install #6 with a 50amp breaker. Its all in the money you want to spend and not put in your pocket.

 

[brian john]

What makes you think an adjustable OL is worst or better that one with a fixed trip?

 

[jap]

Because the thermal overload on the face of a compressor motor trips due to the heat that is imposed on it from the temperature of the metal housing, not the temperature of the current that is going thru the branch wiring.

 

[billsnuff]

Because the thermal overload on the face of a compressor motor trips due to the heat that is imposed on it from the temperature of the metal housing, not the temperature of the current that is going thru the branch wiring.

sound like the motor has OL protection, the BC has OL and SC protection

 

[jap]

Wheres the BC OL Protection if its going through a 2p GD Contactor with no overloads?

 

[iwire]

Wheres the BC OL Protection if its going through a 2p GD Contact with no overloads?

On the compressor, all motors are required to have some type of thermal protection.

It does not mater if the OLs are on the motor or on the starter either way the result is the same. The conductors can not be subject to prolonged over current.

 

[iwire]

Because the thermal overload on the face of a compressor motor trips due to the heat that is imposed on it from the temperature of the metal housing, not the temperature of the current that is going thru the branch wiring.

I think your mistaken, on a hermetically sealed compressor the OLs are sealed inside the unit. I think you are looking at a low or hi pressure cut out.