A/C compressor breaker/fuse

[Richard Roshak]

For 13 years I have called out for repair when the panel breaker and/or disconnect box fuses do not match the manufacturer plate on the compressor. Today I have an electrican tell me per NEC 2005, 440.12 section 1, that the disconnect fuses can be 150+/-% of the max allowable breaker/fuse. Anyone hear of this?

[Jim Luttrall]

Manufacturers more stringent rules trump general code provisions.
He is all wet and does not understand or refuses to acknowledge the need for properly sized breakers to protect the compressor. There is a reason the data plate calls for a specific breaker and using a breaker, say a 75 amp when a 50 amp is called for will fry the compressor in the event the breaker is needed.

[James Duffin]

Attached is a table that shows how much each type of motor can be overfused at the breaker/fuse.

[Jerry Peck]

Attached is a table that shows how much each type of motor can be overfused at the breaker/fuse.


Not if the nameplate says something else.


Manufacturers more stringent rules trump general code provisions.


The nameplate specifies the minimum circuit size allowed and the maximum overcurrent rating allowed. The nameplate rules and trumps all else.

[James Duffin]

The table I posted is to be used along with the entire code section on motors. I would hope that everyone knew that. Most motor data plates only list FLA and it is up to the electrician to wire it properly.

[Richard Roshak]

I don't understand why tables on motors are being posted here. This is a system with electronics.

[James Duffin]

I was showing you why the electrician could be correct and why the motor data plate may not tell the whole story in the overcurrent protection size for a motor. Sorry for the confusion.

[Jerry Peck]

and why the motor data plate


James,

We are referring to the nameplate on the a/c condenser unit, not a motor data plate.

The nameplate requirements on the a/c condenser unit are what is required to be followed.

But you knew that.

[James Duffin]

Nope.... didn't know that....the OP said "manufacturer plate on the compressor". If he had of said manufacturer plate on the condensing unit or heat pump unit I would have known then.

[Jerry Peck]

Nope.... didn't know that....the OP said "manufacturer plate on the compressor". If he had of said manufacturer plate on the condensing unit or heat pump unit I would have known then.

James,

It is a common mistake here, and elsewhere, to refer to outdoor units as "the compressor" with it is the "condenser" unit ... er ... that is why I started out with "outdoor units" as it may be a heat pump - in which case the units are more correctly referred to as "indoor unit" and "outdoor unit" as each serve the purpose of "condenser" or "evaporator" depending on if it is heat pumping heat into the structure (acting as a "heat pump") or heat pumping heat out of the structure (acting as an "air conditioner"), when, in all reality, it is simply a "heat pump" and pumps "heat" in the desired direction, which ever that is and/or which ever that is set up top be.

I.e., even a "straight cool" unit is a "heat pump" in that it pumps heat from the indoor unit to the outdoor unit.

I have always referred to the "outdoor unit" as the "condenser unit" but am trying to retrain myself to "outdoor unit", likewise the "evaporator unit" is the "indoor unit" as it may indeed not actually be serving as the "evaporator unit", it is simply the "indoor unit".

Hopefully I did not screw up the common use of "condenser unit" and start another feud about what to call things. :D