Refrigeration Compressor Motor Rating

[rocyr]

When looking at Refrigeration Compressors there are two listings for motor amperage. One listing is on a Service Guide Table then there is another listing on a Performance Based Table (This is based on coolant temperature). The Performance Based Table amperages can be almost 50% less than the Service Guide Tables. In the past I have always used the larger amperages in the Service Guide Tables when calculating for Max Over Current Protection.

My question is can I use the Performance Based Tables when calculating for Max Over Current Protection?

 

[bob]

Re: Refrigeration Compressor Motor Rating

The electrical equipment install by the members of this forum relates to a unit package with a name plate on the unit that details the mimimum circuit capacity and the max OC device.
I think you should contact the MFG for their opinion on your question.

[ January 28, 2005, 03:32 PM: Message edited by: bob ]

 

[craymon]

Re: Refrigeration Compressor Motor Rating

I have a question that relates to package unit overcurrent protection. We are working on a Corps. of Eng. job in Ft Polk Louisiana. The HVAC contractor is installing Make up Air units in the attics of some Barracks.The units have a supply fan, exhaust fan, and a heat wheel. Total of 14 amps. Nameplate rating shows max. overcurrent protection of 25.5 amps. units are 120/208 The panel schedules on the project show providing a 3 pole 35 amp breaker and # 8 thhn.
The inspector insists we provide breakers and wire as shown on the schedules even though our specifications tell us to check with the equipment being installed and provide breakers accordingly.Isn't this a code violation?

 

[jtester]

Re: Refrigeration Compressor Motor Rating

craymon
It would be a violation to use a 35 amp cb for the unit OCPD, but if you put a fused disconnect with properly sized fuses at the unit, you would overcome the problem.
Our inspectors will often insist that the plans match the installation. In your case, they would be asking for the engineer who prepared the plans to modify the panel schedule and issue an addendum, not just have the correction made in the field.
As an engineer, I appreciate that philosophy. If I made a mistake, I can learn from it, and if I didn't make a mistake, I can be sure the project is built as designed.
Jim T

 

[craymon]

Re: Refrigeration Compressor Motor Rating

Jim,

Thanks for the reply.
My whole point to the inspector was that the unit needed to be protected at the nameplate rating. I like your idea of having the inspector reaching back to the Engineer so he is plugged in when changes are made.
One point I failed to address is that each component of the unit is internally fused and is wired for a single point connection.

Craymon M.