480 power service and 240 motor

Status
Not open for further replies.
D

Duuuuug

Member
Service: 480Y/277.
Pump 20HP/3PH/240VAC
1.Is a special transformer required to get 240/3ph for this pump or is a SQD "General Purpose Transformer" adequate?
2. Transformer Size? Motor FLA x 1.25?
They want to keep the pump because of the cost of pulling it and replacing it with a 480v pump.
This is just the first time I've had to do this.
 
Re: 480 power service and 240 motor

Is the pump motor dual voltage? If it has nine or twelve leads at the motor cap it can be wired for 480. But one thing A 20 HP motor will draw much more than 1.25 amps? you sure you are reading the right specs.?

[ March 06, 2005, 03:46 PM: Message edited by: hurk27 ]
 
Re: 480 power service and 240 motor

The Pump is 20HP, I have asked them for more information on the pump to see if it can be wired for 480 (This would be ideal).
Preparing for worst case.
The FLA is 54Amps@240VAC.
The question was... Is the Transformer sized by the Motor FLA times 1.25
54x1.25 = 67.5Amps
67.5x240VACx1.732=28KVA
Next Standard Transformer size is 30KVA.
 
Re: 480 power service and 240 motor

You do not need a special transformer. The Square D general purpose one you quoted will work.

In most cases sizing a transformer based on 1.25% of motor FLA will be suffcient. Another rule of thumb is 1.1KVA per HP. It seems all of the major vendors, except Square D, list recommended transformers based on motor HP (in this case ACME says 21.8KVA for a 20HP).

[ March 06, 2005, 08:56 PM: Message edited by: jim dungar ]
 
Status
Not open for further replies.
Top