Using a 440V 60hz motor on a 460V 60hz supply
Using a 440V 60hz motor on a 460V 60hz supply
(OP)
I have a 440V 60 hz 184 amp motor (110 KW). The power supply is 460V (on an offshore drilling rig) with the cable and plug rated for 125 AMP, but has a 300 AMP breaker. The motor is connected to a pump and I expect we will not require more than 90 KW and will limit the pressure output of the pump to ensure we do not overload the supply.
Could someone comment if there is a problem or is acceptable using thjs this motor with the supply and what possible risks there may be with this type of setup. I have heard of the 5% rule which would suggest is acceptable to use a 440V motor on a 460V system.
Thanks.
Could someone comment if there is a problem or is acceptable using thjs this motor with the supply and what possible risks there may be with this type of setup. I have heard of the 5% rule which would suggest is acceptable to use a 440V motor on a 460V system.
Thanks.





RE: Using a 440V 60hz motor on a 460V 60hz supply
RE: Using a 440V 60hz motor on a 460V 60hz supply
RE: Using a 440V 60hz motor on a 460V 60hz supply
You should reduce the breaker current to properly protect your cable and plug.
RE: Using a 440V 60hz motor on a 460V 60hz supply
RE: Using a 440V 60hz motor on a 460V 60hz supply
RE: Using a 440V 60hz motor on a 460V 60hz supply
Code requires a wire size that is 125% of the motor current. To me, the reasoning seems to be that the overload is typically set to no more than l25% of the motor FLA so it will protect the wiring as well as the motor.
If you do not have to follow code you could use the breaker as long as you have the motor overload set to trip at 125A so that it protects the wire. The breaker would then protect against a short. This could be a problem during a start since this overload may trip.
I'd be leary of using that cable size without some type of overcurrent protection for it since someone could increase the motor load in the future and overload the plug or cable.
RE: Using a 440V 60hz motor on a 460V 60hz supply
RE: Using a 440V 60hz motor on a 460V 60hz supply
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Using a 440V 60hz motor on a 460V 60hz supply
RE: Using a 440V 60hz motor on a 460V 60hz supply
Not to keep beating a dead horse, but if you are required to meet the NEC, you just can't do what you are suggesting. Everything in the feeder is based on the motor full load amps. The fact that the breaker will protect the cable is nice, but if it is a motor feeder, it is still too small.
RE: Using a 440V 60hz motor on a 460V 60hz supply
RE: Using a 440V 60hz motor on a 460V 60hz supply
RE: Using a 440V 60hz motor on a 460V 60hz supply
The motor you wiring needs to be carefully thought out like any system. As I understand it you have a 440 Volt motor and the Full Load Amps are 185A. With just this basic information you can tell alot of what you need to do for a safe system. 1)440V Motor can run on a system with a 10% variant from nominal. 2)fla of 185Amps tells me I need a 250A MCP Breaker Thermal Magnetic (Not Just any Breaker) set at 13X the FLA. 3) The FLA of 185A tells me the overload size but I need the Service Factor (SF) of the motor to tell you how to set it. If the service factor is 1.15 then the overload will be set to 1.15 x FLA, if 1.00 then .95 x FLA. After the motor and wiring has been checked (Insulation Resistance Test) then you can bump the motor for rotation, if correct you may proceed with a 15min run to determine the run current of all phases. Please take this into consideration when determining a motor circuit and control of that motor circuit. This will help you in the Safety of personel and equipment. The Cable should be well thought out as well, you must take in account current, raceway and de-rating in the application.
Electrical Power Solutions Ltd.
www.e-p-solutions.com
RE: Using a 440V 60hz motor on a 460V 60hz supply
RE: Using a 440V 60hz motor on a 460V 60hz supply
Code allows a breaker rated up to 250% of the motor FLA. If that breaker won't permit the motor to start, the breaker is allowed to be increased to 300% of motor FLA for breakers rated greater than 100A.
So, you need wire rated for at least 125% of motor FLA and you can use a breaker rated up to 300% FLA (if a 250% rated one doesn't work). In theory, the installation could have been correct for a 100A motor. In reality, the likelyhood of needing a 300% rated breaker is slim.