Motor Fuse Size and Overload Settings

You should check the name plate for the Full Load Amps(FLA). If you must use the

132 kw, the approx amps = 132 kw/(.415 x 1.73) = 184 amps. IF you apply the power factor the amperage will be higher. Using a PF of 0.80, the FLA is 230 amps. What is the ampacity of you conductor? You need to go by the local code for this information if you have a code.

On a Star-Delta starter, you size the over load relay at 58% (1/1.732) of the motor nameplate FLA because you are using 6 leads going to the motor, and only 58% of the current goes through the main set of conductors (connected to the main contactor).

But the fuses supply the entire motor circuit and are located ahead of where the power splits to the Delta and Star contactors, so fuse sizing must be based upon the entire motor FLA. You are obviously not in the US, so I cannot help you to size the fuses because that will depend on your local codes, but again, the basis is the entire motor FLA, not the lesser amount associated with the OL relay.

i have decided on what cable to use i just want to know is why you can't just use 132000/415 to work out the current ??

lost.instro,

how long have you been working in that your work now ?

for 3 phase motor as you state before, we MUST devide with square root ( three ), that is about 1.73 for calculating current.

tx..

regards...

thanks for all your help i have sorted it out :)

active power = square root 3 times rated phase-to-phase voltage and also times phase to phase current of your device, multiplied again by power factor. in your system, it is 132kw=√3 *415V*I*0, then u can have the current.

A <...Fuse...> is there to protect the wiring.

<...have been told...>

Circuit protection is covered under the topic of co-ordination, and can be found in the applicable national electrical standard prevailing; in the UK, for example, BS7671 applies.

If in doubt, consult a qualified local Electrician, who will design, select, install, test and certify as safe the installation being considered under the standards prevailing in the country of installation.