Variable Drive Motors

[andyb]

Has anyone been involved with variable drive motors?
I've been asked to run a feed for one and although the supply cable is only 2.5mm, I've been asked to install a 16mm earth.
Can anyone explain?

 

[jpmiff]

Hi,

i assume variable drive motors you mean a motor driven by an invertor?

if so the 16mm2 earth is most probably to handle any harmonics you generaly get with invertor drives

 

[thepurple1]

Also use silflex cable from the inverter to the motor

 

[Darkwood]

Not sure on the 16mm earth if the motor is earthed correctly and sheilding rounded as per inverter manual requests then im not sure what 16mm is going to achieve, the high frequency noise can be dampened by sheilding the cable effectively, the only reason you need to back up the sheilding which is prob' swa in your case is due to the length of cable run as i take it the inverter is not close to the motor, in these cases additional earthing is required.
It was a long time ago i needed to do this so forgive my vagueness.

 

[pmac10]

a motor supplied by 2.5sq conductors via a variable speed drive will certainly not require a 16mm sq earth conductor. it serves no other purpose than to carry fault current. v.s.d 's have built in electro-magnetic- compatibility filters which you will not even need to use if you have grounded/shielded cable. they are only required for noise sensitive enviroments

 

[silva.foxx]

Er...I'm sure I'm clutching at straws but could a mistake have been made and the specified earth conductor be 16AWG ie 1.5mm2

Can you provide the details of the drive?

I know that high switching frequencies within in the drives increase earth leakage, but I've never come across large earths on small drives in my 15 years of automation.

 

[Darkwood]

Im with the majority here as somethings sounds wrong, although as mentioned before about 15yrs ago i did supply supplementary earthing of about 10mm^2 because the motor was 20 meters away and the guidelines of the invertor manual stated that this was required, although i think the industry was in it infancy with rf and emf noise when it came to motor control, not seen it or employed this method since.