Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 9 replies
  • Subscribers 32 subscribers
  • Views 830 views
  • Users 0 members are here
Options
You may also be interested in
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

EMI suppressor and protective earth

Chris Pearson
I would be most grateful if the boffins in here could explain something please.


This suppressor was fitted to my lathe on the load side of the VSD. Something went wrong when I was parting off the other day - the tool dug in and the motor stalled - and now it is running roughly. Back to square 1!


In an attempt to determine whether the VSD has been damaged, I tried connecting another motor, but I was unable to demonstrate protective earth continuity. The cable from the green terminal on the suppressor goes to the motor's earth terminal. I expected that the case of the suppressor would be the supply side of the PE, but apparently not. So with the suppressor fitted there is no PE to the motor, which I find a little disconcerting.


FWIW, the capacitance between red and black is about 0.5 µF, the resistance is 470 kΩ, and the capacitance between each of red and black to green is 9 nF.


Would somebody kindly explain whether this is safe please?

83550124b8831caa7e200218ed497ebc-huge-20200629suppressor.jpg
Parents
  • 0
    Difficult to answer without seeing the machine ... sometimes motors that are part of a machine or appliance are earthed by being bolted to the casing of the machine (as in my tumble dryer for example) rather than having a separate protective conductor.


    A suppressor may well be earthed in the same way, usually through the can.


    Having said that, is the motor (when mounted in the machine) intended to be double-insulated? If so, a suppressor can still be fitted, and connected to the metal parts of the motor (often arranged to connect the Class Y capacitors from L and N to the rotor through the bearings) - this is how some Class II vacuum cleaner motors have their suppressors connected. It still sorts out the EMC issue relating to the motor, but no connection with Earth is necessary. And yes, in such Class II appliances, the motor (or its rotor) may well sit above Neutral potential, which is no problem of course in machines where the user doesn't have access to the motor or any conductive parts connected to it.
Reply
  • 0
    Difficult to answer without seeing the machine ... sometimes motors that are part of a machine or appliance are earthed by being bolted to the casing of the machine (as in my tumble dryer for example) rather than having a separate protective conductor.


    A suppressor may well be earthed in the same way, usually through the can.


    Having said that, is the motor (when mounted in the machine) intended to be double-insulated? If so, a suppressor can still be fitted, and connected to the metal parts of the motor (often arranged to connect the Class Y capacitors from L and N to the rotor through the bearings) - this is how some Class II vacuum cleaner motors have their suppressors connected. It still sorts out the EMC issue relating to the motor, but no connection with Earth is necessary. And yes, in such Class II appliances, the motor (or its rotor) may well sit above Neutral potential, which is no problem of course in machines where the user doesn't have access to the motor or any conductive parts connected to it.
Children
No Data

Community Rules & Guidelines