DOL starting 3 Ph Motor and an RCD

[gerard]

Hi,

I am having trouble with a 3 phase motor (about 1kW I think) and a tripping RCD. The motor is DOL started through a contactor and thermal overload.
Starting the motor causes the RCD to trip instantly. Is the starting of the motor causing this and would soft-starting the motor solve the problem? If so, could I just take the RCD out of the circuit?

Cheers guys

 

[netblindpaul]

Why RCD on motor cct?
What is the environment?
Is this a 30mA RCD?
Need more detailed accurate info please?

 

[gerard]

It's a 30mA RCD. I got the machine from another branch of our company and they told me it didn't work so i am testing it by plugging it into a 3 phase socket protected by the 30mA RCD. It's a dry clean environment - a bakery to be precise. Would you recommend putting it on circuit with no RCD or up sizing the RCD to 60mA?

 

[Engineer54]

It's a 30mA RCD. I got the machine from another branch of our company and they told me it didn't work so i am testing it by plugging it into a 3 phase socket protected by the 30mA RCD. It's a dry clean environment - a bakery to be precise. Would you recommend putting it on circuit with no RCD or up sizing the RCD to 60mA?

Er, ... i think so!!!

 

[netblindpaul]

Doubtful you will get a 60mA RCD.
Why do you want an RCD in the first place.
What machine, what motor, guessing it has a motor, what motor starter/drive, what else on the machine etc.?

 

[Darkwood]

First thing you should do is PAT test the motor is seems clear you have a earth leakage somewhere, there shouldnt be a reason for a leakage on a good sound motor, what does the motor do?

 

[telectrix]

seems like all the motor does at the moment is trip the RCD.

 

[netblindpaul]

Darkwood,
Sorry mate but I wholly disagree with your use of the term PAT test the motor in the post above.

 

[telectrix]

agree , paul. the correct terminology is " shove a megger up it"

 

[Knobhead]

Have you taken any IR readings? I can't understand why you've got a RCD on the drive, but never the less it shouldn't trip it. Makes you wonder why your other department gave it away?

 

[Darkwood]

Darkwood,
Sorry mate but I wholly disagree with your use of the term PAT test the motor in the post above.

LOL yes well recently got my PAT cert and a free Martindale Micropat so just zapping everything with it but yes megger will do but just done 20 motors with 3phase socket kits on so just went on my own tangent.

 

[gerard]

The machine has one DOL motor and a 1ph - 3ph inverter to drive a drum type motor. The machine is plugged into a socket in a factory and that socket is protected with an RCD. So you think there is no need for an RCD for this machine?

 

[gerard]

Have you taken any IR readings? I can't understand why you've got a RCD on the drive, but never the less it shouldn't trip it. Makes you wonder why your other department gave it away?

I checked the ohm readings across the motor windings as I dont have a megger. The motor is in sound condition. The reason for the RCD is because the machine is portable and can be plugged in at a few locations around the factory.

 

[netblindpaul]

You may find that the inverter has design leakage to earth of more than 30mA.
Check the manuf' instructions for the inverter.

 

[Darkwood]

What inverter are you on about Paul?, O/P says its DOL with contactor and overload, makes sense now about you PAT comment which defo' wouldnt do through an inverter, hes only enquiring about whether soft starting would cure the problem.:whatchutalkingabout