Conveyor with ground fault protection

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travish

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Central North Carolina
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Electrician
Hey,

I need a little help. I have a conveyor made by Dynamic Conveyor. it is an underwater parts conveyor in a cooling tank for injection molded parts. The motor is located above the waterline, it is driven by a small frequency drive .When we installed the conveyor we installed a GFCI 120v 20a receptacle. the receptacle trips when we run it. It trips regardless if there is water in the tank or not. there are no obvious shorts and it is a pretty simple set up the supply cord goes into the back of the Freq drive which is on the left side of the conveyor, then a cord goes to the motor 1ft away to the motor. all of the conveyor parts (frame, belt, and connecting pins) are plastic with the exception of a few stainless steel screws. so I am sure there is some leakage in either the motor or the freq drive. I have not tried a breaker rated for equipment protection, only the receptacle rated for personnel protection.

the environment is on cement, normally water on the floor, and operators reach into the tank every hour to check parts.

Does anyone have a good solution?
 
My guess is there is some kind of capacitor or EMI filter on the drive that is allowing enough current flow to ground to trip the GFCI.

Best bet is to make the conveyor people deal with it.
 
conveyor runs fine on a regular receptacle, I have called the conveyor company they are looking into it.

petersonra, I think your reply is what I was looking. there is some device in the drive leaking. may or may not be a failure but is leaking enough current to trip a receptacle GFCI

This being in an industrial plant 210.63(6) indoor wet and damp locations, I guess it has to be GFCI?
 
First confirm that there isn't something broken in the system. It is possible that there is some sort of high impedance fault which is letting current leak to ground and tripping the GFCI, but not enough fault current to prevent the system from functioning. Does the manufacturer recommend or require a GFCI? If a required GFCI is tripping, then something is broken.

The motor you are using doesn't run on DC. It runs on 3 phase alternating current provided by the BMUD120-A2, and even worse the AC is very likely pulsed at high frequency. This high frequency easily couples right through any insulation to create leakage current that trips the GFCI. (The fact that it is called a 'brushless DC motor' is a historical artifact of how drives developed. Trust me, what is flowing between the drive and the motor is _AC_.)

The manual for the BMUD120-A2 specifically addresses this issue; see page 6 of

They recommend Mitsubishi Electric Corporation NV series ELCB devices, however I believe these are not class A GFCIs for personnel protection:
www.mitsubishielectric.com

Product Features Low-voltage Circuit Breakers Earth-Leakage Circuit Breakers MITSUBISHI ELECTRIC FA Factory Automation

MITSUBISHI ELECTRIC FA site introduces Earth-Leakage Circuit Breakers of Low-voltage Circuit Breakers.
www.mitsubishielectric.com

You may be able to provide additional filtering and shielding to reduce high frequency leakage current.

IMHO your best bet is to change the installation to prevent any requirements for class A GFCIs, and then provide personnel protection via other means, including guarding and redundant bonding. I do not know the code requirements for GFCI protection in your situation.

-Jon
 
travish said:
wrong code ref 210.8 (b) (6)
Click to expand...

210.8 Ground-Fault Circuit-Interrupter Protection for Personnel.
Ground-fault circuit-interrupter protection for personnel
shall be provided as required in 210.8(A) through (E).
...
(B) Other Than Dwelling Units.
...
(6) Indoor wet locations
Click to expand...

Location, Wet. Installations underground or in concrete slabs
or masonry in direct contact with the earth; in locations subject
to saturation with water or other liquids, such as vehicle washing
areas; and in unprotected locations exposed to weather.
Click to expand...
I don't know if your area is "wet" or not. Better safe than sorry though.
 
thanks for all the help, conveyor company isn't being to helpfull. we are probable going to put a different motor and gear box and do away with the speed control unit
 
travish said:
thanks for all the help, conveyor company isn't being to helpfull. we are probable going to put a different motor and gear box and do away with the speed control unit
Click to expand...
get your purchasing department involved. the conveyor company sold you something that in general comes with a warranty of merchantability. that means it is supposed to work under normal conditions. they certainly knew (or should have known) that a conveyor in a wet area with a cord would likely need to be plugged into a GFCI. if they supplied something that cannot work that way, they are liable to fix or replace it, or refund it.
 
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