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#216768 - 02/14/16 10:01 PM Verifying bonding conductor resistance  
LarryC  Offline
Joined: Jul 2004
Posts: 783
Winchester, NH, US

Starting a new job in a facility full of CNC machines. Ongoing issue is the failure of machine electrical components. Several machines came from another facility with clean power and rarely failed. Since arrival, the same machines have suffered multiple failures.

Initial suspect is power quality issues. Power quality studies have been performed on some of the busses in the building. Machines have been relocated within the building. Parts of the building electrical system have been upgraded.

Looking to purchase a power quality analyzer to get an understanding the system existing condition. In addition, I am looking to verify the condition of the bonding and grounding systems.

I am familiar with the ground bond testing systems for plug in equipment, but I am not aware of a system to test the bonding conductors of installed machines. I see standards for telecom and IT systems but nothing for industrial machines.

I think there are two separate issues here. Resistance of the "grounding" network and resistance of the bonding conductors to the grounding network.

Any suggestions?

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#216769 - 02/14/16 11:42 PM Re: Verifying bonding conductor resistance [Re: LarryC]  
twh  Offline
Joined: Mar 2004
Posts: 915
Regina, Sask.
What kind of failures? What other equipment is in the building, or nearby buildings? I'm thinking about harmonics.

#216770 - 02/15/16 12:54 AM Re: Verifying bonding conductor resistance [Re: LarryC]  
LarryC  Offline
Joined: Jul 2004
Posts: 783
Winchester, NH, US
I am aware of servo amp power supplies and servo amps failing. The UPS for the server room also sends high and low input line voltage messages.

The one servo power supply I opened up has a a rectifier module that has a 3 phase input and 2 wire DC output. I assume it is a 6 diode rectifier and that will generate the 5th and 11th harmonics.

I believe there are several things going on concurrently. Excessive harmonics, utility surges and sags, transients both internally and externally generated. No idea yet if there are also redundant N-G connections, poor connections, or a deteriorated ground networks. The building is 100+ years old with multiple additions.

To add to the fun, there multiple types and manufacturers of each type of machine.

#216771 - 02/15/16 07:55 AM Re: Verifying bonding conductor resistance [Re: LarryC]  
geoff in UK  Offline
Joined: Dec 2002
Posts: 183
For an example of bonding tester google "Megger BT51"

#216772 - 02/15/16 02:08 PM Re: Verifying bonding conductor resistance [Re: geoff in UK]  
LarryC  Offline
Joined: Jul 2004
Posts: 783
Winchester, NH, US
Thanks Geoff.

#216773 - 02/15/16 03:36 PM Re: Verifying bonding conductor resistance [Re: LarryC]  
twh  Offline
Joined: Mar 2004
Posts: 915
Regina, Sask.
Harmonic currents find their way to capacitors and can damage devices that are between the source and the capacitor or even the capacitor.

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