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Ladies and Gentleman, especially certified electricians:
Due to many KSU power supplies failing, I believe in addition to the grounding prong of the KSU power cord that we should also be installing a direct ground wire to the cabinet.
I would appreciate all EXPERT opinions on this.
Thank you.


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Have to disagree with you. Most Nortel KSU do NOT have a connection point for that.

I believe it is because when their 1st electronic KSU's came out (the Vantage series), I was still at Bell. Bell was having a problem with KSU's blowing from lightning so they commissioned several of their "top-notch" PBX Repair Techs to do a province wide (maybe even a country-wide) study comparing results of those that were & were NOT grounded.

Apparently they found little difference if any as to the potential risk, with or without being grounded.

I'm sure few will agree with me but in my experience I've only had to change one KSU that was a known lightning hit.


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The biggest mistake made in grounding is your equipment being a different ground potential than the electrical. That's why most use the third prong only. You never want to be the best or worst ground source.


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First question I need to ask is why are they failing so much? Bad design or an external event causing the failure.

Nothing you can do about a bad design, but you can do lots about external events causing them to fail.

Do you have them plugged into a good surge suppressor/line filter and or a good UPS that supplies the same?

Have you checked the voltage and current between ground and neutral to see if you have a bonding issue or such?


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Would their be warranty issues with manufacturers on failed systems that haven't been grounded via their grounding lug.


Bob

With all the variables involved, I am amazed when any voice and data technology works like it is supposed to.
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Ground potential is a major concern. I just had two IP office telephone sets go down after a storm.
Note: Almost everything is now made in CHINA.
The Chinese make mistakes in their electrical engineering designs
e.g. back up power supplies.


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No matter what you do you can't do it all.

Example: When I was with Bell, we had issues with our computer. The computer center in Montreal told us to call \our local Building dept. Called the Building Dept and they put a line recorder on the electrical outlet for a week. Nothing. Then we called the "CCNS" dept (data group) who put on a $50000 test set & within 3 04 4 minutes they had found the problem. Voltage was all over the map between 80 and 145 volts for just parts of a second.

Hydro Quebec had to get involved.






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If an external ground is desired...and the AC outlet that provides power to the system has been checked and tested...consider using a grounding block. Plug the key system into the block and plug the block into the electrical outlet. The block should provide a suitable ground point for the telephone system.

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Originally Posted by justbill
The biggest mistake made in grounding is your equipment being a different ground potential than the electrical. That's why most use the third prong only. You never want to be the best or worst ground source.

That's absolutely correct. If you ground the system and/or rack you always want to make sure there is no voltage difference between the ground prong on the line cord and whatever ground you are using. Only way to insure that is to bond to the electrical receptacle. I have actually had systems destroyed because of a voltage between the power cord ground and where I had the system ground connected. And incidentally, the ground screw on KSUs is only there to satisfy UL who requires that the premises wiring through the KSU be grounded in the event that the line cord is disconnected from the receptacle.

Originally Posted by Telesystems
Ground potential is a major concern. I just had two IP office telephone sets go down after a storm.

I seriously doubt that the phone damage had anything to do with grounding. Over the years I have seen ethernet ports on various equipment as well as TDM phones and the associated ports on the KSU destroyed be lightning. It's because the EM pulse from the lightning induces a voltage on the cable itself. Only thing that will help with that is transient suppressors at both ends of the cable that are grounded properly.

-Hal

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Question: Isn't the the green ground wire in the power cable harness also tied to frame ground inside the electronic KSU cabinet?






Forty six years and still fascinated with Telecommunications!
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