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




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.
Posted By: hbiss Re: Grounding of KSU's directly to the cabinet - 03/14/14 09:06 PM
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
Question: Isn't the the green ground wire in the power cable harness also tied to frame ground inside the electronic KSU cabinet?




Posted By: hbiss Re: Grounding of KSU's directly to the cabinet - 03/17/14 06:08 AM
Yes it is. Read my explanation above as to why the ground screw is there. If the receptacle is properly grounded the ground screw is only needed if the plug is pulled. Grounding the ground screw isn't going to be any better than you already have and can actually cause problems if not done the way I said- which isn't always the way the manufacturer recommends.

-Hal
Thanks Hal!
Well, yes and no. If the power cord from the AC supply goes directly into the KSU AND the grounding conductor is extended within the KSU to a metal KSU ground plane, then the system is "effectually" grounded via the electrical cord.

There are plenty of KSUs that have the power cord enter the KSU cabinet and then go to a transformer and the grounding conductor is connected to a piece of copper or aluminum "foil" square gluded to the KSU plastic housing. There is no way this is an effective ground.

Then there are the system with external power supplies that require a ground be externally connected.

Here where it really comes down to a point. The CO telephone cable head ground and the KSU ground should be exactly the same, provided the building ground at the main service panel and the telco cable head ground are less than .1 volt difference.

IT people are much too cavalier when it comes to grounds. They think a cabinet ground is sufficient if the cabinet is grounded to the "floating" rack. This is ridiculous.

When I was at Bell, it was manditory that the ground for the cable head, PBX and all ancillary equipment be identical. When the 1978 NEC came out, we were required to make sure the building ground and our ground were identical and it has been that way ever since.

But, of course, the Bell system never actually adopted the NEC as a standard. The IEEE National Electrical Safety Code was the actual "Standard" that the Bell System adopted as the official code. This may be recognized by all the OSP people as the "Code Bible." Within that code, it is manditory that all sheath, ground lugs and grounding "devices" be bonded together and extended to all equipment served by such devices. Here is where it gets a little complicated. In large buildings where the primary electrical supply may be 480VAC or higher and individual floors are supplied through transformers, bonding becomes a nightmare, both for the electrician and the telephone company. Here's where impedance mismatches can cause more harm than not having a ground at all. That is why one may see a 1/0 ground cable running to all floors from the teleco cable head in the large buildings to maintain a good cable ground.

Rcaman
Posted By: hbiss Re: Grounding of KSU's directly to the cabinet - 03/17/14 04:24 PM
Quote
Well, yes and no. If the power cord from the AC supply goes directly into the KSU AND the grounding conductor is extended within the KSU to a metal KSU ground plane, then the system is "effectually" grounded via the electrical cord.

There are plenty of KSUs that have the power cord enter the KSU cabinet and then go to a transformer and the grounding conductor is connected to a piece of copper or aluminum "foil" square glued to the KSU plastic housing. There is no way this is an effective ground.

I agree that that doesn't constitute an effective ground but it's really poor design. What does the ground screw connect to and why is it not tied to the power cord ground like it's supposed to be? Same with external power supplies- there either should be a ground conductor in the interconnecting cable or the power cord ground gets connected to the negative of the supply voltages along with all metal parts. Are the two grounds not connected together because the manufacturer found out that there may be a damaging difference of potential due to how they (improperly) recommend the external ground be provided? I do understand what you are saying but I'm not sure this separated ground problem exists today with newer systems- at least it shouldn't. Easy way to find out is a simple continuity test between the ground prong and ground screw.

-Hal
Hal,

The ESI uses a 2 wire power plug from the electrical receptacle to an external transformer and then a two wire coax power connector to the KSU. There is NO physical connection between the electrical receptacle and KSU. The ground stud of the KSU is internally connected to the metal hardware of the KSU and the ground conductor of the CO ports. I am sure ESI is not the only system like this.

Rcaman
I posted this because plenty of Partner proccessors, some Merlin KSU,s AT&T Spirit, Vodavi DHS, Vodavi STS, Panasonic KX-T etc. etc. seem to get hit by some type of surge, then go belly up. I thought this grounding redundancy may help alleviate such misfortune for the customer.
Originally Posted by Telesystems
I posted this because plenty of Partner proccessors, ... seem to get hit by some type of surge, then go belly up. I thought this grounding redundancy may help alleviate such misfortune for the customer.
Grounding (as some have described) is essential and defines hardware protection. But what some have posted does not completely describe what you must understand to have a useful answer.

For example, do not ground equipment to earth a surge. That simply makes equipment a best and destructive current path. Equipment must be bonded. But a surge current path, to avert damage, must be on a path that goes to earth AND not on a path into or near equipment. That is one reason why electronic ground and chassis ground remain electricaly separate (therefore dfferent) and only interconnected at a single point.

Do not assume both ends of a wire are electrically same. For example, safety ground in a mains breaker box is electrically different from earth ground. Earth ground is essential for protecting electronics. Safety ground in a wall receptacle will not properly connect to earth (ie too much impedance) and can even make damage to nearby equipment easier.

Do not confuse bonding with a low impedance connection to earth. That low impedance path must connect destructive currents to earth so that current does not enter a building. This rule applies to every incoming wire - not just telco cables.

Damage apparently exists because a current has connected to earth destructiveely via a KSU.
There is another fact that may be overlooked: There is no device, ground or method of grounding that can withstand a direct lightning strike. With a potential for a billion volts, the puny grounds and surge devices are incapable of containing a direct strike. Telephone equipment is exposed three ways. 1 through the electrical service, 2 through the telephone CO trunks and 3 via static through the telephone instrument cabeling. Many of the "fried" systems may be a victim of static electric which traveling through the telephone instrument wiring, in winter months, is extremely likely and can have potentials high enough to cause lightning like damage, but on a much smaller and less dramatic scale.

The bottom line here is make absolutely sure the telephone equipment is bonded and NOT the "best" ground in the facility. Take accurate readings and make sure the telephone equipment bonds are not mis-matched impedance wise from the good ground. If you are in a smaller facility, take the time and make sure there is a solid metallic ground with a bonding jumper across the water meter. In large, transformer fed facilities, make sure your telephone ground is the building main ground and not a high impedance electrical ground being derrived from a step down service transformer. The NEC and the NESC both require large buildings to maintain structural steel bonding. Don't be fooled. Take readings. Not only is this an equipment protection situation, it is also and, more importantly, a life safety issue.

Rcaman
ATT TP -76416 has some usefull stuff in it.
Originally Posted by Rcaman
There is no device, ground or method of grounding that can withstand a direct lightning strike. With a potential for a billion volts, the puny grounds and surge devices are incapable of containing a direct strike.
The many who are educated by hearsay and advertising only assume. Fewer who actually do this stuff use real world numbers. And learn from over 100 years of well proven experience and science.

Your telco's switching computer is connected to wires all over town. It suffers about 100 surges with each thunderstorm. How often is your town without phone service for four days while they replace their $multi-million computer? Never? Because direct lightning strikes without damage is routine ... when someone does not use wild speculation. And when someone does not use plug-in (adjacent) protectors that can sometimes make damage easier.

The engineer who did this stuf warns all of the naive who make 'woe is me' claims. Direct lightning strikes to electornics atop the Empire State Building without damage - 23 times annually. Direct strikes to electronics upon the WTC were 40 per year without damage. Only those who learn science(and not entertain hearsay) know how to spend less money on superior solutions ... so that even direct lightning strikes need not cause damage.

Relevant numbers means voltage (ie billions) is irrelevant and mythical. A lightning strike is about current - typically 20,000 amps per surge. A less expensive and supieror 'whole house' protector start at 50,000 amps. So that a direct lightning strike does not even damage the protector. As demonstrrated by telcos that suffer about 100 surges per storm - without damage. As demosnstrated by 23 direct strikes to Empire State Building electronics without damage.

Anyone who posts by first learning well proven science would know these numbers. The naive, educated by hearsay, only speculate about billions of volts ... wildly and without responsiblity.

This is about why scams work and that informed consumers learn from engineers who did this stuff. Direct strikes to cell phone towners without damage is routine. Using princples demonstrated even by Ben Fralnklin over 250 years ago. Informed homeowners are strongly advised to learn from engineers who recommend better earthing and a 'whole house' protector rated at least 50,000 amps. A superior solution even sold in Lowes and Home Depot. The superior solution is that easy.

Protecting a KSU is about how every wire insiide every incomign cable enters the building. And about the single point earth ground. Not about bionding. Protection is about a low impedance (e 'less than 10 foot') connection from each incoming wire to that essential (and best) earth ground.
Posted By: hbiss Re: Grounding of KSU's directly to the cabinet - 03/21/14 04:11 AM
Westom, please complete your profile with your occupation so that we can know who we are talking to.

-Hal
Excuse the advertising aspect of my post, it is designed to be enlightening not commercial.

We had issues with the old Prostar 816 and one day I was at the CES show in Vegas and EFI (Utah company) had a 2500 volt, 2500 watt circut blowing up other people's surge protectors then substituting theirs, and the light bulb stayed on.

We made installing one of the EFI surge protectors a mandatory part of every system sale. We stopped having problems with dead 816s. We used them on EVERY system.

One day a recent Toshiba customer called up to say his system was dead. Balderdash, Toshibas don't die. All the display screens were dead, we unplugged the power cord from the EFI surge protector that had NO green light, put it in the wall and the Toshiba worked fine.

The surge protector was a mass of burned parts inside, we received a warranty replacement. You can say all you want about grounding, power spikes kill systems and they are so transient that you can't recognize them.

Sorry if anyone is upset that I recommend a REALLY GOOD company, but we made money selling EFI surge protectors, our dead power supply problems went to zero and the trouble you go through with warranty repairs stops with an EFI "One millionth of a second response" from their units.

No, I don't get paid for this advice, not even a free surge protector, they just saved our asses a lot of trouble and I felt the need to pass this on. Bracha
I don't take it as advertising. As techs, we need to know what works and what doesn't.
Hey Westom,

I happen to live in Western PA and Westinghouse spent multiple millions of dollars building a man made lightning lab in Hunker, PA. Those statements are NOT wild speculation. The examples you site as proof electronics can survive direct lightning strikes are Faraday cage protected. If you want to know about telephone companies being wiped off the air due to direct lightning strikes, just do a simple Google search. There are MANY incidents.

The information given is well documented and real world proven.

Rcaman
Telesystems: Grounding (as some have described) is essential and defines hardware protection. But what others have posted does not completely describe what you must understand to have a useful answer. Some cite another's facility as if it proves they also know what those others know.

One cites a Faraday Cage while completely ignoring what should have been obvious. Described by proper earthing and current flows were the basic concepts of a Faraday Cage. If he understood what I had posted, then he understood I was discussing what makes a Faraday Cage effective. He did not understand I had posted 'Faraday Cage' concepts.

Appreciate these concepts are mostly unknown to electricians (technicians). Electricians are taught what must connect to what mostly for human safety. Concepts relevant to your questions include impedance. Electricians are not taught about impedance. Or why metallic conduit, sharp wire bends, and longer wire increase impedance. Even wire thickness is mostly irrelevant to impedance.

Fundamental to protecting a KSU is to identify how a surge connects to earth. Earth the surge; not its victim (KSU). Chassis bond (safety ground to meet UL or NEC requirements) is irrelevant. Hardware protection is about a current that does not enter a building (to duplicate what a Faraday Cage does). When a surge does cause damage, then professionals eliminate the human mistake that made damage possible. hbiss introduced some of this. Others do not even know that proper earthing routinely makes direct lightning strikes irrelevant. One even invented a mythical number (billions of volts). Remedial efforts focus on correcting the only and most important component that must exist in every protection system - single point earth ground.

Yes, ground redundancy can be part of a solution. As long as it does not violate what is important - single point ground. Protection is a building wide solution. Protectors adjacent to a KSU can even make damage easier for many reasons. Including no low impedance connection to earth.

Significant useful information can be provided if asked for. Some of that was summarized in what was only an executive summary. No reason to provide relevant details for others who only want to deny, attack, contradict 100 years of well proven experience and science, and who do not provide specific and useful recommendations. Protection is always defined by the most important component in every protection system - single point earth ground.
Posted By: 1864 Re: Grounding of KSU's directly to the cabinet - 03/22/14 05:09 AM
Westom, You should of named yourself, "Mr. Ground"
This is still pinned in Outside wire construction and after a quick read I'd still say it's still pretty spot on.

Everyone's opinion has value, but proper grounding and bonding can save you and the customer some bucks. We've all learn a few tricks and experience is worth it's weight in gold.
Ok guy's...Been watching this thread and everyone all has some great ideas as to what happens with power/ground ! But now were starting to question each others knowledge and turn it into a wizzing match...Let's try to keep it on the topic and not on each other if we can..That's what the forum is for to learn..heck I can argue with my wife..:-)

Thanks

...bob...
Why do some manufacturers not put grounding lugs on their KSU. Like x16. Is it because they do not need them?
That's probably fodder for another topic so we don't hijack this one.
© Sundance Phone System Forums - VOIP & Cloud Phone Help