Grounded Neutral systems 2

[drknexus02]

well i am having some confusion as far as what the NEC requires for grounding your neutral on power distribution systems...
250.2 A (5) EFFECTIVE GROUND-FAULT CURRENT PATH-
Electrical equipment and wiring and other electrically conductive material likely to become energized shall be installed in a manner that creates a low-impedance circuit facilitating the operation of the over-current device or ground detector for high-impedance grounded systems. It shall be capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur to the electrical supply source. THE EARTH SHALL NOT BE CONSIDERED AS AN EFFECTIVE GROUND FAULT-PATH.

now the way i understand that is that Neutral should not be connected to ground because the only reason you do that is for ground fault-paths for overcurrent conditions or for disharmony within a transformer or genset. but there are also regs like 250.184B and C. can someone clarify this for me?

 

[rbulsara]

Your understanding is incorrect. Read the whole Article 250 not just a few paragraphs. It is all in there. There is no point reiterating whole article here. If you do not have it, get the NEC Handbook which has explanatory notes and pictures.

It appears that you haven't grasped the concept of system grounding and you need to take a few classes or sit down with a good electrical engineer friend.

Rafiq Bulsara

http://www.srengineersct.com

 

[drknexus02]

the only reason i mention this is because i have worked with comm equipment and we always let the neutral be isolated from ground. mind you there were varistors connecting ground to neutral but the bonding plate was removed. that was the requirement for their equipment due to the K-Factor by type of Load they fell on.

 

[drknexus02]

i have been considering going to the grounding and bonding class NFPA 70 so they may be able to explain it to me

 

[rbulsara]

While it is always good to learn, key to success in life and career is that let the professionals do their work. While you are good a comm. side (inside an electronic device), let a power engineer handle the power side (outside the comm box).

You may also want to look up IEEE Std. 1100. Recommended practice for grounding sensitive electronic equipment and systems.

Rafiq Bulsara

http://www.srengineersct.com

 

[waross]

In all properly installed and inspected comm aqnd data systems, the power guys have learned not to waste time trying to educate comm types. We wait until you leave and make the system safe and code compliant by connecting your ground bus to the main system ground bus. This has probably saved the lives of a number of comm types over the years.
As well as providing a low impedance path to ground, grounding also establishes equi-potential zones. Your isolated neutrals often defeat the establishment of equipotential zones and create dangerous situations.
I have never heard of a comm, data or instrument problem caused by installing proper grounds. Most comm types are pretty narrowly focused and do not even realize that the power people have brought their equipment up to code.
If you go back about half a century, when POS data systems were coming into use, the data guys made a foolish assumption. They had problems. They then made further false assumptions as to the cause of the problems.
Not good engineering.
Had they chosen top check the electrical code, they would have found that the original installations were in violation of the codes. Had the original data installations been designed to be code compliant we would probably not have isolated neutrals today.
Try it the right way. You may be surprised to find that a code compliant installation DOES NOT cause the problems that an isolated ground is supposed to avoid.
By the way; The original issues were caused by comm types trying to save one data conductor.
Why am I wasting time trying to help a comm type with safe and effective grounding methods?


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[drknexus02]

actually i am a air force power production journeyman. the problem that i have is that i have a ground loop in the system. 2+ points where neutral and ground are bound. now what i also have to do is figure out what else is wrong with the system. i admit i am only a maintainer and not an engineer and that is where part of the problem lies. interpretting the NEC is somewhat complex. the equipment i have to maintain and understand are essentually under R&D but are poorly designed. we have had dozens of power supplies for computers to signal amplifiers blow as a result to poor engineering. the engineers i have to deal with are biased because they designed the system and they arent electrical engineers. they specialize in communications, telementry, and aeronautics. i saw this site and i figured this would be a good place to gather data from unbiased engineers.

 

[rbulsara]

Multiple bonding of neutral to ground may not be code compliant but it cannot possibly the cause of the power supply failures. Look for other reasons, such as over voltage, voltage spikes, cheap power supply, overheating etc.


Rafiq Bulsara

http://www.srengineersct.com

 

[waross]

OK I'll cut you some slack.
Your ground loops may not be an issue. Sometimes you get current sharing between a neutral and a ground. The problems that this can create in a large system with ground current protection may never arise on a small system.
Did you know that every properly wired, utility supplied home in North America has ground loops?
Tell us the voltages you have and need in the format that I suggested please.
Also, your transformer creates a serarately derived system. A ground connection at the generator and another at the transformer secondary will not create a ground loop.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[waross]

Contrary to the belief of many comm types, there is more to power systems than a simple application of Ohm's law, and more to safe grounding than a jumper to the chassis.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[drknexus02]

i am not sure about this but i have been doing a bit of reading and is this bond from neutral to ground suppose to be just a cable or a bracket? i was under the impression that you are suppose to use a high impedance resistor or a varistor for that connection. i understand that you are suppose to connect that at some point if not more. but i was under the impression that you had to use a voltage limiting device to attach to your ground grid.

 

[rbulsara]

NO. Read the authentic information like applicable Code books and IEEE/IEC standards.

I hate to be blunt, but you and your employer need a power electrical engineer.

Rafiq Bulsara

http://www.srengineersct.com

 

[waross]

Agreed, Rafiq.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[fsck]

You may be surprised to find that a code compliant installation DOES NOT cause the problems that an isolated ground is supposed to avoid.

First I am NOT advocating improperly grounded installations.

That said, I've seen many a smoked port where what was safe was not what would work, or otherwise made issues. [If "red side" "black side" and KG84 dredge up memories...]

For that reason, I have a mantra I often cite:

Fiber is your friend

Fiber just solves all end of messy comm problems. Ports worship the smoke god every time Mother Nature goes bowling? Crap floating on the data circuit return? Whatever... remember your friends. I can't even imagine how substation/gen plant SCADA systems ever worked in the pre-fiber era.

 

[davidbeach]

I can't even imagine how substation/gen plant SCADA systems ever worked in the pre-fiber era.

The simple answer is that those that worked were designed by power engineers and were sub-optimal comm and control equipment, but very robust. The cr@p designed by comm and control engineers may have been highly optimized comm and control equipment, but would fail on every ground fault.

That said, I agree 100% about fiber solving all sorts of problems.

 

[alehman]

Seriously drknexus, please heed these guys and find a power professional. This is matter of life safety.

As you might guess from the responses, you have struck a nerve. I think you are well-intentioned, but there is a history of communications technicians creating fatalities over the past 50 years.

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[drknexus02]

that is the primary reason that i came here and asked this question. i read a few forums online and they said otherwise. the conclusion i came to here is that i need to simply advise my supervisors and up that we need to redline the system and seek consultation from some form a power systems engineer. well thanks for the help everyone. i am going to do more research and talk to more people to get a what seems to be a much needed better understanding on interpritation of the NEC.

 

[rasevskii]

In the Good Ole Daze, before there were even transistors, It was all done wih relay systems, telephone switching style. At 48, 50, or 60VDC. Telemetering and remote control were all electromechanical. Reliable, slow, and maintenance-intensive. Who ever heard of, today, things like pulse-duration telemetering, once widely used in the electric and water utilities. And pulse-frequency telemetering, using a punched hole rotating disk and photocell on a kwh meter shaft to get the KW reading remotely. Does anyone around know what a Lincoln Thermal Converter did? It converted CT and PT inputs to DC millivolts to get the KW reading onto a self-balancing recorder such as a Micromax from Leeds and Northrup, once a common furnishing in control rooms...

We could go on about all this, but I will spare the younger ones out there.

rasevskii

 

[fsck]

rasevskii:

I started in pipelines; I recall tube-based Taylor PID process controls; it was a big step up from the pneumatic ones!

And we had a North Electric Paracode supervisory system, with relay array A-D converters; units, tens, hundreds, 0/1 thousand PSI. On bad nights, I can still hear them, and I'm not sure I have all the chart recorder ink off my fingers yet.

Is it any wonder I went back to get an EE degree?

 

[drknexus02]

figured out what was wrong btw. i was on the right path and i tore the equipment apart. the neutral terminal strip was grounded out. so i lifted that and kept the transformer and the generator grounded. the line nose is almost non existent now .4V. Thanks for all the advice. because of this and my lack of understanding i might go back to school and become a power systems electrical engineer. would help me a lot now and in the near future. Grounding is far too complicated for a technician to assess.