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Re: Comments anyone?

Hal,
For the most part that document is well written. I still have not been convinced that there is any real benefit in a low resistance connection to the earth.
Don
 
Re: Comments anyone?

I have a question about one of the statements towards the end in the shared neutral section. I realize a lot of electronics manufactures have been lowering the ground to neutral voltage tolerances but .5V seems like a pretty hard goal if the grounding is indeed done correctly. For example: if i had a distribution unit 50 feet away from a rack of computers that required no more than .5V difference that would require a 6awg neutral to support up to 10 amps... Does this sound right or are electronic equipment manufactures trying to pass the liability for faulty equipment?
 
Re: Comments anyone?

I realize a lot of electronics manufactures have been lowering the ground to neutral voltage tolerances but .5V seems like a pretty hard goal if the grounding is indeed done correctly ...
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Properly designed electronic equipment wouldn't care about a voltage between the grounding and grounded conductor.
Don
 
Re: Comments anyone?

I agree completely. Why is it then that equipment would require such a rating? is it a UL requirement to make up for the cheap engineering?
i guess my comment is just that i don't belive that grounding standards should be written to accommodate such low equipment requirements. If microprocessor based manufactures could put a rating of .1V i'm sure they would, but at what point should an electrician stop trying to meet those ratings? things like that will just encourage people to try to short cut the grounding system. in a data center type environment this could be detrimental to the rest of the equipment.
am i way off base here or does anyone else think .5V is asking a little much?
 
Re: Comments anyone?

Originally posted by dave_asdf:
am i way off base here or does anyone else think .5V is asking a little much?
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Is it possible for the answer to be "both"? :D
 
Re: Comments anyone?

By Don: I still have not been convinced that there is any real benefit in a low resistance connection to the earth.
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That is a valid concern.

In high frequency events the resistance of the Earth bond would depend upon the frequency of the event including the rate of rise and time of fall. But in DC to 400hz the resistance to Earth would be important. Like you it seems like they are more concerned about low frequency or DC (which don't pose much of a interference threat) HF events can resonate even on a ground of less than .001 ohm DC resistance, this would put the length of the conductor as being most important in HF events. but that is because at a HF the impedance of that same wire could be very high.
This is where the shorter leads for TVSS units comes from. TVSS events are almost always a HF event.
This is where someone without the understanding of how HF events propagates on conductors tries to write rules or guides to go by.

HF = High Frequency

[ January 06, 2006, 03:18 AM: Message edited by: hurk27 ]
 
Re: Comments anyone?

Originally posted by LarryFine:
Is it possible for the answer to be "both"? :D
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heheh thanks for the reply larry, you're probably right. i get spun up on these types of things. being the only electrician working in a sea of IT guys does that to me.
 
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