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History of Grounding

Merry Christmas
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karl riley

Senior Member
Re: History of Grounding

Bennie, I will follow the results of your research. It's easy to get sidetracked, so I like your idea of ferreting out why 25 ohms first. It might have been related to how much loss was tolerable back then with earth-return transmission systems. Nowadays the specs require much lower impedance for the many SWER (single wire earth return) distribution systems in use in Australia, NZ, S. Afica, Alaska, Utah, etc. They loose a lot from the impedance and are justified only because of the savings on installation.

But let's not mix this up with the use of local grounding at buildings as a "safety" measure. They are two separate involvements of the earth.

Good luck on your research.
Karl
 
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pierre

Senior Member
Location
Westchester County, New York
Re: History of Grounding

Hello Karl

Could you expand on your last paragraph, maybe provide some more detail.
(I mean this in a friendly sort of way, it seems of late people are taking some of the comments in the wrong way)
I would like to know more

Thanks

Pierre

BTW - Bennie the NEC Digest is free, maybe you could become a contributer!! The future info is kind of cool.
 
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bennie

Esteemed Member
Re: History of Grounding

There was two types of dynamos in the 1890's. Constant pressure(voltage), and constant current.

The constant pressure system won the competition for the final and present standard.

The constant current system was used with the earth return concept.

A 1200 watt load at 120 volts would be 10 amps. This would be 12 ohms resistance, add 25 ohms earth resistance, makes 37 total. 37 times 10 equals 370 volts. This is the pressure required to have 1200 watts of power.
Figure the wasted power and it is easy to see why this system was discontinued.

I am not stating that this was the origin of the 25 ohms. I will continue to search for documented evidence.

[ June 16, 2003, 06:16 PM: Message edited by: bennie ]
 
K

karl riley

Senior Member
Re: History of Grounding

Pierre,
The use of grounding electrodes to conduct neutral return current over miles to the originating transformer is different from the use of an electrode to conduct lightning strikes and high voltage surges to ground.

If the 25 ohms originated from earth return systems in the early days of transmission, it would not make sense today as a reason for 25 ohms in service entrance grounding electrodes.

Did I answer what you were asking?
Karl
 
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bennie

Esteemed Member
Re: History of Grounding

The only conductor that is solidly connected to earth is the multi-ground neutral. The active line conductors are connected to the earth through the lightning arrestors, or MOV's.
Why can't the MGN be connected to earth the same way?

I don't think 25 ohms, or 50 ohms, will make a difference to transients.

I am thinking more towards the 25 ohms or less as originating with the SWER systems. I will try to substantiate my thinking.

[ June 16, 2003, 09:22 PM: Message edited by: bennie ]
 
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