[AT] grounds

[charlie hill]

Dudley,  I think I can tell you the reasoning but I can't explain the answer 
as I don't understand it myself.  The problem is the posibility of a 
"potential difference" between the two grounds.

When you do safety training on industrial sites one thing that usually comes 
up is what to do if you are running a piece of equipment that comes in 
contact with an energy source (power line, etc).  They always instruct the 
operator that if they must leave the equipment to hop down to the ground 
with both feet together and not touching the equipment.  Then hop away with 
both feet kept together at all times.
The reasoning is that if there is a difference in "ground potential" along 
your path that with your feet together you are in the circuit at one point. 
If they are apart or if you touch something with your hand then the current 
might try to equalize through you, using you for a ground conductor in the 
same way my furnace and bath tub were doing in my other post.  At least 
that's the way I understand it.  I think that applies to the two ground 
rods, however I would not have thought it would be a problem for 100 feet 
or even 20 feet unless you were dealing with extreme high currents.

Charlie
----- Original Message ----- 
From: "Dudley Rupert" <drupert at premier1.net>
To: "Antique tractor email discussion group" <at at lists.antique-tractor.com>
Sent: Monday, December 17, 2007 4:20 AM
Subject: Re: [AT] grounds


> Warren,
>
> I am not suggesting at all that you doubt your' friend but I am curious as
> to what his reasoning would be for advising you not to connect the sub 
> panel
> in your' shop to its' own ground rod ... or at least this is what I think 
> I
> hear you saying.
>
>
> I wired the house I am living in with 400 amp service (this is more like
> commercial than the typical residential service) and then ran 3-wire 240
> from the house down to the barn and put a 100 amp sub panel there with the
> ground lug connected to a ground rod (and, of course, to the neutral wire
> from the house panel).  This was permitted/inspected but it was thirty 
> years
> ago so maybe something has changed since then.
>
>
> I did redo the main entry service to my daughter and SIL's place this past
> summer.  The main house has the 325 amp service coming in from the road. 
> I
> don't know if the 325 amp service is available all across the country or 
> not
> but for little more $$ than it costs for a 200 amp service (particularly 
> if
> you've got dad providing the labor for coffee/sandwich/cookies) you've got
> closer to a 400 amp service than 200.  Their guesthouse, shop and barn 
> each
> has its' own sub panel and grounding rod and is serviced by 3-wire 240 
> from
> the main house.  This was permitted/inspected as well but as I wasn't 
> there
> when the inspector came I can't say for sure that he would have even 
> looked
> at the service to/at the "out buildings" as I applied only to change the
> main entry service.
>
>
> I can think of three or four other inspected services I've done where I've
> installed a sub panel/grounding rod (in addition to the main service) but
> none within the past ten years so that bit of history/memory is of no 
> help.
> My copy/edition of the NEC is thirty or more years old so it's of no help
> either.  In conclusion I guess I've just been trying to give a bit of my
> thinking as to why I am wondering at what your' friend told you regarding
> not installing the ground rod at your' shop but I am most likely the one
> that's got some new learning to do.
>
> Dudley
> Snohomish, Washington
>
> -----Original Message-----
> From: at-bounces at lists.antique-tractor.com
> [mailto:at-bounces at lists.antique-tractor.com]On Behalf Of Mogrits
> Sent: Sunday, December 16, 2007 10:24 PM
> To: Antique tractor email discussion group
> Subject: [AT] grounds
>
> This is all anecdotal but nevertheless:
>
> I have a 10kw briggs powered generator with a grounding lug on the 
> generator
> housing. When I use the genset to power the house I connect the 
> houseground
> to the generator by a copper wire I leave connected and coiled up just 
> below
> the house service.
>
> When I built my shop a few hundred feet from the house and wanted to power
> it from the house service instead of a separate meter I asked my 
> electrical
> engineer friend about installing a ground rod and he advised me to NOT
> separately ground the building. He says the ground should come from the 
> same
> source as the power, so I ran four-wire mobilehome service cable up to the
> shop.
>
> Warren
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> 11:29 AM
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