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Posted by BobK207 on September 19, 2006, 12:54 am
Tom The Great wrote:
>
> >
> >Tom The Great wrote:
> >>
> >> >
> >> >
> >> >If a small diameter ground rod (1/2" or 5/8") doesn't give the 25 ohms
> >> >(or less) to ground.....would a larger (3/4" or 1") diameter rod in the
> >> >same soil do better?
> >> >
> >> >Is the soil the culprit or the soil / rod contact resistance? The
> >> >larger diameter rod contacts more soil..better grounding behavior?
> >> >
> >> >cheers
> >> >Bob
> >>
> >>
> >> IMHO,
> >>
> >> I've found (through discussing with electricians) that soil conditions
> >> have a greater effect on grounding effects, when comparing 1/2 to 1"
> >> rods.
> >>
> >> Remember, if you are concerned about resistance for code, just drive
> >> the second rod. Then you don't even have to check ohms, since even if
> >> you don't have the min, the code only requires a second rod.
> >>
> >> The idea is that everyone grounds the 'neutral' the voltage on teh
> >> grid will be 'stablized' so you are only adding a drop to the bucket
> >> (the grid) and helping your line to your house.
> >>
> >> FYI: Ground rods aren't for ground faults.
> >>
> >> later,
> >>
> >> tom @ www.BlankHelp.com
> >
> >
> >I know that the code says if you fail the 25 ohm level drive another
> >rod 6' away.
> >
> >But I was curious about the variables that effect the performance of
> >the rod / soil system. I also really liked the technique that someone
> >posted as to how to test a ground rod; simple & pretty cool :)
> >
> >Don't everyone jump on me but I'm not a huge fan of codes in
> >general.....they tend to substitute blind adherence for understanding
> >of what's rally going on
> >
> > ie what is the intent behind the code.
> >
> >also having worked on committees I know that codes tend to minimum
> >standards that everyone in the room at the time could live with; either
> >due to lateness or lack of energy
>
> imho:
>
> Codes are designed for safe operation of you electrical system. The
> completion of work below codes is dangerious, and the completion of
> work 'over' codes is just extra money spent. Also, if you don't do
> 'standard' work, another electrician following you will have to
> 'figure out' what you did.
>
> So, depending on who is spending the money, you might be wasting it.
>
> later,
>
> tom
>
> >
> >if one has ground rod that "fails" & puts in another.....conceivably
> >one could still be above the 25 ohm level but still "meet code".
> >
> > I'd rather know that my installation was good & I'd rather know what
> >parameters improve my chances of having a good installtion.
> >
> >that's why I asked if bigger was better.
> >
> >looks like longer is better.... I gues that's the way things go :)
> >
> >cheers
> >Bob
Tom-
I agree with your post about work "over" or "under" code (& the
non-standard stuff potenttially being hard to figure out later, that
should be avoided)
but I happen to know of examples of work when done per code (UBC /
IBC structural stuff) will yield a poorly performing system but it
satisfies the code
Example....with the new wood preservative for sill material the code
allows galv or stainless fasteners.....the perfromance difference
between glav & SS is miles
another example....block wall rebar requirements vary all over the map
( a factor of ~3 low to high) from city to city in
SoCal.....earthquakes do not stop at the city limits
I actually have more faith in the NEC (maybe 'cause I don't know it as
well as the structual stuff)
but if the code wants 25 ohms max to earth but it lets you do two rods
& not test?????......where is the performance in that? It's an
assumption that it's probably "good enough" but it could be pretty
bad, couldn't it?
the code is a minimum standard (like a doctor that just barely passed
med school) I'd rather go a little over code (cost impact is usually
prety small) than "at code".....there might be very little margin if
things do not go as expected
btw independent of who is spending, unnecessary overkill is wasting
money.......money spent for no performance increase or a performance
increase that is "unnecessary"
I tend to use SS fasteners for outdoor applications; IMO SS fasteners
(esp in trim, fence, deck or patio cover applications) are worth the
extra cost. SS fasteners in dry locations indoors are wasting money.
I seen a lot of really nice gates ruined by rust stains from galv nails
when less than $20 worth of SS fasteners would have prevented
it....over kill & wasting money or money well spent
Cheers
Bob
cheers
Bob
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