Generator Grounding [RE-wrenches]

[allan]

>Wrenches,
>Travis wrote:
>Don't ground the contractor specials unless its with the ground carried in
>the SO cord you are plugging into it?
No.  Ground the chassis to its own ground rod, which must be far enough from
anything else in the home system, or anything connected to the home system
ground, to prevent someone from touching both grounds at the same time and
completing a ground loop between the two bonded systems.  The point is to
treat the generator as you would treat a separate outbuilding (referring to
Wiles' discussion in HP72.)
>
>What are we calling "contractor specials"?  Wouldn't this be pretty much
any
>generator with plug ins?
Pretty much a good distinction.  You could also figure it as any generator
where the AC output neutral and chassis ground are internally bonded in the
unit and can't be easily separated.
>
>When is it appropriate to use to multiple ground rods (not bonded
together)?
See Code Corner in HP72 and 73.
>
>For example the 48 volt array is 200' from the house and a non contractor
>generator is 50' on the other side of the house.
See Code Corner in HP 74.
>
>Do you pull a ground out for the array neg. or do you bond the DC neg. to
>the ground at the house.
See above item.  To some degree it's your choice, depending on several
variables, including wire used, lightning risk, length of run, AHJ
preference...
>
>If you don't pull a ground wire out to the array is it OK to drive a ground
>rod for equipment ground purposes only at the array and not bond this
ground
>to the house (AC) ground rod?  Assume you are not bonding the array neg. to
>the the equipment ground at the array.
Not per code, unless you provide branch source circuit overcurrent
protection on both + and - conductors.  (Less certain on this--other
wrenches?)  In real life, as opposed to code compliance, I would probably do
it at 12V, hesitant at 24, and not at 48--you can feel a fault at 48V.  I
prefer to run a ground wire from the system, and something like bare #6
stranded in the trench, to help make a good earth ground in our dry high
desert soil.
>
>Now you pull 3 wires (2 phases and a neutral) out to the 240 generator.  On
>this gen. is a equipment ground lug.  Do you drive a ground rod for this or
>should you have pulled a 4th wire out for the equipment ground?
4th wire to ground rod on internally bonded units, with only the three
current-carrying conductors heading elsewhere.  On gennies where the bond
can be floated, take all four wires (with neutral and ground unbonded) to
the power system, where the neutral and ground both connect to their
respective buss bars, which in most cases are bonded together at one point
only (that is, one DC- to ground and one AC neutral to ground), usually in
the Powercenter or DC disconnect and AC main panel.
>
>I like to hear how ya'll do it?
Grounding on multiple-source systems like PV systems is grossly more complex
than simple grid source-to-load power.  It has reduced skilled electricians
to quivering masses of jelly.  Seriously, the confusion is understandable;
don't kick yourself.
Wiles is pretty good on this.  By the way, he's better to talk with on the
phone personally than in front of an audience--less intimidating, less
abusive.  I have gotten some good common sense answers to problems I have
faced, even some practical solutions that aren't to the letter of the code.
If he gets that you're trying to do the right thing, he's quite helpful.
He's even gone to bat for us when our local inspector was interpreting part
of Sec. 690 wrong and took it to the state head honcho.  He's pretty
accessible at 505 646-6105.  I think his "Suggested Practices" book (based
on the '96 code) is still available for free from Sandia Nat'l Lab, at 505
844-4383.

Allan at Positive Energy
>
>

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