Grounding/bonding of a generator with 3 pole or 4 pole ATS

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Limey Pete

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Tampa Florida
I have installed probably 20 100Kw+ generators over the last 2 years for one customer, but his engineering always seem (to me)to randomly choose a 3 pole or 4 pole ATS. As these are all in existing facilities the grounding changes required for a 4 pole ATS can be substantial.
We install these generators all over Florida and most inspectors seem to have different opions as to grounding requirements.

My 2 questions are:
1.Why can we not always use a 3 pole ATS and make use of the provisions of 250.20 (D) fpn No.1?
2. If installed this way whey should I still need to run a ground rod to the frame of the generator ?(as I have been required to in the past).
 
1. The use of a 3-pole or 4-pole transfer switch is a design consideration, and neither is more suitable if all applicable requirements of the code are met.

2. No, unless required by the manufacturers instructions.
 
bphgravity said:
1. The use of a 3-pole or 4-pole transfer switch is a design consideration, and neither is more suitable if all applicable requirements of the code are met.

2. No, unless required by the manufacturers instructions.
Click to expand...


Thank you for your speedy reply Bryan. As I am now submitting my own plans for some generator installs, including on grade slab and fence where permitted, what "Design considerations" should I be thinking about?.
 
benaround said:
Pete,

The four pole ats is normally used on a 277/480vac system that has GFPE

in use at the supply.
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Thank you, I like that explanation, if any of the installs I have done to date had been 277/480 vac I'd be perfectly content now.

EDIT
OOPS! In fact thinking about it; one was 277/480 volt: That was a 3 pole! Oh Well!
 
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