25 Ohms Or Bust

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iwire

iwire

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Last Month there was a storm on Cape Cod MA, this caused wide spread power outages. As a result we where called in to tie in three 800 KW temporary generators into three separate supermarkets.

Each unit was a very new trailer mounted Caterpillar genset.

While making up the connections we could not help but notice this sticker.

25OHMS1.jpg


Should we have packed up and gone home?

[ January 01, 2006, 10:24 AM: Message edited by: iwire ]
 
Re: 25 Ohms Or Bust

Bob,
What do you think are the chances that they performed calculations to determine, based on maximum expected lighting surges, that 25 ohms is required to keep the controls operating on the gen :)
I hoped you guys checked with a meter. ;)
 
Re: 25 Ohms Or Bust

It's early...shouldn't the sticker state: At least/minimum 25 ohms to ground?
 
Re: 25 Ohms Or Bust

Another mis-informed engineer that failed basic grounding 101 but somehow recovered to get their degree. There seems to be alot of those running around, not on this of course!
 
Re: 25 Ohms Or Bust

Originally posted by fc:
I would think he would still be there banging away.
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:D

Cape Cod MA is nothing but a sand pile in the ocean. Putting in ground rods is about as simple as it gets, however the sand is basically dry until you get below sea level.

I did a larger building on the Cape and we used a 20' sectional rod which went in very easy and most likely is well into the water table. Never did test it as we had building steel and water pipes as well.
 
Re: 25 Ohms Or Bust

Originally posted by bphgravity: Another mis-informed engineer that failed basic grounding 101 but somehow recovered to get their degree.
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Now be nice to us poor mis-informed enjineeers. We didn't get a class on grounding. Besides, that sign was not a product of an engineering mind. It arose from the primordial soup that comprises the corporate lawyers.

As to whether you should have walked away, Bob. Na worries, mate. What makes you think you have to obey a sign installed by a manufacturer anyway? And please don't say 110.3(B). In general, it's not a bad idea to follow the manufacturer's instructions. But you are only required to follow the instructions that were included in the listing or labeling. And that later term does not mean a sign on the side of the equipment. So if you were to check with the instructions associated with the test program that gained the equipment its listing, I would wager that you would not find a ground resistance requirement in those instructions.

Or am I getting cynical in my old age? :roll:
 
Re: 25 Ohms Or Bust

Originally posted by charlie b:
Or am I getting cynical in my old age? :D

I did not lose sleep over the sticker, although I did lose a lot of sleep doing the jobs.

I had a 25 hours OT on the clock between noon on Saturday and 9PM on Sunday. :cool:
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Re: 25 Ohms Or Bust

Well the substation ground has to be 25 ohms or less, so why not connect the generator ground to the substation ground?

Of course this assumes the customer has actually tested his (or her) ground grid to verify this.
 
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