Driven ground at each machine [Archive]

Minuteman

10-23-2007, 08:57 AM

Large industrial plant has a old 200HP air compressor and a air dryer. We are installing power to 3 new 50HP compressors and a new dryer. 480v using EMT. The manufacture of the new compressors sent out a guy yesterday to program the units. He notices that I am installing a EGC in each conduit (per local amendment) and says that it is customary for each unit to have a driven ground rod. What??? :confused: I have never heard of this.

The new machines are in a old metal building. There are under slab piping everywhere.

masterelect1

10-23-2007, 09:00 AM

He is 100% wrong.

Minuteman

10-23-2007, 09:15 AM

He said that it is standard practice in Texas. (Go figure).

masterelect1

10-23-2007, 09:19 AM

He said that it is standard practice in Texas. (Go figure).

Unless he's the AHJ, he cannot enforce what he is stating. There is no code requirement for a driven ground rod at these locations. The EGC is sufficient.

bradleyelectric

10-23-2007, 09:24 AM

Did he show you any paperwork stating this?

TOMWELDS2

10-23-2007, 09:25 AM

is he just looking for an isolated ground to protect his electronics?

Minuteman

10-23-2007, 09:25 AM

No - he is not the AHJ, but he does have the ear of the Plant Manager. The PM acts as if WE missed something. I told the PM that we could install them with a change order, but I need to see a accurate marking of the piping locations first and that even then, we would not be responsible for any damage to what is beneath the slab.

Minuteman

10-23-2007, 09:27 AM

Nope, no paper work. I think I will quiz him about the isolated ground. That might be his concern. :rolleyes:

ITO

10-23-2007, 09:31 AM

He said that it is standard practice in Texas. (Go figure).

He would be 100% wrong here in Texas too.

LawnGuyLandSparky

10-23-2007, 09:31 AM

>snip<The manufacture >snip< sent out a guy >snip< says that >snip<
blah blah blah.

'nuff said.

zbang

10-23-2007, 12:56 PM

He notices that I am installing a EGC in each conduit (per local amendment) and says that it is customary for each unit to have a driven ground rod.

I love these customs :grin:. Since I'm a rabble rouser, I'd ask him when he's taking you to lunch, since 'round here, the mfg's rep always takes the electricians to lunch after the installation. Save some pie for me :D.

petersonra

10-23-2007, 01:00 PM

It used to be pretty common for machinery makers to specify a ground rod at the machine. Never could quite figure out why, but it was very common.

infinity

10-23-2007, 03:14 PM

Supplementary ground rods for machinery are somewhat common. They are not required by the NEC but might be required by the manufacturer.

http://www.mikeholt.com/onlinetraining/page_images/1004224701_2.gif

stickboy1375

10-23-2007, 07:33 PM

Supplementary ground rods for machinery are somewhat common. They are not required by the NEC but might be required by the manufacturer.

I'm very curious as to what a manufacture is trying to accomplish with this supplementary ground rod?

infinity

10-23-2007, 07:44 PM

I'm very curious as to what a manufacture is trying to accomplish with this supplementary ground rod?

I don't know but it's sometimes called, as Mike's graphic shows, a signal reference ground and they're not that uncommon. So IMO the guy making the request was not 100% wrong since supplementary electrodes do serve some purpose.

stickboy1375

10-23-2007, 07:46 PM

I don't know but it's sometimes called, as Mike's graphic shows, a signal reference ground and they're not that uncommon. So IMO the guy making the request was not 100% wrong since supplementary electrodes do serve some purpose.

Whats a "signal reference ground"?

infinity

10-23-2007, 07:50 PM

Whats a "signal reference ground"?

You got me.:rolleyes:

Minuteman

10-23-2007, 09:27 PM

Okay, we finished today and the Plant Manager & the Plant Engineer dropped in to look things over. I asked the PE about the supplementary ground rods. He was didn't see the need, and thought it might set up a "floating ground" situation.

Pierre C Belarge

10-23-2007, 10:10 PM

They want them for lightning purposes...come on where have you guys been... I know you were absent for that class..probably driving ground rods that day and you were too tired for class. :D

brian john

10-23-2007, 11:44 PM

Only issue I see is IF HE IS THE MANUFACTURES rep and he request if it and DOES NOT violate code, machine goes bad for any reason he has a finger to point at YOU for not following their SPEC that was clearly explained to you.

Other than that I see no benefit.

Minuteman

10-24-2007, 12:06 AM

Brian, I hear you, but he only said that:
it is customary for each unit to have a driven ground rod.
Also, the Plant Engineer doesn't want it. However, I would be glad to install them, as long as it is understood that I am not responsible for anything under the slab that might be damaged by me driving the rods.

But hey, sign me a change order, I can use the money. :D

Minuteman

10-24-2007, 12:11 AM

http://i242.photobucket.com/albums/ff264/minuteman_photo/10-23-07_1815.jpg
http://i242.photobucket.com/albums/ff264/minuteman_photo/10-23-07_1814.jpg

Thought I would include some pics.

boboelectric

10-24-2007, 02:27 AM

WRONG, Like the isolated grounds they made us put in ,a separate rod.

George Stolz

10-24-2007, 08:24 AM

He notices that I am installing a EGC in each conduit (per local amendment) and says that it is customary for each unit to have a driven ground rod.
The way you said this, it almost sounds as though he didn't want the EGC - perhaps not an EGC at all - and if my paranoia is anywhere close to the truth, that rep scares me. http://www.fadzter.com/smilies/image004.gif

Minuteman

10-24-2007, 08:46 AM

George, that was my impression as well. Kinda like he didn't want the EGC. He is comin' back Thursday to "fire up" (his words) the Air Compressors.

I love these customs :grin:. Since I'm a rabble rouser, I'd ask him when he's taking you to lunch, since 'round here, the mfg's rep always takes the electricians to lunch after the installation. Save some pie for me :D.

I'm gonna show up for more than lunch and pie. I wanna know more about this dude's notions on grounding. :confused:

FNCnca

10-24-2007, 09:44 AM

I know of a large CNC machine manufacturer that will NOT startup a new machine if it has an EGC attached. They require rods only. They will claim that having an EGC will void your warranty. Service techs will cut the EGC before turning on the power for the first time.
I do not know what their problem is with an EGC, but they do not want them.

Unfortunately, the company I worked, for did not see this as a problem, so it was done per the manufacturers specs. The minute their field techs left the building, we hooked up the EGCs.

How common this is, I don’t know, but it does happen.

I have not dealt with this machine manufacturer in 10 years, so I do not know if this is still their practice.

Minuteman

10-24-2007, 10:08 AM

This is from the local supplement to the 2002 NEC

250.118 is hereby deleted and the following language is substituted:

All raceways or cable assemblies shall include a green or bare equipment grounding conductor. Said conductor shall be bonded to all non current carrying metal parts of the electrical system.

So, he best not be cuttin' my green wire!:rolleyes:

masterelect1

10-24-2007, 08:50 PM

They want them for lightning purposes...come on where have you guys been... I know you were absent for that class..probably driving ground rods that day and you were too tired for class. :D

Are you serious or is this tongue in cheek-- If he wants a lightning arrestor system then he needs to reference NFPA 780.

The last thing I would want in life is to be operating the machine that takes the full brunt of a lightning strike because the facility has no LPS in place>