Grounded vs. Grounding (aka Neutral vs. Ground)

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jerm

jerm

Senior Member
Location
Tulsa, Ok
I found an outdoor sub panel today that I believe one of our guys did wrong and I, er, "fixed" it. He happened to drive up at the end of the day and "caught" me working in "his" panel and claimed I was wrong. He drove off in a fit. I don't know which code articles to cite. So I come to the professionals for guidance! :)

There is a 480v feed coming out to a parking lot light pole- besides the regular wires that feed the light I've got two high voltage hots, and the rigid ground from the panel inside the building. This 'additional' feed goes into a little 40 amp 3r transformer (480 -> 120/240) mounted on a nice unistrut frame back to back from a 3r panel that serves some 120v lighting loads outside. There's a ground rod at this panel. [PS The clamp was above ground. Where's the code for that? I'm going to bust some rock and drive it under on Monday.]

First of all, I think the transformer should have a neutral from H2 and H3 back to the building panel. This is your typical H1 H2 H3 H4 transformer where 480 is applied to H1 and H4 and H2 and H3 are tied together in the middle. But I didn't say that because I wasn't sure. The diagram wasn't clear...

Next, the X2 and X3 (low voltage side) are correctly connected together in the transformer to the neutral bar in the panel (X1 to X4 is 240v and feeds the lugs) but he bonded the neutral in the panel to ground. Again, there's already a ground path from the panel to the local rod via some bare copper and it's grounded to the rest of the system via the rigid conduit. (344.60) I say no bonding here because this isn't a service disconnect or a service entrance panel. And now he's got a parallel ground path to boot.

I know, probably asked and answered a dozen times on this forum, but I've only read posts to page 52 or so and I'm not good with the search results. ;)

I eagerly await your future reply!


Jeremy
Tulsa, Ok
 
To add to Bob's reply...Buy him a cup of coffe and tell him on second thought I realized you were RIGHT..Then go back and re-fix your un-fixing
 
jerm said:
Bob - in this post (http://forums.mikeholt.com/showthread.php?t=93001) you said no bonding at the sub panel. How does this differ?
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I would not call the panel in your post a 'sub panel'.

The panel in your post is different because it is supplied from a transformer which means it is a SDS (separately derived system).

Every time you have a SDS you must bond it. 250.30

Essentially you treat each SDS as a service, ground electrodes, bonding etc.

If you feed another panel from the panel in your post you would not bond that second panel.
 
SDS - RIGHT, I got that from 250.30(1). I agree I owe him coffee and will put the jumper back tomorrow morning. I forgot all about separately derived systems.

Should I drive the ground rod underground? It is my job now, he moved on to another project a month ago...

Thanks guys.

Jeremy
Tulsa, Ok
 
jerm said:
SDS - RIGHT, I got that from 250.30(1). I agree I owe him coffee and will put the jumper back tomorrow morning. I forgot all about separately derived systems.

Should I drive the ground rod underground? It is my job now, he moved on to another project a month ago...

Thanks guys.

Jeremy
Tulsa, Ok
Click to expand...

If it is an 8' rod it should be all the way down, I like to use 10' rod just for the perpose of having access to the clamp or clamps if there is data involved.
 
acrwc10 said:
I like to use 10' rod just for the purpose of having access to the clamp or clamps if there is data involved.
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That could well be a violation of the last sentence of 250.53(G)
 
iwire said:
That could well be a violation of the last sentence of 250.53(G)
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The upper end of the electrode shall be flush with or below ground level unless the aboveground end and the grounding electrode conductor attachment are protected against physical damage as specified in 250.10.

Now do you really think I would put it in harms way?:smile:
 
jerm said:
Should I drive the ground rod underground? It is my job now, he moved on to another project a month ago...
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If the ground rod is 10 feet long there is no requirement to drive it in all the way. Just the first 8 feet.
 
jerm said:
First of all, I think the transformer should have a neutral from H2 and H3 back to the building panel. This is your typical H1 H2 H3 H4 transformer where 480 is applied to H1 and H4 and H2 and H3 are tied together in the middle. But I didn't say that because I wasn't sure. The diagram wasn't clear...
Click to expand...

You do not need to feed this transformer with a neutral.
 
ike5547 said:
If the ground rod is 10 feet long there is no requirement to drive it in all the way. Just the first 8 feet.
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But if it sticks out then I have to "protect it from physical damage" per 250.53(G) -- do you disagree?

Jeremy
Tulsa, Ok
 
jerm said:
But if it sticks out then I have to "protect it from physical damage" per 250.53(G) -- do you disagree?

Jeremy
Tulsa, Ok
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If the situation complies with 250.10(1) it is considered protected. Where is the ground rod located?
 
brian john said:
Data involved? Please tell me more.
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Data collection point?

I have had to install grounding electrode system test points outside the building before.

Basically they had a 4/0 bare grounding ring and at a number of point we had to drive a 10' x 3/4" rod in the bottom of a hand hole with a bolted connection to the ground ring.

It was my understanding this was so they could at any time unbolt the grounding ring and place a test on it.

IMO it was more 'voodoo'.
 
Bob:

This went right by me....I have tested a slew of these. Make the test port BIGGER please. Laying on my belly face down in wet grass or worst mud as I fumble with a connector is a pain.
 
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