service grounding concern

[al hildenbrand]

Re: service grounding concern

Wayne,

What's so unusual about three paths back to the transformer?

Admittedly, I'm showing my innercity thinking when I talk about a common metal water pipe system shared by several houses. Several houses that are also connected to the same transformer. But consider my sketch shown on page one of this thread. Looking at House #3, there are five clear current paths. </font>

• <font size="2" face="Verdana, Helvetica, sans-serif">Neutral</font>
• <font size="2" face="Verdana, Helvetica, sans-serif">Ground rod</font>
• <font size="2" face="Verdana, Helvetica, sans-serif">Water pipe to earth connection</font>
• <font size="2" face="Verdana, Helvetica, sans-serif">Thru the water pipe to the next house's ground rod</font>
• <font size="2" face="Verdana, Helvetica, sans-serif">Thru the water pipe to the next house's neutral</font>

<font size="2" face="Verdana, Helvetica, sans-serif">

 

[dereckbc]

Re: service grounding concern

Al, I think Mike and Wayne are just saying there is no minimum. For example what if the building had no water service, or had a delta service?

 

[hurk27]

Re: service grounding concern

Thanks Derrick. I though Al was trying to say there was a requirment that you have to have three path's back to the transformer.

Quote by AL:

The PoCo side of the disco has to have a minimum of three parallel current paths

This is what cornfussed me

 

[hurk27]

Re: service grounding concern

Also how could the earth be required as any kind of path for any kind of current as the resistance would be to high to carry any usefull current to be of any good much less the unbalanced current of the ungrounded conductor.?
And is even forbidden in the NEC. 250.4 (4)

[ February 24, 2003, 06:29 PM: Message edited by: hurk27 ]

 

[al hildenbrand]

Re: service grounding concern

Wayne,

2002 NEC 250.4 (A)(5), right?

Dereck,

I take your point about possible minimum configuration. However, Steve is asking about a single family dwelling with a 300 amp service with three wires, one of which is grounded. Dollars to donuts it is 120 / 240 volt single ? rather than a corner grounded delta. While the forum unspoken digression algorithm would get us to not talking about the original subject, I thought I might stay with it for a change.

Given that there is concrete work implied by the 25 foot underslab run, it is reasonable to assume that another grounding electrode is used, in addition to the two ground rods Steve mentions, even if the well pipe is plastic. Ergo, three parallel return paths.

 

[hurk27]

Re: service grounding concern

Al I'm sorry if this thread has evolved to a different subject. As I was still commenting on the original question, which was about weather or not Steve could run a EGC with the service entrance conductors to the main service panel located 25' away from the meter. In which is where the gec is bonded. but this would be in violation of the paralleling of the neutral. and is not necessary as per the NEC 250.24 as Glen had spelled out in the old forum link and not 310.4 as Steve had thought. and that Steve's understanding that the purpose of this egc is if the neutral were to fail in which case, it would provide a backup for the neutral. And I dont think this is the purpose of an egc as it would not be sized for it. And I still didnt find where any one said that Steve had a 300 amp service? or where I said anything about a corner grounded delta? But I'm sorry for getting things

 

[sjspad]

Re: service grounding concern

Al
look in your profile

steve

 

[wocolt]

Re: service grounding concern

Although these other systems are listed they are really only alternate pathes back to the source, and for Mike, they do indeed parallel the neutral. and since its a 120/240 volt system it is a true neutral.
Why would anyone bond from the main disconnect to the meter base again redundant grounding. the meter base is already gronded by virtue of the Service neutral from the transformer.
If RGS or EMT is used for landing the service conductors to the main disconnect and another copper wire is run along too this is automatically 3 pathes for the unbalanced current, in addition to the water pipe if it exist and the ground rods.
Back to the service, just two pathes via the neutral and steel conduit creates Objectionable current by parallelling the conduit with the neutral due to the main already being bonded to the case.
AS far as I know this type of objectional current is overlooked. As is the current on the water line especially in a city where 10 or 12 houses are on the same water line. No wonder the plumber carry 'Jumper cables'.
However in a sub-panel whrer there is a neutral to case connection made and neutral current is returning on the conduit as well as on the neutral this is objectional.
Parallel pathes and objectional current.

WOC

 

[wocolt]

Re: service grounding concern

I believe that a ground from the panel to the meter would be a violation of 310.4

Why because there would be a parallel pathes ?
What about if rigid conduit is used, between the meter base and the disconect ???) that does too, it also violates 250.6 objectional current. but in my area of Ohio it is acceptable by our inspectors.


WOC

 

[jtb]

Re: service grounding concern

OK, I have read all the posts, and now I am confused.

You have a grounded meter base.

You have no grounding conductor from the meter base to the panel. PVC conduit under slab.

The neutral (grounded conductor) is bonded to the ground (grounding conductor) at the meter.

So the neutral (grounded conductor) is serving as the sole egc and fault current path at the panel, correct? And also carrying the neutral current?

Isolated neutral panel? or not? Something is either not clear to me or fishy here.

[ May 14, 2003, 03:02 PM: Message edited by: jtb ]