ECN Forum Forums Code Related Discussion NEC & other Code issues Sub-Panel

Don we woulds have loved to be able to talk customers into fiber but it ain't happening in the point of sale or PC world. It is not lightning itself that we were protecting against. It is just the ground shift and transients induced by lightning. I guarantee your problems between buildings will drop to close to zero if you pull a 8ga copper (it could probably be as small as 16ga), along with the LAN cable and bond the machine frames together. Also add ferrite beads to the data cables and the normal point of use protectors.

We were frying PCs and servers almost every afternoon here until we started doing this.

It became a standard for one major hotel chain after we proved it worked.
At the time we were ready to pee on the proverbial spark plug if we could stop this problem. Later the same principle got applied to a big insurance company's remote printer (RS422) and a major retailer's cash registers (IBM "S" loop).

I hear and understand you, I was just laying out the NEC rule as it applies to a separate building.

I never said it made sense.

I don't understand what "doesn't make sense".

You are trying to establish an equipotential grounding grid within a building. If you parallel neutral current in there it will see the voltage drop (actually "rise") on the EGC.
An example. Lets say you compute a VD (rise) on the neutral conductor in a sub-panel 100' from the service panel at 3 volts. Now if I used the neutral at that distant sub as the EGC the case of my equipment would be 3v above the potential of building steel. If I pulled an equal sized EGC and bonded it the rise would only be 1.5v but that is still not a good thing.
If this sub panel was bonded to building steel the steel becomes part of the neutral path, still not a good idea.
Once you get to another building, with no parallel paths you can start over with a new "ground". It will probably be a different level between buildings but if you don't have any other paths, who cares?

In the data world we had a parallel path and it was going to be the thing that resolved "ground shift" differences. Buy a few routers, LAN cards or system boards and a fat copper wire starts looking pretty cheap.

IBM was very careful to make the wire black and call it a "drain" so we didn't kick the article 250 tar baby.

What does not make sense is the invisible line drawn at the service disconnect switch.

On one side parallel paths are plentiful and required on the other side they are a violation.

Can you explain how this makes sense?

gfretwell,
With the price of media converters about $250 a pair and fiber about the same as plemun or wet location CAT-5, I bet what you are doing is very close in cost to using a fiber link, assuming that you are using Ethernet communications. Also I have been seeing a lot of wireless ethernet for point of sales terminals this year.
Don

Because the Service Disconnect tells the Electrons flowing through it, not to wander away from each other, and if they do (such as in parallel conductive pathways), the Service Disconnect gets mad and pouts all day.

The key problem here, is that the Service Disconnect has some minor control issues, and really should see a Counselor about it before things turn very ugly.

(quoted from an article that was produced by the newly founded "Co-Op"- between the IEEE, and the American Board of Professional Psychologists - the "AKA ABPPIEEE - EI,EI,O")

Man, I really need to get out more

Please do not read this message as an insult, just wanted to make everyone laugh!

Scott35

Don I have been out of it for a while but most of our interfaces were not ethernet. Fiber starts becoming a lot more expensive when you need a "S loop" (twinax, RG62AU or whatever) to fiber converter and then converting back. In fact I have never even heard of one. Fiber, overall, was a lot more expensive 10 years ago.
Stringing an 8ga was not really that expensive. In fact we got the first bunch for free from FPL. They were involved in the finger pointing along with IBM, the building owner, the tennent customer, the server vendor and an electrical contractor.

Bob, would it make more sense if we say the magic line is drawn at the grounding electrode conductor connection?
Everything downstream of that is a pure EGC with no current on it, referenced back to the ground electrode, while the neutral is free to fluctuate at the whim of unbalanced current, harmonics and voltage drop.

No it would not.

I think you may be approaching my question from the wrong side.

I am certainly not saying that parallel paths on the load side of the service disconnect are acceptable.

The question is as Don laid out.

Why are parallel paths acceptable on the supply side of the service disconnect?

That is what makes no sense.

That is true, right now I can buy a 4 fiber indoor cable for about the same price as #8 copper and an outdoor rated one for about twice the cost of the copper. You do have to add the fiber ends at about $12 each. We use a connector that does not require field polishing and you can make the fiber termination is just a few minutes.
Don