I running a 70 amp sub-panel to a shop that does have telephone connections to the main house. I know that I need to isolate the ground from the neutral at the sub-panel. I am planning on running 3, #4 wires to the sub-panel and I also have an 8' ground rod, which I will connect as well.

My question is, since I will be using a grounding rod, do I need to run a forth ground wire from the main panel or will the grounding rod be sufficient by itself? If I do need to run a 4th ground wire, can it be of a smaller gauge say, #8?

For a 70 amp feeder, a min of #8 equipment ground is needed, and yes this fourth wire is required, to include the ground rod, or more, driven at the separate building.

The neutral must be kep insulated and isolated at the subpanel, and only white neutrals be connected to the neutral bar. Do not bond the neutral bar in the subpanel to the equipment ground or metal box. The separate ground bar is to be bolted directly to the metal can using machine thread screws, and only have bare or green equipment grounds connected.

Any metal system, water, building steel, etc, in the separate building needs to be bonded to the equipment ground system. The telephone system you mention also must be grounded to the grounding electrode system.

Thanks for the quick response.

I should probably ask one more question about my grounding rod. My sub-panel is located in the middle of my shop. I ran 1 1/2" PVC up through the slab and all they way back to my main panel. Just below the sub-panel, I drove an 8' grounding rod into the soil and brought it up through the slab through a piece of small PVC,just slightly longer than the thickness of the slab. Is this one rod sufficient or should I install a second one, outside, at least 8' away?

Also, how do I properly ground the telephone system? Is one of the 2 wires actually a ground?

Thanks again.

As far as more than one rod being needed depends on the soil conditions in your area. Code requires 25 ohms or less resistance for a grounding electrode. Most are not measured, takes special equipment to measure ground resistance.

Check with your local inspector. Most already know what the local area is like, and know if more than one rod is needed and will help with consulting you. Be ready, as some do not know, or rely on the installer to prove 25 ohms or less, and rely on the installer to know if more rods are needed.

In New England, with the bedrock and rocky soil, most states automatically require at least two rods.


I am no expert with telephone systems. I suspect you may have just run a pair of wires over as a line extension. In this case, no grounding is done. However, typically, an incoming phone line will go through a Demarcation point, in which case contains lightning arrestor that must be grounded to a grounding electrode.

What I am not sure of is if protection is required when entering a separate building with phone lines. It certainly would not hurt, and probably recommended, so as to protect the incoming line from lightning strikes or short circuits that occur in the separate building. I leave Article 800 Communications of the code to the teledata techs, we affectionately call "Tele-Tubies".

"Tele-Tubies"

I like that.

Thanks again for your help,
David

OK, tk, "Tele-Tubie" to the rescue on Article 800! This phone line should have protection on both ends. Yes, he would (should?) have primary protection at the demarc, installed by the telco as part of their NID installation. However, this extension to a separate building constitutes a separate issue--it could be subject to a lightning strike which could back-feed into the phone wiring/system, cooking either the wiring, system, or user. If it were my installation, I'd like to see 5-pin primary protection at each end of this extension.

I didn't dig my code book out on this one, so I'm not sure whether Article 800 actually says anything about this (I think it's kind of silent on this particular detail); rather I've given you the "best practice" from our end of the electrical spectrum. I'll try to do some more detailed checking, but I think this is more of a BICSI standard than an NEC code issue.

Drs--are you aerial or underground with this phone line?

Bill

OK, I just checked and Article 800.90 (A) appears to apply and require primary protection at each end of the interbuilding circuit.

I'm underground. There is a 4 wire cable running to the existing shop. This is an addition to that shop. Two of the wires are used for phone, the other 2 are used as part of an alarm system.

The installer used very good copper, shielded wire to connect the shop to the house. I can ground the shield at both ends. Would that be sufficient?

No, shield grounding really won't do it. I'll get back with some links to the right stuff.

How do you ground VOIP? I don't have a NID. I have a Cisco ATA 186 analog telephone adapter. From it I have the regular 4 wire cable running all over the house with only the red green pair in use.

The ATA has ethernet to a router, then ethernet to a cable modem, and the cable has the jacket tied to the electrical ground rod.

Whole 'nuther issue, labman. Providing your internet is probably cable, perhaps DSL, or if you're really masochistic, 2-way satellite. In any event, cable and phone should have grounding blocks at the NID to either a water pipe or a ground rod, or in the case of satellite, wherever the "installer" chose to put it. This fundamentally covers primary entrance protection. drs72's problem arose from the extension he put between buildings, which provided another point of exposure which needs to be protected. Now, if you've run an interbuilding cable between your house and garage, you need to have primary protection on each end of this extension line. I was taught a method to "roll your own" primary protection by an old telco installer; I won't even print it here because it's so wrong (an RCDD friend of mine almost choked when I told him about it!).