Phone Line Customer Service Box

[Andy]

Andy asks:

I recently had to have the phone line replaced between the street and the DeMark box on the side of my house.

It would have been a lot easier for the contractor to have located a new DeMark box on the side of the house and taken away the old one ---- less tunnelling under driveways, etc.

I was told that the Demark box MUST be installed at the electrical service entrance and the ground wire attached to the service entrance ground rod...

I suggested just putting in another ground rod at the alternate location instead. I was told this was not allowed --- the Demark box MUST go at the meter service entrance. Both the phone company technician and the phone line subcontractor told me this, separately.

So, does anyone here have any expertise on this ? I'd sure like to see some discussion about this requirement.

Andy in Eureka, Texas

[Bob]

do you want to reinvent the wheel too?

[David L. Martel]

Andy,

My phone box was installed by the phone company, Verizon. It is not near the electrical service box. It has it's own ground rod.

Dave M.

[badgolferman]

It's too late now, isn't it?

[hallerb]

On Aug 27, 8:26=EF=BF=BDam, "David L. Martel" wrot= e:

on. It is not near

ALL GROUNDS MUST BE UNIFIED!! Thats why the want the box by the service entrance. seperate ground rods can create a different voltage on grounded things, like during a lightning strike, that can be dangerous.

thats why phone ground, is unified to main house ground rods, incoming water line with meter jumper etc, even satellite dsh grounds should be part of a unified system

[Bob]

you're screwed!

[HeyBub]

Satellite dish grounds are for the sole purpose of dissipating static electricity. There's nothing electrical about them.

That doesn't mean that some officious slug hasn't mandated that they be tied to the central house ground, but I can't see that it would server any purpose.

[salty]

There is potential (no pun intended) to create a ground loop by using two separate ground rods. Ground is somewhat of a relative term. Soil composition and moisture content are two of the major elements that can affect it. Not all earth grounds are equal.

[Art Todesco]

I used to have a Comcast cable attached to its own ground rod 30' or so from the electrical service entrance. There was a lightening strike on a street light on the street behind me. It followed the power cables to the underground area where electrical, cable and telephone is for my house. Because of the 2 different grounds, we had lots of damage .... computer, modem, router, scanner, garage door radio, X10 stuff, and more. The Comcast guy and the telephone guy all agreed the grounding should all be to a single point, the electrical entrance. I know this is not exactly the same thing, but working for the old Bell System, we used single point grounds in telephone offices to prevent lightening from damaging the switching gear. I should have seen this, but didn't until it was too late.

[Jim Redelfs]

That is correct and has been required by code for many years.

Specifically, telco and CATV services must be bonded to the MGN (Multi-Grounded Neutral) wire of the premise using the SHORTEST length of wire as is practical.

This provides the best "balanced potential" in grounding. It is said that such practice lowers the chance that, in a direct lightening strike, the charge will "leap" from a phone or CATV jack to an electrical outlet. I have seen that sort of damage. It's impressive.

For the BEST service and the best protection from transient spikes (surges), you WANT the SNI/D at the electric service entrance.

For the first, hundred years or so, telephone service was brought into a premise at virtually ANY location. They often used a ground rod (4-ft galvanized!) instead of a water pipe for bonding.

The proliferation of electronic devices (MUCH more susceptible to surge damage than the old phones) connected to the network made common bonding imperative.

[terry]

**Not Bell standard then!

Am very surprised. The various grounds are normally 'bonded' together. In our case the power neutral is grounded as it enters the house and has a ground rod. Also the TV cable service and the telephone protector are grounded/bonded to the same ground. We have also taken care to bond our ground to a buried copper wire loop that sits in the trench above the now abandoned one inch plastic pipe to our unused well. Many years ago our neighbour, had a bad leak to ground from his electrical system. Since our systems were all bonded together we had no problems; but he had some weird voltages floating around the grounds in his house until he cleared the problem! It was a buried entrance to his house that had 'gone bad'. The soil resistivity here is high; so driving a single ground rod is often not suitable. Hence most electrical systems now use MGN (Multi Grounded Neutral). This means that except in the case of certain very high voltage line guy wires everything that is 'ground' should be bonded together and grounded. This includes overhead transformer grounds, telephone and cable TV sheaths, pole line guy wires, telephone sparklightning protectors etc. etc.

[terry]

Right on Art: Spent 40 years (1952 to 1992) in telecomm industry here. Grounding is like a few other things you don't need very often ....... but when you do ..... !!!!! Insurance policy, fire extinguisher, accident help, good neighbour etc. etc. Cheers.

[bud--]

. The NEC requires a wire "short as practical" with a max length of 20 ft from phone/cable entry protectors to the power grounding-electrode-system. (For 1 and 2 family dwellings, if the wire has to be over 20 ft it can be longer with a ground rod near the entry protector.) For phones, even 20 ft can be too long.

Phone people like Jim are likely well aware of this. Cable people, particularly contractors, are more of a problem. .

Can?t imagine.

With a lot of electronic equipment connected to both power and phone/cable, you want to minimize the voltage between power and phone/cable wires. Insurance information suggests the most common damage to electronic equipment is from high voltages between power and phone/cable wires. Having a *short* wire from phone/cable entry protectors to the ground at the power service minimizes the voltage between power and phone/cable wires. The power service is the magic point because neutral and ground are bonded at that point.

With a strong surge current to earth the "ground" at the building can rise thousands of volts above 'absolute' ground. You want the power and phone and cable grounds to rise together.

Art writes about high voltage between power and signal wires. There is an illustration of a cable ground wire that is too long starting pdf page 40 in an excellent IEEE guide on surges:

[Ralph Mowery]

All grounds must be connected together. While the dish ground is to dissipate static and such, it still must be connected to the other ground rods . Lets say it is not. If for some reason the other ground rod comes loose from the house wiring and there is a short that should go to ground and it doesn't , and you decide at that time to plug in the dish , you complete the path to ground and get shocked or worse. Also if a lightning strike is near the house it is possiable to develope a big differance of potentional between the two ground.

[mm]

Didn't my Ademco burglar alarm come with instructions to install a separate ground rod? It's connected to the board and not the power supply, I think to prevent induced voltages from lightning from ruining the alarm.

It would have been a lot easier to just hook up to the electrical ground, but I did what the instructions said.

It's been 25 years but I still have the instructions. I will check later.

[Bob F]

Could they have learned anything new since then?

[Bob]

some of us have. :)

[mm]

Sure, but are you saying that's the reason?

Is the requirement described in this thread that grounds be linked together something that has arisen since 25 years ago?

>

[gfretwell]

It has been in the code for quite a while but buried out in seldom read articles (Satellite and cable grounds were in the 800 articles etc) Things connected to the phone line were never really important until people started buying phone equipment with 120v line cords on it (modems, cordless phone or burglar alarms). When they rewrote article 250 a couple cycles ago (the grounding stuff) it got moved there.

[mm]

Good to know. i'm in the middle of reinstalling my alarm, and I'm redo the ground. thanks all.