center screw on phone junction block grounded ... why?

[Chip C]

In my house the phone wires come into the basement (from the externally-mounted demarcation box) to a junction block that looks like this one:

(This isn't mine, it's illustrating an unrelated post that I happened to find. It's also referenced here: On mine, the phone wires are joined under the outboard nuts. On the one in the picture, there aren't any phone wires. But on this one, as on mine, the centre screw is grounded (on mine, to the copper water pipe, near where the electrical service is grounded).

But the block is of some composite material and there is no obvious connection from either wire terminal to that centre screw. So what the heck's the point of grounding it?

I'd like to remove, or at least relocate, this block and modernize the phone cabling.Are devices like this still current? If not, what's the "current" correct replacement device?

Thanks,

Chip C Toronto

[George]

If you backed out one of those screws you would find the obvious connection. There is a carbon spark gap under each screw.

Those carbon spark gap protectors are still in use for old inside demarc points.

[gregz]

The old phones had the third wire ground, go to the phone. To my knowledge, new phones don't use it locally. I used to put movs from two outer to ground for protection.

Greg

[gfretwell]

That is the old style surge protector. It was good enough to save a POTS phone that was not connected to anything else. Some telcos swapped the carbon protectors with gas protectors (under the screws George was talking about) but if you have anything electronic hooked to the phone line, you need more robust protection, connected to your electrical service grounding electrode

[gfretwell]

>

The 3d wire (yellow) was for selective ringing if you had a party line. Pay phones did use a ground start tho. The trick was that you shorted tip to ground and you got a dial tone without a coin drop. That is why phone cords got armored and the mikes got the waffle cover. The handset caps were glued on.

[Robert Macy]

that ugly thing serves a function, don't remove without replacing with 'better' setup.

[trader4]

+1

[LdB]

That block is called a Lightning Arrestor. The name is self explanatory but if you want to know more see

LdB