atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Telecom Service & Providers pedestal grounding

Was wondering if somebody could explain how to tell if there is a good ground on the telephone pedestal. We have excess humming on our cables, and we believe its bad grounding. We just dont know which ped it is. Is there a piece of equipment that can tell us this, like a fluke loop tester or what??? Thanks in advance

Kevin

The only way I know is to test it to the pedestals ground bar with an ohm meter to a known ground, like driving a rod or just driving a screw drive in if you have good dirt, you want close to zero ohms. Having said all that if you have noisy pairs proven at the DEMARC report it to your local phone company, that's their responsibility.

Hum on the lines are usually caused by excess bridge tap, unbalanced pair, power induction or ground on one side of the line.

I should have prefaced this post by saying, i am new to the telco business. There are two of us that are techs in a small telco and we are both new. That is why i was wondering what would cause excessive hum on the cables. We believe that most of the pedestals do not have ground rods in them. Example when i use my headset and put the leads on a pair of lines i hear hum, but when i touch the leads with my fingers the hum goes down considerably. Does that mean a grounding issue with cable.

Not necessarily, when you touch the leads you're changing the impedance of the cable. If there is no grounding at all that could cause power to be induced into the cable. All you can do is test them as described with a volt ohm meter.

I'm going to move this topic to Telecom service and providers.

Welcome to the board.

A Sidekick T&N or 7B could find a (un)grounded cable pair easily. I would assume the metal chassis of the pedestal could be considered a ground. Clip the green lead onto an earth ground (if there is one, or the metal chassis), then clip Sidekick Red lead to Red wire, Sidekick black to Green wire, then put meter to Stress mode. Then lift either the Red or Green lead. The stress meter should go to ~80dB if the cable pair is properly grounded. Further test by driving a screwdriver or small spike into the ground, clip your Sidekick's green lead onto it, then repeat the test.

A constant hum can also be an imbalanced cable pair (i.e. one side, tip or ring, is longer than the other side). The T&N can test for this in Kick mode (I don't think the 7B has the Kick mode). Lastly, hum can also be caused by AC inductance due to really, really long cable pairs, like ones you find out in the rural country parts. Not a lot you can do there (if I am not mistaken) except put load coils on the line or get the LEC to feed you from a closer SLIC or Remote Terminal if one is available.

The most common cause of hum is PF and improper grounds. If there is a difference in ohms between the cable bond or pedestal ground and the building electrical ground, you will have hum. You need a VOM and you need to connect it between the electrical service equipment ground (either a green or bare copper wire) and the cable bond or pedestal ground. Anything above .1 ohms needs to be corrected.

Rcaman