phone tech claims bad ground

[Jeff80]

where would I start to look when a phone tech claims bad ground is killing his modems? I looked at the main and all ground connections are up to code. This is a small service 200amp residential.

 

[charlie b]

Look for a phone tech who understands electricity. :roll:

 

[dbuckley]

Right on

 

[M_J_C]

Look for a phone tech who understands electricity. :roll:

What charlie b said.

If that isn't an option, the first thing I would do is take a hard look at the install surrounding the 'modem'.

Is it an external modem i.e., a Cable or DSL modem?

If so, make sure the incoming and outgoing communication wires (coax and/or twisted pair) and the power supply are plugged into a quality (not the cheapest one at wallymart) SPD. If there already is a SPD installed, don't assume that it is working properly, even if it has an 'indicator light' that shows proper operation. These can malfunction and at best only tell you that the power portion is functioning, not the low voltage portion of the protector.

When we do these types of installs I like to use a name brand UPS that has the telco/coax protection built-in, that way all connections to the modem have a single ground reference point for their SPD's and the unit will still stay powered through a short power interruption.

One important note, most power strip type SPD's or UPS's are not listed as primary protectors, the incoming coax should run through a listed grounding block at the service entrance point and the telco usually has their own device located in the demarc box outside the home.

Of course without more info it could any number of other factors...............

 

[Cold Fusion]

I absolutely agree with charlie b -

So, a few years ago, I'm working on the power to a phone system at a relatively remote site. It has commercial power but it isn't very good. The phone system modules plugged into the back board are burning-up/going bad. My phone tech says the backboard is bad and we need a new one. The phone system factory guy says the bad ground is burning-up the boards. He wants to see .5ohm to ground on the +48Vdc. Our phone managers are not going to send us any more parts until we fix the grounding issue.

The circuit feeding the phone system power supply is about 100 feet of #12 to a small ups fed panel. It has it's own green wire in the conduit. In the same room with the phone system is a nice new 5kw ups feeding some servers. I move the phone circuit to the new UPS panel and connect the phone system to a nice new fat copper ground pad in the corner that goes the new UPS, building steel, and even has a few buried radials.

So, we will get the replacement boards since I fixed the ground. I figure the boards will continue to burn up. And we will get our new backboard.

Well, we got the new boards all right - and they stopped burning up

Was it the ground? Was it the different UPS? Don't know.

cf

 

[brian john]

where would I start to look when a phone tech claims bad ground is killing his modems? I looked at the main and all ground connections are up to code. This is a small service 200amp residential.

Ahhh but the money is made in verifying verything is up to code or job spec.Often we are hired not to prove there is a bad ground as is often the claim but to prove everything is OK then the phone tech and his company have to put the effort into determing what the real issue is.

Verify everything meets NEC
Measure for ground current on all EGC, GEC and neutral bond.
Check all distribution panels/MDPs for EGC's terminated on the neutral bars.
Check all SDS (in particular the generator) for proper grounding.

Write report.