atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Outside Plant OSP Construction Bad A/C Humming on cable pairs...Need seasoned vet help!!

Let me start by I work for a phone company. I am getting a terrible AC hum on a bunch of my customers lines. I have tried everything I can think of with no help. I need suggestions because its driving me crazy.

Here the scoop:
Multiple subs in the same area with bad humming on lines. The hum seems to progressively get worse farther down the line. We talking about 3-4 miles from the CO. At about 3/4 miles the hum starts.

Tried multiple cable pairs
Pounded new ground rods at 17 peds along the way.
No load coils (Running off OCCAM blades)
Bypassed peds for a major part of the route with new cable on the side of the road. (Getting desperate!)
Isolated the suspected problem peds and eliminated with no luck

Also it should be noted when pulling off the bonds in the ped you get a spark.

HELP BEFORE I SNAP!

If you're getting a spark when pulling the bond you have a hot power neutral in a joint bonding situation in the cable. A building, joint trench or whatever. I've seen this before in joint trenches where both bond to the same ground source and I've also seen it in a building where the neutral was hot. Remove your bond and read the sheath voltage to a separate ground rod, bet you see AC voltage and it will build the longer it sits without a ground. So don't mess with it, this could be a pretty dangerous situation.

Someone somewhere has connected the neutral to the hot.

TTT's link is for induced voltage and power transducers will correct this. If you hadn't said you get a spark I'd agree with that link. I still feel you have a potentially dangerous situation, which would be my main concern.

Does your employer know what OSHA stands for?

Has your employer issued you, and trained you on, a B-Voltage tester, or equivalent?

Are you a union member?

You can be killed by the situation you describe. You need to stop now, report it, and stay away from those pedestals until your employer sends someone qualified to deal with it (meaning, an OSP engineer who knows how to dial the emergency number for his counterpart at the local electrical utility).

There is a neutral, or a capacitor bank, that's faulty, neither of which should you be required to detect, analyze, test, or remedy.

Been there, done that, survived, and got the T shirt. Good luck and stay safe.

Have to agree with Arthur, your playing with fire here. Be very careful.

Scary! I am sure dnedeau would never have had to go that far in the old Ma Bell days. I remember over and over my Dad (ex Pac Bell) and co-workers (smattering of ex AT&T and ex Bell) drilling into me that electricity kills. I was once on a job with a dead phone and while tracing the wire I saw it going into a conduit with 120V AC! I packed up, explained to the customer this was unsafe. The customer swore we ran it and demanded I stay. I politely declined and left. My supervisor, who was not too bright, called me on the carpet and threatened to fire me. I replied, "go ahead, better fired than dead." The real brains of the organization (da boss) got involved and told the supervisor I was right and to get someone to site to re-run the cable properly. He was old school and had seen someone killed on a site when their metal fish tape came out of a conduit and managed to get into a live open electrical panel at a construction site.

@ Dnedeau - stick to your guns and stay safe! Beats the alternative. If your employer gives you hassle over this, they are not worth your time because they don't care about your safety. There are things out there that kill...

The hum gets louder as you get farther from the CO because of the cable capacitance effect. Your trouble is actually on the entire cable. When you unhook the bond at the peds and get a spark its because the cable bond from the CO throughout the outside cable plant has been broken or corrupted in some way causing a difference in ground potential between the peds and the cable sheath.

Starting at the CO, every splice case, cross box, sac box and ped must be checked for a solid bond and ground.

Shortcut? Look for recent dig ups, construction, storm damage anything where someone got into the cable.

Finally, look for evidence of cable locators. They have a habit of lifting bonds when locating and not reconnecting them.

I'm still thinking a high voltage capacitor bank that has become unbalanced. I would have the telco engineer contact the electrical company engineer and let them sort it out.

Looks like the OP saw the posts and concern, let's hope he heeds the safety warnings.

Go to a ped where you experienced the sparking. Use your 188 B voltage tester or new style voltage tester, if thats what your company uses now, and check for a hot box or ped. If hot walk away and report it. If not, break the bond in and out and using a vom or sidekick or craft interface unit, check all bonds to earth ground and crossbox or ped to ground in and out. All test points should be 4 or 5 ohms or less to ground.

Example: If you check ten points to ground and get 4, 5, 9, 2, 3, 7, 2, 1, 3, 15 ohms I would look at the 9,7 and 15 sections for grounding or bonding issues.

Good responses all. I think Arthur is correct. The power utility is "supposed" to have a ground wire down every pole and pad that has a transformer or capacitor bank on it. I have been involved with multiple cases of a transformer ground being broken, especially close to a PIC pole splice, and the exact same condition you describe occurs.

The spark is your clue. If you are in a rural area and you don't have access to an OSP engineer, you can determine where the fault starts by lifting the bond at the CO and measuring the voltage between CO ground and the sheath bond. It should read very low, near zero. Next, take a resistance reading from sheath bond to CO ground. That reading should be very low, certainly nothing over 1 0r 2 ohms.

Then, go half the distance to the "spark" bond, again lifting the bond and taking readings. If the bond ground was good at the CO, you will eventually come to a point where you will see a large voltage between the sheath bond and ground, moving from good to the "spark" looking for the jump in voltage. I would say that you, most likely, will find signs of digging, a pole or transformer replacement or vandalism. Remember, if you must do this on your own, use appropriate safety measures. Wear gloves, insulate yourself and never, ever mess with the power utility's equipment. If you see the problem, report it immediately to your supervisor AND the utility company. Make sure they understand this is a life safety issue. Be safe.

Rcaman

PS: When you clear the trouble would you please post your findings.

Thanks.