Relocating an INT

[Russ]

Ok, I've been testing my cables to relocate an INT that was originally placed very close to a substation.

Here are the readings for the exciter pair that is shorted and grounded at the far end (21Kft).

Ohms, t/r=1K ohms, t-569 ohms, r=565 ohms
Vdc- 0 on tip and ring
Vac- 0 across t&r, 31vac on tip and 31 vac on ring.
Noise= >50db
PI= >100db
Long Bal= 51db
Bal is unmeasureable.

These measurements were taken at the CO with the far end shorted and grounded.

I have a 100pair aerial cable leaving the CO which drops to a 50 pair buried cable. total length of the cable is 21,000 feet. The change in size is located at 11,000 feet from CO where it also becomes a buried cable. It changes to a 25 pair at 17,000 feet from the CO. There is a small power substation at 13,000 feet from CO and a large paving plant at 19,000 feet from the CO. It seems like my readings get higher whenever the paving plant is running.

We have rebonded and grounded all access points and placed more connections to the MGN at all aerial connections. We've also placed ground rods everywhere we could. As the cables pass the substations, we've isolated the grounds, leaving only the cables bonded together. I am unsure the size of the GPR zone around the substation. I am awaiting a callback from my power company. There are also three capacitor banks along the run of the cable.

I have tested several customers along the cable to check their PI and noise. Most of the readinngs are in the range of PI= >100 and the noise is >40. The cable pairs test fine in regards to the resistance.

My fingers are tired and my brain is about to explode.

I'd appreciate any thoughts.

Russ
_________________
Ground is ground, the world around.

[Russ]

Update:

Isn't there a formula for placing an INT by finding the electrical center of the cable run? One of my coworkers said an easy way to find a INT location is to find the center of the AC voltage. Go to the middle of the cable run, cut the pair in half and measure in both directions. If the AC voltage is equal on both sides, put the INT there. If it isn't equal, move in the direction of the higher AC voltage reading and test again.

I'm not sure if this works. Anybody ever try this?

Russ
_________________
Ground is ground, the world around.

[Dave72]

We use SNC stuff, usually..

Some decent application notes here
http://www.sncmfg.com/telecom/application_notes/intapp.pdf

[carbon man]

We put one in 2 years ago along a real sandy area that had almost 80vac on the pairs. Found the half way point for AC voltage and now our HDSL circuits don't go down.

[Russ]

My next step is to find the GRP zone and isolate the grounds within. I've contacted our power company to get these info and the guy I talked to wasn't sure what I was talking about. Kinda scary! He said he would refer my question to an engineer.

Just so I have all the best facts in hand, where is the best place to find info on the GRP zone? I've been looking on the internet and haven't found much. Lots of articles but nothing definitive.

Russ
_________________
Ground is ground, the world around.

[mrfabulous]

Talking about the power company not knowing what you're talking about made me laugh.

Last week, one of our splicer was working near a power company's truck yard. Their supply attendant comes out and says one of the linemen found something with OUR company's sticker on it. Nobody knew what was, so it sat in their yard for months. The power guy asks if our splicer can take it...

The splicer gets back to our yard and shows me what they loaded on his truck with the forklift: An HSR!

Nobody at the power company knows where it came from, or how long ago they actually disconnected it...

BTW, an HSR is NOT a one man lift...

Good luck with your trouble.

[Russ]

I just got the call from the power company engineer and he gave me the 300v measurements I need. He said it would about 400 feet from the substation. I have isolated all the cable bonds but I need to do the same to the buried drops.

My next question is: do I have to isolate the drops at the house too? I will isolate at the pedestals.
_________________
Ground is ground, the world around.

[noisebuster]

Hey Russ. The short answer would be yes. All bonds have to be isolated from earth within the GPR zone.

[Russ]

Next question:

I have a 75 pair aerial cable that needs to be neutralized. Can I use a 100 pair INT? We have a 50 pair INT... if we can't get a 100 pair, can we use two 50 pair INTs side by side? How about our 50 pair and a 25 pair side by side?

I've taken a bunch of readings along the 3 mile cable route. Far end has PI of >100, noise of 30 and my balance won't even register. About 2/3 of the way, I took readings and with the pair cut to the field, I got PI of 94, N of 24 and balance of 71.

I found a spot where the PI was 79, noise was 17, balance was 62. This location was 6 poles from the C.O. According to Keith's book, that is the spot where I should place the INT. However that spot is not the electric center of the cable route.

I eagerly await the wisdom of my fellow troubleshooters.

Russ
_________________
Ground is ground, the world around.

[noisebuster]

Hey Russ. I think as long as you treat the entire cable, you can use the 100 pr, (2) 50s or a 50 and 25 pr. I use to find old cm8 cabinets, gut them and reconfigure it to mount whatever INTs I needed.

[Jim Weston]

Hi Russ,
A couple of thoughts on your issue. I noticed that you mentioned that you have made MGN connections and even added grounds rods along this route; however I have not seen mention of testing the current flow of the cable grounding sheath. I assume you did this? I always start a mitigation process verifing current flow starting at the CO and checking the entire route. This can be time consuming; however you never know if someone else has removed a ground conductor for whatever reason and plain just didn't reconnect it. I have seen this often in Peds and splice points. Some techs just will not buy into the fact that bonding and grounding is that important.
As far as placement of an INT, sometimes I have found it's best to think outside the book. I don't know if you have access to a HumZapper but I use this very often for proper placement of an INT.
You also mention a cap bank and a possible high industral power user along the route. I am curious to know if you have access to a meter such as a "Mitigator" using the exploring coil to help find the problem. I am lucky enough to have both pieces of equipment; however I know that is not the case of all companies. I beleive SNC has a rental program if you think they may help you find the issue.
Good luck
jw

[Russ]

I have done some current flow testing, although not the entire route. As for the Humzapper, I have one but haven't had much luck with it. I wish I could get a Mitigator, but the boss says no.

I used a clamp on ampmeter when I first started testing but the readings confused me. Even when I wasn't clamped around a wire, I was showing voltage. Unfortunately I don't have alot of knowledge in using it.

I wish I could get Keith to visit Maine to assist me. I'd even take him fishing.
_________________
Ground is ground, the world around.

[Dave72]

Depending on the model of clamp on ammeter, your's may be reading small amperage in default mode (ie, low range). Since a clamp-on is meant to measure a field of flowing current.. some do display random small values when not clipped to anything.. just fields around you in the 'air'.
You might have to press a button on it to get to the high range.

If I recall, we're usually hunting flows of about 0.5a (or 500mA) to maybe 4a ?

[carbon man]

I would think 140VAC on pairs to ground would indicate some major power problem. Started dropping as the sun went down and was at 50VAC about 2 hours after dark. Adtran H4's will not run with 140 volts AC. Haven't had time to dig in to it. What is the maximum AC amps that should be flowing on telephone cable sheild?