another loose neutral

[telegraphtm]

can someone give me a logical engineering answer to why the shield on the coaxial cable acts as the grounded conductor when a loose neutral connection occurs. The grounding system for this home appears to be in good condition. The copper water line and the supplemental ground rods appear to be solid and without issue. Several coaxial cable outlets burned significantly. I found the neutral connection in the meter socket completely corroded and I assume that is where the open neutral exists. This is a typical 200-amp, overhead service, approximately 15 yrs. old. No other issues noted with the service or premise wiring.
Thank you--Telegraph tpm

 

[JFletcher]

can someone give me a logical engineering answer to why the shield on the coaxial cable acts as the grounded conductor when a loose neutral connection occurs. The grounding system for this home appears to be in good condition. The copper water line and the supplemental ground rods appear to be solid and without issue. Several coaxial cable outlets burned significantly. I found the neutral connection in the meter socket completely corroded and I assume that is where the open neutral exists. This is a typical 200-amp, overhead service, approximately 15 yrs. old. No other issues noted with the service or premise wiring.
Thank you--Telegraph tpm

Welcome. Because that house was likely wired to code, the coax shield is grounded, by a 14ga wire on the first splitter, to the service (perhaps to a ground rod first, but ultimately back to the main panel where grounds and neutrals are connected). So, lose the service neutral, and current can flow back on the coax shield, which is an excellent ground via the cable co, which isnt going to like that (too small for the current) and burn up.

It is unlikely a 15yr old house has any copper water lines other than stubs thru walls connected to PEX. The current isnt going to ground either. It can and will return on the coax cable and burn that up. Also note that when it goes completely, or is cut, you will likely fry 120V equipment if there is any significant difference in draws between legs.

eta: tho rare, this would typically happen on the coax line leaving the house back to the pole. are you sure it wasnt a lightning strike that fried the coax outlets?

 

[telegraphtm]

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Thanks for the response. I agree with you on the issues that your bring up. However, it is a copper line that comes in from the street, and they drove 2 supplemental ground rods. That is whats throwing me. I could understand if it was a less than suitable ground, but by all accounts the ground was sufficient. The coaxial was grounded via a typical 14 ga. wire from the meter socket to a exterior splitter. This is not the first time that I have seen coaxial ground picking up the neutral. And your right it cannot handle the load and burns.

If I need to zero in on the lack of a good ground and its associated electrodes, do you think I should start thinking about purchasing a digital meter to read exactly what my ground resistivity and ohms to ground are. While the loss of neutral is one issue and the responsibility of someone, I beginning to think that a poorly grounded system may be the other issue and another area of responsibility. Thanks for your time.

T

 

[kwired]

Thanks for the response. I agree with you on the issues that your bring up. However, it is a copper line that comes in from the street, and they drove 2 supplemental ground rods. That is whats throwing me. I could understand if it was a less than suitable ground, but by all accounts the ground was sufficient. The coaxial was grounded via a typical 14 ga. wire from the meter socket to a exterior splitter. This is not the first time that I have seen coaxial ground picking up the neutral. And your right it cannot handle the load and burns.

If I need to zero in on the lack of a good ground and its associated electrodes, do you think I should start thinking about purchasing a digital meter to read exactly what my ground resistivity and ohms to ground are. While the loss of neutral is one issue and the responsibility of someone, I beginning to think that a poorly grounded system may be the other issue and another area of responsibility. Thanks for your time.

T

Resistance of your grounding electrodes has nothing to do with your problem. Your cable shield is in parallel with another conductor, one that is capable of carrying more current then the shield is. When things are in good condition the cable shield has more resistance then the other conductor. It still will carry current because electric current will flow in all available paths, the least resistance paths however carry the bulk of the current. Now sever that neutral conductor and suddenly your cable shield is carrying most or maybe even all the neutral current because it is now the lowest resistance path available.

 

[lielec11]

I'm sort of high jacking this thread because it reminded me of a problem I occasionally have with the TV in my living room. Once in awhile (typically when the AC kicks on), the cable TV will go out for a second or two. There are no other issues like lights flickering, etc.

Could this be a similar issue regarding the grounding of my CATV service? I checked the neutrals in the panel and they're solid but did not think to go all the way back to the CATV service.

 

[JFletcher]

Thanks for the response. I agree with you on the issues that your bring up. However, it is a copper line that comes in from the street, and they drove 2 supplemental ground rods. That is whats throwing me. I could understand if it was a less than suitable ground, but by all accounts the ground was sufficient. The coaxial was grounded via a typical 14 ga. wire from the meter socket to a exterior splitter. This is not the first time that I have seen coaxial ground picking up the neutral. And your right it cannot handle the load and burns.

If I need to zero in on the lack of a good ground and its associated electrodes, do you think I should start thinking about purchasing a digital meter to read exactly what my ground resistivity and ohms to ground are. While the loss of neutral is one issue and the responsibility of someone, I beginning to think that a poorly grounded system may be the other issue and another area of responsibility. Thanks for your time.

T

You could drive 30 ground rods in a ring around the building and connect them all with 1/0 back to the panel, it wont help. Grounding doesnt matter here because the current is trying to return to the source, not to ground. You would have to get resistance to ground down below 3 ohms to have a chance of tripping a 120V 20A breaker. Grounding is not for clearing faults, nor a substitute for the service neutral

The service neutral is effectively zero impedance. The coax shield, tho grounded, is in parallel with the service neutral, it has some resistance. Under normal conditions, i.e., good neutral, the coax never carries any current. Now, remove or otherwise open that neutral connection, and the coax shield will try to carry any and all current imbalance. and since some rather thin foil and small braids cant carry more than a few amps, it melts and burns.

Here is an article on it with more detail.

http://www.electrical-forensics.com/Open-Neutral/Open-Neutral.html

Note the writer was shocked when he touched the ground as it was live with 120V.

I'm of the belief that CATV systems should NOT be bonded back to the panel, against the NEC. Guess what? Cable installs here, done ca mid 80s, are NOT bonded back to the panel. Cable Co drove at rod at the demarc, installed a copper wire between the two, and left. I have never seen any faults (electrical or signal-wise) on such systems with untouched original wiring.

NEC requires CATV to be grounded back to the panel now. But I bet if you installed a 14ga wire on the neutral in parallel with your triplex drop, you'd fail an inspection in a heartbeart. Bonding the CATV is essentially doing the same thing, but worse.

 

[kwired]

You could drive 30 ground rods in a ring around the building and connect them all with 1/0 back to the panel, it wont help. Grounding doesnt matter here because the current is trying to return to the source, not to ground. You would have to get resistance to ground down below 3 ohms to have a chance of tripping a 120V 20A breaker. Grounding is not for clearing faults, nor a substitute for the service neutral

The service neutral is effectively zero impedance. The coax shield, tho grounded, is in parallel with the service neutral, it has some resistance. Under normal conditions, i.e., good neutral, the coax never carries any current. Now, remove or otherwise open that neutral connection, and the coax shield will try to carry any and all current imbalance. and since some rather thin foil and small braids cant carry more than a few amps, it melts and burns.

Here is an article on it with more detail.

http://www.electrical-forensics.com/Open-Neutral/Open-Neutral.html

Note the writer was shocked when he touched the ground as it was live with 120V.

I'm of the belief that CATV systems should NOT be bonded back to the panel, against the NEC. Guess what? Cable installs here, done ca mid 80s, are NOT bonded back to the panel. Cable Co drove at rod at the demarc, installed a copper wire between the two, and left. I have never seen any faults (electrical or signal-wise) on such systems with untouched original wiring.

NEC requires CATV to be grounded back to the panel now. But I bet if you installed a 14ga wire on the neutral in parallel with your triplex drop, you'd fail an inspection in a heartbeart. Bonding the CATV is essentially doing the same thing, but worse.

That shield will carry some current, all segments of a parallel path will carry current, how much depends on the voltage across them and the resistance of each path. The neutral conductor does have resistance. It is very low, but the more current it is carrying the more voltage drop will be across it, and the more current will flow in other paths with higher resistance (like the CATV shield).

One problem is CATV uses the shield as a conductor of the system AFAIK. A local antenna or dish doesn't connect to several other houses in a neighborhood, telephone cables only ground their shield but don't use the shield as a conductor of the system, so they could be isolated more easily and not effect performance. Gas piping is isolated by dielectric unions so it doesn't become an electrode or parallel conductor.

 

[JFletcher]

I'm sort of high jacking this thread because it reminded me of a problem I occasionally have with the TV in my living room. Once in awhile (typically when the AC kicks on), the cable TV will go out for a second or two. There are no other issues like lights flickering, etc.

Could this be a similar issue regarding the grounding of my CATV service? I checked the neutrals in the panel and they're solid but did not think to go all the way back to the CATV service.

any way you can take a video of this? do you have cable boxes and the like? does this happen with other TVs?

wag, but I'd say the voltage drop from the AC kicking on is causing an upset with the TV's electronics.

ime, a solid 80% of CATV problems are bad/uncapped terminations or bad wiring inside the customer's home, and of the 20% left, 80% of those problems are too many splitters or amplifiers set wrong. that leaves 4% of total problems for everything else combined.

 

[lielec11]

any way you can take a video of this? do you have cable boxes and the like? does this happen with other TVs?

wag, but I'd say the voltage drop from the AC kicking on is causing an upset with the TV's electronics.

ime, a solid 80% of CATV problems are bad/uncapped terminations or bad wiring inside the customer's home, and of the 20% left, 80% of those problems are too many splitters or amplifiers set wrong. that leaves 4% of total problems for everything else combined.

It was very sporadic..sometimes I would hear it turn on there would be no issues, other times it would go out. Since it's getting cooler now the AC is off at the moment.

From what I noticed the builder ran a single feed to both my compressors outside, which are on the complete opposite side of the house compared to the panel. The feeder appeared undersized as well. My question is why would it only affect a TV and nothing else?

EDIT: Do you recommend I go and check all splitters for termination caps? I know for a fact they all aren't capped, so do you think this will help?

 

[JFletcher]

That shield will carry some current, all segments of a parallel path will carry current, how much depends on the voltage across them and the resistance of each path. The neutral conductor does have resistance. It is very low, but the more current it is carrying the more voltage drop will be across it, and the more current will flow in other paths with higher resistance (like the CATV shield).

One problem is CATV uses the shield as a conductor of the system AFAIK. A local antenna or dish doesn't connect to several other houses in a neighborhood, telephone cables only ground their shield but don't use the shield as a conductor of the system, so they could be isolated more easily and not effect performance. Gas piping is isolated by dielectric unions so it doesn't become an electrode or parallel conductor.

Older homes, like this one, that had a ton of stuff wired to one circuit, could see maybe 25A on the neutral because the possibility of all 120V loads being on one leg is not as unlikely as you'd think. You're correct in that phone and dish systems do not have this problem, and that the coax ground does function as a conductor. That ground on the CATV providers end is very likely tied into the same grounds on the poles as the POCO xfmr. Thus, parallel path and fried coax if you lose the neutral.

I rewired all the CATV in the house some years ago because when he had central air put in, the ductwork guys sliced up a lot of the coax in the crawlspace; one of Continental Cable's less endearing qualities was their installers would leave huge loops (80+ feet) of terminated cable (beautiful, embossed cable at that, but too much) under the house rather than carry it back out. I did not bond it to the service. I am not going to bond it to the service. I dislike that idea more than most people dislike AFCI breakers.

Still, the OP had fried coax other than the service. That is unusual, which is why I was wondering if lightning had hit it. Yes, bad neutral and lightning hit would be exceedingly bad luck, but it's not out of the realm of chance by any means.

 

[kwired]

Even if the CATV doesn't tie to the POCO ground out at a pole, it will tie into all the neighbors houses and have multiple paths to the POCO grounding system via those routes. One neighbor loses their service neutral, their neutral current may be coming through your electric service via the CATV.

 

[Bugman1400]

My guess is this is only a potential problem for overhead service lines. I've seen hundreds of cases where neutrals have been gnawed in two by squirrels...typically, resulting in an overvoltage on one leg and an undervoltage on the other. The microwave is usually the first appliance to show the signs followed by the TV.

 

[kwired]

My guess is this is only a potential problem for overhead service lines. I've seen hundreds of cases where neutrals have been gnawed in two by squirrels...typically, resulting in an overvoltage on one leg and an undervoltage on the other. The microwave is usually the first appliance to show the signs followed by the TV.

You must have some pretty nasty squirrels there. Only time I ever hear of a squirrel being an electrical problem is when he becomes a conductor to medium voltages.

Seen many service drops get rubbed in two by a tree branch but never seen squirrels damage them.

 

[JFletcher]

It was very sporadic..sometimes I would hear it turn on there would be no issues, other times it would go out. Since it's getting cooler now the AC is off at the moment.

From what I noticed the builder ran a single feed to both my compressors outside, which are on the complete opposite side of the house compared to the panel. The feeder appeared undersized as well. My question is why would it only affect a TV and nothing else?

It might just be that TV. I am by no means an expert when it comes to electronics, but a significant voltage dip could upset it enough to momentary cause signal/picture problems.

Do you have incandescent lighting? If so, do they dim for a moment when the AC comes on?

This is one of those little aggravating things that you probably have to live with. This house has a ridiculously long, small-for-the-service drop from the pole and lights flickering during the summer is a normal thing. I know I saw at least 4 threads over the summer asking about that; if it's all lights, it's on the POCO side more than likely. If it's one room or circuit, then it's in the branch wiring; loose connections are pretty common finds for lights that flicker in one room.

Does the cable cut out momentarily at times other than when the AC kicks on? Bad CATV connections are the most likely culprit. (bad also means anything other than a correct compression termination; screw on and crimp on connectors are garbage because they are NEVER installed correctly) Cap off any unused ports on splitters, or better yet, get a smaller splitter.

 

[ggunn]

ime, a solid 80% of CATV problems are bad/uncapped terminations or bad wiring inside the customer's home, and of the 20% left, 80% of those problems are too many splitters or amplifiers set wrong. that leaves 4% of total problems for everything else combined.

I ameliorated the too many splits problem by installing a video distribution amp at the entrance point of the cable. It worked like a champ until I got an active cable box that needs to talk back to the cable company's servers. I googled "bidirectional video distribution amplifier", not knowing if such a thing exits, but it turns out that it does. I installed one and it worked most of the time, but there were issues (dropouts, missing channels, etc.). I bought a bag of 75 ohm coaxial terminators and capped the unused ports on the amp and any drops that didn't have a TV connected - problem solved.

 

[JFletcher]

I ameliorated the too many splits problem by installing a video distribution amp at the entrance point of the cable. It worked like a champ until I got an active cable box that needs to talk back to the cable company's servers. I googled "bidirectional video distribution amplifier", not knowing if such a thing exits, but it turns out that it does. I installed one and it worked most of the time, but there were issues (dropouts, missing channels, etc.). I bought a bag of 75 ohm coaxial terminators and capped the unused ports on the amp and any drops that didn't have a TV connected - problem solved.

:thumbsup:

 

[Gene B]

I'm of the belief that CATV systems should NOT be bonded back to the panel, against the NEC. Guess what? Cable installs here, done ca mid 80s, are NOT bonded back to the panel. Cable Co drove at rod at the demarc, installed a copper wire between the two, and left. I have never seen any faults (electrical or signal-wise) on such systems with untouched original wiring.

The coax would often still be bonded inside the house via equipment (TVs and cable boxes [if they use a 3-wire plug], surge protectors, etc). The entrance bond at least reduces the EGC-coax voltage inside the home.

The safest solution would be to require isolation at the demarc.

 

[ggunn]

I ameliorated the too many splits problem by installing a video distribution amp at the entrance point of the cable. It worked like a champ until I got an active cable box that needs to talk back to the cable company's servers. I googled "bidirectional video distribution amplifier", not knowing if such a thing exits, but it turns out that it does. I installed one and it worked most of the time, but there were issues (dropouts, missing channels, etc.). I bought a bag of 75 ohm coaxial terminators and capped the unused ports on the amp and any drops that didn't have a TV connected - problem solved.

Followup: I still sometimes have problems when I move things around (missing channels, "goat boy" audio (old SNL reference), pixillation, etc., and jiggling/squeezing/bending connection points makes them come and go. For many years I have been using the "garbage" connectors that JFletcher alluded to and I agree with his assessment. I finally broke down and got some good compression connectors and the tool to go with them.

 

[fry6]

Please also remember that the CATV company bonds their outer jackets/equipment to our power company equipment(transformers/down grounds ETC).
So when our(I was a trouble shooter for JCP&L NJ) service drop neutral goes bad, the house current looks for a alternate path to our pole top/pad mount transformer. This is where thinks can get ugly, when we loose our neutral to your house.
thanks

 

[GoldDigger]

You might try a very light coating of antioxidant on the cable center wire that forms the male connection.

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