CATV coax melted

[rf1031]

I am low voltage guy (A/V and phone system), but I have an electrical issue across multiple trades and this seems a good forum to find experts.

My client has an RG6 cable TV feed from TimeWarner that got so hot it melted! I had electrician measure the ground resistance and everything seems perfect from his end. He thinks it is result of cable entry not being grounded.

I know this could come from faulty neutral in this house or even another house sharing timewarner feed and using our good ground as path for voltage. I've read that it could be induced by magnetic field.

I've become the point man for solving this but I think it comes from the other two providers. I'm afraid to put in surge protection for coax as that would just be a better path to ground.

Any suggestions on how to solve and point the other trades in a good direction?

Thanks

Randy

 

[don_resqcapt19]

Where did the jacket melt? Inside the house or on the feed to the house? Is the coax shield grounded at the point of entrance to the building as required by 820.93?
Don

 

[rf1031]

Melted inside the house. Don't know for sure but electrician did not see ground wire.

Randy

 

[LarryFine]

I know this could come from faulty neutral in this house or even another house sharing timewarner feed and using our good ground as path for voltage.

In my opinion, this is still the likely culprit, and you need a good electrical troubleshooter.

Re-grounding the coax bond would relocate, but not eliminate, the improper current.

 

[don_resqcapt19]

If it is inside the house I would be looking for some kind of problem with the equipment that is connected to the coax. Grounded conductor problems for this house or other houses should show up on the street side of the shield grounding connection.
Don

 

[brantmacga]

was it near an open flame or heat source, such as a stove or some other appliance? hey, it never hurts to ask! that's pretty impressive to have actually melted the wire.

 

[rf1031]

Grounded conductor problems for this house or other houses should show up on the street side of the shield grounding connection.
Don

What shield grounding connection? Cable doesn't have grounding block or ground wire from splitter that we can see. Cable tech says their usual practice is to ground once per city block or wherever active electronics are present.

I would say the problem IS street side of all house stuff. A single RG6 coax comes from cable company rooftop tap (splitter feeds multiple houses - this is a row house in NY city) through an airvent in roof/ceiling directly to a 2-way splitter for modem feed and equipment rack jumper. Equipment rack jumper feeds a 3-way splitter to 3 cable boxes in rack.

2-way splitter was burning hot with first few inches near splitter of both feed and jumper melted. Coax to modem was not melted.

Randy

 

[rf1031]

was it near an open flame or heat source, such as a stove or some other appliance? hey, it never hurts to ask! that's pretty impressive to have actually melted the wire.

Nothing near at all. Melted itself and then melted through speaker wire it was next to. Speaker was humming like it was plugged into a wall outlet for audio source! And amplifiers were unplugged!! So ac voltage was definitely present to make speaker blast 60 HZ with no amplifier.

Randy

 

[LawnGuyLandSparky]

TW of NYC's practice is to bring the RG6 in and bond it at the 1st coupling.

 

[kbsparky]

WE had a bad neutral scenerio where the coax shield became the sole return path for all the unbalanced loads from a house.

The entire length of the wire melted the outer sheath from the discharge block back out to the street.

It got so hot that the pedestal out by the highway burst into flames!!

That was quite a sight to behold that night when the fire dept was called in to deal with it.

POCO discovered the underground neutral was corroded right through, nothing but white powder remained from the aluminum conductor.

The cost to repair/replace the damaged items in the house went into the thousands of $$$$.

 

[Rampage_Rick]

Reminds me of the time I struck an arc between a mast and the steel messenger on some 7/8" hardline coax. Turns out the neutral on the triplex drop was a good 200' longer than the messenger wire since they attached at opposite ends of the building, plus a pole span at the street to get to the transformer.

I wrongly assumed that there was no potential due to the existing cables using the same attachment points. What I didn't realize was that the bonding on the 4 existing messengers had failed, so there was a decent voltage across the spool. That spark made me jump a few feet. Pulled out the meter and found about 3 A through the messenger. Lucky for me it wasn't the full unbalanced neutral (probably 40-50A)

 

[don_resqcapt19]

Randy,

Cable doesn't have grounding block or ground wire from splitter that we can see. Cable tech says their usual practice is to ground once per city block or wherever active electronics are present.

Then their usual practice is in violation of the NEC. See 820.93.
Don

 

[rf1031]

TW of NYC's practice is to bring the RG6 in and bond it at the 1st coupling.

It was the TW tech that said they usually do one ground per city block or wherever active amps are located. Second tech came and told homeowner he would ground to conduit at AirConditioning unit. Will that be safe?

Randy

 

[LarryFine]

Second tech came and told homeowner he would ground to conduit at AirConditioning unit. Will that be safe?

Much better to bond to a cold water pipe or the service GEC.

 

[rf1031]

Is it safe now?

Is it safe now?

Thanks to all who posted in the "coax melted" thread. This is continuation of sorts but wondering if problem is solved or an accident waiting to happen. TimeWarner has now addressed their lack of a ground but how can I be sure my client is safe?

They added a ground lead from their rooftop splitter to an electrical conduit at the air conditioner on roof. They also added an in-line isolator of some sort in the closet. This should remove any chance of juice flowing along coax ground into the house, but how can I be sure they were the culprit? I know they should have grounded coax before it entered the house (especially when that coax was connected to every other house on the block!) But can I be sure that my clients are safe? Is there anything else I or their electrician should check? Could something downstream of the cable boxes have caused melting coax upstream of them?

To recap (with extreme detail):
I am audio/video/phone system provider for a town house (row houses with contiguous roofs) in New York city. I am not an electrician. My system consists of a rack full of equipment in a closet on top floor. Rack has 3 cable boxes and an audio/video switching/distribution system to send video to flat screen TVs throughout house via cat5 wiring. These are the only cable boxes.

I should note that for some equipment, signal ground is also chassis ground so the shield of the A/V wires is therefore tied to earth ground in the rack. And just to complicate things, the A/V controller also controls the phone system's door boxes so there could be common ground there, too.

On roof, cable company has splitter and feeds jump from house to house. There was no grounding of coax except at amplifier for whole city block. From roof splitter, RG6 cable came straight from roof through 6" vent hole in top of closet to a 2-way splitter in the closet. That splitter feeds 2 jumpers- 1 to cable modem in same closet and 1 to the rack. Rack has 3-way splitter to feed those 3 cable boxes. That is it for the coax. The 3 cable boxes and the cable modem are all right there in the closet with a hole to the roof.

Problem: First the jumper between the splitters melted. TimeWarner sent tech who found the bad spot, cut it out, and re-terminated it. A few hours later the same jumper plus the feed from roof melted within a few inches of first splitter and started to melt into adjacent speaker wire. AC was clearly present since that speaker started to buzz loudly as if plugged into a wall outlet. The jumper to the cable modem was never affected.

So I ask again, given that the cable boxes and modem didn't fry, nor any other equipment, could the problem have originated inside my client's home? Could I have a bad TV or amplifier? Might there be a faulty neutral at my rack, or at any of the TVs (connected by cat5 to this system)? If so, wouldn't equipment failure or cat5 meltage have happened? Can I be sure that the unsafe voltage originated externally since problem was right where it came into the house? And most important, can I sleep knowing they are safe from anything I have done?

Thanks

Randy

 

[LawnGuyLandSparky]

It was the TW tech that said they usually do one ground per city block or wherever active amps are located. Second tech came and told homeowner he would ground to conduit at AirConditioning unit. Will that be safe?

Randy

Nothing will be "safe" if the service neutral is corroded or defective. Many older NYC services have no secondary ground connection, like to a water pipe. Or if it does, it's been rendered useless due to improper disconnection. This makes any properly bonded shielded cable the next best place for a service to dump it's unbalanced load.

ConEd is having serious problems with their secondary distribution systems all over the City. There are hot manhole covers and streetlight & traffic signal poles all over because (IMHO) ConEd treats their neutrals like bastard redheaded stepchildren. And it's still the NYC DOT's policy for ConEd's service to public facilities like streetlights to be 2 wires - 1 hot and one neutral, and that neutral is bonded to the metal poles and doubles as a ground. There are no other ground rods or supplementary grounded electrodes. If a ConEd neutral is corroded and presenting resistance (In a manhole, they're ususally on the bottom, covered in muck) the poles become live.

 

[rf1031]

Nothing will be "safe" if the service neutral is corroded or defective.

Where is the danger, in my case? Inside house? Out on streetpoles? If our electrician did a good job internally, are people or wires still in danger? Could problem be something else?

Please see my new thread "Is it safe now?" as I summarize my concerns and describe entire scenario.

Thanks very much

NOTE: I have merged the "new" with this one...no need to have two open threads on the same subject.

 

[don_resqcapt19]

They added a ground lead from their rooftop splitter to an electrical conduit at the air conditioner on roof.

That does not meet the code rules. See 820.100(B).

So I ask again, given that the cable boxes and modem didn't fry, nor any other equipment, could the problem have originated inside my client's home?

Yes is could be in the home.

 

[LawnGuyLandSparky]

I am curious about the setup - you say "typical rooftop splitter" but little in NYC is "typical." What kind of residence is this, how does TW get it's coax from the street (ariel, underground?) to the premisis? Where is the splitter in relation to the POE?

 

[rf1031]

I am curious about the setup - you say "typical rooftop splitter" but little in NYC is "typical." What kind of residence is this, how does TW get it's coax from the street (ariel, underground?) to the premisis? Where is the splitter in relation to the POE?

I believe TW is underground to each city block. There they have some active splitting and (so the TW tech says) a ground connection. Somewhere they come above ground because all I see is rooftop to rooftop big coils of RG11 to splitters/taps from one residence to the next. You can see RG11 come from splitter on next rooftop. As described above, house is a row house (townhouse).

Randy