Electrical Problem?

Brian

I'm not sure if I have a problem or not. First, a little background.

About a year ago I had digital phone service installed. The installation took a very long time (if I remember correctly it was 3 hours). The installers had a lot of problems getting it to work. Almost immediately I started having problems with the cable television and cable modem.

They subsequently rewired the house with new coax and everything worked fine for a short period. When they rewired they grounded the cable to the riser conduit from the meter.

At some point our service started acting up again. We had numerous technicians out. They would replace connectors at the splitter, ran a new line from the drop box, replaced more connectors, etc.

Last week the technician said our connector at the splitter was hot to the touch and suggested a grounding problem in the house. He ran a new ground for the cable directly to the ground, rather than the conduit. Service has been fine for the past week.

Any thoughts on what is going on? Is a grounding problem possible?

Thanks,
Brian Phillips

mdshunk

What you're experiencing is due to a law of physics knows as "Kirchoff's Law". In a nutshell, it says that current (electricity) does not flow on the path of least resistance... current flows on ALL AVAILABLE PATHS. With that in mind, let's examine the typical residential electrical service and evaluate possible reasons why enough current is flowing on the shield of the coax to make the splitter warm.

Your house is served by a 3 wire, 120/240 volt service. To simplify this, the current for all your 120 volt loads flows "in" a hot wire, and out on the bare neutral wire, back to the "XO" terminal on the utility's transformer. This XO terminal at the utility's transformer is bonded to a ground rod at the pole, and any messenger support cables for telephone and cable lines that may also be on that pole, so that they are all at the same potential.

At your house, your neutral line is bonded to your metal water lines, ground rods in the ground, the metal of the meter can, and the metal riser conduit. Now, on to Kirchoff's law. Of all the current flowing on the neutral line back to the transformer, some of it also flows on your ground wire, to your ground rod, through the earth, to the utility's ground rod at the pole, and back up their ground wire to the transformer. It is a very small amount of current that flows this way, but it is still measureable. IF... you developed a loose connection in the regular neutral wire, a larger portion of the neutral current would flow on the grounding electrode conductor, out the ground rod and into the earth, trying to get back to the transformer. This still doesn't explain how current could flow on the coax ground.

Now consider this... Consider that a neighbor has a loose neutral connection, and a greater than normal amound of neutral current from his property is flowing on his grounding system trying to get back to the transformer. He could very well have his neutral current flowing on your incoming coax (since his grounding system is still connected to the coax splitter), in your coax to your splitter, from that splitter ground to your riser conduit, and back to the transformer via your neutral line. This is an all too common scenario, which can be particularly troublesome. The offending party doesn't realize what's occuring, and you can't exacltly remediate the issue since you don't own it. This phenomenon is commonly called "stray current".

Since they removed the splitter ground from your conduit (which was well connected to the utility neutral by several means),and connected it to their own cheesy gound, the splitter cools off. This is because hardly any current can flow this way now. If you own an clamp type amp meter, you could connect that splitter ground back to the riser conduit and see what kind of amp reading you get. I'll betcha it's in the order of several amps. If you do this and get an amp reading, turn off all your breakers and recheck the amp reading to eliminate your property as the possible offender (which it won't be).

Fun, fun.

PipeGuy

YOU are the man. Great post.

ContractorSon

Nice!

mdshunk

In fairness, there could also be an issue with one of the cable modems, set top boxes, or televisions in the house that is shorted to the cable, putting voltage on the cable shield. I very highly doubt that this is the case. This is something that would be incredibly obvious to the cable man as soon as he puts his super cool cable man meter on the line.

Atricaudatus

I agree! I've been doing electrical work for about twenty years; but I still learn a lot from these forums and particularly from most of Marc's posts. He possesses an uncommon wealth of knowledge and command of obscure or otherwise little-known facts. Not to mention being very well versed in the NEC.

Keep up the good work guys. I really enjoy this site (and those who frequent it.)

__________________
-Rhett
Licensed electrician and plumber