Rewards Points: 10
Voltage on house coax cable
Hi, I’m a cable co. technician and have a question I can’t seem to get a straight answer on, I’ll try to describe as best I can.
From time to time I run into customers who have ongoing intermittent issues with their cable service, most of the time their modems. Everything has been checked out with the cable yet problem persists. Then either I feel a little shock outside at the ground block or I will just pull out the multimeter, pull of the coax feeding inside, and I find 50-60v AC on the line, measured with the red lead on the center conductor of the cable, and black lead on the ground wire.
This last time was just the other day, it was 1 cable feeding 2 TV’s, on a common circuit. I tried to troubleshoot by unplugging devices and what I came up with was that whenever ANY device is plugged into that circuit and also connected to the coax, the voltage backfed on the cable. I assumed it is something wrong with the electrical wiring.
One of the outlets looked like it had been added aswell, so I suggested she call an electrician. Not sure how often electricians run into this and if it is easy for one to troubleshoot.
Does anyone have an idea of what’s going on. Everytime I’ve run into this, it’s always 45-60v and same symptoms with the cable equipment.
Oh also the last tech that was there before me said that the cable at one of the connectors outside was melted when he got there.
ElectricianTalk.com – Are you a Professional Electrical Contractor? If so we invite you to join our community and see what it has to offer. Our site is specifically designed for you and it’s the leading place for electricians to meet online. No homeowners asking DIY questions. Just fellow tradesmen who enjoy talking about their business, their trade, and anything else that comes up. No matter what your specialty is you’ll find that ElectricianTalk.com is a great community to join. Best of all it’s totally free!
Warning: The topics covered on this site include activities in which there exists the potential for serious injury or death. ElectricianTalk.com DOES NOT guarantee the accuracy or completeness of any information contained on this site. Always use proper safety precaution and reference reliable outside sources before attempting any construction or remodeling task!
Originally Posted by mxslick
Most common causes, in order of number of times I have run into them:
- Defective cable box;
- Defective TV/VCR;
- Miswired receptacle;
- Loss of the customer’s grounding and/or neutral;
- Lightning/surge damage;
- Faulty CATV line amp;
- Customer making illegal (and poorly done) tap into cable line.
I am sure others on here will come up with more.
Based on the melted cable outside it is possible that #4 on my list is the culprit, and it requires the attention of an electrician.
My first thought was, the added outlet has hot/neutral reversed!
#3 Miswired receptacle
An electrician should be able to determine this very easily!
OK, so what’s the speed of dark?
10-17-2011, 02:55 PM
Join Date: May 2009
Location: Chapel Hill, NC
Rewards Points: 644
I also think it is a problem with the ground or neutral. If there is too much current on the ground then the coax can pick it up.
I don’t think this is a service problem The modem or TV will usually be a non grounded appliance. The inductive /capacitive component of the internal circcuitry will be fed through all extenal components by virtue of contact or connection.The current levelis insignificant and voltage levels are consistent with this type of problem. The cure is to ensure that coax cables are gounded. You will not find any voltage to measure if you try to take a reading with good grounding in place. This is not a dangerouse problem but a factor consistent with most electronic equipment
Without first determining the source of the voltage it’s ill-advised to state a problem isn’t dangerous.
Was born in HACKensack, NJ
10-17-2011, 05:18 PM
Join Date: Oct 2010
Location: Houston, Tx
Rewards Points: 1,000
Originally Posted by Dennis Alwon
I will allow this thread as it may be helpful to you but this site is for electricians and work done should be done by a trained electrician. Please keep response to what causes it and not how to fix it.
Weird. Down here it’s a one stop shop. Be it coaxial or romex, we do it all.
Originally Posted by dronai
B4T just had this problem, and found the source. I don’t remember exactly what he did, but I think some wiring splices were done by someone not qualified.
It was a bunch of bad splices with a nail touching ground and hot. it would not blow the circuit because the ground was not connected in one of the splices..
120v was back feeding through ground into coax through TV. really wired set of events with the hack changing wire colors in receptacles to get 120V at the recdeptacles..
My handy receptacle tester showed all receptacles wired properly.
Welcome to ET. where the clowns don’t need a tent to try and make people laugh.. http://steelturman.typepad.com/photo. f_clowns_2.jpg