voltage on coaxil cable

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willdalrymple

willdalrymple

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I had a service call the other day where Time Warner cable TWC stated that there was voltage to ground on there lines and it was causing problem with the hi-def cable picture. Yes there is voltage to ground. 56volts on high def line. unplug tv and converter box and voltage disappears. tv only plugged in 22volts, converter only plugged in 32 volts. At both the outside and inside panels there is 0 volts between ground and neutral. Can this voltage be attributed to the equipment and is there a fix I don't know about.

Thanks Will
 
ive seen this before from a broken or loose neutral. also make sure the cable is properly bonded where it comes in.
 
The cable shield probably isn't grounded. You are probably just reading a ghost voltage.

Steve
 
willdalrymple said:
56volts on high def line. unplug tv and converter box and voltage disappears. tv only plugged in 22volts, converter only plugged in 32 volts.Thanks Will
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The two voltages adding to the total is not normal, even with the usual poor neutral issue. That's really weird. I wonder if they're not on the same circuit? You need to determine if they're the 'perpetrators' or just 'victims.'

I'd start with an independent known good earth ground and check for voltages between all of the parts that should read no voltage, such as equipment chassis, power neutral and ground, incoming cable shields, etc.

You should check each piece of equipment in a separate receptacle, such as the laundry. While you're at it, I'd also check the neutral and grounding at the panel, including the line-to-neutral voltage on both phases.
 
steve66 said:
The cable shield probably isn't grounded. You are probably just reading a ghost voltage.
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This is a good reason for using a solenoid-type tester for basic troubleshooting. Knowing real sources of voltage is more important than knowing the exact voltage. High-impedance-neutral problems need a load to show up.
 
My helper received a 57v shock while taking a coaxial connection apart. Tested the voltage with a wiggy - voltage was definately present. The lady was somewhat of a pain in the butt - I just told her to let her cable co know about this. I am assuming it was coming from a converter box / cable modem , since the shock came from the "load side" of the connection.

~Matt
 
TOOL_5150 said:
I am assuming it was coming from a converter box / cable modem , since the shock came from the "load side" of the connection.
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Maybe, maybe not. That's why I suggest using an independent reference to test against. It's as possible the voltage is coming from within the house as from without.

A non-contact voltage sensor can also help in cases like this, since it uses the 'earth' as its reference.
 
LarryFine said:
Maybe, maybe not. That's why I suggest using an independent reference to test against. It's as possible the voltage is coming from within the house as from without.

A non-contact voltage sensor can also help in cases like this, since it uses the 'earth' as its reference.
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But Larry, The voltage was coming from the shield from the [disconnected] premise wiring. The test was taken from shield of premise wiring to ground on CATV drop, which was connected to the electrical panel [I hate those little clips] The shock came from the premise side. I touched the drop side.. nothing.

~Matt
 
TOOL_5150 said:
But Larry, The voltage was coming from the shield from the [disconnected] premise wiring. The test was taken from shield of premise wiring to ground on CATV drop, which was connected to the electrical panel [I hate those little clips] The shock came from the premise side. I touched the drop side.. nothing.
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All I'm saying is that you have a confirmed voltage difference between two points, but which one is the offender? It is posible that the service neutral, to which all 'grounded' parts should be bonded, is not at zero volts relative to the world.

You may also be 100% correct that the inetrnal equipment and/or wiring is at fault. You need to determine the source of the offending voltage. I'm merely saying to not assume that which should be ground always is.

It could be as simple as electronic equipment expects the receptacle it's plugged into to be properly wired, the hot and neutral may be reversed, and internal bypass capacitors are energizing the chassis of the equipment, and thus, the coax shield.

That's why I suggested testing against a good ground reference, such as stringing a wire from the service to the equipment loaction, and carrying each piece to a known circuit (such as the laundry receptacle) and testing again.
 
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