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phoneman
join:2014-07-13

phoneman

Member

[TV] Nextbox 2.0s putting voltage on Coax

I have 2 Nextbox 2.0s. I have noticed, that I feel a shock when joining the cable from the box to the wall jack. I checked it with my volt meter and found that with either box plugged in to the power, there is 52v on the shield of the wire going to it. The coax that goes outside from the wall jack is grounded at the box so when I connect the coax to the wall jack, the voltage is gone. I was wondering if this is normal. Can someone else check if there is voltage on the coax when the coax is not connected to the wall but the box is plugged into power?

Acrimonius
join:2014-12-06

Acrimonius

Member

It's never normal when there's an electrical current running through your coax cable. Because the issue occurs with both Nextboxes IMHO that would rule out a faulty box. Sounds like you need an electrician to diagnose the issue. Somehow live current is getting into the cable line.

Remember: Faulty electrical connections cause fires. I'd be staying a mile away from the faulty wall jack period.

Napsterbater
Meh
MVM
join:2002-12-28
Milledgeville, GA
(Software) OPNsense
Ubiquiti UniFi UAP-AC-PRO

Napsterbater to phoneman

MVM

to phoneman
Voltage on the coax is never normal.

Some of your outlets may be wired backwards (Hot and Neutral switched). Home Depot, Lowes or most improment stores should have somthing like this (»www.amazon.com/GE-3-Wire ··· 02LZTKIA) which can show this issue.

But I agree an electrician should be consulted/hired.

sbrook
Mod
join:2001-12-14
Ottawa

sbrook

Mod

This can be an unfortunate problem with cheap Switch Mode Power supplies used in consumer electronics. They are often capacitively coupled to the AC input supply. So, the chassis and inside "0V or ground rail" can end up with a high impedence connection to either the neutral or the live depending on how the power cable is connected internally or how the power outlet is wired as Napsterbate suggests.

It isn't good but it isn't harmful. The current down the coax shield is under 1 mA. I have it on an older SA PVR ... the outlet is correct ... but there's that sense of a charge on the case, and it causes a hum on the audio and creates purpleish and greenish hum bars on the TV. One day I'll do something about it ... right now it's a nuisance. The TV appears to be wired correctly, but not the PVR!
phoneman
join:2014-07-13

phoneman

Member

The outlets are wired correctly. I think it might be what sbrook was saying. I am using a fluke true rms multimeter which even finds 40 VAC on the hdmi (gold metal shield part to ground) and 60 VAC from the coax barrel of both boxes to ground even when the boxes are connected only to a known good outlet.

Acrimonius
join:2014-12-06

Acrimonius

Member

Well, if there's enough voltage there that you get a shock then you got a problem son. Get the thing checked out before something bad happens. You need to find out for sure where the voltage is coming from to guarantee there isn't a bigger issue at play here.

sbrook
Mod
join:2001-12-14
Ottawa

sbrook

Mod

There is a very old saying amongst electrical and electronics people ...

"It's the Volts that Jolts, but it's the Mils that Kills" ... meaning that voltage is what gives you the tingle or kick, but it's the current that flows through you that is the killer.

In this case, as soon as he connects the cable shield to the box, the induced voltage by the capacitive coupling is reduced to 0. But even then holding the cable connector in one hand and touching the metal of the cable box with the other will give you less of a "shock" than putting a 9v battery on your tongue!

This is NOT a safety issue. These devices are UL and CSA approved like this. It's how they come right out of the box.

Acrimonius
join:2014-12-06

Acrimonius

Member

Not going to argue about it. The OP said the coax reading was 52v. If common sense can't prevail here then so be it. Does anybody actually think the device would still be CSA approved with that much voltage on the coax?

Minimizing a problem does not make it go away. 'nuff said.

sbrook
Mod
join:2001-12-14
Ottawa

sbrook

Mod

Look at power line workers ... they can work on operating power lines at 400 Thousand Volts. As long as they are sufficiently insulated to ensure that no more than about 25-35 mA flows through them, they are perfectly safe.

I'm not minimizing the problem at all ... I've told you WHY it happens (capacitive coupling in Switch Mode power supplies), that it is NORMAL, and why it's not dangerous.

If you want to get rid of the problem, you need to get something called an ISOLATION transformer so the power supply in the device is not connected to the electric outlet. In daze of yore, that's how they made power supplies, but they are costly, so manufacturers went to Switch Mode supplies.

zong
Premium Member
join:2005-07-21
Scarborough, ON

zong

Premium Member

I'm going to agree with sbrook %100 on all counts including the description of the p/s.

I've had a similar situation with a cheap piece of kit before, circuit was wired correctly. It's disconcerting when you feel it and notice it, but it is not a safety issue nor does it indicate something is wrong with the mains supply.
cepnot4me
join:2013-10-29
L0C 1K0

cepnot4me to phoneman

Member

to phoneman
The shock, the voltage is normal.
When the box is connected to coax at the wall and a proper ground is installed on your drop, you will feel no voltage, it is dissipated to ground.

Disconnect it from the ground we install, you feel it.

There is a return carrier on the coax, whole home adds a second carrier, as well as Hum. On the HDMI This comes from your TV, your other electronics, induced or residual from the box. Lots of voltages everywhere.

This is why we are required to install a ground at the point of entry.

Disconnect the riser from the rest of the plant, you become the only path to ground.

Reconnect the riser (if we are grounded outside) and you won't feel a thing.
phoneman
join:2014-07-13

phoneman

Member

Thanks guys.