Freesat box seems to be LIVE!!!

[mypetearthling]

We have Freesat, it was installed when the previous owner of the house was here, so I have no idea if it was done properly.

The box has always been a bit 'buzzy', giving a slight tingle if you touch the top panel. I eventually got round to swapping the box for another today, and it seems that this one is live too! Looks like the problem is in the satellite/cable, not the box as I had thought.

Any ideas why this could be, and what on earth I should do to fix it? Is the satellite supposed to be earthed? I don't think it is, but need to try to get a better look during daylight.

K

 

[JBR]

Assuming it is not earthed, capacitive coupling. See 'Electrics' forum.

Mine does the same. I'm told it's at a potential of about 240V, but negligible current. That's why you and I are still here!

 

[Sam Gangee]

See http://www.satcure.co.uk/tech/shock.htm

 

[Monkeh]

Is the satellite supposed to be earthed?

That would be quite a feat, as it's over 20,000 miles away from earth.

If the shocks really bother you, the solution, as Sam's link indicates, is to have the cable shield connected to earth properly. This is not a particularly cheap job.

 

[Sam Gangee]

I think this should do the job safely:
http://cpc.farnell.com/vermason/j63...=Products From This Range&MER=e-bb45-00001003

Simply connect a multistranded, insulated wire from the plug terminal to any chassis screw on the receiver.

 

[Monkeh]

I think this should do the job safely:
http://cpc.farnell.com/vermason/j63...=Products From This Range&MER=e-bb45-00001003

Simply connect a multistranded, insulated wire from the plug terminal to any chassis screw on the receiver.

Problem with that is it funnels any lightning strike straight down through the receiver and into a socket. This is not desirable.

Also, it's made for ESD control and is explicitly not to be used for earthing appliances.

 

[Sam Gangee]

Yes but the idea isn't to "earth the appliance" but to let the floating current leak away. It's not a "mains safety earth" (not required for "double-insulated" equipment).

Any lightning entering the equipment already has a direct path to the plug socket.

(Interestingly, when a friend's TV aerial was struck last year, it blew every darn mains socket and light socket off the walls/ceilings and destroyed every piece of equipment EXCEPT the Sky Digibox, which turned out to be working fine after the TV was replaced!)

 

[Monkeh]

Yes but the idea isn't to "earth the appliance" but to let the floating current leak away. It's not a "mains safety earth" (not required for "double-insulated" equipment).

But the reality is that's precisely what you're doing: Earthing the otherwise floating appliance.

Any lightning entering the equipment already has a direct path to the plug socket.

It's a lot more likely to enter once you connect that!

 

[Sam Gangee]

I don't follow your logic. It's already connected to the mains power outlet by a mains power cord. Connecting a 1M Ohm resistor via a wire isn't going to increase the lightning strike "risk" one iota. Have you witnessed the aftermath of a lightning strike? There's very little left to bury. The lightning can track a metre or more across a bare wall without a conductor in sight. (Bear in mind that it's already zapped through a kilometre of fresh air before reaching the ground.)

Believe me, if lightning ever hit, the 1M resistor wire would be the least of your worries.

 

[Monkeh]

Fair enough. I just don't see the point in a half-assed job which, in my opinion, increases the risk of a lightning strike on the dish without reducing the damage potential of it (as a proper earth connection would).

I also don't see the point in spending £10 on a plastic block with a 2BA stud (really, 2BA? Hello, metric world has been here for some time now.) and a 1M resistor in it.

*shrug*, non-problem anyway really. Just, y'know, don't touch the box without expecting a tingle. Much like you don't scuff your way along a woolen carpet without expecting a fun discharge next time you touch something metal.

 

[Sam Gangee]

I just don't see the point in a half-assed job which, in my opinion, increases the risk of a lightning strike on the dish without reducing the damage potential of it (as a proper earth connection would)..

Again, I don't follow your logic. How would a 1M Ohm resistance to mains earth inside the house affect lightning outside the house?

Anyway, in all the years I've been involved in satellite TV, I've neither seen nor heard of lightning striking a dish in the UK. However, earthing the dish would certainly increase the (tiny) risk because lightning follows the easiest path to earth.

However, if you want to protect the house from a strike on a dish, the simplest method is to loop the LNB cable(s) down to ground level then back up to the hole in the wall, some distance away. Lightning doesn't like sharp bends so it would travel down the cable and jump to ground at the loop.

To remove static charge on a dish (far more likely), you simply run a thin wire direct from the dish to ground.

 

[Sam Gangee]

Back on topic:

I also don't see the point in spending £10 on a plastic block with a 2BA stud (really, 2BA? Hello, metric world has been here for some time now.) and a 1M resistor in it.

It's probably American. They haven't caught up yet.

I proposed the simplest solution. I never suggested it was cheap. (If it were mine, I'd buy a 50p plug, remove the L & N pins, connect a resistor to the earth pin and run a wire from that.)

 

[Monkeh]

I just don't see the point in a half-assed job which, in my opinion, increases the risk of a lightning strike on the dish without reducing the damage potential of it (as a proper earth connection would)..

Again, I don't follow your logic. How would a 1M Ohm resistance to mains earth inside the house affect lightning outside the house?

Potentially providing a lower resistance path to earth than another 12 feet of air (the resistance of which is RATHER higher than 1M, you measure things like that in nanosiemens rather than ohms)

To remove static charge on a dish (far more likely), you simply run a thin wire direct from the dish to ground.

Which, on the outside, is pretty harmless (it'll just vaporise and the lightning will continue to follow the ionised air). When that thin wire is the coax running through your house, however, I take issue.

However, if you're not in a lightning prone area, I agree the risk is minimal. But he could be the only one for miles around on top of a hill, at which point it's a concern.

It's probably American. They haven't caught up yet.

With a 2BA thread and a BS1363 mating plug? Suppose it could be that they still think we use 2BA!

That and there's a lot of black magic and tradition when it comes to things like ESD. Odd mix of intricate attention to detail in materials and handling and just plain strange, pointless things they refuse to stop doing because they've always done them. Could be worse, could be the RF black magic (inside of an LNB is fascinating and slightly mind warping).

 

[Sam Gangee]

But he could be the only one for miles around on top of a hill, at which point it's a concern.

My friend's house that was struck is in a valley. Height doesn't seem to matter. Surrounding houses on the hills were not struck. Go figure! (Beats me.)

That and there's a lot of black magic and tradition when it comes to things like ESD. Odd mix of intricate attention to detail in materials and handling and just plain strange, pointless things they refuse to stop doing because they've always done them. Could be worse, could be the RF black magic (inside of an LNB is fascinating and slightly mind warping).

I agree with you totally on both counts. Been to the seminars. Got the T-shirts. BTW if you want to get charged up I can recommend these methods.

1. Remove a plastic rubbish sack from a plastic bin and hug it tightly. Now go to the nearest tap. Ouch!

2. Find a stairway with nylon-coated banisters and run down, sliding your hands on the bannisters. Instant 40,000 volts. (Pat a passing child while nobody is looking.)

3. Put on nylon clothing; sit on a seat with brushed nylon seat covers (e.g. car); Shuffle about; stand up and touch an earthed object (wife's nose never fails to amuse).

Inside an LNB, most the the inductors and capacitors are etched copper on the PCB. I had the interesting task of designing an all-electronic LNB switch (no relay). It worked surprisingly well.

 

[Monkeh]

BTW if you want to get charged up I can recommend these methods.

1. Remove a plastic rubbish sack from a plastic bin and hug it tightly. Now go to the nearest tap. Ouch!

2. Find a stairway with nylon-coated banisters and run down, sliding your hands on the bannisters. Instant 40,000 volts. (Pat a passing child while nobody is looking.)

3. Put on nylon clothing; sit on a seat with brushed nylon seat covers (e.g. car); Shuffle about; stand up and touch an earthed object (wife's nose never fails to amuse).

Let me add a fourth:

Stand in a plastic folding pallet/crate (I'm sure there's a proper name, I'm also sure you know what I'm on about) full of nylon mouldings and start filling plastic bags with them. Proceed to lean on the conveyor coming into the crate and nearly have a heart attack. I could've sworn the damn thing was live until I realised what I was standing in.