46 volts between two grounds.

Trevorus · #1 06-14-2006, 07:11 PM

The ground on my bass amp and the ground on my tv antenna has 46 volts between them. What the hell is up?

superbassman2000 · #2 06-14-2006, 07:20 PM

your hair, if you get zapped by it

rebelbass · #3 06-14-2006, 07:21 PM

Your bass amp should be grounded to your service box;which should have a copper rod driven into the earth. Your tv antenna should also have an earth ground. If you have that much voltage between them,something is terribly wrong. I would suggest someone with experience (preferably liscenced) to check it out. You could fry your amp,tv,blender or your ass!

Trevorus · #4 06-14-2006, 07:32 PM

Quote:

Originally Posted by rebelbass

Your bass amp should be grounded to your service box;which should have a copper rod driven into the earth. Your tv antenna should also have an earth ground. If you have that much voltage between them,something is terribly wrong. I would suggest someone with experience (preferably liscenced) to check it out. You could fry your amp,tv,blender or your ass!

That's the thing, I am experienced with electrical. I just haven't tested the outlet yet, and I was wondering if there is some common problem that causes this so I can save some time.

JansenW · #5 06-14-2006, 07:49 PM

Is it 48 volts AC or DC?

Do you have an TV booster or antenna rotor on the roof?

Trevorus · #6 06-14-2006, 07:54 PM

Quote:

Originally Posted by JansenW

Is it 48 volts AC or DC?

Do you have an TV booster or antenna rotor on the roof?

AC, and it's bunny ears. I don't have any signal amplification at all on the antenna line.

JansenW · #7 06-14-2006, 08:02 PM

Do you get any voltage when your TV and bass amp share the same outlet?

Do the following... Check the voltage between...

1. TV outlet ground and bass amp outlet ground
2. TV antenna and the TV outlet ground
3. bass and the bass amp outlet gournd

IanStephenson · #8 06-15-2006, 03:05 AM

May not be a problem...

Your TV ariel isn't supposed to be grounded - if it was it couldn't pick anything up! The job of the antennae is to create an AC voltage by picking up radio waves - 46V does sound like a lot though,and I'd expect that unless you have a good meter you wouldn't be able to measure it anyway (as the meter would ground it).

Volts aren't really a problem - it's AMPS which can kill you. A static shock can be 10,000 volts but its factions of a milli-amp. Your TV arial could be generating a large voltage (which is good - as it means you get a nice picture!) - kinda the same as a guitar pickup does, but unless there IS a fault it won't be able to back that up with any current. As soon as you try to "use" those volts they'll disapear.

Check the earth pins of the mains surplies against the amp - provided they're 0 then you're safe.

Also check the chasis of the TV.

Ian

(disclaimer - I've been out of the electronics game for years, and I was never much good at it!).

paulraphael · #9 06-15-2006, 10:52 AM

Quote:

Originally Posted by IanStephenson

May not be a problem...

I bet it's a problem!

You might expect minute voltages on an antenna, but not 46V.

I would assume that it's not harmless voltage (as in static) largely because it's measurable, and because the source is likely your mains supply, which has plenty of current capacity to do all the things mentioned.

Static charges work the way they do because the actual accumulated charge (number of free electrons) is low. So voltage can accumulate, but the instant the circuit is closed, all the charge depletes and the voltage drops to zero. This is why you don't see large (or even easily measurable) currents from high voltage static shocks. But if the source of your charge is the municipal electrical system, the dynamic is different.

elros · #10 06-15-2006, 03:14 PM

I'm educated as a radio/TV repair tech (I don't work as one, though), and I think I can say what the cause of this is.

The TV set has a power supply (PSU) which isn't fully isolated from the mains. It has a simplified switching PSU, because it is cheaper and less heavy compared to a "proper" PSU.
This means that the "ground" of the TV set is floating on one of the mains supply lines. So, between the TV set ground and the "real" ground, you can often find about half of the mains voltage.
This is also the reason why in a TV repair shop, you'll find the tech hooking up the TV through an insulating transformer: his oscilloscope is grounded, so if he was to connect the scope ground without the insulating transformer between the TV and the mains line, he'd short circuit the mains line...

Ergo: this is perfectly normal. And it usually isn't a problem.

xyllion · #11 06-15-2006, 03:25 PM

If that TV set has UL approval, then that is not normal. UL would never approve any electrical device with 46V potential on exposed metal. You are definitely looking at a safety hazard.

Hookus · #12 06-15-2006, 04:03 PM

Quote:

Originally Posted by xyllion

If that TV set has UL approval, then that is not normal. UL would never approve any electrical device with 46V potential on exposed metal. You are definitely looking at a safety hazard.

Sure they would. Ever seen a CB radio or an ametuer radio? 10 watts of power derived from 12 volts produces over 800 milliamps of current, which is very realistic potential to be felt on a transmitting antenna. It takes about 5 milliamps to kill a human. Elros is right on the money. No actual reception/transmission component of any electronic antenna is EVER grounded. I spent the better part of my adult life as a communications electronics tech in the military, and cannot count how many times I have seen people burned from an antenna.

Bob Lee (QSC) · #13 06-16-2006, 06:51 PM

Does it only appear when the TV is on?

BTW, I've seen lots of grounded shields in antenna coax in broadcasting. Cable TV coax is often grounded at the entrance to the home or building, too. It isn't necessary, though, on home receiving antennas.

NJL · #14 06-16-2006, 07:02 PM

Quote:

Originally Posted by Trevorus

AC, and it's bunny ears.

There're your problem, you jerk, why did you have to bring a poor little bunny into this?

Trevorus · #15 06-16-2006, 07:11 PM

Yeah, I totally forgot about my CB radio experience! Duh.

That makes sense. I moved the antenna, and I checked the outlest just in case. They are wired correctly with a proper ground, but as was said, TV's usually have a floating ground. No 3 pin plug.

I'll just keep myself away from the antenna when playing bass.

rebelbass · #16 06-23-2006, 05:19 PM

I remember having a tv antenna and having a ground wire,probaby a lightning ground not connected to the antenna. Thats why I suggested getting some one who definitly knows. Thanks for the lesson,guys!

Hookus · #17 06-23-2006, 07:09 PM

The coax, and mount for the antenna may be grounded, in fact, the coax shield should be grounded, but not the element itself. It cannot be grounded at all, or no transmission/reception.