Interference on TV

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B W E

Member
Hey guys, this one has me stumped. A guy calls because his paper shredder, blow dryer, and electric massager all cause interference (visible static) on his TV and (audible static) on his radio.

They cause static when plugged into different (but not ALL) receptacles. The paper shredder causes interference on the TV when plugged into the kitchen Island outlet, but not the disposal outlet. It does it when plugged into it's normal wall receptacle (a newer, all copper addition), as well as when plugged into a surge suppressor.

There is no correlation between the shredder outlet and the tv outlet, nor between any of the other devices (different circuits, different phases, etc.) The original house is aluminum, and was pigtailed, but upon inspection yesterday, the guy used red wire nuts, but no Noalox. All copper/aluminum connections are dry.

The cable service coming in to the house is grounded, but it goes from the ground block where the cables are coupled together to a little clamp on a piece of 1/2 emt with the paint scraped off. The emt runs through two bell boxes before it gets to the panel.

The neutral/ground bar of the main panel has a #4 neutral (going to a sub panel) as well as the #6 solid landed on the same lug. There is no other place for it to go.

There is a driven rod at the main panel with the #6 passing through the ground clamp and going on to the cold water.

The sub panel does not have a separate ground bar, or a ground wire. There is one ground wire coming in to the panel from the house that is landed on the neutral bar. The circuit that the shredder plugs into is fed by the sub panel (Copper). The TV and clock radio that are receiving the interference are on the main panel Aluminum).

I thinks thats about all I can tell you. If you have any advice I'd love to hear it.
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
They cause static when plugged into different (but not ALL) receptacles.

Look for something in common between the receptacles.

You may have a neutral or bonding issue, causing the neutral conductor to act like an antenna.

Check for other devices on the circuits that make the problem occur. One of them may be acting like transmitter. Unplug them one at a time and re-check.

The other issue is the FCC Part 15 requirements have not been met on the TV and radio. Part 15 requires that the not only do they not cause harmful interference, but must accept any and all interference. We have seen many such devices that were certified with filters but then were not made with them.

That may be a silver lining indicating a problem somewhere that would have went unnoticed until something bad happens. With all the transitions between CU and AL the chance of having a high resistance neutral is pretty good.
 
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kwired

Electron manager
Location
NE Nebraska
Hey guys, this one has me stumped. A guy calls because his paper shredder, blow dryer, and electric massager all cause interference (visible static) on his TV and (audible static) on his radio.

They cause static when plugged into different (but not ALL) receptacles. The paper shredder causes interference on the TV when plugged into the kitchen Island outlet, but not the disposal outlet. It does it when plugged into it's normal wall receptacle (a newer, all copper addition), as well as when plugged into a surge suppressor.

There is no correlation between the shredder outlet and the tv outlet, nor between any of the other devices (different circuits, different phases, etc.) The original house is aluminum, and was pigtailed, but upon inspection yesterday, the guy used red wire nuts, but no Noalox. All copper/aluminum connections are dry.

The cable service coming in to the house is grounded, but it goes from the ground block where the cables are coupled together to a little clamp on a piece of 1/2 emt with the paint scraped off. The emt runs through two bell boxes before it gets to the panel.

The neutral/ground bar of the main panel has a #4 neutral (going to a sub panel) as well as the #6 solid landed on the same lug. There is no other place for it to go.

There is a driven rod at the main panel with the #6 passing through the ground clamp and going on to the cold water.

The sub panel does not have a separate ground bar, or a ground wire. There is one ground wire coming in to the panel from the house that is landed on the neutral bar. The circuit that the shredder plugs into is fed by the sub panel (Copper). The TV and clock radio that are receiving the interference are on the main panel Aluminum).

I thinks thats about all I can tell you. If you have any advice I'd love to hear it.

What are voltages both loaded and unloaded at the TV and at the offending appliance as well as at the service?
 

B W E

Member
Look for something in common between the receptacles.

You may have a neutral or bonding issue, causing the neutral conductor to act like an antenna.

Check for other devices on the circuits that make the problem occur. One of them may be acting like transmitter. Unplug them one at a time and re-check.

The other issue is the FCC Part 15 requirements have not been met on the TV and radio. Part 15 requires that the not only do they not cause harmful interference, but must accept any and all interference. We have seen many such devices that were certified with filters but then were not made with them.

That may be a silver lining indicating a problem somewhere that would have went unnoticed until something bad happens. With all the transitions between CU and AL the chance of having a high resistance neutral is pretty good.

I was unable to find ANYTHING in common between the outlets, other than voltage...118v. The TV is plugged into an outlet on the original aluminum wiring, and is pigtailed improperly to copper. (No Noalox). The offending devices are plugged into different circuits, which are in the addition portion of the house, and on copper wire. There are three items that cause the interference, a paper shredder, an electric massager, and a blow dryer.

The FCC issue would only relate to the three offending pieces of equipment right? They are all causing harmful interference. Is static considered harmful? The TV and radio are supposed to receive interference per the FCC rules, right? All three items have brushed (i think) motors, which, from what I understand, are pretty "dirty" from a EMI standpoint.
 
The FCC won't be concerned about the motors, just the TV. On the one hand, I'd try either the TV or other offending device on a long 3-wire extension from elsewhere in the house. OTOH, I'd say don't use the shredder/etc when watching TV.
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
I was unable to find ANYTHING in common between the outlets, other than voltage...118v. The TV is plugged into an outlet on the original aluminum wiring, and is pigtailed improperly to copper. (No Noalox). The offending devices are plugged into different circuits, which are in the addition portion of the house, and on copper wire. There are three items that cause the interference, a paper shredder, an electric massager, and a blow dryer.

The FCC issue would only relate to the three offending pieces of equipment right? They are all causing harmful interference. Is static considered harmful? The TV and radio are supposed to receive interference per the FCC rules, right? All three items have brushed (i think) motors, which, from what I understand, are pretty "dirty" from a EMI standpoint.

The devices that cause the interference are not Part 15 devices but nonetheless are unintentional radiators. The FCC can and has made people stop using non certificated devices that were causing interference. If the devices were causing interference to your neighbor's TV the FCC could make you stop using them. The interference issue for TV's and radios is not the same as telephones. Telephones absolutely have to reject the interference. TV's and radios do not, but they must not create any. Look for an FCC sticker on the radio and TV. The requirements should be on a label somewhere. I think I said that TV's and radios must be able to reject. That was an error. It's telephones.

The legalities are strange but the crux of the biscuit is that you have something up. What concerns me is that the interfering devices stop interfering on certain circuits.

What do those circuits have in common?

I wish I was close enough to actually help you. I love chasing down RFI problems.
 

Electric-Light

Senior Member
Well, find the outlet where there isn't an interference. Plug an extension cord there, then use the hair dryer where it does cause it. If it goes away, its line conducted. If not, its air transmitted.

Shredders, hair dryers, vacuums, battery powered devices have brush motors where interference originates.

RC cars often use a pair of capacitors. Two in series with the center connected to the shell of motor and the ends to power connection of motor to prevent interference with the RF system.

"burst load" like shredders are unlikely to be of concern to the FCC. It's like complaining that the garbage truck is loud at 5AM. It doesn't happen often and long enough to be of substantial effect.

If either the RF noise, or acoustic noise at garbage truck level were to be sustained for long periods of time, then it maybe of concern for regulatory agencies having jurisdiction over the matter.
 

cadpoint

Senior Member
Location
Durham, NC
From the service point out, it sounds like you don't have a complete bond to all receptacles.

Now the funny part is most of the equipment you've spoke of is only two prong(thinking out load) the answer has already been given!
mjf
my immediate thought is you have a loose grounded conductor (neutral).

But from your statement, the secondardy panel is not boned correctly!

My other guess's;
It also sounds like the circuits are crossed, and or poor connections(as said) through out.

Once you know the a run of a circuit, megger it to know if it's worthy to remain.
 

bob

Senior Member
Location
Alabama
These devices you are using probably have universal motors that have brushes that are arcing. The arc is the source of the TVI. Google TVI and universal motors and you will likely see a solution. It is usually connecting a small capacitor between each conductor and the frame of the device or ground.
 
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