3 Wire Service with MWBC's

[brandon2177k]

Opinions Please....
Do you guys think that a older house with a 3 wire service coming in from main disco outside and terminating to a main lug panel inside, with numerous MWBC's, would cause a fuzzy TV picture whenever you run a motor driven appliance, such as a blender. This is the case in my house and it annoys the heck out of me. Or.. do you think this would happen any way if you had a 4 wire service coming in from main disco outside and terminating to a main lug panel? As it sits now with the 3 wire service, the neutral and ground is bonded at the disco outside, and at the panelboard inside. If it were a 4 wire service the neutral to ground bond would only be at the disco outside and not at the panel inside. No major issue here, just trying to satisfy my curiosity.

 

[Dennis Alwon]

It should be a 4 wire regardless unless the conductors are in metal conduit.
I don't think that is causing the fuzziness. Try tightening all the connections in the panel. That can be some of the problem.

 

[mdshunk]

...would cause a fuzzy TV picture whenever you run a motor driven appliance, such as a blender...

You'll get this phenomenon when running most appliances that have a "universal motor", such as mixers, blenders, and vacuum sweepers.

 

[480sparky]

Somewhere on the back of the TV is a disclaimer:

"This device complies with Part 15 of the FCC rules.....
(2) This device must accept any interference received, including interference that may cause undesired operation...."

Meaning, your TV set is picking up an radio signal from the antenna produced by the appliances. It's not electrical.

 

[al hildenbrand]

Brandon,

The spark gap is the oldest form of RF (radio frequency) generator. The wires leading off from the spark gap broadcast the RF into the space around. The signal is messy and broad spectrum.

The blender has a motor with brushes delivering power to the armature windings. This is a "universal motor", as mdshunk notes. The brush to commutator contact is a great spark gap creator.

The TV is most susceptible if rabbit ears are used, the antenna is physically close to the RF source, the antenna (or cable) lead is poorly shielded, and/or if the TV is tuned to lower numbered channels (lower frequencies).

 

[brandon2177k]

Thanks for all the info, I guess my way of thinking was off course. Somehow i had in my mind, that this "electrical noise" was backfeeding on the neutral, if you will, and causing the fussiness. But I never claimed to fully understand electricity either.

 

[al hildenbrand]

But I never claimed to fully understand electricity either.

Welcome to the club.

The one thing secure in understanding electricity is that there is always more understanding to do. . .

:smile:

Keep asking questions.