Noise on power lines

[KE7XD]

I have some very bad noise in my shack. The worst is light dimmers in the house.. The shack is fed by four wires to a building about 140 feet away from the house. I put in a sub panel to feed the circuits. The panel box is grounded to the main box in the house, and the neutral is also tied to ground at the house. The new panel box also has ground rods at its site. For noise where should I put some bypass caps, from the legs to neutral or to ground? Should there also be a cap from neutral to ground? For lighting protection it sounds like everything should be grounded to a common point, but can I tie the ground and neutral together? I have read a lot of articles, however I have not come up with suggestions when using the four wires.

 

[popnokick]

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Self-installing caps on supply mains? Tieing ground and neutral together? Strikes me as not quite good practice, but don't take it from me. And your homeowner's insurance might be kinda slow to pay a claim if anything happens. Tell your power company you have a radio interference problem coming from their equipment, and follow their advice. Or a licensed electrician who understands RF noise suppression.

 

[Thayne]

The only place the neutral should be connected to ground is where the overcurrent protection or metering is located. That is the only place the interconnection between the neutral and grounds whether it be a water pipe or ground rod or both. (Codes require both now)
You should never tie them together at any other place, especially at a sub panel or another building. The ground wire going to your building should not be connected to any neutral conductor but only be used as an equipment ground at he building; and needs to be sized properly. Some of these things being not right could possibly cause noise problems but I doubt it.

 

[N0YFE]

I agree that the neutral and ground should never be bonded together at all. As for the ground rod at the sub panel that does sound OK from what I remember with NEC for that distance. If you've got them bonded and have any tranient voltage from the neutral to ground, that could be causing a large part of your noise problem.

It would not hurt to have an electrician come out and inspect the entire electrical setup to see if they can find any additional problems.

 

[AK9R]

I agree that the neutral and ground should never be bonded together at all....It would not hurt to have an electrician come out and inspect the entire electrical setup to see if they can find any additional problems.

Any residential electrician will tell you that the National Electric Code requires that the neutral and ground be tied together at the main breaker panel.

 

[N0YFE]

Any residential electrician will tell you that the National Electric Code requires that the neutral and ground be tied together at the main breaker panel.

Thanks for the information. I see my mistake now.

 

[SCPD]

I have some very bad noise in my shack. The worst is light dimmers in the house.. The shack is fed by four wires to a building about 140 feet away from the house. I put in a sub panel to feed the circuits. The panel box is grounded to the main box in the house, and the neutral is also tied to ground at the house. The new panel box also has ground rods at its site. For noise where should I put some bypass caps, from the legs to neutral or to ground? Should there also be a cap from neutral to ground? For lighting protection it sounds like everything should be grounded to a common point, but can I tie the ground and neutral together? I have read a lot of articles, however I have not come up with suggestions when using the four wires.

Buy some better switches. Most of the newer switches have RFI filters built in.

e.g.

Shop Lutron Maestro 5-Amp White/Gloss Digital Dimmer at Lowes.com

Also, you might want to invest in some Corcom filters. Depending on how much amperage you use there are several relatively low-cost solutions to help cut down on noise getting into the shack from house mains.

General Purpose RFI Filters

(Used models can be found on EBay and/or you can buy them from electronic supply places like mouser, etc.)

The Corcom filters work great.

Unfortunately, filters won't help you if you have this: http://www.youtube.com/watch?v=8SgW9JjIUac