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Re: Topband: AC line bypass capacitors

To: "Roger Graves" <ve7vv@shaw.ca>, <topband@contesting.com>
Subject: Re: Topband: AC line bypass capacitors
From: "Tom W8JI" <w8ji@w8ji.com>
Reply-to: Tom W8JI <w8ji@w8ji.com>
Date: Wed, 4 Feb 2015 15:19:21 -0500
List-post: <topband@contesting.com">mailto:topband@contesting.com>
My 160 TX is causing RFI to one of my baseboard heater programmable thermostats (switches modes, temperature, when I transmit). The thermostat has a 2 wire connection to 240VAC in a metal receptacle box that has a third wire common ground wire. I would like to try bypassing the AC line. Can someone suggest an appropriate (safe) capacitor for this purpose, e.g. a Digi-Key or Mouser part number? Should I use one capacitor across the 240VAC or two capacitors, one from each 120VAC line to the common wire? Thanks for the help.
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The safest bypass method for 120V is to put one 250 VAC rated cap across the line, and one more cap from neutral to safety ground.

The safest method for 240V would be to use two caps, one from each 120 to neutral. Then use a single cap from neutral to safety ground if it exists.

This method ensures you do not screw up any GFI stuff, and if a cap faults it faults from a hot directly to a current carrying return and not into a safety system.

The caps are UL VDE CSA rated line bypasses, available from Mouser and others. I would use a 0.01 uF capacitor. They are about ten ohms on 160 meters, if I remember right.

73 Tom
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