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[rufunky]

First things first, let me make sure I have this straight. In a 2 wire switch, the electric current needs to travel through the light fixture providing a path back to the electrical panel doing the job of the absent neutral wire?

If this is the case, wouldn't lack of a neutral wire in turn cause more EMI thus possibly creating more noise at the switch or lights themselves? I ask this because I am thinking about adding a common wire to my switches to minimize the buzzing of the switches coil.

[Brian H]

The two wire X10 and other brand wall switch dimmers. The line goes into the switch and out the load wire. Through loads line input of the fixture and back to the neutral connection on the fixture through the bulb. They are designed for incandescent bulbs that are resistave.
There is always a small amount of current flowing in the circuit. So the wall switch gets it power. That is why things like dimmable LED bulbs may not act correct. Glow or pulse. While others of a different design may not glow or pulse.

Adding the neutral connection on the dimmer switch would prevent the need to steal power through the load. Adding the neutral will not prevent the inductive coil on the load output from buzzing. That is usually how the coil is wound and how tight the winding are on the coil form.

The EMI comes from the noise generated when the triac switches. Adding a neutral may not do too much for EMI.

[rufunky]

The two wire X10 and other brand wall switch dimmers. The line goes into the switch and out the load wire. Through loads line input of the fixture and back to the neutral connection on the fixture through the bulb. They are designed for incandescent bulbs that are resistave.
There is always a small amount of current flowing in the circuit. So the wall switch gets it power. That is why things like dimmable LED bulbs may not act correct. Glow or pulse. While others of a different design may not glow or pulse.

Adding the neutral connection on the dimmer switch would prevent the need to steal power through the load. Adding the neutral will not prevent the inductive coil on the load output from buzzing. That is usually how the coil is wound and how tight the winding are on the coil form.

The EMI comes from the noise generated when the triac switches. Adding a neutral may not do too much for EMI.

Thanks Brian, what are the ramifications of a two wire switch used with dimmable LED lights?

[Brian H]

How they work depends on the LED bulbs electronics and how they react with the dimmer in question.
I have tested some brands. Some glowed when Off. Some would not react to any X10 power line commands even the ones over 5 volts with the XTB-IIR in place. Some would not go On but if On from the local button go of with an X10 command.
Some flickered when not at 100%.
I have seen some reports here. Of some bulbs being totally OK.

Some recommend you buy a few for test and see how they worked.

I know one Insteon user that does large installations for customers. Buys bulk LED bulbs and tests them all. Returns the ones not acceptable. Normal production tolerances can make some LED bulbs act differently. I have a LED bulb from a four pack. That would probably be unacceptable to you. It has a faint high pitched noise coming out of it and it is on a mechanical on off switch. No electronics involved at all. My thoughts are. It may have some loose component or its driver is not encapsulated as much.

Insteon dimmers have a neutral power connector and still can have issues with some LED bulb models. They do make a two wire one and it is for incandescent loads only and does not do an X10 Primary Address. Insteon no longer lists X10 support. Some unofficially still do but no guarantee it will on the next hardware revision.

[rufunky]

How they work depends on the LED bulbs electronics and how they react with the dimmer in question.
I have tested some brands. Some glowed when Off. Some would not react to any X10 power line commands even the ones over 5 volts with the XTB-IIR in place. Some would not go On but if On from the local button go of with an X10 command.
Some flickered when not at 100%.
I have seen some reports here. Of some bulbs being totally OK.

Some recommend you buy a few for test and see how they worked.

I know one Insteon user that does large installations for customers. Buys bulk LED bulbs and tests them all. Returns the ones not acceptable. Normal production tolerances can make some LED bulbs act differently. I have a LED bulb from a four pack. That would probably be unacceptable to you. It has a faint high pitched noise coming out of it and it is on a mechanical on off switch. No electronics involved at all. My thoughts are. It may have some loose component or its driver is not encapsulated as much.

Insteon dimmers have a neutral power connector and still can have issues with some LED bulb models. They do make a two wire one and it is for incandescent loads only and does not do an X10 Primary Address. Insteon no longer lists X10 support. Some unofficially still do but no guarantee it will on the next hardware revision.

As far as I can tell, my LEDs work fine. They dim all the way down / up no noise coming from the bulbs. Seem to work ok with x10 commands although I think I may have to add a coupler in the electric box as sometimes it takes a few tries before the command goes through for the newly wired LED can lights downstairs. The only issue I have had is the louder than normal (at least I assume it is louder than normal) buzz that comes from the switch coil.

The LED lights I am using are HALO rl560wh6830 and I found a spec sheet ( https://images.homedepot-static.com/catalog/pdfImages/5f/5f281b96-c7dd-4661-a411-3e66eb780c3c.pdf ) of compatible dimmers. I did find some great information including, they use reverse or forward phase-cut dimmers and most of the compatible dimmers use a triac which I believe it was you that stated in another post that this is what the x10 switches use. 

The one thing I can not find is if all of the compatible dimmers use a neutral wire ( white wire).

[JeffVolp]

Thanks Brian, what are the ramifications of a two wire switch used with dimmable LED lights?

Contact me privately and I may have a fix for your 2-wire X10 wall switch.

Jeff

[dave w]

$0.02
I agree with Brian H about adding a neutral wire in effort to reduce either switch buzz or EMI. I don't think it will have an effect on those two items. It does fix the 40 watt minimum load spec. I have a couple applications where I am driving a 120V relay from a WS467 and had to add a neutral to get the relay to work (unlatch). Don't try this with a pre-"soft on" or "resume DIM" switch. That slow ramp up, ramp down is pretty hard on the relay. 

But EMI is caused by the harmonics created when the triac is gated ON when the AC waveform is above zero. The deeper in to the half cycle the triac is gated ON the more RF hash is generated. I don't think a neutral will change that. A larger choke might. But then physical space is the limiting factor.

[rufunky]

$0.02
I agree with Brian H about adding a neutral wire in effort to reduce either switch buzz or EMI. I don't think it will have an effect on those two items. It does fix the 40 watt minimum load spec. I have a couple applications where I am driving a 120V relay from a WS467 and had to add a neutral to get the relay to work (unlatch). Don't try this with a pre-"soft on" or "resume DIM" switch. That slow ramp up, ramp down is pretty hard on the relay. 

But EMI is caused by the harmonics created when the triac is gated ON when the AC waveform is above zero. The deeper in to the half cycle the triac is gated ON the more RF hash is generated. I don't think a neutral will change that. A larger choke might. But then physical space is the limiting factor.

Thanks for the added information Dave. 

[Brian H]

Adding the neutral wire may lower the off current through the load. No way to test it as I have no modified X10 dimmers with a neutral wire added.

40 watt incandescent bulb load for all the dimmers I tested. Radio Shack meter.
Old WS12A 28mA AC Off. Full On 17 VAC dropped across the switch.
Old WS467 29.4mA AC Off. Full On 16.75 VAC dropped across the switch.
Z-Wave HCA20C 19.1mA AC Off. Full On 4.0 VAC dropped across the switch.
Lutron S-600H Has a minimum dial setting so 53mA AC maybe the lowest it could go. Full On 7.83 VAC dropped across the switch.
Old dial type dimmer. 2.15mA AC Off. Full On 1.89 VAC dropped across the switch

[rufunky]

Adding the neutral wire may lower the off current through the load. No way to test it as I have no modified X10 dimmers with a neutral wire added.

40 watt incandescent bulb load for all the dimmers I tested. Radio Shack meter.
Old WS12A 28mA AC Off. Full On 17 VAC dropped across the switch.
Old WS467 29.4mA AC Off. Full On 16.75 VAC dropped across the switch.
Z-Wave HCA20C 19.1mA AC Off. Full On 4.0 VAC dropped across the switch.
Lutron S-600H Has a minimum dial setting so 53mA AC maybe the lowest it could go. Full On 7.83 VAC dropped across the switch.
Old dial type dimmer. 2.15mA AC Off. Full On 1.89 VAC dropped across the switch

Thanks, looks like the neutral wouldn't help as the off current isn't causing much emi. The Noise is at its highest at mid dim.

[Brian H]

Highest noise at mid dim makes sense. The Triac is turning on close to when the AC wave is closest to its peek.

The added neutral wire. Would reduce the off current through the load. That sometimes makes dimmable LEDs pulse when the switch is off.

[JeffVolp]

40 watt incandescent bulb load for all the dimmers I tested. Radio Shack meter.
Old WS12A 28mA AC Off. Full On 17 VAC dropped across the switch.
Old WS467 29.4mA AC Off. Full On 16.75 VAC dropped across the switch.

While some of that "off" current powers the switch itself, much of it is out of phase with the AC waveform due to the transformerless power supply, and does not result in real power dissipation.

I was surprised by the voltage drop across the switch.  When conducting the voltage across the triac should be under 1 volt, and there should also be little drop across the series inductor.  Considering the switch is rated for a 500 watt load, at 120V that would be over 4 amps, resulting in 70 watts dissipation in the switch.  While dimmer switches can warm up under a heavy load, there is no way it could dissipate 70 watts.

So I measured one myself with a 60W bulb.  The actual voltage drop across the switch when the triac was conducting ran between 1V and 2V at the peak of the AC waveform.  Then I used a meter (both digital and analog) to measure across the light, and indeed it read just 109V with our AC line at 124V.  The discrepancy is due to the triac taking almost 2mS to turn on.  But since the voltage is relatively low during that portion of the waveform, the missing portion represents relatively little loss in power delivered to the light bulb.

Jeff

[Brian H]

Thanks for the detailed explanation.