Cold-Switched 3-way with Neutral as the Common

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Matt N

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Alameda, CA USA
Old knob and tube wiring ran as I described in the heading. The clients want me to install a low-voltage track light (50-watt MR-16s) with a dimmer. So would a DVLV work with the neutral as the common--or more importantly--is it safe?
 
LarryFine said:
My bad. A 3-way dimmer is merely a 2-wire dimmer with one of the two wires internally connected to the common of a 3-way switch.
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Which means that you can switch from both locations, but only dim from one. Also, some two wire dimmers get their power between hot/switched terminal and EGC. Not going to work with a switched neutral?
 
GoldDigger said:
Which means that you can switch from both locations, but only dim from one. Also, some two wire dimmers get their power between hot/switched terminal and EGC. Not going to work with a switched neutral?
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That's my question: can I dim the neutral going into the transformer for the MR-16? The constant hot is in the light box and 3-waying the neutral.
 
190923-1952 EDT

The logic of a so called 3-way circuit is the same whether switching is done in the hot or neutral wire. Since the circuit is AC and diodes are not used as logic elements there is no difference in operation.

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gar said:
190923-1952 EDT

The logic of a so called 3-way circuit is the same whether switching is done in the hot or neutral wire. Since the circuit is AC and diodes are not used as logic elements there is no difference in operation.

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Click to expand...

But the desire for a dimmer changes the situation. A true two terminal dimmer will be unaffected. A three terminal dimmer (more likely for one intended for controlling an LV transformer) will not necessarily be able to see the hot to neutral/ground differential it needs.
 
He is asking if switching the neutral is okay.... It is not compliant but will it work? Try it

A DVLV is a Lutron Diva dimmer that is magnetic low voltage. If the track has an electronic transformer you may need an DVELV
 
190924-0820 EDT

GoldDigger:

With a 3 wire dimmer the wire that would have gone to neutral would now go to hot. So we can still provide power to operate the dimmer electronics.

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