Is there any reason testing the neutral line on a dimmer light socket wouldn't work?

Question

I am repairing a vintage lamp and replacing the socket with a dimmer socket.

When I do a continuity test on the old socket, both the hot and neutral lines work. That is, they make a high-pitch noise telling me the circuit is closed.

Now, when I try this same test with the new dimmer socket, the continuity test only works on the hot line. I don't get any indication of a closed socket when testing the neutral line. Conventional wisdom tells me that there is something wrong with this socket, but I actually went back to the store and tested another socket, and experienced the same thing.

The old socket is dead-simple -- there are no special electronics in it. The new dimmer socket is a lot more complicated with a potentiometer, capacitors, resistors, etc:

My question is, is there a logical/electrical reason that this socket works correctly, but doesn't give me a successful continuity test on the neutral line?

Answer 1

Figure 1. A typical triac-based dimmer switch schematic. Source: Homemade circuits.

Your continuity check is being interrupted by U1, the triac. This is a semiconductor switch which can vary the amount of the mains waveform getting through. Read the linked article for more.

Answer 2

The continuity tester tests continuity, at the risk of stating the obvious.

As you have wired it, the neutral is not continuous. There is a slug of electronics in the way. (again at the risk of stating the obvious).

Unless you are an electronics expert and willing to do the modeling of what will happen, you should expect unpredictable results when applying a continuity tester or any tester.

I am a little concerned that the dimmer is on the neutral side. That is okay IF turning the knob all the way to the "hard off" position operates a mechanical switch which cuts the hot line.

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Make sure you are using components from reputable vendors which are listed by UL, CSA, TUV or other independent testing lab. These marks are often faked. CE is not a testing lab.

Vendors unsuitable for equipment that goes into mains wiring include: eBay, Alibaba/Ali Express, Amazon Marketplace etc. Amazon, unfortunately, obfuscates the source of their items, you need to know what to look for:

Not to condemn those particular vendors, I've used uxcell myself, just not in mains wiring or any other life-safety application.

Answer 3

Because the dimmer contains a whole bunch of electronics that's designed to work on AC mains voltage. It may barely conduct at the tiny DC voltage your multimeter puts out.

But I'd be worried that you have continuity on live, but not neutral. That suggests that the dimmer is in the neutral line. So when the dimmer is turned right down, the lamp is off, but the socket is still live.

Answer 4

You should have continuity to the neutral wire on the plug to the threaded base and the MT1 connection on the Line connection to the bulb centre should be high impedance ( until turned on. )

Check the wiring for MT1, MT2 or A2,A1 on the schematic in @tranny's answer such that MTI1 or A2 is switched hot to lamp.