Purchased a Panasonic VL-SWD275 video intercom from Australia to replace my 2-wire intercom in the US to avoid rewiring the whole house with a 4-wire system.

The Panasonic VL-SWD275 requires 220v and 24v DC at 6amps. I purchased and installed a Zerone AC 100-240V to DC 24V 6-9A Switching Electricity Supply Module 150W step-up transformer into the outlet thinking I could wire the non-polarized main monitor directly to the DC output of the transformer.

I've read on this site that a non-polarized device like a clock wouldn't care if it was rewired with a polarized replacement wire and plug of the same gauge.

The Panasonic VL-SWD275 kit includes a 220/240v power supply that has a non-polarized AC input, and a 24v DC -/+ terminal output. The main monitor includes 2 power input terminal wire ports, but says the wires must be non-polarized!!!

Can I power the VL-SWD275 with the red and black +/- 24v DC output wires from the Zerone step-up transformer and omit the power supply in the kit????

2 Answers 2


Yes, purchasing a DC power supply that was designed and tested for the US market and sold there is the best approach.

The polarization issue is irrelevant. The thing you heard about (for example) clocks is for devices that work entirely on AC power, without a DC PSU. If they were designed with unpolarized plugs, and you replace their plug with a polarized one, they will still work. In your case, the replacement (Zerone) PSU may or may not have a polarized plug, according to its own design. If it comes with a polarized plug, use it.

The DC output is ALWAYS polarized so make sure the PSU's positive DC output (marked + or with some color perhaps red) is connected to the intercom's positive or + input.

  • Thanks for the brain cells you've spared me. I've been researching and researching feeling I missed something. I've been wondering why Panasonic would even stipulate that non-polarized wires be connected to the main monitor power input terminals, when the power supply they include in the kit is AC input and 24v DC output from positive and negative wire terminals.
    – Novice1
    Dec 29, 2022 at 0:22

No, this is terrible. You have a whole string of code violations here:

NEC 110.2 equipment must be approved (i.e. UL Listed). That cheap Chinese power supply you bought mail order, is not. And the power supply is what really matters here because it touches AC mains power.

Honestly, "wall wart" type power supplies that are (UL) approved are far, far more readily available than non-approved supplies. That's because everyone who makes electronic equipment needs an approved wall-wart to throw in the box, so you have a huge domain of potential customers. Whereas a non-listed wall wart can only ever be sold on Amazon/eBay to hobbyists who don't know any better. As such listed ones are such a total commodity that there is no cost savings to be had on non-listed ones.

NEC 110.3 equipment must be installed according to instructions. Your instructions specifically say that the power supply must be cord-and-plug connected, not least to serve as a mandatory disconnect.

Never ever buy AC mains electrical gear mail-order, unless you are buying approved kit from extremely reputable vendors such as homedepot.com or mouser.com. You need to go to mouser.com and get an appropriate, plug-in wall wart. Amazon Marketplace (which is basically eBay, and entirely full of cheap junk off AliBaba) is the very definition of "not reputable". Sorry if your Prime membership is semi-wasted. I have one too even though I never buy electrical gear from Amazon.

NEC 800.133 separation of AC mains from low voltage systems. Vis-a-vis your inter-mixing of AC and low-voltage wires inside a junction box.

Proper power supplies provide for the necessary separation; note the design of approved 24VAC thermostat and doorbell transformers. Or any wall-wart that just plugs in to a 50 cent, UL listed power socket.

  • Thank you so much for explaining this. Our 25 year old home was constructed with only a low voltage 24v DC conversion module in the junction box where the old video monitor was connected. Looks like the AC wires were likely dropped down from behind the M & S Systems main intercom panel above it. I would like to hardwire the intercom monitor so that a long cord is not hanging down the wall. That Panasonic video intercom is dated. So, I'm wondering if the mandatory disconnect feature is obsolete given the over-voltage, over-current and short circuit protection built into the module. Thoughts?
    – Novice1
    Dec 29, 2022 at 8:24
  • I also discovered that Zerone is a brand name, but not the manufacturer. The product/part is WX-DC2416 and is made in China like many electronics, but is supposed to be CE certified.
    – Novice1
    Dec 29, 2022 at 8:52
  • 1
    @Novice. It sounds like "the last guy" did a bunch of dangerous hack work. Correct it. No, the mandatory disconnect feature is not obsolete. You are indulging in wishful thinking. CE is a European government spec, and the European government only enforces it inside Europe against Euro manufacturers. On all the China stuff, the mark is entirely faked. Dec 29, 2022 at 9:27

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