Question About AC Plug Polarity

[shapirus]

There is certain equipment such as some models of gas boilers that requires a specific arrangement of line and neutral connection. They won't work for example from a battery-powered AC inverter, unless you connect one of its output wires to mains earth, thus emulating neutral. As far as I understand, it's because of the way their flame detection circuitry works.

[james_s]

There is certain equipment such as some models of gas boilers that requires a specific arrangement of line and neutral connection. They won't work for example from a battery-powered AC inverter, unless you connect one of its output wires to mains earth, thus emulating neutral. As far as I understand, it's because of the way their flame detection circuitry works.

I suspect that's because the entire metal chassis is earth grounded. Even then though I don't know why the line polarity would matter, unless it's using a transformerless non-isolated supply? It could also be a safety feature where it detects wrong polarity and shuts down.

[shapirus]

I suspect that's because the entire metal chassis is earth grounded. Even then though I don't know why the line polarity would matter, unless it's using a transformerless non-isolated supply? It could also be a safety feature where it detects wrong polarity and shuts down.

I'm not sure really. I just know they exist and that people who have them need to use workarounds to make them work from inverters. And *maybe* they actually need an earth connection rather than a specific line/neutral polarity, but all mentions of this that I encountered told that those boilers required a neutral, not earth.

My gas boiler doesn't care about earthing or polarity and has no problem running from a DC->AC inverter. Maybe someone who has one of those which require a neutral will eventually come to comment .

[james_s]

I've installed a few gas forced air furnaces recently and now that you mention it I think they did say they required correct polarity but that was never a concern since they are hardwired and it's easy enough to get the wiring right.

[CatalinaWOW]

Just a plus one on not counting on the correct connections.  In half of all of the houses encountered in my family one or more sockets was incorrectly wired.  Some were homeowner botches but some of the worst were "professionals" though I have no idea whether they were union pros or not.

It goes beyond that.  I recently installed a couple of 6 bulb chandeliers that SWMBO selected for appearance.  These came with each of the sockets installed and the wires from the sockets run to the central housing, but it was left to the owner to do final connection.  The instructions included repetitive warnings to connect appropriate colors and match when attaching to the supply.  But when I checked I found exactly half of the sockets the white (nominally neutral) wire was connected to the tip. 

That left me with three options.  Completely rewire the lamp, wire it electrically correctly and leave a mish mosh of interconnected colors, or connect the appropriate colors and have a slightly less safe chandelier.  I elected the latter.  I started down the first route and found that the sockets were not reworkable, and decided it wasn't worth the effort to redo the work I had done connecting it color matched.

[ejeffrey]

There is certain equipment such as some models of gas boilers that requires a specific arrangement of line and neutral connection. They won't work for example from a battery-powered AC inverter, unless you connect one of its output wires to mains earth, thus emulating neutral. As far as I understand, it's because of the way their flame detection circuitry works.

I suspect that's because the entire metal chassis is earth grounded. Even then though I don't know why the line polarity would matter, unless it's using a transformerless non-isolated supply? It could also be a safety feature where it detects wrong polarity and shuts down.

Yes, it uses flame rectification and leakage between live and the chassis (which is grounded) to detect the presence of absence of the flame.  The cathode is generally the burner tube itself so it isn't desirable to connect that to the line.

[ejeffrey]

Flame rectification sensors are also used on some gas cooktops which are likely to be plugged into a normal outlet rather than hard wired. 

It's still a relatively uncommon scenario and one that is pretty easily addressed when necessary as long as the installer knows what they are doing.

[Conrad Hoffman]

I've found seeing how power distribution is wired can be helpful. There are few good site, but this one is OK. Scroll to the bottom for typical US wiring.
http://waterheatertimer.org/How-to-identify-transformer-wiring.html