Home AC Reverse Polarity Protection ?

I have a main switch after the electrical meter that supply power to the entire house. Now sometimes, the smart people who climbs on poles to fix the wires. They mess up the wires wrong, even they are colored red and black(Yea smart certified people). Causing the entire home to have reverse AC current supply in wall sockets. Talking to them is no benefit as they are "smart" people. Here none of them care if polarity is reversed.
So I manually have to check whether the hot line of AC is at right side. And swap the wire in main switch at home if not.
But is there any device I can plug in middle so it auto fixes the polarity ? or something that doesn't turns on if polarity is reversed? The load could be 2kW to 5kW. Dont know for sure.

A relay (double throw) could be wired so it switches one way or the other, based on whether current finds a path through the relay coil to earth. The relay would need to be rated for the Amperes going through that branch.

If auto polarity-detection is not feasible, then you are needed to decide what to do. A manual switch might be sufficient.

You should be permitted to install a relay or switch, if you install the correct box, and comply with local codes.

BradtheRad said:

A relay (double throw) could be wired so it switches one way or the other, based on whether current finds a path through the relay coil to earth.

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What kind of relay that would be ? All I know they all turn on no matter in which direction current flow to coil. There are other kind of relays that selects NC/NO by the flow of current ?

Hi,

Here I see the safety problem...it needs to be connected between one live wire and EARTH GND.

* if wrongly connected then the relay is continously ON...continously current flow to earth GND.
If EARTH wire is broken then ALL in house EARTH connections carry live voltage.

For safety reasons i'd limit the EARTH current to below 0.5mA with double safety. Two properly selected, each rated for full voltage, in series. Maybe driving an optocoupler. Or a MOCxxx device.
Then a triac driving the relay, supplied by L and N.

How often does this happen? Is it worth the effort?

Take care of safety regulations. Here in Germany it is not allowed, or at least critical, to switch N.

Klaus

KlausST said:

Here I see the safety problem...it needs to be connected between one live wire and EARTH GND.

* if wrongly connected then the relay is continously ON...continously current flow to earth GND.
If EARTH wire is broken then ALL in house EARTH connections carry live voltage.

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Exactly, I was saying exactly the same thing in youtube comment section.

KlausST said:

How often does this happen? Is it worth the effort?

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It may/may not happen, whenever the electricians climb on the poles to fix the broken wires or for timed maintenance. They mess it up. But I think it doesn't worth flowing the current to ground, making it riskier.

KlausST said:

Take care of safety regulations. Here in Germany it is not allowed, or at least critical, to switch N.

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I do not know about here, but I'm not switching N. I'm just making it correct. Its their fault to not make it right in first place. Maybe thats what you meant

Thank you.

I wonder what's the actual need of correcting the polarity. Even with polarized mains connectors the neutral line in a device connected through a socket outlet must be expected to carry a potentially hazardous contact voltage. It becomes e.g. live if the neutral wire is broken.

So if at all, a dedicated neutral terminal provides some extra safety for specific devices.

I agree with KlausST that a relay which draws current from the ground wire involves additional safety risks and is most likely incompatible with safety standards. Voltage against ground could be sensed with an electronic relays.

Any equipment running on AC will work equally well with the wires reversed, the polarity is alternating anyway. I can see a potential safety issue if you are using 'live chassis' equipment but I would consider that very dangerous regardless of polarity issues.

As in Germany, here in the UK it would be illegal to switch N unless L was switched at the same time but all electrical installations have to be tested and certified for safety before they can be used. Using a change-over relay is a solution but its contacts would need to be rated to carry all house current (80A in the UK) and you would have to be very careful how the L and N were detected relative to Earth as all installations in the last 15 or so years have detectors that cut the AC if leakage to Earth is detected from either wire.

The cheapest solution, assuming the lines don't get swapped often, is to use a neon screwdriver to find the incoming L wire and swap the wires manually at the master switch if necessary.

Brian.

It should be added that European utility grids have usually TN-C-S earthing with protective earth and neutral connected in the central distribution point (usually meter switchboard) of a building. https://en.wikipedia.org/wiki/Earthing_system

It's impossible here to switch neutral and live without tripping the ground fault protection of the transformer. I assume that the discussed distribution system is implementing TT earthing without a protective earth wire between transformer and houses and no local ground connection of the neutral wire. In this case the assignment of neutral and live isn't very reliable, at least in single-phase wiring, and nothing you should rely on.

FvM said:

I wonder what's the actual need of correcting the polarity. Even with polarized mains connectors the neutral line in a device connected through a socket outlet must be expected to carry a potentially hazardous contact voltage...

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European plugs can be be inserted either way and the concept of phase (line) and neutral (distinct from earth which is local) is not really there. However, the line and neutral at the socket are expected to be the correctly oriented.

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FvM said:

It's impossible here to switch neutral and live without tripping the ground fault protection of the transformer...

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Do you mean that there are no local ground and the neutral and earth connections are same? I always thought that the neutral is connected to the transformer common point (three phase input and three phase + neutral line output) from the transformer. How about single phase domestic connections?

I installed this automatic transfer switch and system that starts a generator, then transfers.
You could wire it to sense wrong polarity through the coils & micro switch. That would Snap it to the other position and swap polarity. (The micro switches open the coil circuit when snapped into place.)

I agree that swapping L1 & L2 has no effect. Swapping either line with neutral would be a very bad thing. Neutral & ground are tied together in my breaker panel. If they swapped either line with neutral, it would blow their fuse and they would have to do it right.

Do you mean that there are no local ground and the neutral and earth connections are same? I always thought that the neutral is connected to the transformer common point (three phase input and three phase + neutral line output) from the transformer. How about single phase domestic connections?

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No, I assume that the OP has TT earthing, separate earth grounds at transformer and home, neutral grounded at the transformer side. As described in the link in my previous post, but only single phase, L1 + N.