My UPS reverses the L N

[Mike45]

My checker shows me that the wall outlet has the correct wiring.

When I measure the output of my APC UPS it shows reversed.

Without rewiring the UPS can you think of an easy way to make this work correctly?

[Crossy]

I had a similar problem with an AVR. A simple lead that re-crossed L-N sorted the issue (I later took the beast apart and sorted it properly).

That said, a L-N cross to your PC isn't going to cause any issues.

[RichCor]

I believe the MAJOR issue with L - N being reversed is

incorrect in-line fuse/breaker position

SPST Power Switch leaving entire circuit potentially live

Fuse: If the fuse is on the working N leg then it can't act as a safety if the circuit shorts to ground.

SPST: If the power switch is Single Pole - Single Throw, turning the switch to OFF on an L- N reversed device will disconnect the device from Neutral, but the entire circuit has the same potential as ON. Normally, when wired correctly and the SPST switch in the OFF position, the circuit should only have the potential of Neutral to Ground, so maybe a few volts but not lethal. A DPST or DPDT Switch would disconnect both legs/lines so wouldn't create this issue.

I've witnessed on many occasions someone turning off a power switch on a multi-outlet extension and getting a shock when a finger accidentally made contact with a pin as they unplugged something. Most ungrounded outlets use SPST but the two-pin plug allows it to be plugged in backwards, putting the switch and the fuse on the N side.

Is the APC UPS input cord hard-wired? Some use a C13 or C14 connector, same as a desktop PC, in which you just need to find the correctly wired replacement cord.

If not, then you could do as Crossy did, make sure the L on the same side as the working fuse/breaker.

[IMHO]

APC UPS's that accept UK plugs do indeed have Active and Neutral reversed to suit the UK style plugs used in Malaysia and Singapore.

The ones that don't accept UK plugs use 'normal' American (NEMA)/Thai polarisation though.

I guess the big question is, what are you plugging into it? That will determine whether it's a problem or not.

[Mike45]

APC UPS's that accept UK plugs do indeed have Active and Neutral reversed to suit the UK style plugs used in Malaysia and Singapore.

The ones that don't accept UK plugs use 'normal' American (NEMA)/Thai polarisation though.

I guess the big question is, what are you plugging into it? That will determine whether it's a problem or not.

LED TV, computer, router, phone chargers.

[Crossy]

LED TV, computer, router, phone chargers.

I would suggest that none of those have an issue with polarity reversal.

But as RichCor suggested do watch out if you are using a power strip with switches as they may not open the live (actually many of them are wired incorrectly anyway).

[Mike45]

LED TV, computer, router, phone chargers.

I would suggest that none of those have an issue with polarity reversal.

But as RichCor suggested do watch out if you are using a power strip with switches as they may not open the live (actually many of them are wired incorrectly anyway).

For now I'll do nothing. I still have to tackle the CU RCBO problem.