Reverse polarity

CallumE · Jun 24, 2021

Hi! I recently purchased a house we've been living in since 2015 as renters, and this week we had British gas switch us over to a smart meter. While the engineer was fitting it and running tests, he asked if we realised that all the kitchen sockets had L and N switched over! I did some digging and not only is it the sockets but the oven, microwave, dishwasher, induction hob, hob fan, the whole lot! There's a separate consumer unit in the kitchen with thick gray cables run from the meter, which whoever installed it, got the L and N mixed up. My question is how after all this time has it not caused issues with all the above and kettles, blenders, chargers etc all running from this? Thanks!

SPECIAL LOCATION · Jun 25, 2021

For basic functional and operational aspects, polarity has negligible effect on any domestic appliances...

as UK mains supply is an alternating current at 50Hz....

Which means 50 times every second the polarity reverses between +/- in relation to earth..

So the appliances really don't care which way round the wires are as the supply is alternating....

e.g it's not a fixed direct current, (DC) like in you car supplied from a battery!

But...

In the event of fault...

or if trying to turn a circuit off via a single-pole switch..

Then dangerous voltages with respect to earth can be present if the polarity is wrong!

So basically polarity only becomes a problem during faults and/or maintenance work...

Geoff1946 · Jun 25, 2021

That doesn't mean that you don't need to get if fixed. It is dangerous.

1. There is no fuse protection between your appliances and the main supply fuse, which could be as high as 100amps. A short circuit fault in an appliance could result in fire.

and 2. Everything is live all the time, with the switches OFF.

ProDave · Jun 25, 2021

If the kitchen CU has it's own "thick grey cables" (meter tails) straight to the meter, then why did the meter monkey not swap them over to correct the fault once he had discovered it?

Isn't finding a fault and then not putting it right verging on negligence?

CallumE · Jun 25, 2021

ProDave said:
If the kitchen CU has it's own "thick grey cables" (meter tails) straight to the meter, then why did the meter monkey not swap them over to correct the fault once he had discovered it?

Isn't finding a fault and then not putting it right verging on negligence?

I've no idea Dave. The meter that he worked on is in a separate room, also the only fault he did Mark was an IP issue on a switch to that CU that overhung the board and is accessible from the back. Either way I'm calling an electrician today to get it sorted.

CallumE · Jun 25, 2021

Geoff1946 said:
That doesn't mean that you don't need to get if fixed. It is dangerous.

1. There is no fuse protection between your appliances and the main supply fuse, which could be as high as 100amps. A short circuit fault in an appliance could result in fire.

and 2. Everything is live all the time, with the switches OFF.

Thanks Geoff, I thought as much and will be calling an electrician today.

SPECIAL LOCATION said:
For basic functional and operational aspects, polarity has negligible effect on any domestic appliances...

as UK mains supply is an alternating current at 50Hz....

Which means 50 times every second the polarity reverses between +/- in relation to earth..

So the appliances really don't care which way round the wires are as the supply is alternating....

e.g it's not a fixed direct current, (DC) like in you car supplied from a battery!

But...

In the event of fault...

or if trying to turn a circuit off via a single-pole switch..

Then dangerous voltages with respect to earth can be present if the polarity is wrong!

So basically polarity only becomes a problem during faults and/or maintenance work...

Makes sense, I'll be getting a spark out to fix it.

Murdoch · Jun 25, 2021

Be aware that some basic testers show "reverse polarity" but actually the fault maybe no earth

Either way you do need to get this looked at

Please let us know what the outcome is

CallumE · Jun 25, 2021

Murdoch said:
Be aware that some basic testers show "reverse polarity" but actually the fault maybe no earth

Either way you do need to get this looked at

Please let us know what the outcome is

Will do, while I'm not a spark I did test the L-E. N-E using a multimeter and it confirmed that the N-E is 230v and L-E 0v. Which also confirmed what the socket tester showed. Now to find an electrician - I'm 0 from 3 calls - all too busy!

Geoff1946 · Jun 25, 2021

ProDave said:
If the kitchen CU has it's own "thick grey cables" (meter tails) straight to the meter, then why did the meter monkey not swap them over to correct the fault once he had discovered it?

Isn't finding a fault and then not putting it right verging on negligence?

I think I can understand that. It would be far beyond his remit to modify the house installation. What if he introduced a fault or a hazard?

Just imagine what horrors he may see in a week of replacing meters! I wonder if they have the authority to refuse to re-connect an installation?

His obligation would be, (in my opinion) , to point out the error/danger, which it appears he has done, though perhaps he should have emphasised the need to correct it.

Geoff1946 · Jun 25, 2021

CallumE said:
I did test the L-E. N-E using a multimeter and it confirmed that the N-E is 230v and L-E 0v.

OK, but be aware of what you are doing. Assuming you are using a typical DIY multi-meter, with probes rather like an inch nail held in a ballpoint casing, you are putting yourself at risk. If you were to touch an earthed bit of metal at the same time as the live terminal, or possibly even set the meter wrongly, the probe would vaporize in your hand.

Professional probes have a very limited contact tip area and fuses incorporated.

Not trying to frighten you, but do be aware what you are dealing with.

Andy™ · Jun 25, 2021

ProDave said:
If the kitchen CU has it's own "thick grey cables" (meter tails) straight to the meter, then why did the meter monkey not swap them over to correct the fault once he had discovered it?

Isn't finding a fault and then not putting it right verging on negligence?

discovered, or caused it?

CallumE · Jun 28, 2021

Geoff1946 said:
OK, but be aware of what you are doing. Assuming you are using a typical DIY multi-meter, with probes rather like an inch nail held in a ballpoint casing, you are putting yourself at risk. If you were to touch an earthed bit of metal at the same time as the live terminal, or possibly even set the meter wrongly, the probe would vaporize in your hand.

Professional probes have a very limited contact tip area and fuses incorporated.

Not trying to frighten you, but do be aware what you are dealing with.

Thank you Geoff, I was very careful and treated it with the respect it deserved. Still no luck on finding an electrician....

Andy™ said:
discovered, or caused it?

If they did, the whole house would be reversed so pretty confident the fault has always been there. It's only the kitchen CU that has the issue and can see clearly they got the tails mixed up when they ran it. It does beg the question though why it wasn't picked up when installed.

Geoff1946 · Jun 28, 2021

CallumE said:
It does beg the question though why it wasn't picked up when installed.

Simple answer, no testing, not even with a basic socket tester. It passed the "bang", test when powered up, so job done.

Badger · Jun 29, 2021

What area are you from op and have you. Managed to source an electrician yet regards

kerching · Jun 29, 2021

Meter monkeys are highly qualified and trained

my daughters friend is a meter monkey

qualifications?........ex pole dancer

Andy™ · Jun 29, 2021

well many probably are highly qualified and trained.... just not at electrics or changing meters

CallumE · Jun 30, 2021

Badger said:
What area are you from op and have you. Managed to source an electrician yet regards

Nottingham and got someone coming around next week, the earliest I could get....next available one was August!

CallumE · Jun 30, 2021

kerching said:
Meter monkeys are highly qualified and trained

my daughters friend is a meter monkey

qualifications?........ex pole dancer

I'm sure there's some transferrable skills there.....somewhere??

Fleeting · Jun 30, 2021

CallumE said:
I'm sure there's some transferrable skills there.....somewhere??

Let us know the outcome would be interesting to know if it was blatant human error or something more.

CallumE · Jul 9, 2021

Hi all, so finally found an electrician who came round today and simply switched over the tails to the kitchen CU from the main feed near the meter. They had simply wired them the wrong way round and blatantly didn't test the circuit other than switching something on. I've got him booked in to run a full EICR to see what else may be amiss before we start playing around with additions, re-wires etc. Thanks everyone for their input and glad it got sorted.

Reverse polarity

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