Reversed Tails at Board

[wicksygas]

Apart from swapping them over, what would you do if you came across Live & Neutral tails reversed at the consumer unit?

 

[littlespark]

take the original installer round the back and explain, harshly, why it might be frowned upon.


wheres the other end of the tails? Ive seen it when they only had brown, so used brown for both and taped the ends blue on the neutral, but not just swapped over.

 

[timhoward]

Test and Test again.
Check incoming Blue to incoming Earth is 0v or negligible and incoming Brown to supplier Earth is 230v.
At that point, having triple checked everything, and all connections in CU and any sub boards I'd swap them.

Deleted 2nd bit - didn't spot it was an RCD on left.

 

[littlespark]

it looks to me that the B40 mcb is being fed FROM the rcd in question... and another rcd feeding the next lot of breakers.

 

[timhoward]

Deleted

 

[timhoward]

it looks to me that the B40 mcb is being fed FROM the rcd in question... and another rcd feeding the next lot of breakers.

Yep agreed. I deleted that bit in the meantime

 

[timhoward]

My eyes really aren't working tonight.
We seem to have an S type 100ma RCD main switch, then a downstream 30ma RCD?

 

[wicksygas]

Can we see photo of other end where (presumably) the main switch is too please?

 

[wicksygas]

take the original installer round the back and explain, harshly, why it might be frowned upon.


wheres the other end of the tails? Ive seen it when they only had brown, so used brown for both and taped the ends blue on the neutral, but not just swapped over.

Fed from main switch in 16mm T&E so no excuse there.

 

[pc1966]

Unless the DNO head is wrong, that is a C1 fault for reversed polarity!

Have you actually checked the polarity at the CU? (i.e. L-E has 230 volts, N-E practically none)

 

[timhoward]

The main and most urgent question is the one @pc1966 just asked (and I asked earlier in post #3)
(plenty of other secondary questions there, like single insulated tails, what earthing system is, why the 100ma RCD, what the 40amp circuit is for...)

 

[pc1966]

Apart from swapping them over, what would you do if you came across Live & Neutral tails reversed at the consumer unit?

Assuming they are swapped, then you MUST correct them!

Otherwise all of the OCPD (both MCBs and 13A plug's fuses) are in the neutral circuit and a L-E fault (N now being L) is a fire starter as no meaningful OCPD (beyond the 60-100A DNO fuse).

Here is it simple as there is an isolator to allow the CU to be powered down without a visit from the seal fairy, otherwise it would be absolutely justified to pull the DNO fuse to fix it (or call them and tell them it is an immediate fire hazard).

Even if both ends are swapped (so just wrong colours) it is still a serious risk going forwards because you can be the next change has a high risk of not verifying polarity. Even though it is a tick box on the EICR report, etc, etc. So to me even that case requires swapping to get it correct.

Plain cable with colours sleeves is easier to change ends without disconnection via coloured tape, but rare outside of 3-phase. Still in my book they should correctly identify cables of such importance.

 

[7029 dave]

As above if reversed polarity is confirmed you must correct it.

 

[Dave OCD]

That 16mm T&E is atrocious the way it's been left in the meter box. And I assume there's no main bonding requirements as the only earth to the CU appears to be the 6mm of the T&E.

 

[-Matt]

Be careful! I came accross this on a job a few years ago, so swapped it back around.

However the boiler PCB board went BANG when i re-energised.

Seems plumber had obviously discovered the incorrect polarity, so rather than getting it rectified, he swapped the polarity in the FCU ?

So when i corrected the polarity at the DB, the boiler PCB then got reverse polarity!!!

 

[timhoward]

That 16mm T&E is atrocious the way it's been left in the meter box. And I assume there's no main bonding requirements as the only earth to the CU appears to be the 6mm of the T&E.

I'm also intrigued by the S-Type 100ma RCD, whether it is there simply for discrimination, or because it's TT....in which case the 6mm main earthing conductor could conceivably support the bonding.

 

[pc1966]

I'm also intrigued by the S-Type 100ma RCD, whether it is there simply for discrimination, or because it's TT....in which case the 6mm main earthing conductor could conceivably support the bonding.

We would need more of a picture of the supply end to see if that goes to a rod or is somehow attached the the supply cable/cut-out.

Being TT is the most likely explanation, but given how new the cut-out looks it might well be TN-C-S now.

 

[wicksygas]

Thank you for your replies guys.
Like you, I asked myself why? and triple checked everything, so swapped them back over.
As there is now no C1 and no place to record "rectified revered tails at board". Is there any need or requirement to report this to, either, whichever company may have made the mistake, The landlord, The tennant, or any official body?

 

[MrPupsi]

Be careful! I came accross this on a job a few years ago, so swapped it back around.

However the boiler PCB board went BANG when i re-energised.

Seems plumber had obviously discovered the incorrect polarity, so rather than getting it rectified, he swapped the polarity in the FCU ?

So when i corrected the polarity at the DB, the boiler PCB then got reverse polarity!!!

This is exactly why I would not just swap them over.

I’d get permission/price approval from the landlord/agent before making any changes so that you’re not liable for any issues.

Could end up being an expensive favour.

 

[pc1966]

This is exactly why I would not just swap them over.

I’d get permission/price approval from the landlord/agent before making any changes so that you’re not liable for any issues.

It is a C1 case though, the most serious category of errors listed for any inspection.

While obviously the owner/landlord should be informed, the choices for making it safe are somewhat limited - correct it, or power off.

Could end up being an expensive favour.

Realistically no normal equipment should be damaged by a L-N swap itself, as it either implies some failing in the insulation or it has some very unusual functional earth feature (like some RCBOs). That is the reason for doing IR testing L+N to E as all "live" conductors should be adequately separated from the CPC & Earth.

Doing a global IR check (so supply isolated, and L+N for all to E) would reveal odd functional earths as a low R (typically RCBO's functional earths look like couple 100k ohm-ish)

But you do raise an important point that all socket outlets, etc, ought to be checked with one of those plug-testers just to make sure that somebody in the past did not "fix" the reversed polarity at the CU by also swapping at some accessories.

I suspect if it came down to some claim for damages, you would have a very strong case against whoever installed the boiler, etc, in the first place as they broke the rules by installing against accepted electrical practices (i.e. failing to report or correct a C1 fault, and knowingly hiding it by a deliberate incorrect installation of the socket/FCU).

 

[MrPupsi]

I carry out EICRs for quite a few agents, Dexters Group being one.

I’ve been implicitly told by them NOT to do anything without permission of the landlord/owner.

Obviously this plays on the mind and I can only go as far turn off the main switch, which we all know will be turned on by the time I leave.
The responsibility for the safety of the installation is then passed to the landlord/agent as I’ve informed them of the issue. If they don’t want to fix it, I can’t forcibly do it.

I have done this before adding a circuit on to a fuseboard that I found in the same situation, and had the RCD trip due to 2 x hard wired appliances with reversed polarity.
Then spent a couple of hours emptying out kitchen cupboards looking for impossible to reach isolators so I could rectify this, for which I didn’t get paid for and had to cancel my next job because of.

Morally it’s the right thing to do of course, but not as simple as just swap it over in my opinion.

 

[Lucien Nunes]

Realistically no normal equipment should be damaged by a L-N swap itself, as it either implies some failing in the insulation or it has some very unusual functional earth feature (like some RCBOs).

Indeed. I've heard stories of things that went bang or stopped working when the polarity was reversed, and the likely explanation was that they already had an undiscovered L-E fault that had been lying low as an N-E fault. Other than the unusual case of the RCBO, I cannot think of any piece of single-phase equipment that will malfunction or be damaged by reversed AC polarity, even other things with functional earths.

Polarity means totally different things for AC and DC. On DC, it refers to which way the electrons go round a circuit, and reversing that will destroy most electronics or at least stop them working. But on AC, polarity refers to which of the two wires is earthed and if all the live parts of the equipment are insulated from earth as they normally should be, it will function equally well regardless of which supply lead is earthed (although there may be safety implications from SP fusing and switching).

In the first half of the 20th century, with 3-wire DC mains, the significance of the different meanings of polarity was more apparent. With the middle wire earthed and thus neutral, half the properties with a 2-wire service had a positive live and half had a negative live (live was then the correct term for what we now call line.) In some situations what mattered was live / neutral, e.g. all light switches needed to be in the live. In other situations the live / neutral polarity didn't matter but the positive / negative did. e.g. with AC/DC radios and TVs that used half-wave rectified mains as HT. If you plugged in your radio and the valve heaters glowed, but there was no sound, you would reverse the 2-pin connector on the back of the set. This allowed the polarity to be put right without rewiring the plug (if it was 3-pin.)

 

[Mike Johnson]

Apart from swapping them over, what would you do if you came across Live & Neutral tails reversed at the consumer unit?

View attachment 87894

Would not touch it until I had instructions from the owner/landlord, if I did not know them then a duplicate book with the instruction written out and signed by them prior to any work being carried out.

 

[timhoward]

The responsibility for the safety of the installation is then passed to the landlord/agent as I’ve informed them of the issue. If they don’t want to fix it, I can’t forcibly do it.

It's relatively early days for the new law, but there is provision in it for the local housing authority to serve a remedial notice, or in the case of urgent remedial action being required by the most recent EICR they can in theory agree directly with tenants for an authorised person to carry out the urgent remedial action.

As things stand I cannot see how this can ever really be triggered though, unless there is an agent involved and they are chasing up (which I know some do, as I get phone calls asking if I've done the remedials yet!)
But in the case of a private landlord who directly rents, who's to know if a C1 gets dealt with?

I do wonder whether when the dust settles and the shortcomings are established and agreed the CP scams will eventually require C1's not immediately dealt with to be reported directly to the housing authority.

 

[Mike Johnson]

Perhaps it should be a requirement for insurance companies to ask for the EICR and any other certificates and check to see if the building/installation conforms, solicitors also should be liable to check upon building sales, lets face it they charge enough, and insurance companies are the ones financially at risk, the only specialist in all of this is the Actuary who specialises in advising on how the claim can be reduced, is it time for more legislation or a clear indication who is liable?