Pulling live meter tails from isolater switch in consumer unit

[3435hobiton]

Hi, could someone advise me of the safest procedure when pulling live meter tails from the isolator switch at the consumer unit. I know about switching off the main switch to take out the load, but will not be cutting the seal and pulling the fuse from the cut-out. On this occasion I need to pull out the live first... connect to a Henley block and then the neutral and do the same. When reconnecting I will connect the neutral first and then the live. I was wondering if anybody could offer any helpful advise that I may have overlooked.
Regards Paul

 

[Simon47]

For instance (i have had it before ), some numpty had installed the tails the wrong way round. So everything within the installation was of a reversed polarity. Immediate code 1 for the entire installation. More practical for me to work live and change those tails around at the ccu rather than the risk to the client while waiting for a dno response (council as well so another ball ache entirely time+safety wise).

The ONLY reasonable option in that case is to pull the fuse to make dead. If not accessible, you call whoever and wait.

I have been incredibly fortunate,
Any time I have ever needed to work on tails, the seal wasn’t there when I turned up on site.

Two times I've had someone out they've not sealed the head. One was a contractor fitting an isolator at my home - I rang my supplier, they did it f.o.c. The other time was a DNO engineer who couldn't find any seals in his van.

From a health and safety point of view time and cost are not mitigating factors when risk assessing whether you should work live and demonstrates a lack of H&S knowledge when assessing the hazards

Actually in general time and cost are a consideration when assessing risk & avoidance/mitigation measures - hence the R in ALARP.
But, I've seen nothing in this thread where working live could be considered a reasonable course of action. I can't think of any normal situation where working live on a domestic supply could be considered to be the ALARP option.

 

[UNG]

Actually in general time and cost are a consideration when assessing risk & avoidance/mitigation measures - hence the R in ALARP.
But, I've seen nothing in this thread where working live could be considered a reasonable course of action. I can't think of any normal situation where working live on a domestic supply could be considered to be the ALARP option.

I think you need to reread the ALARP guidance as the R makes no reference to cost or time and references keeping risks As Low As Reasonably Practicable whilst costs are mentioned in the guidance this is only in connection with disproportionate and proportionate costs relative to the risk CBA for the situation

 

[Simon47]

And what is "reasonable" ? That is where time and cost are factors.
Taking things to extreme for dranatic effect ... We (mostly) have to have our cars tested (MoT Test) every year. At one extreme, the test could be scrapped altogether - that would clearly not reasonably mitigate the risks from faulty cars on the road. At the other extreme, we could need a test every week - which would clearly incur a time and cost penalty out of proportion to the risk being mitigated. For the time being, TPTB have decided that annually is a "reasonable" period.

Back to this discussion ...
Clearly working on live tails is not reasonable except for a few corner cases.
But if you argue time and cost aren't relevant then the only reasonable approach is to have the DNO come out and switch off the 11kV to the substation, and positively earth the outgoing service before allowing the service fuse to be pulled - how else do you positively ensure no conductor (including PEN) can become live while you are working. That would clearly be safer than just pulling the fuse - but the TIME and COST would be disproportionate to the level of risk being mitigated.
If the guidance for working on tails doesn't adequately cover these factors then that's not a problem with my understanding of ALARP. If you ignore time & cost then you are talking about AFAP - and that's a whole new can of worms.

 

[davesparks]

For instance (i have had it before ), some numpty had installed the tails the wrong way round. So everything within the installation was of a reversed polarity. Immediate code 1 for the entire installation.

No it isn't, it's a C2 if you are carrying out an EICR.

More practical for me to work live and change those tails around at the ccu rather than the risk to the client while waiting for a dno response (council as well so another ball ache entirely time+safety wise).

No it isn't, it is hardly an emergency situation requiring immediate action, you can take a couple of minutes to think about a reasonable and safe way to correct it.
Reversed polarity on the tails has probably been there a good few years and not become dangerous yet. The fact that you have now seen it and identified the potentially dangerous situation does not make it suddenly start killing people.

You can take a few minutes to stop and think rationally, find out who has the keys to access the ryefield board, arrange access and do the work safely.

And even if it has somehow become an immediately dangerous situation that needs emergency action just turn the installation off. That removes the danger and gives you time to think and make a safe plan to fix things.

 

[loz2754]

No it isn't, it's a C2 if you are carrying out an EICR

Not according to Electrical Safety First BPG4. 'Reverse polarity at the origin of the installation C1.'

 

[davesparks]

Not according to Electrical Safety First BPG4. 'Reverse polarity at the origin of the installation C1.'

What is the immediate danger?

 

[Simon47]

That there's no earth fault protection on the circuits ? That things "switched off" will be live ? That nothing has happened yet doesn't mean it isn't dangerous now.
If you think reversed tails should only be a C2, how would you code an installation with no fuses/MCBs - everything just wired to the bus bar ?

 

[davesparks]

That there's no earth fault protection on the circuits ? That things "switched off" will be live ? That nothing has happened yet doesn't mean it isn't dangerous now.

That is potential danger, not immediate danger. Something which is potentially dangerous is something that will become a danger if something else happens, such as a fault occuring.
This is why a lack of CPC, incorrect circuit protection etc are C2 items.

If you think reversed tails should only be a C2, how would you code an installation with no fuses/MCBs - everything just wired to the bus bar ?

That would be a C2 unless a fault is present, the danger of not having an OCPD is a potential danger, not an immediate danger.

C1, immediately dangerous, is for items which present an immediate danger without requiring a fault or similar to occur. An exposed live part, such as with a missing DB blank, is an immediate danger. An exposed part which will become live under fault conditions is potentially dangerous.

C1, C2, C3 does not represent levels of how bad you think something is, they are codes with clearly defined meanings.

 

[loz2754]

What is the immediate danger?

Good question. I think the reasoning is that there will be parts that are live that are reasonably expected not to be, even with the protective device switched off or the fuse removed. Whether this is classed as immediate danger seems to be open to interpretation.

 

[davesparks]

Good question. I think the reasoning is that there will be parts that are live that are reasonably expected not to be, even with the protective device switched off or the fuse removed.

Yes everything connected to the neutral bar at the DB will be at line voltage, but it will all be behind covers which needs to be deliberately removed before being touched.
The neutral is defined as being a live conductor and is protected from touch in normal use in the same way that a line conductor is.

The danger of touching the neutral bar of the DB would be immediate once the cover of the DB has been removed, but with the cover fitted the danger is only potentially there.

Whether this is classed as immediate danger seems to be open to interpretation.

I don't see how,
Immediate danger - you can touch it without removing any covers.
Potential danger - it's dangerous if you remove the cover.

 

[Simon47]

An exposed live part, such as with a missing DB blank, is an immediate danger.

Playing devil's advocate.
It's not immediately dangerous if someone doesn't stick their fingers in. "Most" people wouldn't think of sticking their fingers in.
An ES lamp in a holder without a big shroud will have an exposed live shell - waiting to zap people who would not expect it to be live. So why isn't that immediately dangerous - it doesn't need a fault to be live. And it will still be live when switched off at the wall if it's a single pole switch.

.C1, C2, C3 does not represent levels of how bad you think something is, they are codes with clearly defined meanings.

In theory - but look at how many "discussions" we have here about coding !

Yes everything connected to the neutral bar at the DB will be at line voltage, but it will all be behind covers which needs to be deliberately removed before being touched.

AND everything in the whole installation connected to neutral. Like ES lamp caps, and the pins in BC lampholders. Even when a reasonable user might expect things to be off because "switched off".

 

[davesparks]

Playing devil's advocate.
It's not immediately dangerous if someone doesn't stick their fingers in.

It is immediately dangerous because someone can touch a live part without a fault occurring, cover being removed etc.
The immediate danger is that a person could make contact with a live part.

An ES lamp in a holder without a big shroud will have an exposed live shell - waiting to zap people who would not expect it to be live.

Yes it will, but I don't see how that is relevant to the debate.

The debate is around the advice that reverse polarity at the incoming supply is a C1 but elsewhere in the installation is a C2.
The case of the exposed ES lamp cap would make it a C1 regardless of where the reverse polarity is in the installation.

So why isn't that immediately dangerous - it doesn't need a fault to be live. And it will still be live when switched off at the wall if it's a single pole switch.

It is immediately dangerous, I have not suggested it isn't.

I am not suggesting that a reversed polarity fault can't be immediately dangerous, I am saying that it is not always immediately dangerous.

In theory - but look at how many "discussions" we have here about coding !

Yes there are many discussions, that doesn't change the fact that the codes are clearly defined. The number of discussions, and the content of many of them, show something about the knowledge and understanding of some of the people carrying out EICRs and highlight the problems with some of the published guidance.

AND everything in the whole installation connected to neutral. Like ES lamp caps, and the pins in BC lampholders. Even when a reasonable user might expect things to be off because "switched off".

The pins in BC lamp holders are always there regardless of the polarity and are always a danger. The BC lampholder is only allowed because there is no reasonable way to get rid of it, if a lampholder with exposed pins like that was invented today it would never be allowed.