3 phase supply, advice required

[lurch]

Some advice please. . . I have a local community centre (old prefab) that has a 3 phase TNS supply from the local DNO. I have carried out a EICR which has unsatisfactory on various points, however I am trying to locate the regulation that covers isolation. . . . the scenario is 3 phases in to 3 phase meter, and then 3 separate single phase domestic Consumer units, all located within a cupboard.

My concern is that there is no single point of isolation on the 3 phase supply. I want to give this a C2 but not having come across this scenario before and want to know the regulation that covers this . . . if there is one. Or is it totally acceptable to have this setup as it is. . . . constructive answers always welcome.

 

[Ian1981]

Now we are moving into the realms of assuming that everyone is foolproof, just because they are a tradesman. Today's "super regs" have been drawn up, assuming that everyone that's not electrically qualified is a moron. The incident i brought up happened in the days before thins like RCDs MCBs etc, but a single point of isolation would have saved his life.

Suppose there was a single of isolation, what if said isolation switch was faulty and only isolated say the neutral.
Unskilled personal who do not use safe isolation and testing procedures should not be working on Electrical installations full stop.
Trained skilled personnel would only have isolated the circuit to be worked on anyway.
It’s very unfortunate and a tragedy but they should no their limits.
An isolation switch or a lack of is not to blame in this case.

 

[Steve Bramah]

Each consumer unit has a means of isolation to their respective circuits.
I can’t see how not having a single point of isolation may result in potential danger to the user of the installation of anyone else.

Hi Ian, you are assuming that the installation you are about to work on, "does exactly what it says on the tin".
In my experience, most EICRs that i have carried out have incorrectly marked boards, due to modifications and additions by "electricians" who haven't altered, or updated the legend. Especially love the one that says "sockets in bobs office". His office was demolished 5 years ago, and Bob doesn't work here anymore. Its not a perfect world we work in.

 

[Ian1981]

We replaced the DBs in a similar setup, fitting a 4 pole isolator marked installation main switch. This was the last job we ever used MK consumer units.
View attachment 41620

Cpc’s should’ve enter the same hole as the tails
The only exception is where a swa has a parallel cpc running with it and non ferrous gland plates etc.
Good job non the less tho haha

 

[Ian1981]

Hi Ian, you are assuming that the installation you are about to work on, "does exactly what it says on the tin".
In my experience, most EICRs that i have carried out have incorrectly marked boards, due to modifications and additions by "electricians" who haven't altered, or updated the legend. Especially love the one that says "sockets in bobs office". His office was demolished 5 years ago, and Bob doesn't work here anymore. Its not a perfect world we work in.

Which is why we carry out safe isolation and testing.
As an electrician if we wanted to work on bobs office sockets then we wouldn’t isolate the whole installation by switching off the main isolator would we?
In This case we would be isolating all 3 consumer units causing possible disruption to the rest of the installation.

 

[Steve Bramah]

Which is why we carry out safe isolation and testing.
As an electrician if we wanted to work on bobs office sockets then we wouldn’t isolate the whole installation by switching off the main isolator would we?
In This case we would be isolating all 3 consumer units causing possible disruption to the rest of the installation.

I think we are moving away from the point. What you have stated is correct, but the point i am trying to make is don't believe what is on the legend.

 

[telectrix]

Could happen anywhere switching off the wrong Mains Switch, just an important question, was the Plumber trained in the Safe Isolation Procedure? seems not in this
instance.

plumber trained? contradiction in terms there, pete. you can train a dog, but never a plumber.

 

[Spoon]

but all it takes is for joe public to look in cupboard and isolate wrong board

Unskilled personal who do not use safe isolation and testing procedures should not be working on Electrical installations full stop.

As above, 'joe public' should not be messing with the boards.

 

[streamer]

If you were to fit an isolator, then really you should get the supply company to fit an isolator in order to allow you to fit an isolator, in which case you wouldn't have to fit an isolator at all!

 

[suffolkspark]

it is in the regs that there should be a single point of isolation for an electrical installation,,,, but its definition of an installation is poorly worded meaning you can have more than 1 "installation" within a premise.... so its a grey area, imo it at the most warrants a C3

 

[hightower]

537.1.4 is the reg I think relates to this, but I'm with @Pete999 and the others - what you've got here is 3 SP installations rather than a TP install. I'm failing to see how it's unsafe.

 

[Pete999]

this highlights the point I am making. . . if there was a single point of isolation then this wouldn't of happened. we are obsessed in this country on cutting into meter tails and hooking in additional cu's .

You could argue that Mate, but in this case the Plumber was at fault for not observing the correct isoation procedures.

plumber trained? contradiction in terms there, pete. you can train a dog, but never a plumber.

OK I'll give you that one.

If you were to fit an isolator, then really you should get the supply company to fit an isolator in order to allow you to fit an isolator, in which case you wouldn't have to fit an isolator at all!

The circle of life continues

it is in the regs that there should be a single point of isolation for an electrical installation,,,, but its definition of an installation is poorly worded meaning you can have more than 1 "installation" within a premise.... so its a grey area, imo it at the most warrants a C3

You have isolation at the three inputs to the three SP&N CUs no need to code imo.

 

[Pete999]

this highlights the point I am making. . . if there was a single point of isolation then this wouldn't of happened. we are obsessed in this country on cutting into meter tails and hooking in additional cu's .

Still doesn't distract that the "Safe Isolation Procedure" should have and should be adhered to at every point of isolation in my opinion, regardless of how many switches are involved.

 

[suffolkspark]

You have isolation at the three inputs to the three SP&N CUs no need to code imo.

I wouldn't code it either pete, but this subject of single point of isolation for an installation has come up before

 

[westward10]

I would definitely Code it.

 

[Pete999]

I would definitely Code it.

So what would you code it as and why?

 

[westward10]

I tend not to discuss what Code I would list it under as that that is personal opinion and different circumstances may give different outcomes. As in #35 by HT I would refer to Reg 537.1.4 and I certainly don't sway with this more than one installation in an installation where there is only one source of supply.

 

[telectrix]

i would not code it, but maybe fit a notice " ensure that the correct isolation procedure is carried out before working on this installation". a bit like " all the right notes, but not necessarily in the right order".

 

[Ian1981]

It’s all down to interpretation again.
Each DB has a linked main switch and as such has a single point of isolation for each DB.
However the regulation points out that each installation shall have a point of isolation as close to the origin of the installation capable of switching the supply on the load side as a means of isolation.
I recall Napit put out a column in professional electrician magazine saying that a standard consumer unit supplying final circuits and a separate consumer unit supplying say a shower circuit or economy 7 can be classed as separate installations.
I myself did an EICR a couple of years back but failed to mention the single point of isolation on the Eicr.
An Niceic inspector who did a site visit as part of the company annual assessment said although it didn’t warrant a code , a comment should have been made in the relevant section of the Eicr.
But I get the view of ‘they can only be one installation etc’
My opinion....... I wouldn’t code this example but I’d mention it on the report.

 

[davesparks]

If it was my job, i would fit a 4 pole 100a isolator, much the same as your electrical utilities supplier would fit. Not expensive, and sorts out the "one point of isolation" reg. Hope this helps.

That should be either a TP isolator or a TP&N isolator if it is intended for on-load switching.
A straightforward 4 pole isolator won’t necessarily have late break/early make on the fourth pole.

 

[Dillb]

An Niceic inspector who did a site visit as part of the company annual assessment said although it didn’t warrant a code , a comment should have been made in the relevant section of the Eicr.

Since when is it any business of the NICEIC what the regs state? Its either compliant or its not, yet they make a comment that neither confirms it or isnt. Yet people still fall over themselves for these scams.

 

[Ian1981]

Since when is it any business of the NICEIC what the regs state? Its either compliant or its not, yet they make a comment that neither confirms it or isnt. Yet people still fall over themselves for these scams.

Am not a QS so was not present during the inspection, this was just feed back from my supervisor.
It’s always stuck in the back of my mind tho.

 

[lurch]

Not a bad idea Steve, but if you relyon the Isolator you mention as the single point of isolation, problem occurs in one particular SP system, then you would isolate all three CUs. Just a thought.

. . . this is the case on any 3 phase installation with a TPN board

 

[lurch]

Not a bad idea Steve, but if you relyon the Isolator you mention as the single point of isolation, problem occurs in one particular SP system, then you would isolate all three CUs. Just a thought.

. . . this is the case on any 3 phase installation with a TPN board

 

[lurch]

Each consumer unit has a means of isolation to their respective circuits.
I can’t see how not having a single point of isolation may result in potential danger to the user of the installation of anyone else.

. . . picture this scenario. Fault on circuit 1 on DB 1. "quick isolate that circuit Dave!" Dave goes to cupboard and isolates first main switch he sees. "Done" . . . but is it??

 

[lurch]

As above, 'joe public' should not be messing with the boards.

I would not hesitate in asking a customer who has rung me to report a smell of burning to go to mains and isolate a main switch until I can get there. This is hardly messing with a board !!!