3 sp circuits off a tp isolator

[Rockingit]

537.2.1 - 537.2.2.6

Though not specific it give a good guidance

Then

523.6.3

for starters.

Sorry mate, but 'straws' and 'clutching' are the only two words I see when I look those references up.

Stick with the muesli; you know where you are with a decent bowl of muesli.

 

[Outspoken]

Sorry mate, but 'straws' and 'clutching' are the only two words I see when I look those references up.

Stick with the muesli; you know where you are with a decent bowl of muesli.

If you consider that a helpful answer to a question then I feel sorry for your customers or clients.

The simple fact is there is nothing specific in BS7671:2008 that states you cannot do what the OP has witnessed, the reasoning being is that no sensible and decent engineer or electrician would do it so it has not come onto the radar of those writing the Regs. That is why we need to fall back on the Regs I listed as GUIDANCE...in other words, apply ruddy common sense and if you do not understand why you should not do this then your a shiite electrician who should be a bus driver!

 

[D Skelton]

I think everyone knows why it's a bad idea on three socket circuits, there are various reasons, however it's common practice on lighting circuits so that might be one of many reasons why there is nothing specific in the regs about it.

Just my thoughts?

 

[Rockingit]

Don't have a Regs book to hand, but certainly section 53(?) Selection and Erection would cover this, but also any reg that deals with using the correct equipment for the correct job would be appropriate..further, the design of an installation is covered by other regulations, such as CDM and also would such an installation pass any "proper design" guides from the ECA, NICEIC or any Industry body such as the IET or CIBSE

I will look up the regs later if no-one has done so, it amazes me how many here seem to have a problem with looking up a regs book themselves!

If you consider that a helpful answer to a question then I feel sorry for your customers or clients.

The simple fact is there is nothing specific in BS7671:2008 that states you cannot do what the OP has witnessed, the reasoning being is that no sensible and decent engineer or electrician would do it so it has not come onto the radar of those writing the Regs. That is why we need to fall back on the Regs I listed as GUIDANCE...in other words, apply ruddy common sense and if you do not understand why you should not do this then your a shiite electrician who should be a bus driver!

Now.... I'm almost starting to enjoy the sport in this! Which post is it, exactly?

Look, when in a hole stop digging. No-one has yet to suggest that this set-up is a good idea, far from it. No-one here is a shiite sparky - those that are went all glazy eyed and went to the pub several pages ago not having a clue about the finer-ish points of 3ph theory and harmonics.

But the original OP was asking the question of 'is it a code'? And as you have just so succinctly pointed out, no it isn't as you can't justify holding that opinion [of it being so] based on the rules we abide by.

 

[D Skelton]

What he said! ^^^^^

 

[ackbarthestar]

I think i would agree with that, DSkelton,

559.6.2.3 allows a 3-phase circuit to be split across three single phases sharing the same neutral as long as the three single phase circuits are isolated and protected by one 3-phase MCB/MCCB. Therefore treating the whole as a single three phase circuit.

However, it only specifically mentions lighting and not sockets. But then it doesn't condemn the use of other single phase outlets. So it might be a case of reducing ambiguity and applying common sense and waying up the probabilities of a possible loss of neutral where portable appliances are used.
I believe 'they' call it 'Risk Assessment'.....

 

[D Skelton]

I believe 'they' call it 'Risk Assessment'.....

Or as others have rightly pointed out, common sense! Lol

 

[Rockingit]

Or as others have rightly pointed out, common sense! Lol

Oi you....we'll have none of that fancy talk in here!

 

[Engineer54]

Can't quite believe what i'm reading here!! Am i to understand that qualified electricians here, would actually apply a 3 pole/phase MCB to supply 3 single phase circuits using a single neutral conductor?? Then start talking about commonsense and risk assessment!! i've heard it all now!! lol!!

 

[D Skelton]

I think you need to read the WHOLE 10 pages again Eng! Lol. No one here, regardless of our opposing views on certain matters have condoned this practice at all!

Edit: socket circuits we're talking about here.

Lighting circuits are a different matter, I have and will continue to apply this method of installation where suitable to certain types of lighting circuits.

 

[Engineer54]

I think you need to read the WHOLE 10 pages again Eng! Lol. No one here, regardless of our opposing views on certain matters have condoned this practice at all!

Edit: socket circuits we're talking about here.

Lighting circuits are a different matter, I have and will continue to apply this method of installation where suitable to certain types of lighting circuits.

Not on any of my projects you wouldn't!! You would actually wire all the 3 phase lighting loads, with the same single neutral conductor?? ...Wow!!

 

[Darkwood]

As i said on the first page i have come across 3ph and n track lighting which by its nature can only have 1 neutral... in the correct set-up its ok an no-one i believe has even indicated its a good method or practice regarding the OP's set-up but at most in some views that its not really something to get too concerned about although it has a finite chance that harmonics etc could lead to over-current on the N conductor now it would be a strange loading set-up on the sockets to even bring this in as an argumentative angle although its good for the debate to realise the potential exists even if very slim.

As for design the OP set-up shouldn't be designed as such as most would agree here but it is the case the OP has found the set-up as is.

Its in my understanding that the BS7671 is partly designed with probability in mind and this does show up in various regulations and of course will lead to the lengthy debates we see in this thread.... if probability wasn't at the core of some reg's then we wouldn't be working and installing systems at the voltage we do.

 

[D Skelton]

Not on any of my projects you wouldn't!! You would actually wire all the 3 phase lighting loads, with the same single neutral conductor?? ...Wow!!

That's your perogative, but I do so myself safe in the knowledge that given the right set up it is a perfectly safe and well recognised method of installation (although not hugely common) that is permitted by regulation.

 

[Darkwood]

Ive come across this method on more than a few occasions and installed it twice over 25yrs on lighting systems, designed right it is perfectly safe and is an economical method. Various ways exist if you want to go the extra mile like N monitoring where loss or overloading of N would drop out all 3 phases this is really only needed when existing install make it impractical to rewire and can open up the field of utilising a shared N.

I personally don't design my installs this way but thats not to say its not an option, its a method has been practised for decades and i would have thought if it was such a disaster waiting to happen then im sure the IET would have addressed it in the Regs.

 

[Engineer54]

As i said on the first page i have come across 3ph and n track lighting which by its nature can only have 1 neutral... in the correct set-up its ok an no-one i believe has even indicated its a good method or practice regarding the OP's set-up but at most in some views that its not really something to get too concerned about although it has a finite chance that harmonics etc could lead to over-current on the N conductor now it would be a strange loading set-up on the sockets to even bring this in as an argumentative angle although its good for the debate to realise the potential exists even if very slim.

As for design the OP set-up shouldn't be designed as such as most would agree here but it is the case the OP has found the set-up as is.

Its in my understanding that the BS7671 is partly designed with probability in mind and this does show up in various regulations and of course will lead to the lengthy debates we see in this thread.... if probability wasn't at the core of some reg's then we wouldn't be working and installing systems at the voltage we do.

If your talking about 3 phase bus bar type affairs with plug-in connections, then fine your never going to loose the neutral along it's length are you. But conventional lighting wiring methods no way, that neutral single conductor can end up three times the length of the phase conductors if wired in banks per phase!! Breaks in that single neutral conductor could add more than a little interest too!! Now why would you not run a separate neutral conductor with each phase leg, and if you are going to use a 3 pole breaker why not a four pole, so that if fault did occur, the breaker would isolate ALL live conductors!!