3 sp circuits off a tp isolator

[D Skelton]

If your talking about 3 phase bus bar type affairs with plug-in connections

This (and other similar types of set up) is exactly what we are reffering to.

You can rest easy Eng!

 

[Darkwood]

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!!

As i have said before i said a carefully designed set-up with added monitoring or pre-designed system like track lighting, we all seem to be arguing the same side of the coin from a different angle its just the case that its not the most common method in most members experience hence it throws up a lot of interest if ever mentioned and yes 4pole devices if they could fit your board as long as it early make / late break on the n cos we wouldn't want to be zapping the lighting with a voltage spike as you star point the N by accident.

 

[Knobhead]

In = √((Ia²+Ib²+Ic²)-((Ia*Ib)+(Ia*Ic)+(Ib*Ic)))

 

[johnboy6083]

I did try and offer that calc as a way of calculating neutral currents earlier. We have raised this formula before, and I proved through a power analyser (screen shots I posted) that it doesn't work where harmonics are involved.

however in the instance I used, the harmonics were large enough that an active filter was used. The OP discussed sockets, in which only a crystal ball can predict future usage.

 

[Knobhead]

A couple of weeks back 4 transformers failed in Nottingham, from what I can gather it was the neutrals that failed. I live in student land so lots of SMPS’s. It’s a wonder the leccy board don’t put a zip fastener along the cable runs. No sooner have they filled one hole in their digging another, neutrals failing.

The neutrals in Victoria Centre are near melting! It’s only going to get worse. The transformers taking the brunt of it as they are the main filter for harmonics.

 

[Outspoken]

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?

We will have to agree to disagree on that but I hold your position to be questionable.

Running three single phase lighting circuits in one location to load spread is indeed common practice, but the only time they should be on a common 3P+N MCB/Isolator etc is when contractor controlled so they are effectively a 3 phase circuit and should be treated as such. Neutrals should not be looped though and may come back to a common point but should be separate for each on the lighting legs.

If you are talking about standard lighting circuits with conventional switching etc then they should be on separate MCB's and not a 3 pole. They should not have shared neutrals and to do so would be extremely bad in my humble opinion.

Oh by the way, just got off the Phone with the NICEIC who agree with me on this, as do NAPIT and ELECSA. I have also conferred with the IET who have condemned the notion of running single phase circuits, except as stated where controlled via a contactor, via a 3 pole MCB/Isolator whether the neutral is shared or not.

I will admit that no-one could specifically point to a regulation to prevent someone doing this, but all stated they would not consider this good practice or good design.

 

[D Skelton]

When I refer to common practice I am only referring to the pre wired, modular trunking systems and busbar lighting track which are common in larger commercial installations. I agree and when I have installed these they have always been contactor controlled, I wouldn't do it any other way. With regards to wiring standard lighting circuits in this way, I am fully aware that this is a big no-no. I should have made it clearer and said something like this:

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

Apologies for the confusion.

 

[D Skelton]

When I refer to common practice I am only referring to the pre wired, modular trunking systems and busbar lighting track which are common in larger commercial installations. I agree and when I have installed these they have always been contactor controlled, I wouldn't do it any other way.

With regards to wiring standard lighting circuits in this way, I am fully aware that this is a big no-no. I should have made it clearer and said something like this:

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

Apologies for the confusion.

 

[Engineer54]

When I refer to common practice I am only referring to the pre wired, modular trunking systems and busbar lighting track which are common in larger commercial installations. I agree and when I have installed these they have always been contactor controlled, I wouldn't do it any other way. With regards to wiring standard lighting circuits in this way, I am fully aware that this is a big no-no. I should have made it clearer and said something like this: Apologies for the confusion.

Well that's cleared that one up then...!! lol

To be honest, i was more than a little surprised you were in favour of installing such a system, while the confusion was still reigning!!

I have seen such systems in use, and seen the consequences when things go wrong too!! It was on a NEC spec'd project and can still see clearly in my mind how the single neutral was branched off to supply light fittings. ....Yep you guessed it WING NUTS!! A good 30 or so of them!!

Haven't seen that guy about much here lately, that reckoned the Yanks multi branch circuits for both sockets and lighting, were going to be the way of the future in the UK!! He really was a classic with some of his ideas!! lol!!

 

[Engineer54]

As i have said before i said a carefully designed set-up with added monitoring or pre-designed system like track lighting, we all seem to be arguing the same side of the coin from a different angle its just the case that its not the most common method in most members experience hence it throws up a lot of interest if ever mentioned and yes 4pole devices if they could fit your board as long as it early make / late break on the n cos we wouldn't want to be zapping the lighting with a voltage spike as you star point the N by accident.

As far as i'm aware, most 2 and 4 pole breakers, (certainly those supplied to us by Schneider (MG)) have a designated Neutral pole for that very reason.

 

[Knobhead]

Don’t know about the smaller MG breakers, but the larger MCCB’s and ACB’s you can specify simultaneous break. I had to use these for high current double pole single phase supplies, up to 4000A where we doubled up the poles in a 4 pole unit.

Check the specification and you’re requirements first.

 

[ackbarthestar]

We will have to agree to disagree on that but I hold your position to be questionable.

Running three single phase lighting circuits in one location to load spread is indeed common practice, but the only time they should be on a common 3P+N MCB/Isolator etc is when contractor controlled so they are effectively a 3 phase circuit and should be treated as such. Neutrals should not be looped though and may come back to a common point but should be separate for each on the lighting legs.

If you are talking about standard lighting circuits with conventional switching etc then they should be on separate MCB's and not a 3 pole. They should not have shared neutrals and to do so would be extremely bad in my humble opinion.

Oh by the way, just got off the Phone with the NICEIC who agree with me on this, as do NAPIT and ELECSA. I have also conferred with the IET who have condemned the notion of running single phase circuits, except as stated where controlled via a contactor, via a 3 pole MCB/Isolator whether the neutral is shared or not.

I will admit that no-one could specifically point to a regulation to prevent someone doing this, but all stated they would not consider this good practice or good design.

Lol, .....This sounds as though you are rewriting 559.6.2.3 and you claim to have NICIEC, NAPIT, ELECSA with even the IET agreeing with you?

Maybe the IET made a mistake?.......Lol.

 

[Rockingit]

In my experience, those who shout loudest normally have the least to say.

 

[D Skelton]

In my experience, those who shout loudest have the sorest throats

 

[Engineer54]

No matter what, supplying/wireing 3 single phase circuits via a 3 pole breaker with a single neutral conductor is not a very good idea at all. As far as i'm aware, only the Yanks and maybe, the now very few countries that have based their codes on NEC would use such a system...

 

[Outspoken]

Lol, .....This sounds as though you are rewriting 559.6.2.3 and you claim to have NICIEC, NAPIT, ELECSA with even the IET agreeing with you?

Maybe the IET made a mistake?.......Lol.

I have re-written nothing and it was after reading that I decided to contact the relevant organisations to get clarity. I'll admit that each one interpreted the "common neutral" in a slightly different way, and I would question if the NAPIT chap I spoke to understood the difference between common neutral and borrowed neutral, however I believe he actually meant the same thing as the others but was poor at explaining that.

I believe, based on the conversation had with the IET that the regulation is meant to be interpreted as each line of lights from a phase would have it's own neutral, but as these would be contactor controlled the neutrals would return to the output side of the contactor, thus making them common, but not borrowed between the phases as would be the case if looped across the phases. The contactor in turn would be protected on the load side by a TP+N MCB and a single phase supply (Taken from one phase) for the coil.

Now that is no different to what I believe the majority of us have done over the years and is in perfect agreement with 559.6.2.3 and I believe (please correct if wrong Mr Skelton) that this is what D.Skelton actually meant in his posts too

Now if you want to interpret the regulation to mean you can use a common neutral and a TP+N on three lighting circuits across phases with the neutral looped and no contactor then good luck to you, but I do believe you would be interpreting it incorrectly and may be criticised during an inspection for this.

 

[D Skelton]

please correct if wrong Mr Skelton

Almost, but not quite lol. The modular pre wired trunking systems and busbar track lighting that I have installed have a neutral that is common and 'looped' between the phases.

This is not classed as 'borrowed' regardless of what some chumps in some corporate entities say as the lighting circuit, although spread across three phases, is still only ONE circuit. Installed correctly, contactor controlled, equally balanced and protected by a TP OCPD in an installation that is properly maintained there is absolutely no danger in this method of wiring.

Worst case scenario, someone makes a hash of a neutral connection and we end up having to replace all the lamps! Which is far different from when the DNOs get it wrong and peoples microvaves and tellies start exploding lol.

 

[Outspoken]

Almost, but not quite lol. The modular pre wired trunking systems and busbar track lighting that I have installed have a neutral that is common and 'looped' between the phases.

This is not classed as 'borrowed' regardless of what some chumps in some corporate entities say as the lighting circuit, although spread across three phases, is still only ONE circuit. Installed correctly, contactor controlled, equally balanced and protected by a TP OCPD in an installation that is properly maintained there is absolutely no danger in this method of wiring.

Worst case scenario, someone makes a hash of a neutral connection and we end up having to replace all the lamps! Which is far different from when the DNOs get it wrong and peoples microvaves and tellies start exploding lol.

Yep, installed a few systems like this over the years and totally agree, fully safe system that is not a borrowed neutral as everything is "self-contained"

 

[Lou7]

How far apart are these sockets ?

 

[Tidy Max]

Been back to the job to fit an insect-o-cutor so i disconnected the singles from the isolator and pulled in a couple of twins. There was a sp db that had been installed next to the tpdb and it had a couple of spare 20A rcbo's in it. Basically its a refurb of a barn into a restauraunt and the previous sparks have done a pretty nasty job from the looks of things!

 

[Dan]

Just bumping some threads in the Electrical Wiring Theories and Regulations forum category here on our Electricians Forums. If this specific topic isn't current, just ignore it, it'll drop off the list in no time. However, if it's something you'd like to contribute to, feel free to reply and bring it back into current discussion.