3 sp circuits off a tp isolator

[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.