Lighting cct - shared neutral

[kanewesley]

Whats the best way of making good this lighting problem?

In a dist. board, there are 3 x separate fuses feeding 3 x separate lighting circuits. However, the 3 circuits share the same neutral back to the distribution board.
A notice has been given to put this right.
It's impracticable to run out 3separate neutrals as they are quite a way across the factory site.
Lord knows why the test and inspection company haven't picked up on this before as the wiring has been like this for 25 years or more.
A suggestion from the electrical tester is to take all 3 lighting circuits, from the individual fuses, through a triple MCB then out to their respective circuits??
How will this correct the problem?
is it so the MCB will be out of balance if one circuit fails? or to work on any one of the circuits, the MCB has to be locked off so all 3 circuits are dead?

Thanks

 

[cireland]

Whats the best way of making good this lighting problem?

In a dist. board, there are 3 x separate fuses feeding 3 x separate lighting circuits. However, the 3 circuits share the same neutral back to the distribution board.
A notice has been given to put this right.
It's impracticable to run out 3separate neutrals as they are quite a way across the factory site.
Lord knows why the test and inspection company haven't picked up on this before as the wiring has been like this for 25 years or more.
A suggestion from the electrical tester is to take all 3 lighting circuits, from the individual fuses, through a triple MCB then out to their respective circuits??
How will this correct the problem?
is it so the MCB will be out of balance if one circuit fails? or to work on any one of the circuits, the MCB has to be locked off so all 3 circuits are dead?

Thanks

Is it a single phase or three phase board?

 

[PS Electrics]

A suggestion from the electrical tester is to take all 3 lighting circuits, from the individual fuses, through a triple MCB then out to their respective circuits??
How will this correct the problem?

Because shared neutrals present a shock risk on the circuit that is isolated to work on while the other circuit(s) are energized. So the idea is to isolate all of the 3 circuits simultaneously.

There are some downsides and potential problems with this approach especially on a 3 phase board.

 

[littlespark]

How is running out new neutrals impractical?

Is one neutral carrying the power of 3 circuits? Might be worth measuring the return load with a clamp ammeter…

Being a factory, isn’t the wiring in surface containment?
There’s always a possibility…

 

[kanewesley]

How is running out new neutrals impractical?

Is one neutral carrying the power of 3 circuits? Might be worth measuring the return load with a clamp ammeter…

Being a factory, isn’t the wiring in surface containment?
There’s always a possibility…

No pal...it's far from modern...its run inside buildings, outside buildings, between buildings, across the factory yard, strung on catinery wires...etc etc its many many years old....its not been nicely installed .
It is what it is !
The lighting works it just has a notice on it to correct it from the neutrals point of view.
Yes, the neutral will carry the 3 rturn currents but this has not been commented on by the inspection and testing guys...they are just concerned to make the ccts ok by the use of an MCB

 

[kanewesley]

Because shared neutrals present a shock risk on the circuit that is isolated to work on while the other circuit(s) are energized. So the idea is to isolate all of the 3 circuits simultaneously.

There are some downsides and potential problems with this approach especially on a 3 phase board.

So the use of an MCB will suffice ?

 

[westward10]

Not uncommon for large factory/commercial sites for the lighting to be across three phases with a shared neutral with the stipulation being they should be protected by a linked protective device.
See Regulation 559.5.5.

 

[PS Electrics]

So the use of an MCB will suffice ?

see #7

But I was going to say obvious downside is you lose 3 lighting circuits with any fault.

Also the potential problem if it is 3 phase is if the 3 lighting circuits aren't currently on 3 different phases then you have to mindful not to introduce 415v into locations that previously didn't have it.

Also as it is a factory if lighting phases are moved around just be mindful that stroboscopic effect protection if there was any is still preserved.

 

[kanewesley]

Is it a single phase or three phase board?

It's on a 3ph board with each of the 3 ccts on a different phase

 

[kanewesley]

see #7

But I was going to say obvious downside is you lose 3 lighting circuits with any fault.

Also the potential problem if it is 3 phase is if the 3 lighting circuits aren't currently on 3 different phases then you have to mindful not to introduce 415v into locations that previously didn't have it.

Also as it is a factory if lighting phases are moved around just be mindful that stroboscopic effect protection if there was any is still preserved.

OK with 1st paragraph


Not sure what 2nd paragraph means ?

3rd paragraph dont apply...lighting cuts are nowhere near each other

 

[kanewesley]

So....after all the comments...what's the answer...to take them through a linked triple mcb ??

 

[westward10]

A linked device partially solves the problem but you still have the unlinked fuses so it depends how well this is clarified. The fact they are on different phases is not relevant.

 

[PS Electrics]

Deleted

 

[kanewesley]

It wasn't clear that the circuits were all on different phases I see you have since clarified that.

The 3 pole is going to go across 3 phases so if your original circuits were on L1, L1, L3 for instance one of them would be moving a phase.

Doesn't ANY 3pole MCB go Cross 3 separate phases ?
eg a three phase motor protected by a 3ph mcb has 3 separate phases going across it ?

I used this forum once before and all I got was nit picking....individuals finding fault with everything.

If....if....if....




I thought I'd ask a reasonable question...can I feed the individual ccts through a 3 pole mcb.



Please....yes or no !!!

 

[PS Electrics]

Deleted