4 CORE CABLES ON MCB'S

[0151]

guys ive come across a scenerio of a 4c swa cable supplying lighting columns and cameras although they terminate into 4 pole cutouts in the column base back at the dist board the cable is terminated into 3 single pole breakers two labbelled up lights and one cctv.

am I right in thinking this is wrong as the cable could still be live. but saying that its only the same as 3 seprate fuses yes??

whats your thoughts please

thanks

 

[Badger]

are all those breakers the same amperage, ie all 6 amp/10 amp etc, if they are, what type is the bus bar as you may be able to fit a 3 pole mcb (ie 3 phase) where all the mcbs are linked thus taking away the isolation issue if there is a fault on that cable

 

[0151]

good point badger ive got 2 x10 and 1 x 6

 

[Badger]

so assuming the cctv is on the 6 amp couldnt you put it through a 3 pole 10 amp mcb then ? as the cctv should have dedicated spurs to each camera :|

 

[0151]

yes thats what im going to reccomend. what catagory would you put this?

 

[Andy™]

i hope they dont share a neutral

 

[bengie]

sounds like its a bit shady right now as you have 3 circuits with only one neutral between them which isn't right, not sure on regs about this but i'd be happy to have 2 seperate circuits in a 4 core SWA(so thats 2x neutral and 2x live).

 

[0151]

doh!!!!!!!!!!!!

how embarresed am i Andy

cheers pal cant see the trees for the wood as it were

 

[Lurch]

not sure on regs about this but i'd be happy to have 2 seperate circuits in a 4 core SWA(so thats 2x neutral and 2x live).

Perfectly fine. Can't see a regulation that specifically prohibits it, and it's no different to 4 cables for 2 circuits in a conduit. Using a 4 core for 3 circuits would technically be fine if it were sized for the combined neutral CSA of all 3 circuits, but would then fall foul of other regulations about sharing neutrals, 314.4 for one.

As long as there is no interconnection between any seperate final circuits then you're fine.

 

[spinlondon]

This is a joke right?

This is a standard arrangment for street lighting, and many other 3 phase applications.

Have none of you got any experience of 3 Phase?

Why are you conducting PIRs when you haven't got a Scooby about what you are doing?

 

[Lurch]

This is a joke right?This is a standard arrangment for street lighting, and many other 3 phase applications.

Have none of you got any experience of 3 Phase?

Why are you conducting PIRs when you haven't got a Scooby about what you are doing?

Is this a joke? Have you got any idea about how 3 phase works?

 

[ianmacd]

Perfectly fine. Can't see a regulation that specifically prohibits it, and it's no different to 4 cables for 2 circuits in a conduit. Using a 4 core for 3 circuits would technically be fine if it were sized for the combined neutral CSA of all 3 circuits, but would then fall foul of other regulations about sharing neutrals, 314.4 for one.As long as there is no interconnection between any seperate final circuits then you're fine.

Since the neutral is not isolated by the MCB's, 314.4 would not apply.

 

[Lurch]

Since the neutral is not isolated by the MCB's, 314.4 would not apply.

So say, a 10mm 4 core with 3 10A MCB's feeding 3 cores and all sharing the 4th core as the common neutral would be fine according to BS7671?

I think not, although this is half the fun of the BRB, tomato\tomato!

 

[ianmacd]

So say, a 10mm 4 core with 3 10A MCB's feeding 3 cores and all sharing the 4th core as the common neutral would be fine according to BS7671? I think not, although this is half the fun of the BRB, tomato\tomato!

Or potato/potato?

I Can not see anything that suggests that would be incorrect as long as all the line cores were isolated at the same time.

 

[Lurch]

Or potato/potato?

Is that your Harley impression?

I Can not see anything that suggests that would be incorrect as long as all the line cores were isolated at the same time.

But then they'd be one circuit, assuming by isolated you mean at the CPD? If so, it;'s not going to work if you wanted to use HRC's, and a circuit wiring method should comply on any CPD, should it not?

 

[ianmacd]

Is that your Harley impression?But then they'd be one circuit, assuming by isolated you mean at the CPD? If so, it;'s not going to work if you wanted to use HRC's, and a circuit wiring method should comply on any CPD, should it not?

Would they be the same circuit? They would be on different CPD's just ones that opperate at the same time.

 

[Lurch]

Would they be the same circuit? They would be on different CPD's just ones that opperate at the same time.

3 phase MCB, one circuit. 3 interlocking single phase MCB's, dunno, open to interpretation.

 

[ianmacd]

3 phase MCB, one circuit. 3 interlocking single phase MCB's, dunno, open to interpretation.

Much like the rest of the big red comic.

 

[Mr Smith]

mr lurch

your comment was out of order

and has been removed

perhaps an apology would be in order

mr smith

 

[Andy™]

This is a joke right?This is a standard arrangment for street lighting, and many other 3 phase applications.

Have none of you got any experience of 3 Phase?

Why are you conducting PIRs when you haven't got a Scooby about what you are doing?

is that supposed to be a joke?

you do not know if this is TP or SP (OP has not state if its TP or SP)

either way, this is 3 seperate circuits sharing a neutral, its a little different from a TP street lighting circuit with the same neutral (as its 1 circuit). working on the TP street lighting, you would expect the neutral to be used between all 3 phases. but if you have 3 different circuits, you would not expect them to be connected as one by the neutral

and then there is the neutral current - if its SP, then neutral current is all 3 circuits combined, which may be well above what it can safely take

i would suggest you get your facts right before making statements like that