Two Live Wires One Neutral

[Harvey]

Came across CU in shed which is TT supplied by two 2.5 in parallel but one 2.5 neutral from another Db.So this is like a ring for the live wire .The supply cable is SWA buried The two 2.5 wires are on a 30A rewireable.What do you think ?   Satisfactory or not

 

[Robin Spark]

If Im understaning this correctly you have the neutral supplied from on DB and the Line from another DB.  If this is correct then no it is dangerous especially for TT which requires both Line and neutral conductors to be disconnected for Isolation purposes from one double pole switch.

Also thinking about it further then if the cct was fully loaded then all of the current would be flowing down a single neutral conductor and you cant run undersized line conductors in parallel to share a load.

 

[Harvey]

Sorry both 2 live and  1 neutral from the same Db going to CU

 

[SLIPSHOD & SLAPDASH]

So its a 3 core SWA with 2 cores as L & 1 core as N ? Whats the OPD ?

 

[steptoe]

all LIVE cables need to be of the same csa.

 

[Andy™]

2.5 on a 30a isnt a good idea..

 

[Robin Spark]

Oh right quick before im off for tea, Line and neutral conductors need to be same csa so one of the line conductors needs to be disconnected and protective device suitably downrated taking into consideration design current and voltage drop. 

Need more info is this one or two armoured cabled? 

 

[Harvey]

Thats correct

 

[steptoe]

nothing wrong with having cables in parallel,

but the neutral needs to be the same size as the LINE.

 

[Robin Spark]

So its a 3 core SWA with 2 cores as L & 1 core as N ? Whats the OPD ?

Harvey hasnt told us its one 3 core cable as of yet.

 

[ProDave]

Okay, so you use 2 cores of the SWA one for L, one for N.

You size your OPCD for the cable CSA and it all works. (which I don't think it is in this case)

But the volt drop is marginal, right on the limits, and you notice the light in the shed dim a little when you switch the heater on.

So you connect the spare core in parallel with the L core to lower the volt drop a bit.

Nothing is being overloaded.

What's technically wrong with it?

Yes is might break a regulation or 2, but it's not dangerous is it?

 

[Andy™]

Yes is might break a regulation or 2, but it's not dangerous is it?

yes, a circuit that is designed for 30a, but the cable (neutral anyway), probably cant take that

 

[ProDave]

yes, a circuit that is designed for 30a, but the cable (neutral anyway), probably cant take that

No

I was saying size the OPCD for ONE cable, so say 16A.

Then the neutral can comfortably handle it, and the two parallel L's can handle double the current.  What's TECHNICALLY wrong with that?

In the OP's case, with a 30A OPCD it probably is wrong.

 

[Andy™]

No

I was saying size the OPCD for ONE cable, so say 16A.

Then the neutral can comfortably handle it, and the two parallel L's can handle double the current.  What's TECHNICALLY wrong with that?

In the OP's case, with a 30A OPCD it probably is wrong.

nothing wrong with doubling up on only line, provided OCPD is designed for the single conductor, but in the OP's case, it cant

 

[Blue Duck]

WTF is an OPCD?

:coat

 

[ProDave]

WTF is an OPCD?

:coat

My fingers typed OCPD in the wrong order and my eyes didn't see it :coat

 

[Blue Duck]

I'm not the spelling police, far from it. h34r:

Thought it was some new thing that I had missed in the amendment and found myself thinking what is an OPCD!!?? A new type of RCD!?  :slap