Multi-core neutrals and earth

[Gigsy]

Hi,


I am currently training to become an electrician. I have passed all relevant C&G level 2 exams along with C&G level 3 inspection and testing and principles of electrical science.


I have been asked to help design some garden circuits but been given specific instruction on how the circuits will be protected.


Could you please give me feedback on the attached plan.

Specific questions are ;


1) If the 4mm2 cores of the SWA have a current carrying capacity of 37A, can I use only 2 cores for my neutrals and 4 cores on separate circuits.


2) Are my earthing arrangements correct? i.e. 4mm2 through the house then using the SWA armour as the earth to the front gates.

 

[westward10]

Cpcs can be shared across circuits, neutral conductors cannot.

 

[Silly Sausage]

I would be installing DBs in the shed and green house, supplied with 2 or 3 core SWA, and local RCD.

For the gates, again, probably be a local (to the gates) DB because you're going to require an enclosure to split your 7 core into the individual circuits anyway.
Whether I'd have the RCD there or back in the house, hmmm, depends on inconvenience level if it trips.

 

[davesparks]

Each circuit must have its own seperate neutral, sharing a neutral between circuits is very dangerous for anyone working on these circuits in the future.

 

[Deleted member 26818]

Is 3 phase available?

 

[Gigsy]

Is 3 phase available?

3 Phase is unavailable

 

[Gigsy]

Each circuit must have its own seperate neutral, sharing a neutral between circuits is very dangerous for anyone working on these circuits in the future.

It is more of a parallel conductor design than being a shared neutral in my opinion. The person I am working for is electrically qualified and this is how he said we wire it. I am unsure that is the reason I am asking here.

In this configuration it is impossible to get a dangerous voltage on the neutral so long as the neutral is terminated in the consumer unit, same as any circuit. It is not like a situation when you borrow a neutral from a different lighting circuit. It is not a dangerous configuration.

 

[Gigsy]

Apart from the shared neutral being dangerous, which I do not think it is in this configuration, is there any reason why we could not wire it as shown?

 

[westward10]

If you don't think a neutral conductor shared between circuits is dangerous then maybe you should step away from this job.

 

[Gigsy]

I know of configurations in which sharing a neutral can result in a dangerous voltage on the neutral. I knew this thread would go down this path. I could draw the situation, can you? If so draw it then explain how the fault relates to this design.

 

[westward10]

You either need cables which incorporate more cores for individual neutral conductors or fit distribution boards at the areas the circuits are required.

 

[Gigsy]

If you don't think a neutral conductor shared between circuits is dangerous then maybe you should step away from this job.

 

[Gigsy]

That situation could never occur with the design I have drawn

 

[Gigsy]

Actually thinking about it, You are right. Exactly this situation could occur, you could leave a circuit powered then disconnect the neutral at the termination at the end of the SWA and the neutral from another circuit could become live. Sorry you are right. It could be dangerous. Thank you

 

[FatAlan]

I would be installing DBs in the shed and green house, supplied with 2 or 3 core SWA, and local RCD.

For the gates, again, probably be a local (to the gates) DB because you're going to require an enclosure to split your 7 core into the individual circuits anyway.
Whether I'd have the RCD there or back in the house, hmmm, depends on inconvenience level if it trips.

I know I’m only a trainee but that design does look over complicated. DB at each location and 3 core SWA calculated on max demand and distance.