Running additional neutral to 3 phase panel.

[Huw]

Hi, I hope some one can help.
I am running a 3 phase supply to a panel (160KW).
I was thinking of using some existing cable 2 X 95mm 3 core. The problem I have is the panel has a requirement for a neutral, running off the neutral bar in the panel is only 2 ,1.5mm wires (I think they may just going to the door fans but not 100%).

I don't do cable runs like this every day so not 100%
1) can I just run a 6mm neutral to the panel as I believe the circuit to be polyphase?
2) Fit a small 415v to 240v transformer and run the 240v equipment through that?

Thanks for taking the time to read, Huw.

 

[Adam W]

In the absence of any other information I'd probably try to install a fresh 4 core cable if possible, then you can be sure.
Failing that is there anyone you could ask, ie the person who built the panel? I'm quite lucky in that I have an electronics engineer who's really switched on (pardon the pun) who would be able to give me a definitive answer as to what the requirements of the panel are - if he doesn't know, he'd know where the drawings would be; in the worst case scenario I'd have someone to share the blame if it all went pear-shaped.

Out of the two options you've given, option 2 sounds the 'tidiest' to me, but it would be worth waiting for other opinions...

 

[bigbalu]

Using the supplied details, I think the simplest answer would be to use a 415/230 volt transformer of an adequate rating, fuse both phases on the primary side and a fuse for the line on the output side with the neutral connected to a suitable earthing point. Hope this helps

 

[Marvo]

Not sure about UK regs but where I am all 'line' conductors must be equal CSA regardless of the load so running a smaller neutral wouldn't fly. As suggested by Bigbalu above, I'd use a 420/230 Tx especially if it's just ancillary loads like fans and maybe a dehumidifier.

 

[Huw]

Thanks for the replies. Sorry for the lack of info, I am going to look at the drawings today so should have a better Idea what is run on 240.

 

[Leyland30]

Hi, if the manufacturer of the panel requires a neutral then this must be provided. If you run a reduced size neutral you will need to provide over load protection for it I.e. 4pole protection device. Personally I would run a suitably sized cable with sufficent integral cores for the job. You can make use of your existing cable on another project.

 

[westward10]

Not sure about UK regs but where I am all 'line' conductors must be equal CSA regardless of the load so running a smaller neutral wouldn't fly. As suggested by Bigbalu above, I'd use a 420/230 Tx especially if it's just ancillary loads like fans and maybe a dehumidifier.

It is permitted providing the requirements of Reg 524.2.3 are met. How you enter the separate neutral through the same hole as the line conductors of the SWA cables to comply with 521.5.1 may be tricky, probably not worth the grief.

 

[Huw]

Thanks again for all the replies.
After looking at the drawings the panel has 2 feeds the main 400A supply through the main isolator and then a non isolated single phase supply ( for lighting and laptop plug ).
So I will the two fans off that supply.