Neutral current

[bigpaul]

Hi, if you have a 3 phase 400v distribution board where all the outgoing loads are 1 phase 230v do you need to size the supply neutral bigger than the supply phases. i.e. lets say the supply was from a 100KVA generator. Assuming pf of 0.8 I would have 80KW of power which is about 115amps/phase. Therefore typically use a 25mm SWA as the supply cable

However If all loads are single phase surely all current will flow back down the neutral? How do I size neutral. Anyone know where I can fing out more info

Thanks

PAul

 

[pevvers]

Not as far as I'm aware, and I've never seen it in any installations...

I'm thinking that the neutral flow would still be 120 out of phase with each other, but I'm not great with 3 phase theories.... I learnt it a long time ago and have never used it since then, something that I really wish to rectify in my next job!!

 

[zupos40]

Hi, if you have a 3 phase 400v distribution board where all the outgoing loads are 1 phase 230v do you need to size the supply neutral bigger than the supply phases. i.e. lets say the supply was from a 100KVA generator. Assuming pf of 0.8 I would have 80KW of power which is about 115amps/phase. Therefore typically use a 25mm SWA as the supply cable

However If all loads are single phase surely all current will flow back down the neutral? How do I size neutral. Anyone know where I can fing out more info

Thanks

PAul

It depend on what type of loads you are going to connect, eleectronic equipment produces large harmonic current that could require increase sizing of neutral, http://www.beama.org.uk/information/downloads/default.asp?pg=4&gpg=BITB then you looking Beama installation technical bulletin and downloads page 4. or read section in the Iee design book

Otherwise if it possible try and balance the loads across each phase to minimise the current in the neutral, what type of loads are we talking about.

 

[pevvers]

Interesting reading, harmonics are what I came up with too from a brief Googling....

Cheers!!

 

[bigpaul]

installation is for an IT server farm. Its been proposed to the customer to install 3 phase distribution boards within the server farm area. Distribution boards will then feed a Number of "cabinet"within the area. Customer is telling me each "cabinet" could potentially use 8KW single phase. He wants a 32A 3 pin blue commano plug to each cabinet.

i'm concerned about neutral current. Harmonics and pf correction + the high leakage to earth for this equipment. I assume i'd have to run a seperate "functional " earth.

Zupos40. Whats / where can I get the lee design book?? Or anything to help with these IT installations.

Thankyou

 

[zupos40]

Electrical Installation Design Guide: Calculations for Electricians and Designers

By Paul Cook

Price: £20 / $28
Available: 2008
Format: Wire-bound
Product code: PWR05030
ISBN: 978-0-86341-550-0
Pagination: 200 pp.

Amazon, IET or any book shop. try IET web site for info