Tn-s 3 phase?

[Ross1]

Evening guys,

I`m doing a small commercial job involving 2 x 3 Phase boards. The secondary board is 15 meters from first and is gonna supply up to potentially four 3 phase machines plus a ring main supplying portable single phase equipment.

Help sizing the supply cable for the second DB. Not used to dealing with start up currents etc. Here is a list of the max amount of equipment to be used. This is info customer has given to me.

Planer: 3 phase, 1.5 Kw, Full Load 3.6A, starting current 21.6 A

circular saw: 3 phase, 4 - 6 Kw, (other details unavailable)

Chopsaw: 3 phase or single, 2 - 3 kw

pillar drill: 3 phase or single, 1 - 2 Kw

Lathe: 3 phase, 3 - 4 kw

bandsaw: single phase, 2 - 3 kw

mortiser: single phase, 1 - 2 kw

cheers

 

[Darkwood]

Whats your incoming supply size first, although the list above is only small rated motors it will give me an idea what is your best front end fusing size.

 

[Ross1]

Whats your incoming supply size first, although the list above is only small rated motors it will give me an idea what is your best front end fusing size.

16mm mate

 

[telectrix]

top of my head, you want around 25kW over 3 phases, say 9kw/phase, thats 40A. allow for inbalance , my poor guesswork, and future expansion, gives 10mm on a 63A type C. as a starter for 10. now work out Zs values and disconnection times.

 

[Ross1]

would I continue with a 16mm/sq earthing conductor to the second db or would 10mm do?

 

[Darkwood]

16mm mate

Was meaning the cutout fuse rating, you have to try avoid frontend fusing the dist' board higher than the incoming cutout fuses, although i wouldnt consider a load issue here but need to know the limitation first befor suggestion a cable size.

 

[Ross1]

All wiring is surface, so am I right in saying that only circuits supplying portable equipment would need to be on RCD or would it just be easier to put everything on RCD?

 

[Ross1]

was meaning the cutout fuse rating, you have to try avoid frontend fusing the dist' board higher than the incoming cutout fuses, although i wouldnt consider a load issue here but need to know the limitation first befor suggestion a cable size.

100a !

 

[telectrix]

would I continue with a 16mm/sq earthing conductor to the second db or would 10mm do?

you need to do the calcs. to decide. remember that the max. Zs for C type breakers is 1/2 what it is for type B.

 

[Darkwood]

Are any of the D.B's already in situe or are you designing the full install?, avoid subbing the second board off the first as you will not get discrimination, if you have a short on any of the DB2 circuits it may take out a 63amp mcb before say a 10amp downstream.

 

[GLENNSPARK]

All wiring is surface, so am I right in saying that only circuits supplying portable equipment would need to be on RCD or would it just be easier to put everything on RCD?

if your on about the proposed ring final serving these points for your portables...then by all means provide additional protection....but the other stuff?...skilled and/or instructed person/s....and also surface run......

 

[GLENNSPARK]

you need to work out the best ballance that can be acheaved over the 2 boards....

 

[GLENNSPARK]

it would be useful to enquire as to which machinery is most likely to be on all the time...or throughout the working day....

 

[Ross1]

Hmmm.....got sum recapping to do by the looks of it. Not my everyday domestic single phase stuff!

 

[Ross1]

it would be useful to enquire as to which machinery is most likely to be on all the time...or throughout the working day....

The client has given me worst case senario and has also said even more unlikely that all machinery will be on at same time.