Submain for a cafe

[JM ELECTRICAL]

Hi everyone,

A local pub is changing one of there function rooms in to a cafe, there plan was to have all gas equipment so i done the cable calcs and installed a 16mm 3 core swa as the submain cable from the main 3 phase db in the pub to what was going to be a single phase db in the cafe.

Then the gas man has came out to install the gas pipe and has advised the owners they dont have the relevent gas supply for the amount of gas they would need for all gas appliances, so now the want to use a couple of full electric appliances.

So i am now going to run a 3 phase 16mm swa submain from the main 3 phase db in the pub to a 3 phase db in the cafe.

As they have already spent around £200 on a cable thats now no use, and the cost of adding extra points they are trying to save a bit elsewhere.

So my question is can i use the steel wire armour of a 16mm 4 core swa as my main earth for the new submain, or will i need need a 5 core swa, the run is around 35m, i would always just go for the 5 core but im just trying to see if i can help them at all.

thanks for any advise

 

[James]

Yes you probably can.

have you done any calculations for R1 & R2?

If you have a Ze, then do the calculations and post here for a sanity check if you are a bit rusty.

 

[pc1966]

The Prysmian data sheet for SWA has 16mm 4C as R1 = 1.15 ohm/km and R2 (armour) as 3.1 ohm/km. From your supply Zs and length you can check if the planned OCPD will disconnect fast enough.

If the armour R2 is too high it might be worth seeing if a separate 10mm CPC is enough (1.83 ohm/km) as that is probably cheaper than going to 5 core SWA.

 

[pc1966]

Actually if the 3-core SWA is in and supplying a CPC from the single phase plan then adding 4C for 3-phase in the one cable but using that for sufficiently low R2 should be OK.

Make sure both ends of the armour are properly linked to the earth bar / CPC arrangement by a suitable pig-tale style link to the banjo or Piranha / Earthing nut.