3 phase supply cable

[Robo]

Im pricing to wire an industrial shed. I would like some help in calculating the best rating for the circuit and the cable size.

It has as follows

8 x twin 58w fluorescents - switch or high freq (undecided)? 4A x 90% for diversity =3.6A
3 x 70w metal halides 0.9A x 90% =0.81A
11 x double sockets
1 x 32 2p +e blue socket( this will power a porta kabin)
1 x 1500va 110v tx.
And allow for future expansion

How do i calculated diversity for the 11 x sockets, 32a socket and the tx.

I want to calculate max demand after diversity. And then do the relevant cable calc. Using ((mv/A/m) x ib x L) / 1000


The cable route is 115m long. help with the process would me much appreciated.

 

[Robo]

Any1? please

 

[telectrix]

rough estimate is your load would be around 60A. frfom the info you've given, looks difficult to balance loads between phases. think you should be looking around the 16mm to 25mm for cable size. VD is your main concern as it's a long run.

 

[Robo]

Cheers mate. how would you calculate diversity for the 13a sockets. 32a outside sockets and the tx. I think i did it correctly for the lights. I just want to do it properly to get exact figurefor max demand and then do cable calc. If you wouldnt mind could ylou go throught this process telectrix. Iv got another cable calc job to do so want to do it properly. cheers

 

[i=p/u]

for vd if using 25mm , isit 2.5 x 115l x 60A / 1000 =17.25v

 

[telectrix]

for vd if using 25mm , isit 2.5 x 115l x 60A / 1000 =17.25v

yeah, but it's 3 phase, so the load is split. around 20A per phase if it's balanced.

 

[telectrix]

Cheers mate. how would you calculate diversity for the 13a sockets. 32a outside sockets and the tx. I think i did it correctly for the lights. I just want to do it properly to get exact figurefor max demand and then do cable calc. If you wouldnt mind could ylou go throught this process telectrix. Iv got another cable calc job to do so want to do it properly. cheers

you can't get an exact figure. all depends on the anticipated load. no diversity on the 32A to the porta cabin. say 20A on the 32A socket circuit. you need more info on what loads are likely to be applied and then add on top to cover the worst scenario.

 

[i=p/u]

so if it is split equaly it will be 5.7v , what size will his newutral conductor have to be... can it be half of 75mm = 35mm for alll

 

[UNG]

Im pricing to wire an industrial shed. I would like some help in calculating the best rating for the circuit and the cable size.

It has as follows

8 x twin 58w fluorescents - switch or high freq (undecided)? 4A x 90% for diversity =3.6A
3 x 70w metal halides 0.9A x 90% =0.81A
11 x double sockets
1 x 32 2p +e blue socket( this will power a porta kabin)
1 x 1500va 110v tx.
And allow for future expansion

How do i calculated diversity for the 11 x sockets, 32a socket and the tx.

I want to calculate max demand after diversity. And then do the relevant cable calc. Using ((mv/A/m) x ib x L) / 1000


The cable route is 115m long. help with the process would me much appreciated.

Any1? please

How quick do you expect answer with a minute between these posts

And then you don't even give us a clue to what the building is being used for let alone what is in the porta cabin plugged into the 32A socket and how many rfc's are to be used for the 11 sockets

In some commercial premises you can be hard pushed to allow much diversity with the duty cycle of the connected load

I would suggest a C&G 2391-20 course would help you and a little patience

 

[Robo]

Theres no need to be like that. I left more than a minute.My browser says a hour. Its just a rush job that iv been asked to quote last minute and I havent got experience in cable calcs. And i wanted to try get a quick verdict incase of any queries. Sorry if it came across inpatient.

The building is being used for storage mainly and some workshop duties. its about 20m x 10m. Overkill on sockets i think but thats what they want. The porta kabin is a small 1 room office, heater few sockets and lights, its on a 32a blue plug.

Yes i would like to go on the 2391-2 course. Im awaiting results on my 2391-10 at the min.

Im keen to see how the max demand is calculated and then from that how the cable calc is done. Many thanks for the help so far

 

[i=p/u]

you shouldnt be doing this work if you can count in electrix... get hired help and stick to 6A lighting circuits like me, the odd radial and the odd fuse to be replaced,,, this sounds like it could bite you

 

[telectrix]

max.demand is very much a hit and miss affair. it's where you have to go with your gut feelings, knowing the client and what he's likely to load the installation with. i'd go a ball park figure of 20-30A per phase, but look at the balance of the 3 phases.

 

[Engineer54]

You may want to look at taking a parallel supply up to this building if your talking about 115 meter's. Could well turn out cheaper for you using smaller SWA's....

 

[Knobhead]

Maximum demand. You need the HenWay calculator.
View attachment 10451
With the information you’ve given how is anyone going to give a reasoned answer. If you don’t know what you’re doing just say so!

 

[GLENNSPARK]

max.demand is very much a hit and miss affair. it's where you have to go with your gut feelings, knowing the client and what he's likely to load the installation with. i'd go a ball park figure of 20-30A per phase, but look at the balance of the 3 phases.

but always stick a bit more on top.....just to allow for future proofin....