Extending 3 phase supply

[MK1 RS Bruce]

Hi All

Looking for a bit of guidance on cable sizing to extend a 3 phase supply.

We currently have 3 phase power at our "consumer" unit and it is wired in for running motors on our grain dryer.

I would like to take a 3 phase supply from the consumer unit and run it to the workshop.

Its probably 100m worth of cable run, majority of it secured to the inside of existing buildings and maybe a 10m section where it would have to pass in an underground conduit (100mm waving coil) with the existing power cable.

What sort of cable size would I be looking at if I want to run a big transformer Mig welder? My assumption being the current would actually be less than what I would require to retain a single phase supply?

Next question, If I already have a 3 core cable running along that run assuming the core is big enough could I just get it re-wired to provide 3 phase and then strip out a single phase in the workshop to give me my existing single phase sockets?

Apologies for all the questions, but an electrician I am not haha

 

[Westfield-builder]

You may not be an electrician, but I think you require the services of one before you go much further.
Lenght of run, loading and installed conditions can all have an effect on the size of cable required.
3- core cable is not suitable for a 3 phase supply.

 

[dobbslc]

You'll need a 4 core cable for a 3 phase and neutral supply and that could use the swa armour as the earth so your existing the 3 core is no good unfortunately.
If you run the new cable in ducts it'll have to be rated for 'reference method D' just for that short length that's buried.

63 amp (sometimes 80 amp) is the maximum mcb size for most dist boards so that'll give you a decent supply assuming the main building has a good feed to it.
You'll need a 16mm or maybe 25mm 4 core cable but check the calculations on volt drop for that length of run.

 

[MK1 RS Bruce]

You'll need a 4 core cable for a 3 phase and neutral supply and that could use the swa armour as the earth so your existing the 3 core is no good unfortunately.
If you run the new cable in ducts it'll have to be rated for 'reference method D' just for that short length that's buried.

63 amp (sometimes 80 amp) is the maximum mcb size for most dist boards so that'll give you a decent supply assuming the main building has a good feed to it.
You'll need a 16mm or maybe 25mm 4 core cable but check the calculations on volt drop for that length of run.

Thanks for the reply thats very helpful for cost estimating

 

[MK1 RS Bruce]

You may not be an electrician, but I think you require the services of one before you go much further.
Lenght of run, loading and installed conditions can all have an effect on the size of cable required.
3- core cable is not suitable for a 3 phase supply.

Thank you for your reply but so far I have only gone as far as posting on a forum, so not sure I am ready for the electrician yet

 

[Memmeddu]

I'm an electrician ,you gonna need something like 15-20kW in your workshop so roughly 40-50A
You will need 16mm² copper cables
You will start with 415V and you'll have 407.4V in your sockets which translates in 1.83% voltage drop
It will work 100% up to 39.7A and it can manage up to 61A
You will need 16mm² PE conductor and dispersers in your workshop
Hope to being useful

 

[MK1 RS Bruce]

I'm an electrician ,you gonna need something like 15-20kW in your workshop so roughly 40-50A
You will need 16mm² copper cables
You will start with 415V and you'll have 407.4V in your sockets which translates in 1.83% voltage drop
It will work 100% up to 39.7A and it can manage up to 61A
You will need 16mm² PE conductor and dispersers in your workshop
Hope to being useful

Thanks Thats great Info