New garden office, Cable selection and method...?

[srl-8]

Hello Guys,

I will be installing an electrical supply to a new garden office and I want to run my thoughts about my installation past you all, to see if I have got this right in term of cable selection and load, or if anyone can suggest another way of doing this…

The Office will use the following load, I have rounded all amounts up to be safe.

3 x 1.5 kw heaters = 4500w = 20Amps

8 x 50w down lights = 400w = 2 Amps

4 x computers = (allow 250w per machine) =1000w = 5 Amps

Possible additional usage (microwave/printer/phone charge/fan etc) allow approx 1000w = 5amps

TOTAL AMPS = 32



I plan to install a 10mm PVC multi-core cable from Fuse board, (Protected by a 40 or 45 amp MCB or RCBO) through the house, until outside, then change to 10mm SWA up to the new installation. (Approx 15 meters away)

A new garage board will be installed with rcd in the new office, protecting the relevant new circuits.

(It is yet to be decided if client wants to have a new main fuse board in the house or install a separate unit fed from the Henley block.. The old fuse board is re-wireable fuses and non-rcd. I believe the earth arrangement is PME at this stage.



I would like your opinions and suggestion please

Thanks!

 

[malcolmsanford]

Hello Guys,

I will be installing an electrical supply to a new garden office and I want to run my thoughts about my installation past you all, to see if I have got this right in term of cable selection and load, or if anyone can suggest another way of doing this…

The Office will use the following load, I have rounded all amounts up to be safe.

3 x 1.5 kw heaters = 4500w = 20Amps

8 x 50w down lights = 400w = 2 Amps

4 x computers = (allow 250w per machine) =1000w = 5 Amps

Possible additional usage (microwave/printer/phone charge/fan etc) allow approx 1000w = 5amps

TOTAL AMPS = 32



I plan to install a 10mm PVC multi-core cable from Fuse board, (Protected by a 40 or 45 amp MCB or RCBO) through the house, until outside, then change to 10mm SWA up to the new installation. (Approx 15 meters away) What type of cable would this be? would depending on the cable and erection method, need RCD additional protection. Is the CPC the same size as the LIVE conductors?

A new garage board will be installed with rcd in the new office, protecting the relevant new circuits. If the multi core cable in the house needs additional 30mA protection will you have an issue with RCDs in series

(It is yet to be decided if client wants to have a new main fuse board in the house or install a separate unit fed from the Henley block.. The old fuse board is re-wireable fuses and non-rcd. I believe the earth arrangement is PME at this stage.



I would like your opinions and suggestion please

Thanks!

Will this office have services, such as a bathroom and therefore a water supply, is the construction of the building metallic at all, What type of earthing system do you have?

 

[srl-8]

No no services at all, no water supply, Earth is unknow at this stage, I believe it is PME.. It is defo NOT TT.

 

[malcolmsanford]

ok and the other points about additional protection etc

 

[srl-8]

Do you mean, "burried cable etc" , what are you getting at malcolmsanford?

 

[srl-8]

I would probs install 100MA RCD at House end and 30Ma RCD at garage end. This should allow garage to trip first, and not the house RCD

 

[malcolmsanford]

The cable going through the house, what kind of cable is it, and if is buried anywhere will you need to give it RCD protection?

If it is T + E and 10mm your CPC will be 4mm and your SWA CPC will either 10mm extra core or the armour, will that 4mm if T +E be man enough?

 

[Andy78]

Is it feasible to take the SWA right back to the CU ?

 

[srl-8]

Is it feasible to take the SWA right back to the CU ?

No Andy, it is impossible to run the SWA back to CU, I will have to make a connection somewhere on the outside wall etc.

cable for inside the house will be same as typical shower cable 10mm twin & earth
Cable for outside 10mm SWA

 

[telectrix]

as above comments, and, if using 10mm T/E in the house, run a separate 10mm earth with it.