Supply cable to portacabin

[Beanyman]

I want to install a supply to portacabin ..details as follows:
Cable distance 35m - from CU - through ceiling void - exit main building - underground for 10m to unit.
Supply at CU in main building is TN-S.
As I understand the regs - TN-S supply means I don't need to spike at portacabin??
Does the SWA need any additional protection underground (apart from marking with electrical warning tape?
Does the SWA need to be terminated at an external/internal isolator at the p/cabin, or can it be directly connected to the CU in the p/cabin?
Finally, does the supply require RCD protection at the first CU or is RCD protection at the P/cabin CU sufficient?
Thanks in advance.

 

[buzzlightyear]

As I understand the regs - TN-S supply means I don't need to spike at portacabin??

I would seek advice from a spark to calculate the loading .I'm waiting for some one to give the op the answer .

 

[multimick]

these are basic questions ,not sure if op has sufficient knowledge to do this safely?

 

[buzzlightyear]

what is the loading on the end of it could be a bob hope farm .

 

[Spoon]

Welcome to the forum mate.
As above. Talk to the electrician who will be testing this new circuit. I'm presuming you will want a cert for this..?

 

[rustynails]

As I understand the regs - TN-S supply means I don't need to spike at portacabin??
Does the SWA need any additional protection underground (apart from marking with electrical warning tape?
Does the SWA need to be terminated at an external/internal isolator at the p/cabin, or can it be directly connected to the CU in the p/cabin?
Finally, does the supply require RCD protection at the first CU or is RCD protection at the P/cabin CU sufficient?
Thanks in advance.

As long as there are no extraneous conductive parts in the p/cabin no reason why you cannot extend TN-S. Provided CPC/Armour are calculated correctly, cable sized and adequate protection provided.

You can lay the swa directly in the ground or put it in duct.

You can put an isolator in, I'm not sure why you would want to do that as you would probably have a main switch in a small db in the p/cabin.

 

[Beanyman]

Rustynails...thank you.

 

[telectrix]

RCD at the cabin. calculate cable size allowing for current and volt drop. SWA can gland direct into cabin CU.get the slide rule/cackulator/tables out. i don't trust them cackulators. you can see what a slide rule is doing. not so in that digital witchcraft. mine once added up materials for fire alarm at 5+K. should have
been 3+K. almost lost the job.

 

[davesparks]

Supply at CU in main building is TN-S.
As I understand the regs - TN-S supply means I don't need to spike at portacabin??

Finally, does the supply require RCD protection at the first CU or is RCD protection at the P/cabin CU sufficient?
Thanks in advance.

You're understanding of the regs is incorrect, the type of incoming supply does not dictate the need to establish a seperate earthing system, it is dependant on the need to bond extraneous parts in the remote building and the size of bond required.
If any main bonding is required in the portacabin such as for water, gas, steel framework etc, then this needs to be sized according to the incoming supply to the installation.
So if the main bonding for the installation needs to be 25mm then you need a minimum 25mm to the extraneous parts in the portacabin.
If the submain only needs to be 6mm cable then it may be better to set up a seperate earthing system than run an additional 25mm earth. However if the submain already includes a 25mm or greater cpc then its suitable for main bonding and a seperate earthing system may not be the better option.

If you don't know where RCDs are required then are you sure you should be designing this circuit?

 

[cliffed]

I want to install a supply to portacabin ..details as follows:
Cable distance 35m - from CU - through ceiling void - exit main building - underground for 10m to unit.
Supply at CU in main building is TN-S.
As I understand the regs - TN-S supply means I don't need to spike at portacabin??
Does the SWA need any additional protection underground (apart from marking with electrical warning tape?
Does the SWA need to be terminated at an external/internal isolator at the p/cabin, or can it be directly connected to the CU in the p/cabin?
Finally, does the supply require RCD protection at the first CU or is RCD protection at the P/cabin CU sufficient?
Thanks in advance.

Connect directly to DB.
Swa can be protected by mcb,then-local Db Rcd protected.
Tn-s ok,minimum bond conductors 6mm if required.

 

[cliffed]

You're understanding of the regs is incorrect, the type of incoming supply does not dictate the need to establish a seperate earthing system, it is dependant on the need to bond extraneous parts in the remote building and the size of bond required.
If any main bonding is required in the portacabin such as for water, gas, steel framework etc, then this needs to be sized according to the incoming supply to the installation.
So if the main bonding for the installation needs to be 25mm then you need a minimum 25mm to the extraneous parts in the portacabin.
If the submain only needs to be 6mm cable then it may be better to set up a seperate earthing system than run an additional 25mm earth. However if the submain already includes a 25mm or greater cpc then its suitable for main bonding and a seperate earthing system may not be the better option.

If you don't know where RCDs are required then are you sure you should be designing this circuit?

Exactly,Tncs not allowed though.

 

[davesparks]

Exactly,Tncs not allowed though.

Since when is it not allowed? The same rules apply for all commonly used earthing systems, you either extend the equipotential zone or create a seperate earthing system.

 

[buzzlightyear]

Multicore 90°C Armoured Thermosetting Insulated Cables
Tables Apply to: H6942XL, H6943XL, H6944XL, H6945XL, Tuff Sheath,

Voltage: 230V

Load: 14.72kW / 64A

Length: 45m

Method of Installation: Direct in ground or in ducting in ground

Cable Size: 16mm²

 

[rustynails]

I guess he's referring to the broken pen scenario.

 

[davesparks]

Connect directly to DB.
Swa can be protected by mcb,then-local Db Rcd protected.
Tn-s ok,minimum bond conductors 6mm if required.

Yes 6mm is the minimum, 25mm is usually the maximum for TNS, but without details we cannot know what size is required for this particular installation.