Supply to Portable buildings and portacabin/container

[Thebonse]

Hi Fellas

Sure i had another login but seems my account has been recycled......anyway.

Im running a supply to multiple portacabins and shipping containers.

The Supply is a TNS and is approximately 95m away.
I have decided on a 63A 3phase circuit and calculated the cable size @ that length to be 25mm (total volt drop at this distance is 11.5v (Calculated)).

It will be supplying a new DB which will be enclosed in an Ip rated enclosure and separate circuits to be supplied to each of the units/containers.

Ok so now my question, i have been reading the regs and guidance notes regarding this and it clearly says no PME which i completely understand, But what about a TNS supply?

I get that there can be a difference in potential between the earth supplied and the true earth but if theres an Earth rod for each unit.

I personally cannot see why this is not acceptable but please let me know what you guys think in this situation.

cheers

Darren

 

[Thebonse]

I have also considered going from TNS to TT at the new DB location but as i stated above.....Do i need to?

 

[Strima]

You might want to recheck with regards to volt drop as well. 11.5 just on the distribution circuit means all the circuits off the connect DBs will be below the required minimum especially the lighting.

 

[Thebonse]

The new circuits are within a few meters of the new DB. my mistake its more like 8.4 total volt drop. 11.5 is 5%

 

[Strima]

What about lighting at 3% (6.9 volts)?

 

[telectrix]

TN-S is fine. the reason PME is frowned on is that a loss of the supply N ( and hence the site earth) would lead to the metal structures possibly becoming "live".

 

[telectrix]

What about lighting at 3% (6.9 volts)?

install LED lighting.

 

[Thebonse]

Hmm...

How can this be done then? The Regs don't specify a figure for 4 core cables over 25mm

 

[Strima]

install LED lighting.

Stop thinking, it makes you tired...

 

[Thebonse]

?

 

[Thebonse]

TN-S is fine. the reason PME is frowned on is that a loss of the supply N ( and hence the site earth) would lead to the metal structures possibly becoming "live".

Yeah i know mate i was looking for clarity as the regs make no mention of TNS (for this kind of installation)

 

[Strima]

Hmm...

How can this be done then? The Regs don't specify a figure for 4 core cables over 25mm

What cable are you calculating for?

 

[Thebonse]

well a bigger one than 25mm.... my original calc was for 25mm

 

[Strima]

70c SWA?

 

[jackhammerJIM]

TNS is acceptable . in swa 4 core cables are specified up to 400mm