Shipping container.

[flameport]

There are 2 separate issues here - using the armour as a cpc, and using the armour as a protective bonding conductor.
The cpc is required for all circuits, a protective bonding conductor is only required where the garage/shed etc. has extraneous conductive parts (metallic service pipes or the shed itself is metal as in this case)

The armour of SWA can be used as the CPC in most cases, this is what those 2 tables in the wiki attempt to show, although those only indicate compliance with table 54G (54.7 in the current regs), and this isn't the only way to determine if the cable is compliant or not.

To use the armour as a protective bonding conductor, it has to have the equivalent conductance of the required size in copper.
Since the minimum size is likely to be 10mm copper, and copper is about 8 times more conductive than steel, you need steel armour of 80mm or more to be equivalent to 10mm copper.
Only cables of 70mm+ have armour of 80mm or above. The armour in all sizes below that is far too small to be equivalent to 10mm copper.

You would therefore require a minimum of a 10mm, 3 core cable with one core used as the bonding conductor, or a separate bonding conductor. Both of these will significantly increase the cost, particularly if the SWA cable being used was less than 10mm.

 

[plugwash]

I would think you be better off making the container a TT supply.

Is it not advisable to carry the earth through from the TN-S system in the house ?

As you may or may not be aware there are rules that say that caravans cannot be supplied from a TN-C-S supply because of the extra dangers they pose in the event of a lost neutral. While there are no such regs for shipping containers I think it would be inadvisable to supply one with a TN-C-S supply for the same reason.

TN-S should be ok but the trouble is it's virtually impossible to tell if you have as true TN-S supply. Just because the neutral and earth are seperate when they arrive at your property does not gaurantee that they remain seperate all the way back to the supply transformer.

As such IMO it is better to make such a container a TT system with it's own earth rod. The house earth can still be used to protect the supply cable armour provided you make sure that nothing connected to the armor is touable at the shipping container end.

Note that earth rods MUST be tested, with most electrical installation testing is done with the expectation it will pass but rods can be a rather hit and miss thing and depending on soil conditions longer rods or multiple rods may be needed to get an acceptable earth electrode.

 

[Aragorn84]

Flameport:

This PDF suggests that 6mm 3 core XLPE insulated SWA has a 23mm^2 steel armour, which is the equivalent of 7.39mm^2 copper:

http://www.earthingnuts.co.uk/pdf/pvc_xlpe.pdf

So as you suggest the Armour alone wouldnt be enough to act as a protective bonding conductor.

What about using the armour AND one of the cores of the SWA?

Alternatively using 4 core 6mm SWA gives you armour with a copper equivalent of 11.5mm^2, and you've then got two spare cores you could also double up as earthing conductors if you so wished.

 

[Adam_151]

Alternatively using 4 core 6mm SWA gives you armour with a copper equivalent of 11.5mm^2, and you've then got two spare cores you could also double up as earthing conductors if you so wished.

Careful how you go when you are finding a 'copper equivelent' the figure you are using is related to the adiabatic thermal withstand of the conductor and is for checking withstand against fault currents, when sizing a bonding conductor this is largely irrelevant, and the regulations call for the conductor to have an equivlent conductance as the size of copper conductor that would ordinarly be used, and for steel the ratio is around 8.9, so you need a cable that has an cross section of the armourings of at least 8.9mm is you want to se the armouring as a bonding conductor.

Don't even go though with trying to 'add' the core to it, it doesn't work like that.... for a start you'd be introducing inductance, before we get onto the difficulties of sizing it this way....

 

[ban-all-sheds]

You would therefore require a minimum of a 10mm, 3 core cable with one core used as the bonding conductor, or a separate bonding conductor.

As I read more and more "what if I..." suggestions, the more I thought, "FFS, just stick 10mm² 3-core in, and be done with it".

Both of these will significantly increase the cost,

12m of 10mm² compared to 12m of 4mm² is hardly a significant increase.

 

[barcelona]

You would therefore require a minimum of a 10mm, 3 core cable with one core used as the bonding conductor, or a separate bonding conductor.

As I read more and more "what if I..." suggestions, the more I thought, "FFS, just stick 10mm² 3-core in, and be done with it".

Both of these will significantly increase the cost,

12m of 10mm² compared to 12m of 4mm² is hardly a significant increase.

I am perfectly happy to do that if it's adequate for the job.
Any suggestions on the best product to bond the doors to the main body ?

Thanks.

 

[flameport]

Any suggestions on the best product to bond the doors to the main body ?

A short piece of 10mm with a ring crimped on each end, bolted to the container and doors at the hinge side, the wire forming a U shape to allow for the movement of the doors.

Or don't bother, as the doors will already be electrically connected to the container via the substantial metal hinges. (unless the door comes off the hinges, but if that happens, bonding it to the container will be the least of your problems.)

 

[barcelona]

Any suggestions on the best product to bond the doors to the main body ?

A short piece of 10mm with a ring crimped on each end, bolted to the container and doors at the hinge side, the wire forming a U shape to allow for the movement of the doors.

Or don't bother, as the doors will already be electrically connected to the container via the substantial metal hinges. (unless the door comes off the hinges, but if that happens, bonding it to the container will be the least of your problems.)

Thats what I thought to use. Then thought there might be some braided stuff that will withstand fatigue better. I have seen some somewhere but not sure where or on what.

Cheers.

 

[barcelona]

You would therefore require a minimum of a 10mm, 3 core cable with one core used as the bonding conductor, or a separate bonding conductor.

As I read more and more "what if I..." suggestions, the more I thought, "FFS, just stick 10mm² 3-core in, and be done with it".

Both of these will significantly increase the cost,

12m of 10mm² compared to 12m of 4mm² is hardly a significant increase.

Am I right in thinking the third core, used as earth should be kept separate from the armour at the container side ? So the armour is connected to the container and to the earth in the house c.u, but not to earth in the container c.u ?

 

[barcelona]

What is the best way to exit the adaptable box with the exposed swa leads to the c.u ?

Thanks everyone for your input.

 

[flameport]

If you are using the earth from the house, you don't need a separate box, fix the SWA directly into a metal CU.
The armour and earth bonding core must both be connected at both ends.

 

[barcelona]

If you are using the earth from the house, you don't need a separate box, fix the SWA directly into a metal CU.

The armour and earth bonding core must both be connected at both ends.

The consumer unit in the house is plastic. Or am I missing something ?

 

[RF Lighting]

Use an earthing nut or piranah nut.

 

[barcelona]

If you are using the earth from the house, you don't need a separate box, fix the SWA directly into a metal CU.

The armour and earth bonding core must both be connected at both ends.

So I may as well double them up ?



Thanks R F Lighting, will do.

 

[ban-all-sheds]

Or don't bother, as the doors will already be electrically connected to the container via the substantial metal hinges. (unless the door comes off the hinges, but if that happens, bonding it to the container will be the least of your problems.)

Unless there are nylon inserts...

I'd use braid, or tri-rated, ordinary 6491X won't like the repeated flexing.