replaceing consumer unit in shed (with no earth)

[Avidude]

hi i am looking to take my napit exam.
i want to replace a garage consumer unit,
i have looked and found that it is using the swa as the earth (2 core swa)
what can i do?
can i use the swa as the earth for the new consumer unit?
i don't want to have to use a TT system.
thanks for any input
avidude

 

[telectrix]

what size SWA. and can you get a Ze reading from the garage end? might be better to make sure the SWA armour is earthed at the house end only, then TT the garage. That way you will only be assessed on your work in the garage. be sure to RCD/RCBO both circuits.

 

[Avidude]

Hello
the swa is only 2.5 2 core,
i fond that the swa was not even connected at the board (So there was no earth)
i have never worked with tt system before.
where can i find out where to buy and how to use earth rods?

 

[Guest123]

What type of earthing system is present in the house???

 

[telectrix]

i.d start by replacing the SWA. 6mm at least, maybe 10mm, depends on your load.

 

[ezzzekiel]

any wholesaler will sell you a rod and clamp for about £10, just knock the rod into the ground fit the clamp on the end and tie your earth to it.

alternatively run a seperate earth from the met to the garage (exporting of earths may or may not be an issue)

 

[Avidude]

it is a tns system

 

[dsb electrical]

welcome to napit i am also a napit memeber 12428 i agree with telectrix as a tt would remove any doubts this was mentioned in the napit main forum a while back and will make it more simple to pass

 

[Avidude]

I think that it is a good idea to use earth rods,, is there any way that i can get away with using the 2.5mm swa 2 core cable to save me from digin up the whole garden?

 

[Guest123]

As it's a TN-S system, using the armour as the CPC is totally acceptable.

Make the SWA a 20A radial circuit from the house CU and install a garage CU at the garage end. Most likely it will come with a 40A 30mA RCD, & 1 x 16A & 1 x 6A MCB's.

Make sure the SWA is glanded correctly at both ends and there wont be an issue.

 

[telectrix]

as both previous posts. earth rod,(missing drains etc) drill concrete floor, whack it in, no aggro with exsported earth, connection in proper box and flagged with safety earth blah, blah tag., 10mm G/Y in pvc tube to CU. nice job.

 

[Guest123]

Why all the additional work though???

 

[Avidude]

thanks so much for all your input.
do i need to rcbo the swa from the house to the shed?

 

[Amp David]

Some questions are making me think are you actually ready for a NAPIT inspection yet

 

[Amp David]

As it's a TN-S system, using the armour as the CPC is totally acceptable.

Make the SWA a 20A radial circuit from the house CU and install a garage CU at the garage end. Most likely it will come with a 40A 30mA RCD, & 1 x 16A & 1 x 6A MCB's.

Make sure the SWA is glanded correctly at both ends and there wont be an issue.

This is what i'd be doing too.

 

[Amp David]

No cos its protected by the wire armour.

 

[Avidude]

thank you for all your help.

 

[Avidude]

i thought that you all might be interested that the swa was fed by 30amp fuse
the swa was only 2.5mm and outside there was a consumer unit with 30amp and 5amp fuses.
is this the level of workmanship about 20 years ago?

 

[Avidude]

one more thing,, the swa is part runing along the fence not under ground.. there is no poblem with this right?
thanks

 

[telectrix]

no prob. along fence as long as it is adequately secured .

 

[Deleted member 9648]

as both previous posts. earth rod,(missing drains etc) drill concrete floor, whack it in, no aggro with exsported earth, connection in proper box and flagged with safety earth blah, blah tag., 10mm G/Y in pvc tube to CU. nice job.

Aggro with an exported TNS earth.....????........
Regardless of whether you TT or take the sensible option of 'exporting that nasty old earth' you will have to ensure the armour of the SWA is effectively earthed,that will mean earthing it from the supply end,if you are having to do that anyway what is the point of separating it at the garage and rodding?

 

[Des 56]

i thought that you all might be interested that the swa was fed by 30amp fuse
the swa was only 2.5mm and outside there was a consumer unit with 30amp and 5amp fuses.
is this the level of workmanship about 20 years ago?

There were good bad and ugly standards 20 years ago as there are nowadays

Electricians in the past were generally trained through apprentiships in a much broader field than training for being a domestic installer, which seems to the way of the present

As in all walks of life there will be all sorts to make up an industry
Critisism of standards is a thorny issue to take on board

How do you measure a satisfactory standard,some older more experienced sparks on this forum would not take kindly to a sweeping statement of those standards of 20 years ago