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Discuss supply to a shed on a tns system in the Electrical Forum area at ElectriciansForums.net

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Hi everyone
I have a question I have been asked to look at a job this week and I am a bit puzzled.
A chap I know has a shed connected to His down stairs ring to a garden shed via a 2 core swa cable. Its connected to the rear of a outside socket the armour of the swa is connected to the cpc at the outside socket and in the shed the swa cable armour is connected into the earth terminal in a garage consumer unit that just has 2 mcbs in it no rdc. A 6amp mcb that powers a 2ft led batten and a 20amp mcb that connects to a double socket and then there is a 16mm cpc that connects to a earth rod beside the shed is this acceptiable
It looks a bit naff to me the fact that the tns set up has a earth electrode in it as well
thanks phil
 
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Rpa07

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Phil, you need some punctuation to help that to be readable - without punctuation it does come across as a ‘lash up’!
 

buzzlightyear

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TNS with a earth rod are you certain it is a TNS .is metal pipe work in .
The shed needs to be on it own if it has a c/u for the circuits if thats the case .is the circiut that the shed on has any RCD protection .
 
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Richard Burns

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You have effectively described a spur (unfused?) from a ring final circuit supplying two double sockets and a light.
If this is unfused it is not permitted as an unfused spur should only supply a single accessory.
The consumer unit is fairly redundant but the light should be fused down.
However installing a fused spur before the outside socket would resolve most of this.
The addition of an earth rod is probably not really a problem, although in effect it does introduce an earthed conductive part into the shed which might cause potential difference issues, however because it is earthed back to the house CU it should not matter.
Presumably the house ring is 30mA RCD protected and if so this is fine, if not then there are other issues with the house as a whole.
Overall a right old mess.
 
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Hi The house is a TNS system and all circuit in the house are RCD protected the house is only a year or so old. The earth rod has been added at a later date when the shed was erected the rcd protection is from the house DB. Also if the shed supply is from a socket and the shed has a lighting circuit and a socket circuit should this be a notifiable job
Phil
 

Richard Burns

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It is a spur from a ring so not notifiable (unless in Wales as garden power). It would be hard to state you had complied with the building regulations as it does not comply with BS7671.
 
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not sure I will ask tomorrow what should he have should the be a set of test results for the house and a set for the shed
phil
 

Richard Burns

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I doubt he got a certificate for the work but from what you describe it ought to be a minor electrical installation works certificate for a spur, but the installation of a consumer unit, even if it is pointless, is theoretically notifiable and would require an electrical installation certificate; the consumer unit is effectively a couple of circuit breakers in a box and not really a consumer unit as it is supplied from a final circuit.
Installing it as a spur there would be test results for the spur (including the RCD tests).
Installing it as a consumer unit would require tests for the "distribution circuit" (i.e. the ring and spur), and tests for the "circuits" in the shed.
Fusing down at the start of the spur from the ring and removing the consumer unit and earth rod and fitting a further 3A FCU for the lights might be a solution.
 

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