DB2 (TT) trips DB1 TN-C-S

[Broken handle]

In other words Sod the customer you've taken money from!! Magic!!
Any electrician that's fool enough to ditch a perfectly good TN Earth in favour of anything like the totally unreliable recommendations of BS 7671 regarding TT systems, needs Certifying!!

All my TT installations have been perfectly good too!

 

[Deleted member 9648]

Why? Because although at 30m it is far enough away from the house and (probably) any extraneous metal, with a TT I have a separate earthing system which is, if you like, under known control conditions and not subject to problems at the suppliers end. TT'ing I agree is not really an issue where step-voltages are highly unlikely but I generally will always TT an outbuilding combined with 30mA RCD.

Sorry, above should say "Exporting PME....."

But you have installed a 10mm 3c SWA so the third core is of sufficient CSA to double as a cpc and main bonding!!
Question--If you were installing external lighting not attatched to the main house but fed from it would you treat the lights as 'outbuildings' and TT them or use the house earthing system?


Edit....To be fair you have not stated the PME cant be 'exported'....but that you prefer not to.I'd have to disagree but thats your choice.

 

[Broken handle]

No, wirepuller, I only install two core SWAs.

 

[Silly Sausage]

Why? Because although at 30m it is far enough away from the house and (probably) any extraneous metal, with a TT I have a separate earthing system which is, if you like, under known control conditions and not subject to problems at the suppliers end. TT'ing I agree is not really an issue where step-voltages are highly unlikely but I generally will always TT an outbuilding combined with 30mA RCD.

You may as well TT the house using that argument.

 

[GLENNSPARK]

No, wirepuller, I only install two core SWAs.

without checking the earthing arrangements top end first?

 

[Engineer54]

Sorry, above should say "Exporting PME....."

Really, ... I've got some news for you, you're not Exporting PME, You are in fact ''Extending'' an Equipotential Zone!!

All my TT installations have been perfectly good too!

Hmmm, if you say so!! lol!!

 

[Deleted member 9648]

No, wirepuller, I only install two core SWAs.

My mistake...got you confused with the OP.

 

[Meggerman]

In other words Sod the customer you've taken money from!! Magic!!
Any electrician that's fool enough to ditch a perfectly good TN Earth in favour of anything like the totally unreliable recommendations of BS 7671 regarding TT systems, needs Certifying!!

TT or PME, it complies with BS7671 and it is up to him as the installer. Sometimes TT is preferable over PME is bonding is required at sub main. I do either dependant on situation. It is not a case of one size fits all.

 

[Broken handle]

Thinking about it, in the summer I connected power to a DB in a brick built shed (about 5 metres from main house. Customer supplied all materials and I had to take the power source from an existing outside socket (customers preference). 3 core SWA provided so armour and copper core all earthed back to same (PME) earth point. No problem with that from my point of view but when supplying out buildings from which a person is stepping in, and out, potentially hanging on to something live, then my preferred, and standard procedure, is two core (cheaper) SWA, TT earth, and 30mA RCD fed from non-RCD MCB.

 

[Engineer54]

TT or PME, it complies with BS7671 and it is up to him as the installer. Sometimes TT is preferable over PME is bonding is required at sub main. I do either dependant on situation. It is not a case of one size fits all.

Very true, but if you read his posts here again, ....Not for this guy!!