DB2 (TT) trips DB1 TN-C-S

[ipf]

well eng:

i never listened to any of the old drivvel about RFCs then....and i wont now either...
and if young robert who comes out with us starts being indoctrinated by any college slavver about the `dangers` of a properly designed RFC...or how you cant extend a PME then i will be on hand to lead him back into the light...

And stomp down to the college to re educate the firkin board slapper.

 

[GLENNSPARK]

And stomp down to the college to re educate the firkin board slapper.

yep...i`ll grab em by`t scuf ov`t neck...

 

[Broken handle]

Nothing wrong with what he's done (except the rcd's in series) if that's how he has designed it and is happy to waste money on 3 core but not use the 3rd core to extend the pme.
Me I'd have saved some bunce and gone 2 core swa, split the tails at the house into switch fuse out in 10mm on to outbuilding small db with rcbo's

Frenchie I'm in Andover tomorrow if you want me to sort it for you.

Exactly how I would do it (and have on many occasions). At a distance of 30m from main building I would not be exporting PME but relying on TT. For your information, Frenchie, the reasons you do not want two 30mA RCDs in series are something you should be aware of when doing work of this nature.

 

[Deleted member 9648]

Exactly how I would do it (and have on many occasions). At a distance of 30m from main building I would not be exporting PME but relying on TT. For your information, Frenchie, the reasons you do not want two 30mA RCDs in series are something you should be aware of when doing work of this nature.

Why?,,

 

[Octopus]

Why?,,

My thoughts exactly. My shed is about 30m away and I've exported the earth. Why ditch a really god earth for a unreliable one!!

 

[Broken handle]

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....."

 

[Engineer54]

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.

Then you're a fool!! So what happens when that 30mA RCD fails then?? You've been listening to far too many scaremongers!!

 

[Broken handle]

So what happens when that 30mA RCD fails then??

All things are liable to fail. But I do not get in my van and think, better not drive today because the brakes might fail. If everything is designed correctly and works as it should then I should not be having sleepless nights about possibilities of failing components. Once my test & inspection cert. is done (and BTW, I always take photographic evidence of my installs :smiley2 then the installation is as it is and so long as i can stand up in court and prove everything was done within regs. then I am happy - even if I might agree with the view "in hindsight.....":wink5:

 

[Engineer54]

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!!

 

[Octopus]

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!!

Along with the install!

 

[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!!