"TT."... Call me a twat.. plonker.... Idjut... fool etc.. if you want... Just interested in thoughts??

[SPECIAL LOCATION]

Basic question.... "TT Am I missing something Stupid"?

Been to look at an installation today .....
Previous customer moved house... to a more rural location wanting a few jobs done....

Main House TT.. with remote garage approx 20m physical.. maybe 25m+ cable run (6.0mm 3core SWA, Red/Yellow/Blue) between buildings...

Garage CU working Sockets, Light plus onward to garden summer house and driveway gates.
Zbd @ garage 47.4 ohms Off a 32A 60898 MCB at main house..
NO RCD protection on Sub-main from House to garage...

Garage is getting earth from main house rod...

Had this of been a TNS / TNCS at the house, I would have probably TT'd the garage anyway..!

But... Working mostly in an urban part of Midlands, I only get to see maybe two or three TT's every 4or5 years, so not 100% hot on historic requirements..

My gut feeling is that the garage should have had its own rod independent of the House..
Plus the sub-main feeding the garage should have been RCD protected to meet sub-main disconnection times...???

Looks like the kitchen was refurbished more recently Blue/Brown ring final..
I am thinking that Captain Kitchen Fitter replaced the CU during this kitchen refurb, with little or no knowledge of earthing arrangements?

Was this arrangement actually acceptable pre the Harmonised colours??
Thoughts please gents??????????????????

 

[Andy™]

nothing wrong with using the same rod however you would need RCD's unless your earth loop is within max Zs which yours is not. usually 100/300mA time delayed RCD unless the circuit needs 30mA

 

[Murdoch]

Adding a 2nd rod for the garage may be a good idea if the Ze is high ............ done that before, but certainly wouldn't if it was a TNS

 

[SPECIAL LOCATION]

nothing wrong with using the same rod however you would need RCD's unless your earth loop is within max Zs which yours is not. usually 100/300mA time delayed RCD unless the circuit needs 30mA

That's what I thought...
The main house board is a Crabtree dual RCD + couple of non-RCD ways..
{think its wot they used to call a high-integrity CU?}
Standard main switch..
Tails direct from the electric meter..
No up-front 100ma Time delayed RCD.
First non-RCD way is the 32A MCB suppling sub-main to garage..

Garage is a bit of a bodged up metal cased Steeple CU..
Final circuits off the garage do have 30ma RCD...
But the incoming sub-main is only protected by the 32A type B, back at the house..

And with a Zdb of 47.4ohms..
(Also did a PEFC to the metal case of garage CU.. got 4.2amps)..
If the incoming feed to the metal case garage CU, makes contact..
Its just going to sit there happily with a fault current just under 5A flowing back via the earth.. with Nothing to automatically disconnect the supply!

I can't see how this arrangement could have ever complied with BS7671, even to previous editions?

As I said, I am convinced that during the kitchen refurb several years ago, under the previous owners, whoever added the new kitchen sockets ring-final, separate radial for freezer, lights circuit, (and there was a old hot-tub feed as well)..

Just fitted a new CU ignoring the earth arrangements.
Obviously there are NO electrical certificates..
No prev/next inspection date labels... and...
Several of the circuits have no, or incorrect identification labels..

Plus the earth rod is looking a little worse for wear!!!!!!!!

 

[binky]

I can't see how this arrangement could have ever complied with BS7671, even to previous editions?

It doesn't, even very old systems would have had a VOELD on the incoming tails, which were superseeded by TD RCDs.

I would be tempted to separate the garage from the house DB, or install a TD or 300mA RCD on the incoming tails - 300mA is what they recommend for farms for fire prevention in animal sheds (NB I might be out of date with that statement). You won't like the price of 300mA RCDs though, so mini board and TD RCD is probably cheaper than that. As the board is fully RCD, I don't believe you really need any RCD on the tails to that, just the garage supply. I think I would also replace old rod connection, rod itself looks ok, and install another one at the garage - multiple rods only improves earthing!

 

[UNG]

Looking at that earth rod it needs a good clean and a proper termination made with some Penetrox and a wrap of Denso tape to keep the water off it
Open to the elements like that the corrosion and verdigris will no doubt have affected the cable, it would be interesting to check the resistance from the rod to the MET
A second rod properly spaced from the existing rod would certainly help improve the Zs

 

[Andy™]

I can't see how this arrangement could have ever complied with BS7671, even to previous editions?

it never did comply. as binky says, in the olden days it would have had a ELCB. chances are, it did then someone replaced the board and removed the ELCB

Locked to prevent being resurrected (again)