TT in stables - helpppppp

[Richard Burns]

Right then....

I think im going to take out the board and fit a metalclad unit - 100ma main sw and 8 30ma rcbos. 3 rings and 2 lighting and a pv feed all on independent circuits.
An amendment 3 consumer unit would seem sensible in a agricultural location so long as the tails are protected. The main switch should be a time delayed version.
From the document to which you linked I might replace the 30mA RCBO on the PV with an MCB, assuming (since it is on 100mA at the moment) that the circuit cables do not need 30mA RCD protection.

Stake it and bond. Park the core used for earth and armour into a plastic box.
Not definite what you mean by stake and bond, if you mean provide an earth rod and ensure main and supplementary bonding is in place and effective then yes.
Divorcing the incoming earthing system is critical.

I want to try and do the stake in the room where the board is - and go deep as 15ft.
Earth rods inside buildings are not often good as the foundations and the lack of surface water can render them limited in stability and effectiveness but a 5m rod could well overcome this.

Ill install 2 circuits on independent rcbos - one for sockets and one for lighting for the yard.
Again I am unsure about your meaning here but from the above posts you are intending to have a separate board for these circuits. I think you are doing this to avoid total loss of power if the 100mA S switch trips. Yeah you can do that.

That's the plan of attack.

Still unsure about the pv tho - currently fed through a 100ma rcd. I cant see a issue if i put it on its own rcbo but i don't know enough to make a call on it.

If the inside rod proves rubbish - its a concrete pad of 18in id be going through - ill move it outside but then id be cutting out the slab etc to run the wire and want to avoid this if poss - horses afoot.

They have said nobody would stay above as access is a mare - scuse the pun - so i can take dwelling out of it but saying metalclad as it'll be nicer to use with my conduits.

Anywhere i may fall short?

The ideas of the plastic board was to save client some money but may as well go the whole hog - his spec was to make it bombproof lol

See my comments above, the inverter you specify does not of itself require RCD protection, but RCD protection is required for ADS on a TT, therefore 30mA RCD protection would seem to be overkill.
I would not select an indoor location for an earth rod, but you know the layout of the site.
This is the layout on which I have based my comments.

 

[Adrian Sadler]

Im back lol

Ive installed a metalclad board. Normal main switch. 30ma rcbos for every circuit. Tails enter board through a whiska type gland wih no way of them shorting to the metal board. Tails inside the board are covered in plastic flexi conduit for double protection.

Is a 100ma needed in this case? I say not but await comments. My scheme say yes i do where others say no.

I terminated the incoming earth and used a rod on the inside of the stables. 16 ohms with no rain for a few days. Had to use a 8ft rod to get it though.

PV supply is on a 30ma rcbo. Im going to wait and see with this one to see if we get nuisance tripping.

 

[Simonslimline]

Im back lol

Ive installed a metalclad board. Normal main switch. 30ma rcbos for every circuit. Tails enter board through a whiska type gland wih no way of them shorting to the metal board. Tails inside the board are covered in plastic flexi conduit for double protection.

Is a 100ma needed in this case? I say not but await comments. My scheme say yes i do where others say no.

I terminated the incoming earth and used a rod on the inside of the stables. 16 ohms with no rain for a few days. Had to use a 8ft rod to get it though.

PV supply is on a 30ma rcbo. Im going to wait and see with this one to see if we get nuisance tripping.

Are the RCBO's single pole?

 

[Adrian Sadler]

Single

 

[Deleted member 26818]

Sounds ok to me.

 

[HappyHippyDad]

Thankyou Richard for all the time you've taken to write out such detailed and helpful replies... Kind regards, Adrian Sadler.

 

[Midwest]

Im back lol

Ive installed a metalclad board. Normal main switch. 30ma rcbos for every circuit. Tails enter board through a whiska type gland wih no way of them shorting to the metal board. Tails inside the board are covered in plastic flexi conduit for double protection.

Is a 100ma needed in this case? I say not but await comments. My scheme say yes i do where others say no.

Another thread on such a subject, advised that a 100ma S Type was necessary, if using SP RCBO's on TT supply, to negate the possibility of an neutral to earth fault remaining after a SP RCBO has tripped because of an earth fault. If your scheme is giving the same advice perhaps you should follow this advice?

DP RCBO's seem thin on the ground though, which appears strange given the issue.

 

[Deleted member 26818]

A neutral to earth fault will still be there, whether the RCD is SP or DP, and will not care what the earthing system is.
The reason we used to use 100mA 'S' type RCDs originally was just to provide earth fault protection for the entire installation.
Then it was to provide earth fault protection for non 30mA RCD protected circuits.
What would be the purpose if all circuits have 30mA RCD protection?

Protection for the tails between the meter and the first RCD, is provided by double insulation, which has been the case for many years.
What has suddenly changed, so that the double insulation is no longer acceptable?

 

[Midwest]

Don't know Spin, only quoting what was previously said by my more learned colleagues, unless I've misunderstood it; http://www.electriciansforums.co.uk/electrical-forum-general-electrical-forum/109469-tt-systems.html
post #4?

 

[Richard Burns]

Now the double insulation is passing through a metal sheet and this was previously not permitted but as it is now required they must come up with a justification for the change.

 

[Risteard]

As long as the tails are double insulated

They won't be. Ever.

They are insulated and sheathed.

 

[Deleted member 26818]

They won't be. Ever.

They are insulated and sheathed.

Oh here we go again.
Have a look at Regulation 412.2.4.1.
Sheathed cables are considered to meet the requirements for double insulation.
It's not the first time I have drawn attention to this, I guess it won't be the last.