TT board change some pointers please

[robd]

Evening all. Got an upcoming board change in a rural house, TT about 7 or 8 ways I'm guessing. A couple of questions if I may....

...will probably go split load, can I go conventional dual RCD 30mA?...or do I need to go 100mA time delay etc?

Don't don much out in the sticks, am pretty much on TN-C-S auto pilot!be grateful for any thoughts.

Rob

 

[Octopus]

Conventional dual RCD is ok - or a full set of RCBO's if its an old property

 

[SirKit Breaker]

Evening all. Got an upcoming board change in a rural house, TT about 7 or 8 ways I'm guessing. A couple of questions if I may....

...will probably go split load, can I go conventional dual RCD 30mA?...or do I need to go 100mA time delay etc?

Don't don much out in the sticks, am pretty much on TN-C-S auto pilot!be grateful for any thoughts.

Rob

Can't disagree or comment on what Murdoch says, because like you i have little TT experience. But it must be worth half an hour in the BRB just to make sure, that is what i would do, and if still unsure i would be on the phone to scheme provider tech help, Elecsa in my case.

Cheers..........Howard

 

[ezzzekiel]

standard split load will cover your requirements, 100ma is a kick back to when only certain circuits required 30ma protection however now pretty much everything will require 30ma so no need for 100 just cover them all with splitload or rcbos

 

[robd]

thanks to all, didn't know that was why we used the 100A thanks for clearing up

 

[robd]

Can't disagree or comment on what Murdoch says, because like you i have little TT experience. But it must be worth half an hour in the BRB just to make sure, that is what i would do, and if still unsure i would be on the phone to scheme provider tech help, Elecsa in my case.

Cheers..........Howard

Agree Howard, you are right, sometimes the forum is quicker than the BRB though and I don't have to put my adnams down to type on the forum

 

[Deleted member 9648]

Dont forget that the DB MUST be all insulated....if it is metal cased you will either need up front 100ma RCD protection or take extra precautions to ensure incoming tails cannot short onto the case.

 

[robd]

yep got that, don't worry a nice plastic cu will be going in. Cheers

 

[yellowvanman]

Just make sure you don't use a metalclad CU, if you do then you need the 100mA RCD.

 

[Piratepete]

Hi
I'm out in the sticks where there's a lot of TT. Earthing is generally awful - just a bit of old pipe stuck in the ground or lying on the flower bed behind the dog kennel all with exposed connections and no mechanical protection to the cable or rod! May even be to the water pipe!
So be prepared to sink a new rod with the connection in a box (Plastic Inspection Earth Pit - digging required! look in Electrofix Catalogue) and run a new 6sqmm earth wire in conduit if outside. Bonding will probably be crap too! At least that's also only 6sqmm.
On one job (with no proper earth) it was easier and cheaper overall to get thesystem changed to PME TNC-S.
Best of luck. Pete

 

[slocm3105]

You must remember that when doing an install on a tt system, both line and neutral must be disconnected in the event of a fault and as most rcbo's are single pole only it's generally easier to use the standard dual RCD consumer unit option to meet the regulations.

 

[ringer]

You must remember that when doing an install on a tt system, both line and neutral must be disconnected in the event of a fault and as most rcbo's are single pole only it's generally easier to use the standard dual RCD consumer unit option to meet the regulations.

Never worked on a TT yet, so bear with me. How would you wire up a 'standard dual RCD' CU to achieve two-pole disconnection under fault conditions?

 

[telectrix]

you could use 2 pole MCBs/RCBOs. the RCDs will give you 2 pole disconnection in the event of an earth fault, 2 pole MCBs for L/N fault.

 

[slocm3105]

Never worked on a TT yet, so bear with me. How would you wire up a 'standard dual RCD' CU to achieve two-pole disconnection under fault conditions?

I can't, at this moment in time, quote u the BS number but the rcds that come with most consumer units now are double pole.

 

[telectrix]

I can't, at this moment in time, quote u the BS number but the rcds that come with most consumer units now are double pole.

but RCDs will not disconnect in the event of a L/N fault. only L/E or N/E.

edit. a quick scan in brb . it would appear that the requirements of 2 pole disconnection referonlyto earth faults, but this is not absolutely clear. one for you widdler???

 

[Piratepete]

Hi.
I don't understand where the requirement for double pole comes from for fault conditions. IMHO the requirement for double pole is for isolation only - this being provided by the Main Switch.
If you look at examples of TT installations in the On Site Guide you will see only single pole cbs or rcbos.
Pete

 

[Amp David]

I'd go for RCBOs for the whole board. Use the forum sponser to get them, nice and cheap.

 

[SimpleSimon]

Hi.
I don't understand where the requirement for double pole comes from for fault conditions. IMHO the requirement for double pole is for isolation only - this being provided by the Main Switch.
If you look at examples of TT installations in the On Site Guide you will see only single pole cbs or rcbos.
Pete

I'm with you on this one PiratePete. The requirement is for double pole isolation not double pole fault methods and like you say is provided by a main switch.

 

[drew35]

Why mess around with TT, especially if you're changing a consumer unit. Get the supplier out to pull the fuse, and at the same time they will convert you over to PME. Its much safer, takes minutes, and you don't have to worry about beating an earth rod all the way to the earths core to get a decent reading!

 

[Amp David]

Why mess around with TT, especially if you're changing a consumer unit. Get the supplier out to pull the fuse, and at the same time they will convert you over to PME. Its much safer, takes minutes, and you don't have to worry about beating an earth rod all the way to the earths core to get a decent reading!

Is this for definite then?