Protection on 2 garages with TT system

[wadhamfarm]

Hello Guys,
ive been looking through posts for a number of months now and thought its finall time to take the plunge and ask my own question.

I have 2 garages which are supplied from a meter in the first garage. It is a TT system.

The current protection is a 80A RCD on a Metelclad single 6 way board.

At the moment if there is a fault with any circuit as you would expect it trips the RCD and im plunged into darkness.

I would like to upgrade the system to only take out the circuit at fault.

From my research it appears the easiest way is to acheive this a 100mA time delayed Main RCD and then 30mA RCBO's for each circuit.

Would you agree?

Ive provisionaly settled on this setup on the basis of every circuit on a TT system needing fault protection, and also appears from my research that as my CU isnt of plastic construction that the Main switch needs fault protection as well.

THanks in advance for your replies.

 

[GLENNSPARK]

well...there you go.....do that....each final will have its own protection for fault....

 

[wadhamfarm]

Thanks for the reply.
Do you know if it would satisfy the regs?

 

[GLENNSPARK]

well...for a start your better of not loseing lighting in there every time theirs a fault....that on its own constitutes a danger....

 

[jaydee81]

sounds ok if your using a metal clad consumer unit your 100ma td rcd needs to be fitted in an insulated enclosure fitted before the cu

 

[Engineer54]

That would be the way i would go on a TT system. The S type (time delayed) 100mA RCD is to provide addition protection should an RCBO fail. (which is not as uncommon as some may think/wish)
The 100 mA rating depends very much on what type of equipment you have installed in your two garages. High leakage equipment (natural leakage) combined with common natural circuit leakage over the combined circuits within your CU could in some circumstance trip over the head of the RCBO's. But generally speaking in most situations, this is unlikely


To be honest, so long as the tails into the Metal CU are adequately protected with rubber grommet, it's highly unlikely that a sheathed and insulated tail or tails are going to come to any harm entering a metal enclosure.

 

[soulman]

Why not use a insulated enclosure and forget the upfront 100ma rcd.

 

[wadhamfarm]

Thanks for the replies.
Jaydee, so you would suggest putting the 80A 100mA TD RCD in a enclosure, and then running the tails into the CU through conduit maybe, and then have a 80a ISO before RCBO's for the circuits to meet the regs?

 

[Engineer54]

Thanks for the replies.
Jaydee, so you would suggest putting the 80A 100mA TD RCD in a enclosure, and then running the tails into the CU through conduit maybe, and then have a 80a ISO before RCBO's for the circuits to meet the regs?

That what he's suggesting Yes!! But you don't need conduit, tails are generally double insulated (insulated and sheathed), so for short distances wouldn't require additional mechanical protection. All that is required, is a rubber grommet that the tails can pass comfortably through into the metal CU....

 

[wadhamfarm]

Soulman,
the CU is only about 7ft high, and its in a semi-industrial workshop where farm machinery is stored.
For this reason, thought of Metalclad to give impact protection.

 

[Engineer54]

Why not use a insulated enclosure and forget the upfront 100ma rcd.

That would be a very silly move, precisely for the reason given above!!

 

[GLENNSPARK]

yes....why do away with what is a perfecty acceptable....`secondry defense`...if you like?...