TT System updating advice please

[egg661]

i have a TT system in a sorry state. please could you advise on these points

1.The earth cpc has snapped off the earth rod and is to short to reconnect Its is 2.5 csa. What is the required csa for the main earth 10mm or 16mm

2. there does not appear any bonding on the incoming gas supply. What is the csa required 6mm?

3. the consumer unit is rewireable type protected by a RCD (no sure if its 100ma) between consumer unit and incoming supply. 1 lighting circuit, 2 ring, 1 heating and electric cooker

what protection do i need in the new CU and should i remove the old RCD before the CU
thanks in advance
Mark

 

[oharaf]

I'm sure some one will correct me if I get this wrong

The main earth should be at least 16mm

The gas & water should be at least 10mm

(This will depend on distance and when checked for continuity should be less than 0.05Ohms)

The RCD incomer should be 100mA for a TT system.

Hope this helps.

 

[Spark123]

The earthing conductor for a TT system can be as small as sheathed 2.5mm providing it is protected against mechanical damage.
If it isn't protected then sheathed 16mm is required.

The main bonding should be greater than half the size of the earthing conductor and no smaller than 6mm. The resistance of said bonding shouldn't exceed 0.05ohms.

All circuits on a TT system need to be protected by RCD, as you only have a few circuits to look at RCBOs might be a better option (double pole versions).

Replacing a CU is notifiable under Part P of the building regs.

 

[RF Lighting]

Would SP RCBOs not be sufficient if the installation was all RCBO, and did not have a type S main switch?

 

[Spark123]

I don't think so - devices for isolation in a TT system need to be double pole. Also makes you stay clear of the pretend TN-CS situation if there is a N-E fault on a circuit.

 

[RF Lighting]

Oh ok, never thought about that.

 

[Taylortwocities]

For a TT you can use a two x 30mA RCD "17th Edition" board without the need for a time-delayed incomer.

Thats assuming there's no cbs in the unprotected section of the board.