Preferred method of installation

[Rappid]

Had a look at a job the other day, client has brought a MK RCD Garage CU and wants it connected up.
Supply is TNC-S with a 100mA RCCB protecting a BS1361 fuse board which has MCB's

Option 1. Replace the RCCB with a time delayed RCD and connect garage CU to new RCD

Option 2. Henley block the meter tails and connect both CU's to Henley block so both RCD's are in parallel

All wiring will be surface mounted SWA.

Both methods would achieve discrimination, which method would be the preferred one?


Thanks

 

[malcolmsanford]

Had a look at a job the other day, client has brought a MK RCD Garage CU and wants it connected up.
Supply is TNC-S with a 100mA RCCB protecting a BS1361 fuse board which has MCB's Are you sure this is a TNC-S system, if so why as it got this 100mA RCCB

Option 1. Replace the RCCB with a time delayed RCD and connect garage CU to new RCD Expensive.

Option 2. Henley block the meter tails and connect both CU's to Henley block so both RCD's are in parallel

All wiring will be surface mounted SWA.

Both methods would achieve discrimination, which method would be the preferred one?


Thanks

Here is my take on things, Was the system originally TT and been converted to TNC-S and the RCCB never removed. If indeed it is a TNC-S, then, check your Ze reading and if it is a TNC-S then you can redesign your install

 

[Rappid]

Thanks Malcolm

I did suspect it was a TT system but unable to find a connection to a earth rod. It looks like the electricity board converted to a TNC-S when they put a new meter in, they also changed tails to 25mm.

 

[malcolmsanford]

Well I would now confirm if it's TNC-S or TT by a Ze. I would confirm also if the RCCB is actually still operational.

 

[Rappid]

Tested the Ze, got a reading of 0.36 ohms :banghead: cleaned and tightened the contacts and got 0.35 ohms :cheesy: it's not ideal.

The RCCB is still operational.