Hello Gents, I have been out of the trade for a time (hence Im a bit rusty) and need to ask the following so I know where I stand regarding this scenario!
Does a DNO 30mA RCD Isolator satisfy 411.4.204 (411.3.2.2)
Scenario is: Domestic property, late 60's/early 70's, TN-S, old wylex 4 way fuseboard with recent wylex retrofit 60898 Type B MCB's fitted.
There is a 30mA RCD isolator present between the meter tails and consumer tails (rather than a 100A D.P switch). (There is no other RCD present at the consumer unit or elesewhere.)
The EICR is due. The R1+R2 and Zs on individual circuits have not been measured just yet.
Iam concerned that it might not be possible to meet max Zs times on the individual circuits. In such a case, is it permitted to utilise the 30mA RCD mentioned above to provide requirements for fault protection (protection against electric shock) for the individual circuits?
My thinking is (from memory), if on a TT it is ok (usually theres no choice) to have some circuits on one side of a board protected by one 30mA RCD, then why would it not ok to do this on a TN-S / in the scenario above?
If the answer is No, what is the technical reason why not ok?
I do realise fitting a new consumer unit with RCBO's is probably the best solution, but this cant be done at this moment in time.
If the answer is yes it's ok, I have two more questions:
1) When i read the schedule of test results, should I expect to see 1667 ohms written in the "maximum Zs permitted by BS7671" box/column for each circuit?
(assuming the MCB's dont meet max Zs)
and
2) Would item numbers 4.18 and 4.19 on the inspection schedule (page 481 in the regs) be ticked as 'acceptable condition'?
Thanks in advance, I will reply when I can.
John
Does a DNO 30mA RCD Isolator satisfy 411.4.204 (411.3.2.2)
Scenario is: Domestic property, late 60's/early 70's, TN-S, old wylex 4 way fuseboard with recent wylex retrofit 60898 Type B MCB's fitted.
There is a 30mA RCD isolator present between the meter tails and consumer tails (rather than a 100A D.P switch). (There is no other RCD present at the consumer unit or elesewhere.)
The EICR is due. The R1+R2 and Zs on individual circuits have not been measured just yet.
Iam concerned that it might not be possible to meet max Zs times on the individual circuits. In such a case, is it permitted to utilise the 30mA RCD mentioned above to provide requirements for fault protection (protection against electric shock) for the individual circuits?
My thinking is (from memory), if on a TT it is ok (usually theres no choice) to have some circuits on one side of a board protected by one 30mA RCD, then why would it not ok to do this on a TN-S / in the scenario above?
If the answer is No, what is the technical reason why not ok?
I do realise fitting a new consumer unit with RCBO's is probably the best solution, but this cant be done at this moment in time.
If the answer is yes it's ok, I have two more questions:
1) When i read the schedule of test results, should I expect to see 1667 ohms written in the "maximum Zs permitted by BS7671" box/column for each circuit?
(assuming the MCB's dont meet max Zs)
and
2) Would item numbers 4.18 and 4.19 on the inspection schedule (page 481 in the regs) be ticked as 'acceptable condition'?
Thanks in advance, I will reply when I can.
John