High Ze causing headache !

[sythai]

No need to convert to TT

leave it as TN-C-S and you can still use 0.4s / 5s but add rcd as fault protection where required.

Just to check Julie.... how does this work on my EIC please?
My recorded Zs reading for the BS88 will be higher then the max Zs reading of 0.40
Thanks Simon

 

[Julie.]

Just to check Julie.... how does this work on my EIC please?
My recorded Zs reading for the BS88 will be higher then the max Zs reading of 0.40
Thanks Simon

Fill it in with the correct values, but in notes/remarks add something like "ads achieved via rcd as fault protection " - according to each circuit that needs it, for example lighting circuits probably achieve ads with the mcb so don't need it.

Then in 3.1 the last line rcd as fault protection should be ticked (and ideally the appropriate circuit number added - so rfc downstairs, shower... whatever).

You would still need to tick rcd as additional protection as a house requires it for lighting, sockets etc anyhow

 

[sythai]

Fill it in with the correct values, but in notes/remarks add something like "ads achieved via rcd as fault protection " - according to each circuit that needs it, for example lighting circuits probably achieve ads with the mcb so don't need it.

Then in 3.1 the last line rcd as fault protection should be ticked (and ideally the appropriate circuit number added - so rfc downstairs, shower... whatever).

You would still need to tick rcd as additional protection as a house requires it for lighting, sockets etc anyhow

Brilliant thanks - got it now, always learning

 

[Julie.]

Fill it in with the correct values, but in notes/remarks add something like "ads achieved via rcd as fault protection " - according to each circuit that needs it, for example lighting circuits probably achieve ads with the mcb so don't need it.

Then in 3.1 the last line rcd as fault protection should be ticked (and ideally the appropriate circuit number added - so rfc downstairs, shower... whatever).

You would still need to tick rcd as additional protection as a house requires it for lighting, sockets etc anyhow

I don't know if you use particular software, but you may have to jump through a couple of hoops if the software blocks or alerts in the case where Zsmax is exceeded - but that would depend on the software itself.

 

[sythai]

I don't know if you use particular software, but you may have to jump through a couple of hoops if the software blocks or alerts in the case where Zsmax is exceeded - but that would depend on the software itself.

Use Easycert... but sure there is a work around.
Failing have used the Niceic ones direct on their website before

 

[TJ Anderson]

My bad, it isn't only concerned with protective conductors:

434.5.2
A fault occurring at any point in a circuit shall be interrupted within a time such that the fault current does not cause the permitted limiting temperature of any conductor or cable to be exceeded.

Nice one, that's the reg and the one that often gets fell foul of.

 

[westward10]

Even changing to TT, I assume at

Fill it in with the correct values, but in notes/remarks add something like "ads achieved via rcd as fault protection " - according to each circuit that needs it, for example lighting circuits probably achieve ads with the mcb so don't need it.

Then in 3.1 the last line rcd as fault protection should be ticked (and ideally the appropriate circuit number added - so rfc downstairs, shower... whatever).

You would still need to tick rcd as additional protection as a house requires it for lighting, sockets etc anyhow

I wouldn't add a note, BS7671 accepts an rcd can be used for fault protection.

 

[Julie.]

Even changing to TT, I assume at

I wouldn't add a note, BS7671 accepts an rcd can be used for fault protection.

I would add a note, as you say it isn't required, but it provides clarity for anyone that looks at it in the future.

 

[westward10]

I know a lot of people feel designing a circuit on a TN system and relying on a rcd for fault protection is a bad design but this is twaddle and this thread is a good example, a high Ze but even so it is still acceptable.

 

[David Prosser]

No chance of using a BS88-2 63A fuse? I've have access to three different MFT, never got a matching Ze reading from any combination of them. One (Fluke) is always higher than the other two (Megger) with it not unusual to see a difference of up to 0.2 between the Meggers and the Fluke.

Be interested to see what the Zs is when the installation is completed as apposed to the Ze.