Ze at its Maximum Measurement

[ThrownRazor25]

If the Ze on a TNS supply is measured at 0.8ohms, is this still acceptable?

Technically it is bang on the maximum.

DB is 100A Main Switch with 30mA RCBO's on all circuits.

 

[Ian1981]

I would say the question is are your required disconnection times met for the final circuits?
You do however have 30mA additional protection which will provide fault protection also.

 

[Wilko]

Your final circuits need to meet max, and from DNO side that number gives 5 second disconnection for 60A fuse, if I recall correctly.

 

[ThrownRazor25]

Readings for Zs at Cooker on 32A were 1.05ohms and sockets on 32A were 1.24 ohms. Both above the maximum 1.08ohms for a 32A RCBO.

Given the fact there is additional 30mA protection and theoretically 1667 ohms is the maximum value allowed given this would enable a 50v touch voltage, is this allowed? Or would DNO have to be notified?

 

[Nigel]

When your Zs exceeds the max permitted you have to look at design first and foremost. RCDs will become fault protection rather than additional protection and the max Zs permitted should be recorded as whatever rated RCD is deemed necessary to meet those times.

However installing RCDs as fault protection to cover poor design is not acceptable. Goven what you have said then I don’t think this is down to poor design.

Are there any other reasons for RCD protection on all circuits?

 

[Octopus]

I would be checking my dead test figures ....

Ze + (R1 + R2) = Zs

Some RCBO's are well known for giving higher figures....

Out of interest what was the Line to Neutral reading