The accessory pictured is often used in testing when conducting test using what particular method?

The Ze is to be measured as part of the initial verification process, what instrument should be used for this task?

The maximum value of earth electrode resistance for a TT installation protected by a 500mA RCD is given by BS7671 as

A 100mA RCD protecting a TT installation tested at 1/2 I should

The following readings were taken on a test performed on a ring final circuit, Line to Line 0.8 Ω Neutral to Neutral 0.8 Ω cpc to cpc 0.8 Ω . What would be the expected reading between line and cpc at each socket outlet?