What should r1 r2 be

This ensures in the event of a fault, circuitry is not overloaded before a fuse or circuit breaker isolates the fault, and that the fault is isolated within a specified time, based on the circuit type and supply type.

Acceptable Zs values depend on the protection type and circuit rating. If you have RCDs, these are also tested, initially by pressing the button to ensure the RCD trips normally, and then:. The testing device allows a small fault current normally 30mA for most domestic RCDs to flow between live and earth wires. This should trigger the RCD within a set time. The test is carried out on both separate phases of the AC supply. The testing device then allows a larger fault current normally mA to flow.

Email: david devonia-electrical. Puzzled by something electrical? Read our comprehensive Glossary in the Help Centre section. Web View Mobile View. News Legal notice Find us. Electrical Testing Explained. Supply Tests. External earth fault loop impedance, Ze This is a measure of the resistance of the wiring between your Consumer Unit circuit breaker board or fuse board and the supplier's transformer, which may be some way away.

Prospective Fault Current, Ipf This is calculated based on the voltage of your supply and the Ze measurement, and is a theoretical measure of how much current could flow if there was an earth fault current going directly from live to earth or short circuit current going directly from live to neutral.

Circuit Tests. Usually the maximum circuit length will be set by a combination of limiting volt drop, limiting circuit impedance and source characteristics Regards OMS Let the wind blow you, across a big floor. Thanks a lot for your contributions lads, much appreciated!

New here? To participate in discussions, please log in and introduce yourself. Shift Technician. Senior Engineer- Systems Architect. Recruiter: Telent Apply for this job. Project Engineer - Ops Comms. Latest News: Private messages, your photo, profiles, email notifications. Linear : Threading : Single : Branch. Search Topic Keyword. View similar topics. Print this topic. Wiring and the regulations. Kind regards, Mick. The ratio applicable here is simply 2. Using this, your figures are not far off.

With a typical length of 60 metres of cable, the typical measured values at 20 degrees for a ring final circuit wired in 2. The NICEIC assumes no liability whatsoever to anyone for any loss or damage caused by any error or omission in this correspondence, whether such error or omission is the result of negligence or any other cause. Any such liability is disclaimed.