EFLI (Ze) testing
Zs = Ze + (R1+R2)
Zs is determined by:
- measurement of R1 + R2 during continuity testing (see earlier notes) and adding to Ze, i.e. Zs = Ze + (R1 + R2)
Ze is determined by:
-
- measurement (see below), enquiry of the electricity supplier or calculation Ze = Zs – (R1+R2)
- direct measurement using an earth fault loop impedance tester
Verification of test results:
Values of Zs should be compared with BS7671, rule of thumb figures, or EFLI figures given by the designer. To use BS7671:
Take the maximum EFLI from the appropriate table (eg 41.3, page 68, 230v Type B 32A = 1.37Ω)
80% of max Zs (from BS7671) guarantees disconnection within the required time, therefore 1.37Ω x 0.8 = 1.096Ω (round up to 1.1Ω)
Prospective Fault Current
Single Phase – Single Phase – Single Phase – Single Phase – Single Phase – Single Phase – Single Phase – Single Phase – Single Phase – Single Phase – Single Phase – Single Phase –Single Phase – Single Phase – Single Phase – Single Phase – Single Phase – Single Phase – Single Phase – Single Phase – Single Phase – Single Phase – Single Phase – Single Phase –
PEFC = Prospective Earth Fault Current
PSCC = Prospective Short Circuit Current
PEFC – This is a three wire test. Set your MFT to “Loop No Trip” (or “Loop Low”) so that it doesn’t trip any protective devices. When you press test, the MFT sends 6A to the transformer.
PSCC – This is a two wire test. Set your MFT to “Loop High 1” but be aware this will trip any RCBOs as it sends 25A to the transformer.
Three Phase – Three Phase – Three Phase – Three Phase – Three Phase – Three Phase – Three Phase – Three Phase – Three Phase – Three Phase – Three Phase – Three Phase –Three Phase – Three Phase – Three Phase – Three Phase – Three Phase – Three Phase – Three Phase – Three Phase – Three Phase – Three Phase – Three Phase – Three Phase –
Class 1 MFTs (the normal jobby that you will recognise) aren’t able to test all three lines at the same time so we test L1 to N, L2 to N and L3 to N, then multiply the highest result by 2. This is a rule of thumb and errs on the side of caution.
Earth Electrode Resistance
For TT systems. You have the electrode under test and two additional electrodes: the current electrode and the potential electrode. Ram your current electrode into the ground some distance away from your electrode under test (up to 40m is sufficient), then shove the potential electrode halfway between the two. Press the test button on your tester and it will probably say “Err6” or some shit because it’s a Fluke.
RCD Operating Times
Where an RCD with a rated residual operating current (I∆n) not exceeding 30mA is used to provide additional protection in the event of a failure of basic protection and/or the provision for fault protection or carelessness of users, the operating of the device must not exceed 40 ms when subjected to a test current 5 x I∆n. The maximum test time should not exceed 40 ms, unless the protective conductor potential rises by less than 50V.
Example
30mA RCD test on auto:
- 0° 1/2x sends 15mA, result will be >2000ms (no trip)
- 180° 1/2x sends 15mA, result will be >2000ms (no trip)
- 0° 1x sends 30mA, result will be <300ms (trip)
- 180° 1x sends 30mA, result will be <300ms (trip)
- 0° 5x sends 150mA, result will be <300ms (trip)
- 180° 5x sends 150mA, result will be <300ms (trip)
Phase Rotation
Brown (L1) – Black (L2) – Grey (L2)
Correct phase sequence means that the phase sequence of the incoming line conductors (i.e. Brown – L1; Black – L2; Grey – L3) is the same throughout the whole installation. Phase sequence testing is testing to confirm that this is the case.
Certification and Recording
This form will be in the exam and the example that has been filled out applies to the practical. You can ignore the sections that refer to DESIGN and CONSTRUCTION as we are only INSPECTING AND TESTING. Note in the example form I’ve not filled out Continuity results because those were the tests you did last week without me you cunts.
