G8MNY > TECH 12.04.25 07:45z 104 Lines 4469 Bytes #172 (0) @ WW BID : 30120_GB7CIP Subj: Edgcume Peebles Earth Loop Z Path: ED1ZAC<ED1ZAC<IZ3LSV<DB0ERF<DK0WUE<PI8ZTM<PI8LAP<GB7BED<GB7JED<GB7CIP Sent: 250412/0730Z @:GB7CIP.#32.GBR.EURO #:30120 [Caterham Surrey GBR] From: G8MNY@GB7CIP.#32.GBR.EURO To : TECH@WW By G8MNY (Upated Apr 23) (8 Bit ASCII graphics use code page 437 or 850, Terminal Font) This is an old tester the engineers used to use for testing the mains socket & veracity of earths on sockets etc. It is quite useless nowadays with RCD/ELCB protected supplies as it WILL ALWAYS TRIP THEM! ___________ ³ÚÄÄÄÄÄÄÄÄÄ¿³ ³³ .ú'~'ú. ³³ Range 0R2 - 80R ³³ú\ ú³³ Peak Current 30 Amps ³³o \ o³³ Wander probe for ³ÀÄÄÄÄÄÄÄÄÄÙ³ Exterior earth tests. ³ [~~~~~] ³ Þ ~~~~~ Ý Often in a Leather case. Þ Ý No batteries as it Ý Þ uses the mains. Ý Þ ³_________³ PRINCIPLES The meter provides a single half wave pulse of current (30A) from live to earth through a known resistor. The peak voltage across the resistor will equal the supply voltage less the loss due to earth line resistance/impedance. LiveÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄ¿ o _______³______ Pulse/ ³Mains Offset &³ ______ _____ ÃÄÄ´ Peak DetectorÃÄ´BufferÃÄ´Meter³ R ÀÄÂÄÄÄÄÄÂÄÄÄÄÄÄÙ ~~~~~~ ~~~~~ EarthÄÄÄÄÄÄÁÄÄÄÄÙ ³ ³ NeutralÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ If the Earth and Live resistance equals R the voltage across R will be halved. This voltage is compared to the mains so that variation in the mains does not alter meter reading. Because this is fast pulse test (10mS) the earth circuit "impedance" to the pulse rather than just the DC resistance is measured. Also by using a full 30A peak current the capability of the wiring is actually tested. E.g. fine wire strands that may pass the resistance test would be blown up passing this current! This makes the test, what is required for a PROPER SAFETY TEST, even though it hazards other kit plugged in at the time. METER CIRCUIT ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÂÄ2K2ÄÂÄÄÄ¿+80V fetÃÄÙd Cal 5K6 ³ ³ ³ gÚ>³ Ú25KÄ18K´ _³_ZD1 ³+ ³ ³ ÃÄ¿s +/~~~\ ³ ÚÄÄ>1K /_\' === _³_D4 5A -20V³ ÃÄÄ´MeterÃÙ ³zero³ ³ 10u³ /_\ LiveÄo-oÄÂÄÄÄÂÄÄÂÄÄÄ>L ³ 47k \___/ ³ 1K8 ³ ³60v³ 220K ³ _³_ ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄ)ÄÄÄÄÁÄÄÁÄÄÄÄÄÁÄ¿_)|| __ L L-EÚÄÄÄÄ´ ³ \_/SCR Test charge ³ ³-11V 16V ||( Neon 100K ³ ³ÀÄÂÄ100Äo oÄ´<ÃÄÄ)ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ)ÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿__ ||( ÀÄÄÄÄ´ 220K ³ ³ /³\ D1 ÃÄÄÄÄÄÄÄÄÄÄ´ÃÄÄÄÄÁÄÄÂÄÄÄÄ´>ÃÄÄÄÄ¿__)||(__ N ³ ³ ³ 240R ³+ ÃÄ´<ÃÄ¿ u22 ³ D3 8V)|| ³L-N³ ³ ³ 47u=== ³ D2 ÃÄ33RÄÄÂÄÄÄÄÄÄ´-11V 0V³ ³ Neon ³ ³ ³ ResetÀo<ÄÄÄ´ ³ === ³ ³ ³ ³ ³ ³ Test o ³ 100K ³10u ³ ProbeÄ¿ ³ ³ ÃÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄ)ÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ o ³ ³ 10R 30W 1K EarthÄo<ÄÁÄÄÄ)ÄÄÁÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ ³ 220K NeutralÄÄÄÄÄÄÁÄÄÄÁÄÄ>N CIRCUIT OPERATION On connecting the mains the 2 neons should light, indication the mains is SAFE to test. The 5A fuse handles the 30A pulse OK. The transformer's 16V winding charges up the 47uF capacitor via D1 ready to trigger the SCR. The 8V winding via D3 makes a -11V mains reference rail. On testing, a single half cycle +ve peak voltage appears across the 30 Watt 10R (one test per min MAX) and it is attenuated with 1K & 33R & compared to the 11V rail, the resultant peak voltage is fed via D2 (not shorted in test mode) to the u22 storage cap. The voltage across the cap is then read with the FET buffered meter, with its floating regulated power supply. Zero offset & meter gain presets finish off the calibration. Z VALUES To quickly blow a 13A fuse, a current > 26A must flow. So at 220V that needs a total loop resistance < 9 ohm. However with high current main ring circuits of 30A to blow a ring fuse quickly needs a current > 60A, which needs loop resistance < 3 ohm. These are much lower values than you can get with external earths! I once tested a large unused radio tower & earth system with a simple if dangous electric kettle test (no kit on tower) & I was horrified to find it was as high as 14 ohm! See my buls "Earths", "Edgcume Peebles Megger & Low R". "Maplin Mains Meter 2000MU-UK", & also "Mains Power Protection". Why don't U send an interesting bul? 73 de John G8MNY @ GB7CIP
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