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G8MNY > TECH 02.07.22 14:46l 34 Lines 1376 Bytes #999 (0) @ WW
BID : 24882_GB7CIP
Read: GUEST
Subj: Earths
Path: IW8PGT<IZ3LSV<ED1ZAC<GB7CIP
Sent: 220702/1233Z @:GB7CIP.#32.GBR.EURO #:24882 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (New Nov 08)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
Z VALUES
To quickly blow a 13A fuse, a current > 26A must flow. So @ 220V that needs a
total loop resistance < 9ê. However with high current main ring circuits of 30A
to blow a ring fuse quickly needs a current > 60A, which needs loop resistance
< 3ê. These are much lower values than you can easily get with external earths.
AC TESTING A TOWER EARTH SYSTEM (Mains with No ELCB/RCDs only!)
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
originally about 14ê!
Note do not attempt this method if there are ELCB trips.
Test
LÄo\ÄÄÄÂÄ /
NÄÄÄoad 0 ê reference
240-150
Mast to live 150v. Rm = ------- x 24 = 14.4 ê
150
240-169
New Stake to live 169v. Rs = ------- x 24 = 9.9 ê
Now suppose the Neutral is not at ground, say 100V off ground due to unbs
See my bul on "Constant Voltage Transformers", "Edgcume Peebles Earth Loop
73 de John G8MNY @ GB7CIP
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