Hi all,
The UK Code of Practice for vehicle installations is FCS 1362
http://www.fcs.org.uk/my%20files/fcs_pdfs/codesofpractice/fcs1362_2010.pdfIt is a change, in December 2010, from MPT 1362.
The old MPT version said both leads to battery, both fused.
The negative lead did provide an alternative connection from the vehicle chassis to the battery negative and even with the engine/starter earth strap intact the current through the rig was non-zero. With a duff strap it could be over 100A.
FCS 1362 avoids that risk by saying positive fused to battery, negative to nearest chassis bonding point, no fuse.
That does introduce a common negative impedance for the rig and the vehicle electrics, providing a route for import and egress of interference.
The FCS took a value/hazard judgement on the relative magnitudes of the problem and the probability of occurrence.
There is no solution for avoiding both problems but with a substantial chassis and a close or common bonding point for the battery negative to chassis and engine strap to chassis that aspect is minimised. Outstanding then is the vehicle management electronics earthing.
Regards 73 Alan G0HiQ
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