Thread: Thick earth cable vs chassis rail as earth

The main reason is the elimination of high resistance connections being from corrosion / loose connections . May cost a BIT more but when doing heavy load currents /voltage loss every bit counts

Quite simply, an earth cable can be connected to the chassis at both ends so to use two paths in parallel instead of just one. Jump starting is going to benefit from any tiny reduction in resistance.

Hi alittelbit, most auto electricians know absolutely nothing about high current battery to battery set-ups and they are responsible for most of the repair work I have to do.

The biggest auto electricians problems I have to fix is undersized cabling, followed closely and in many cases in the same fix, is poor earthing.

Some vehicles can use the chassis as the earth return but it has to be done correctly and even here, many auto electricians haven't got a clew, and as muddy posted, can stuff up the connections to the chassis.

By running both the positive ( + ) and negative ( - ) cables from the cranking battery to a battery in the rear of a vehicle and/or to a power connection at the rear of a vehicle, you have a known current path and one that is easily examined if you do have some sort of problem.

When using a chassis, there is no way to know or check to see if the chassis will work as the earth return.

The first time you find out the auto electrician has screwed is when you are on a trip and your auxiliary/house batteries are not being recharged while you drive.

As bee utey posted, if you want to try to take advantage of a "potentially" additional earth return, run the negative cable and fix earth straps to the chassis at both ends.

Thanks everyone.
Always nice to know you've done something right.

Just as a matter pf interest, one of the cars I learnt to drive in had a two wire electrical system that was not earthed anywhere. Everything was two wire, and as the ignition was by magneto, there was no reason to need to earth it. A possible reason for this choice was that the body was wooden framed with fabric covering, although the only electrical devices attached to the body were the interior light and the instrument panel. All other lights were attached to the chassis or steel mudguards. Starter and generator were attached to the engine of course, as was the horn.

Thhe vehicle was a 1931 Swift, with electrics by Rotax. (who were taken over by Lucas in 1926, but at this time were still producing their own product line.)

John

Jeez John you are showing your age now mate, (A possible reason for this choice was that the body was wooden framed with fabric covering), LOL, Regards Frank.

Originally Posted by JDNSW

Just as a matter pf interest, one of the cars I learnt to drive in had a two wire electrical system that was not earthed anywhere. Everything was two wire, and as the ignition was by magneto, there was no reason to need to earth it. A possible reason for this choice was that the body was wooden framed with fabric covering, although the only electrical devices attached to the body were the interior light and the instrument panel. All other lights were attached to the chassis or steel mudguards. Starter and generator were attached to the engine of course, as was the horn.

Thhe vehicle was a 1931 Swift, with electrics by Rotax. (who were taken over by Lucas in 1926, but at this time were still producing their own product line.)

John

Originally Posted by Tank

Jeez John you are showing your age now mate, (A possible reason for this choice was that the body was wooden framed with fabric covering), LOL, Regards Frank.

Not necessarily - I was not learning to drive until the mid 1950s, but people tend to forget that there were very few cars sold from 1929 to 1939 due to the depression, and none from 1939 to 1945, and a severe shortage until the mid fifties as post-war production ramped up.

In the 1950s cars from the 1920s were quite common, to the extent that one place I passed in the bus going to and from school specialised in refurbishing Chev fours (last one 1928?) - they even entered one in the 1954 Redex trial. My father actually bought the Swift in 1951 if my memory is correct. And it was a step up from the Model T before that.

'Aero' bodies, using fabric over a wooden frame were very common in the late 1920s, copying the construction of contemporary aircraft, and gave strong a light saloon body that was a lot more air and water tight than a similar weight touring car (soft top) and a lot quieter as well as lighter than a steel body - although at that time 'steel' bodies were wood framed as well. All steel bodies did not appear until the 1930s, Citroen being the first mass produced one.

The Swift was definitely dated by then in using the Aero body in 1931. It did not stand up well to the Australian climate. The car was, in fact a fairly typical late 1920s English car, with a one litre side valve engine driving a four speed crash box with right hand gate change. Four wheel mechanical brakes were surprisingly good, probably because of the light weight. Wire wheels were fitted with 5.00x19 tyres. Swift of Coventry folded in 1931, having started production around 1900. There were very few of them in Australia, I am pretty sure this one was a personal import, by the father of a school friend of my sister, when they migrated to Australia just after the war, and it was sold after the father died.

John

The chassis on a D2 is not specifically earthed, only via the steering box, steering joints and the tailshafts. However the body is earthed with wiring looms connecting to various earth posts.