This is entirely hypothetical of course!
Let's say you had a large petrol powered truck that had to drive along railway lines, and you wanted to earth the truck to the lines. The truck has rubber tyres.
Perhaps a small four steel-wheeled wagon that is dragged along under the truck.
That's the easy part. When driving the truck, how can you see where the wagon is, so that the truck doesn't derail the wagon? The truck would be 100 times heavier than the wagon, so can't really be connected directly to it except by a towbar and a wire.
Possibly a CCTV camera. Yes, that would do. Any other brilliant ideas?
Why is the earthing so important?
The sparking of UK third-rail is reduced by having more than one fitted
so that, most of the time, at least one is in full contact. And you only
get spectacular lightning when the train is using a significant amount
of traction current. If you are only earthing the truck for low current,
the sparking would be insignificant in most cases.
If track occupancy detection is involved, then a low resistance
connection between the rails is vital. On occasion, with track that's
not regularly used, it can miss a single truck. In some places, I've
seen a bead of weld run along the rail surface to ensure that any rust
is removed as soon as the first axle travels along the section.
Another possibility as the OP specifically mentions petrol power, maybe
he's worried about sparks igniting fuel vapour. Or he's trying to arc
I don't see why not? The limited circumference of a wheel would pass
over points with more undulation. I also don't see why you will get
less parking. The unsprung weight will exacerbate contact issues.
A shoe with radiused ends is the typical method of conduction on the
An example shoe though not sure where this type of shoe is used:
If you're passing a lot of current through this setup, surely you'll get
arcing across the wheel bearings. They won't take kindly to that. At
least shoes can be made to take the punishment.
The wheels on the swing arms are only for guidance and some weight
transfer, traction is still through the normal road tyres. You may have
a problem with the width of the vehicle not matching the gauge of the
line, and with double tyres as used on larger trucks , it would be
rather embarassing if the rails were to coincide with the gap between
the pair of tyres on each wheel.
What is the vehicle type? If it's a Land Rover, then the tyres are the
right distance apart already.
Also, have you thought about the difficulty of steering the thing
exactly enough to keep it on the rails? It's not possible at anything
above a very slow speed, and even then, the odds are you'll fall off the
rails onto the track bed within yards.
Possibly something along the lines of a T shaped metal thing with L
shaped brackets on each end, and attached to a towball on the truck
would be the simplest. Just make sure that it's always at the trailing
end to avoid it catching in the joints.
On the other hand, if this also has to trigger the type of track
occupation sensors that most railway lines in this country use, it needs
to guarantee a continuous low resistance from one rail to the other to
work safely. This implies a good, guaranteed contact to both rails.
What most people in these circumstances do is install a hydraulically
controlled bogie with metal rail wheels fore and aft, which carries some
of the weight, guides the rubber-tyred vehicle, and guarantees track
occupation circuitry triggering.
How about giving us a hint as to why you need to earth the truck. Then
we may know of a working solution. Working under tram wires, for
instance, needs a different answer to running a high power transmitter
in the truck. Which needs a different solution to earthing out a
On Saturday, August 3, 2013 8:51:37 PM UTC+12, John Williamson wrote:
g railway lines, and you wanted to earth the truck to the lines. The truck
has rubber tyres.
he wagon is, so that the truck doesn't derail the wagon? The truck would be
100 times heavier than the wagon, so can't really be connected directly to
it except by a towbar and a wire.
nd the track is nice an smooth. The trolley will need to be under the truck
so that people can't touch it.
Well OK, it will be running under an overhead wire at 600V DC, and needing
an earth return. There are several devices that need power, e.g. a welder o
r large motors. It will be driven very carefully along the rails.
Really I just want any other ideas for how to know where the trolley is und
er the truck. I have a spare CCTV camera. Otherwise some kind of indicator
to show how central the trolley is.
And *still* you avoid the T word.... <Grin>
Put the trolley on a towbar with a swivel at each end and drag it
behind, or use clips to attach an earth lead when you stop. If you're
working under a live overhead line, you'll want an exclusion zone round
the truck anyway, so the public tripping over it won't be a problem.
Even if you're not working live, it's good discipline to stop and earth
the truck before working under overhead wiring anyway. Any time you save
by doing it the way you seem to want it will be more than cancelled out
by not complying with safety requirements. Also, if you have a tower on
the truck, it must be dropped before you move near overhead cables
anyway, to keep things safe.
And that's ignoring the risk of working on an earthed platform at height
under live wiring. At 600V, if nothing can get within a foot or two of
the wire, you don't need the earth anyway.
If you're worried about damaging an earth clip or its cable, connect it
via a plug and socket, so if you drive away, it just pulls out.
You seem to be making life both overcomplicated and less safe for yourself.
If you insist on working live, take professional advice.
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