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Trolley Poles
"The trolley poles on top of the trams
were generally steel.
Takeake a look at the counter-poise springs on
the roofs of most trams to get some idea of the strength needed.
Pre-war, the actual pick-up from the wire was a wheel. This
caused a lot of sparking, clearly visible at night, causing the
Tramways Manager worries at the start of World War 2, particularly
the long, exposed run on Seafield Road.
The Department Workshops devised a better pick-up, basically a
manganese bronze large ovoid (for toughness and wear-resistance),
with a large slot in its upper face. The bottom of the slot had some
carbon brushes inserted. This had a number of advantages:
1 It tended to clean the overhead wire as it slid along,
reducing arcing. The wheels just rode over the dirt, breaking
and re-making the circuit, causing the arcing.
2 Being down in the slot, less light would escape.
3 It tended to straighten the wire, giving better
contact
4 Surprisingly, there was much less wear, an important
consideration during the war.
5 An unexpected bonus was that there was much less noise.
I am not aware of any other tram system
adopting the Edinburgh pick-ups; but they were used extensively
post-war on trolley buses throughout the country" |