In article , Charles Ellson
writes
In other words, the resistors keep the rails at the +420V/-210V position
*unless* something else happens to alter this. Hence "loosely tied". But
at all times (absent a major short) the two rails are 630V apart.

They can be both at the same potential if there is a break between one
conductor rail feed and the substation (or only one of the pair of
switches feeding from the next section is closed) and you have a train
in section.

Or if the feed is broken upstream of the resistors.

Good point that I'd overlooked. Thanks.

--
Clive D.W. Feather | Home:
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