Common Return v switched feed

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steve howe
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Common Return v switched feed

Postby steve howe » Mon Jun 08, 2015 1:48 pm

Forgive if this is a numpty question, but wiring is not my strong point...

Trying to work out the multi-coloured, multi-cored spaghetti that is the wiring under 'Watermouth' (see posts under the Cornish Riviera A. G) some of it dating back some 40 years, it seems that the original builder did not use 'common return' in the sense that I understand it, preferring to take all the lives and commons back to the panel, presumably through DPDT switches, so that each section was independently fed and switched. The point motors appear to follow the same principle. My understanding of 'common return' (and which I have always used) uses a thick copper wire 'busbar' under the baseboard to which all the track commons are fed, with a seperate busbar system for the point motor commons. Only the live feeds are taken via spdt switches on the panel to the appropriate section. This I believe greatly reduces the amount of wires going back to the panel...(or am I missing something?)

My question is: what, other than fault-finding by isolating independent sections, is the advantage of seperate switched feeds? and am I likely to compromise the existing wiring by attaching the track commons to one common feed via a continuous busbar?

One of the problems with Watermouth is that the original builder, Pat English, liked to use a different colour wire for every feed, :shock: in some ways this makes tracing the cable runs easier because we simply follow the appropriate coloured wire back to its source, but, as much of the wire was ex-Government Surplus, it varies considerably in gauge and colour variations....My thinking is it would be simplest, having identified the droppers to the actual track sections, to remove all the old wiring and start again.

Anyone living in Cornwall who likes doing electrics? :thumb

Steve

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grovenor-2685
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Re: Cornish Riviera Area Group

Postby grovenor-2685 » Mon Jun 08, 2015 2:52 pm

This I believe greatly reduces the amount of wires going back to the panel...(or am I missing something?)

I don't think you are missing anything.

My question is: what, other than fault-finding by isolating independent sections, is the advantage of seperate switched feeds? and am I likely to compromise the existing wiring by attaching the track commons to one common feed via a continuous busbar?

The only reason to avoid common return is if you are using several controllers off a common transformer winding/low voltage supply. In this case common return will put on a short when one of the controllers is reversed.
Hence the standard is to use independent supplies for each controller so that common return wiring can be used.
Regards
Keith
(Not in range of Cornwall!)
Regards
Keith
Grovenor Sidings

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steve howe
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Joined: Sun Feb 01, 2009 10:16 pm

Re: Common Return v switched feed

Postby steve howe » Tue Jun 09, 2015 8:34 am

Thanks Keith, thats most useful, I did'nt know that. I think Watermouth was originally designed for one-controller operation because it was never intended for public exhibition and very few people visited it when it was originally installed. Having said that, the original panel diagram whch I have copied and laminated to make the new panel, clearly shows the layout divided into three coloured sections. I think we will probably go for two controllers handling arrivals/departures and the goods sidings. I've attached the panel diagram for interest.

3_84_Original_Watermouth_panel_a8da6d[1].jpg
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