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Need some help with Wiring Schematics

Current and future British signalling (UK except Northern Ireland)

Re: Need some help with Wiring Schematics

Unread postby JRB » Sun Mar 4, 2018 8:53 pm

Note that the diagrams are "written circuits". BS 376 also gives 'wiring diagrams' which are more familiar to telecomms and other folk.
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Re: Need some help with Wiring Schematics

Unread postby Ben.A.98 » Mon Mar 5, 2018 5:59 pm

mreccentric wrote:Well, i am understanding it now. But, how are the relay contacts (for ex. in the first circuit) being energised? If different relays are being energised by different coils, then what is the construction of second diagram i have posted (where a set of contacts is been energized by one coil). How does the operator control these relays (if he/she controls the relays 101A, 101B, ....)?


What you have above is one of many circuits that are involved with the control of a set of points. As previously mentioned you need the rest of the drawings to see how these contacts are controlled to allow 101WLR to pick.
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Re: Need some help with Wiring Schematics

Unread postby mreccentric » Wed Mar 7, 2018 3:18 am

Thanks. Sorry for the late reply. But, where do we use the relay of the type in second diagram i've posted? (Because the relays in diagram 1 is controlled by other circuits. When do we use one coil controlling different set of contacts - Both BACK and FRONT) I'm trying to find some free manuals or books. Any links here, or on PM is welcome.
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Re: Need some help with Wiring Schematics

Unread postby Mike Hodgson » Wed Mar 7, 2018 5:02 pm

Not sure I correctly understand your question, but an example that might be easier to understand would be a controlled 4-aspect colour light signal of the conventional type with 4 separate lamps. The aspect displayed depends on the position of three relays, an HR (Yellow aspect) HHR (Double Yellow) and DR (Green Aspect)

The coil of the HR would be controlled by a selection circuit - contacts that are made when the operator has operated the relevant switch or lever, and any necessary points are correctly set, and track circuits clear, etc. So this relay picks only when it is in order to display a proceed indication.
The coil of the HHR can be driven via a front contact of HR for the signal in advance (ie it picks only if the next signal can show yellow or better)
Similarly the coil of the DR needs the next signal but one showing proceed.

So the Red aspect (the RG) would light when the HR back contact is made - ie whenever there is any reason why a proceed aspect should not be shown (including failure of the HR coil).

The other 3 aspects all read over front contacts of the HR.
In the case of the Green aspect, that lamp (DG) would read over front contacts on the HR, the HHR and the DR. All three relays need to pick.
For Double yellow, the second (usually upper) yellow lamp (HHG) would read over front contacts on the HR and HHR but a back contact on the DR. HR and HHR need to pick.
The first yellow lamp (HG) would read over front contact on the HR and back contact on the DR. HR only or HR and HHR pick but not all three relays. It doesn't need to look at the HHR because you need it alight for both single and double yellow, although it must not be extinguished if green is to be shown.

The above is oversimplified, because additional circuitry is typically provided to prove the lamps are actually alight and to act appropriately in fault situations. One example might be showing a more restrictive aspect and triggering a fault alarm in the event of filament failure, or holding the next signal in rear at Danger when unable to display the red aspect. And it's different for searchlight signals etc.
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Re: Need some help with Wiring Schematics

Unread postby mreccentric » Wed Mar 14, 2018 10:22 am

Hello.... I am not able to afford 'The introduction to Railway Signalling' Book from David Kerr for many reasons.
Can anyone provide me free online materials or links for understanding the basics and RRI?
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Re: Need some help with Wiring Schematics

Unread postby Nicko » Wed Mar 14, 2018 1:34 pm

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Re: Need some help with Wiring Schematics

Unread postby HighlandRailwayman » Wed Mar 14, 2018 1:37 pm

Try a google search for IRSE Green Books as the Australian section has digitised the collection and made available as a free download. These books contain a wealth or information about UK signalling practice both mechanical and electrical. No. 7 (Signal control circuits) puts things into a slightly more visual context with what Mike was tying to explain with the operation of a signal head for example, have a look and see what you think.
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Re: Need some help with Wiring Schematics

Unread postby HighlandRailwayman » Wed Mar 14, 2018 1:38 pm



I'd forgotten about this one... also a site with a wealth of information on it.
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Re: Need some help with Wiring Schematics

Unread postby mreccentric » Wed Mar 14, 2018 3:15 pm

Thanks for the replies. I am going through the links.
More are welcome. Will get back to you after understanding.
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