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Quick Help - DCC Sockets - the basics

Over the years, numerous standards have been developed for how to connect DCC decoders to models.

The most basic is using wires, hence the standard wiring colours as defined by the NMRA. In fact, when installing sound decoders into a model that has limited space, it is quite common practise to remove any provided DCC socket, and simply hard-wire the decoder in.

However, where space permits, simply plugging in a decoder to the provided socket is the simplest and quickest solution, so it is useful to have a knowledge of the various types of DCC socket available. This will help you not only understand how to install them, but also aid you in choosing the right decoder for the job.

Where a model comes DCC-Ready, it will be supplied fitted with a blanking plate. You must remove this before fitting a decoder. Your model should come with some instructions on where this is located.

8pin NEM 652 Common in OO, and favoured especially by Hornby. The orange wire is known as pin "1" which is usually marked on the socket so you know which way round to insert the plug. Normally it doesn't matter if you get it the wrong way around though - you'll find out because the loco will drive backwards to what you expected! Simply rotate the plug 180' if this happens. Also, if the model has lights, they won't work unless you get the plug the right way around. Blanking plates are usually very simple things with some of the pins directly soldered to join pickups to motor and to lighting.
6pin NEM 651 Common in N and used in some OO (particularly by Bachmann). The orange wire is once again the index, and will normally be marked on the model's DCC socket somehow, although often not very clearly! If you get it the wrong way around, it is unlikely to cause any damage, and you'll know because the model's lights may come on when you increase the throttle, and the motor may burst suddenly into life when you switch on the lights function! Just flip the plug and re-insert if this happens. Blanking plates are generally very small and must be inserted the correct way around to run on DC again.
21pin MTC Common in OO, particularly in Bachmann, Heljan and Dapol diesel models, as well as some steam models with tenders. These decoders are generally neater internally because there are no wires. The decoder can (theoretically) only be inserted one way around, so there should be no risk of damage, although I've seen plenty of evidence of people forcing one on the wrong way around! There are actually 22 pins, but with an 'index' pin missing, so just check where the index pin is and align it correctly with the model. Blanking plates come in many varieties, some very simple, and others with components built onto them.
Next18 Relatively new to the UK market, the Next18 interface is starting to appear, particurlaly in Bachmann OO tank engines and some Farish N gauge models. The Next18 interface is very neat, with absolutely tiny connections, so you are totally reliant on the model to provide break-out connections on the socket board to connect it to anything. Blanking plates, like Next18 decoders, simply click into the provided socket.
PluX22 Similar in many respects to the 21pin MTC interface, the PluX22 is essentially the opposite, as it has pins on the decoder which plug into a socket in the model, rather than the other way around. PluX models are very rare in the UK market. There is also a cut-down version of this called PluX16 which you may come across in some European models.