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Don, et al,

I tried Cordless Renovations and the connectors are G scale, borderline too big for O scale.

Does anyone know of connectors with 20 gauge wire with smaller end connections?  Miniatronics uses 28 gauge wire and cautions against using them for motors but I like their size.

I tried Digikey for Molex.  It was way too confusing.



Last edited by Ed Kelly

Tony's Train  Exchange.   you can buy them in strips of 50 pins or more, or you can have them cut them for  you.    You have to attach your own wires.    I got 50 3-pin connectors from them a few years ago and have been using them with NCE 408 decoders in older brass with no problems.

It used to cost 50 cents per pin.

Ed, Did you try amazon, I recently purchased some JST lead connectors off amazon for another project (RC) related and bought these 2-pin leads.. Perhaps they will work for you?   Although, I believe Cordless Renovations also carries these and a similar 4-pin connector and they work just find in most O scale locomotive kinds of installs if you need 20-24 awg wire.


Otherwise, I would suggest those mini-connectors like you've seen in Digikey, etc.. I get some as well from TCSDCC for lighting function outputs using smaller awg wire.




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Last edited by Mike DeBerg

A common connector rated at 3A continuous is known as a "machine screw" or "collet". These are typically pins on a strip 0.1" apart and are excellent for confined spaces. The "tail" of one plugs directly into the socket of another. They cut to desired length with a standard hobby knife. Solder one wire into a socket of one strip, and the mating wire to the tail of another strip. Insulate the tails with heat shrink.

Search part number 573-31043164 at They currently list for $5.84 for 64 pins.

Link to Mouser catalog page

Miniatronics used to sell an equivalent part for a lot more money per pin (and they may still do so.)

Ed, as Mike suggested  the same size red 2 pin JST connectors can be found with 24 ga wire.  I just receive some from But the leads are only 3' long which is too short. All Electronics part #230S and 230P have 6" leads. These are definitely thinner than 20 ga wire. But the connector is still the same size.



Ed,  in simplistic terms, voltage drop is essentially current capacity.  Voltage drop equals heating in a connector or a wire.

If the connection gets too warm (hot) the metal loses it's spring and the connector fails.  If a wire gets too hot it

will also fail.  For short distances, such as in locomotives, 22 or 24 gauge wire is just fine.  I use 24 gauge power drops

from 12-16 inches long with a 10 Amp DCC system.  There is never a problem with wire heating under heavy load or

short circuit conditions.


Technical stuff to calculate heating: 

   heat in Watts = Amps times Voltage drop

If you lose .16 volts in a wire with a 4 Amp load you get .16 x 4 or .64 Watts.  .64 Watts spread over a foot of wire is not much,

however it is a lot for a connector because the same heat is concentrated in a small area.  This is why connector mating surfaces

are usually plated with low resistance materials such as gold or silver to lower resistance and reduce heating heating.

Ed - Perhaps you are mixing stall current and continuous current when sizing your decoder wiring.   Our wiring harness don't need to handle stall currents, as without traction tires, property weighted O scale locomotives slip well before the motor can stall.  As a practical matter the wire just needs to be sized to handle the current your motor will draw in layout service.    I've been using AWG 27 stranded wire for my DCC installations (over 40) and have not experienced any performance or reliability issues over many years of operation.   The advantage of using lighter wire in engine - tender steam locomotives harnesses is that it minimizes the bulk of the harness - improving appearance and providing better flex.   For in-boiler decoder installations (my preferred location) thinner wire makes it easier to route and tuck wire safely away from rotating parts. 


I am using a chart entitled American Wire Gauge Table.  It shows the wire gauge and the max amps under two scenarios.  I am using the "chassis wiring" figure because it represents the amps in a chassis, i.e., not bundled.  If I am using a 4 amp decoder, I want to use a wire that can handle 4 amps and that is 23 gauge wire.  Admittedly, it would take a heck of a load to get there but I believe in not maxing out the equipment.  I doubt that any of my engines are weighted so much that they would draw  the 4 amps max in the decoder.  I never test for stall current because even testing for it puts the running gear under wicked strain.

I have been told that one "O" Scale DCC installer uses Miniatronics connectors and has never had a failure even though Miniatronics uses 28 gauge wire, which is rated at 1.4 amps in the table I mentioned above.  I am uneasy with this.

According to the table. 24 gauge wire is rated at 3.5 amps.  This would be my absolute minimum.  I would prefer 22 gauge wire which is rated at 7 amps.

Some of my installations require the decoder to be located in the tender so there is a need for a higher amperage wire.

All I need is a 2 pin connector which uses 24 gauge or better wire.  This would handle the motor.  The other decoder functions require much less current.

I am still looking for this connector even after a half a dozen phone calls and several hours on the web.




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