RMweb Premium Tim Dubya Posted May 7, 2015 RMweb Premium Share Posted May 7, 2015 Hi all Just wondering if 28 swg copper would give sufficient power on 12v DC for track droppers to the main feeds (32/0.2 wire). Iain Rice, in his scribbling that is An Approach to Building Finescale Track, recommends the use of 28 swg copper wire for the various electrical connections within a turnout and for the dropper to the main track feeds. This got me thinking about whether 28 swg would give enough current to all track. I would be using two droppers per length of track (EMGS code 75 bullhead), each length being 480 mm (2 x 60ft panels in 4mm) maximum with just one small loco on a length at anyone time. So the question; is would 28 swg do it or should I use 20 swg or maybe something else? TIA Cheers Link to post Share on other sites More sharing options...
Crosland Posted May 7, 2015 Share Posted May 7, 2015 Iain Rice almost certainly wasn't talking about trackwork for DCC layouts, where you have to consider the short circuit current. It's not clear if your 480mm length refers to the track or the dropper. The length of track fed by a dropper is largely irrelevant but 480mm is way too long for droppers in such thin wire in my book. For a short dropper from the track to a bus immediately below on the underside of the baseboard it will be OK, the fuse current will be around 10 Amps or better. For normal operation the real criteria is how much voltage drop it will cause. That's equal to the 'resistance per unit length' x length x current. In normal operation a single dropper feeding a limited amount of track will be required to pass the same current (i.e to supply the loco) whether DC or DCC. During a short circuit, however, the two droppers (one to each rail) need to have a low enough resistance to allow a high enough fault current to be detected by the booster. current limits are generally much higher with DCC. For a dropper of more than a few cm I would err on the side of caution and use something thicker. If in doubt, remember the "coin" test. Short the track and check that the booster cuts out. Link to post Share on other sites More sharing options...
Grovenor Posted May 7, 2015 Share Posted May 7, 2015 Iain Rice almost certainly wasn't talking about trackwork for DCC layouts, where you have to consider the short circuit current.Neither is the Op, he specifically says 12V DC, and its in the non DCC section. It's not clear if your 480mm length refers to the track or the dropper. The length of track fed by a dropper is largely irrelevant but 480mm is way too long for droppers in such thin wire in my book.Actually he makes it very clear by specifying that the 480mm is two 60ft rails. Also that he will have two such droppers per rail. IMHO it will be fine so long as the droppers are short, say 6 inches or less. The contribution to the overall loop resistance with 32/0.2 feeders will be negligible. Given that, 28 swg is on the thin side while 20 swg would be to big. If you have lots of 28 in stock, OK. If you have to obtain some I would suggest 24swg as a better choice. Regards Keith Link to post Share on other sites More sharing options...
CourthsVeil Posted May 7, 2015 Share Posted May 7, 2015 ... IMHO it will be fine so long as the droppers are short, say 6 inches or less... Tim & Keith, can only agree – my own experience underlines that. Regards Armin Link to post Share on other sites More sharing options...
RMweb Premium Tim Dubya Posted May 7, 2015 Author RMweb Premium Share Posted May 7, 2015 Thanks guys The droppers will be no more than 100mm. All the best Link to post Share on other sites More sharing options...
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