In addition to ensuring good electrical flow, another reason to add an extra pair of feeders is for short circuit protection. Your PowerCab has a built in circuit breaker, but it depends upon good electrical flow to function. On a larger layout, if only one pair of feeders is connected to the layout, it may still function (through probably not as well) but it's short circuit protection may be compromised. This could allow you system to be damaged, and if enough amps are flowing through the rails, something could be melted or catch fire. (There's a prolific poster that likes to tell me I'm full of BS for saying this, but there is photographic evidence out there to back me up. He should be along shortly.)
Try this: At the furthest point from your track connection, lay a quarter across the rails, If the system's circuit breaker does not instantly trip and shut down, you need to add another pair of feeders. For a layout with only 45 feet or rail, your probably OK as far as short circuit protection goes. If your locomotives experience any kind of slow downs at the farthest point from your track connection, you should add another pair of feeders.
What you should be concerned with is 'resistance'. Over distance, and depending on the materials and distance, you will have varying resistance. Nickel silver rails are not the best conductors, and that is why we advise the use of a bus of thicker wire that won't degrade the DCC signal as much as, say, common speaker wire.
DCC systems require robust voltage in order to maintain the signal strength along the track system and its supplying wiring. The greater the distances involved, the more reduction in voltage, and the greater the reduction in voltage, the more the signal attenuates to the point where the short detection circuitry can't tell when the signal is being compromised by shorts. Worse, the system leaves the current coursing through the wiring and rails because it doesn't know to shut down. That's when things warm up a wee bit, turn to liquids, and flow while letting out their magic smoke.
So, despite what has been stated, it really depends on whatcha got. We don't know how you're powering your layout. It could very well be that putting your single set of feeders on one end of 45 feet worth or rails is not going to work due to the magic smoke problem. If you center your main power unit and power only 23' in either direction, that should work fine, provided you have at least two intermediate pairs of feeder wires coming off the bus and powering the rails on either length. It works for me.
I had an HO L layout, 35' x 5' tapering down halfway to 2' then to a 90 deg. 10' x 2' section..
I ran two trains up about 6-7 cars each..I had zero feeders, only the NCE PowerCab panel connect to the track. I had no power problems whatsoever including they climbing a 2.5% grade, on a curve, to boot..
If you ever do have a lack of power you can add a booster unit later...
If you don't already have the PCab, get it.. They're nifty.. M Los Angeles
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