We've decided to go with the 18 gauge. Thanks for all your advice.
I should have added that I only operate pre and early postwar components but did install auto reset external breakers sized per Bob Nelson's recommendations from the past.
swede
Bob:
Once again,. Thank you.
Even if a train draws only 2 amperes, but the circuit breaker trips at 15 amperes, the wire needs to be able to withstand 15 amperes, because that is the greatest current that might flow when a fault (derailment?) happens. Use 14 AWG for 15 amperes (Z, ZW), 16 AWG for 10 amperes (KW), 18 AWG for 8 amperes (V, VW), 20 AWG for 5 amperes (1033).
IMHO, another good reason to use external breakers to suppliment the internal transformer circuit breaker.
There are two considerations in selecting a wire size--voltage drop and safety.
Current flowing in wire that is not a perfect conductor produces voltage drop. Multiply the expected current by the wire resistance to compute the voltage drop. The wire resistance is about 1 milliohm/foot for 10 AWG, 1.6 for 12 AWG, 2.5 for 14 AWG, 4 for 16 AWG, 6.4 for 18 AWG, 10 for 20 AWG. Don't forget that the wire length is twice the distance from the transformer to the track. How much voltage drop is too much is an individual preference; but I try to keep it under 1 volt.
Wire should be heavy enough that it does not get dangerously hot with the greatest current that might flow through it. That current is the current where the transformer's circuit breaker trips (or where some other overcurrent protection limits the current). Even if a train draws only 2 amperes, but the circuit breaker trips at 15 amperes, the wire needs to be able to withstand 15 amperes, because that is the greatest current that might flow when a fault (derailment?) happens. Use 14 AWG for 15 amperes (Z, ZW), 16 AWG for 10 amperes (KW), 18 AWG for 8 amperes (V, VW), 20 AWG for 5 amperes (1033).
Slightly smaller wire can be used for the last couple of inches between a feeder wire and the track, because the nearby connections to heavier wire will couduct away some of the heat. Simple accessories, like lamps and solenoids, should be supplied from wire based on the overcurrent protection; but it is reasonable to use lighter wire for the return side of the circuit when the impedance of the accessory reliably limits the fault current. This exempts turnout controllers from having heavy cables.
Bob Nelson
Swede: Thanks.
Following suggestions of other members, I used 14 gauge stranded wire for the power busses and 18 gauge stranded bi-color speaker wire for the accessories. To date, after 5 years, I have never had an issue.
When we built the layout, we used 14 gauge stranded wire for the leads to the track and "whatever wire was around at the time" for the accessories. (various gauges) Now we are planning to re-wire the accessories with a uniform gauge.
I know it has been asked before but one last time....What is the best (general purpose) gauge for the accessories?
As always, many thanks.
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