022 switches!!

[Kooljock1]

 Just to avoid "newbe" confusion: this thread is about 0-22 switches, NOT O-22 switches, which to my memory have never been made.

 

 Jon 

[lionelsoni]

You described a bunch of alternatives.  But the general rule is that the wire should be protected from overcurrent according to its ampacity.  So, if you run a 24 AWG wire to some combination of lamps and turnouts, you should have a 2.5-ampere circuit breaker or fuse on it.  Heavier wire, higher breaker rating.  Here is a table again:

AWG ampacity
10   30
12   20
14   15
16   10
18    7
20    5
22    3.5
24    2.5

The controller wires are protected by the impedance of the switch-motor coils, so fairly small wire is okay there.  You will have to measure the current to decide the wire gauge.  With an 022, it would be prudent to jam the points before measuring, then measure very briefly to avoid damage to the coil.

[runtime]

Thanks guys, I DO appreciate the full engineering Monty on wire gage, but I'd be very grateful if you could also addresss the questions I had in the 2 paragraphs before the final sentence. Since I would rather not burn my house down.

Thanks!

runtime

[lionelsoni]

Not even close.  The ampacity doubles every 4 AWG sizes.  So two 16 AWG wires can safely carry the same current as a 12 AWG, that is 20 amperes.  Two 24 AWG wires are equivalent to one 20 AWG, which can safely carry about 5 amperes.

The AWG wire table is logarithmic.  That is, each wire size is smaller than the previous one by the same factor.  The table is based on 0000 AWG with a diameter of .460 inch and 36 AWG with a diameter of .005 inch.  This turns out to be close to a system where 10 AWG has a diameter of .100 inch and where the wire cross-sectional area doubles about every 3 numbers and changes by a factor of 10 every 10 sizes.  (The resistance is also close to round numbers:  1 milliohm per foot for 10 AWG copper wire.)

When you figure the theoretical ampacity, based on the resistance and surface area of the wire, it turns out to vary as the 3/4 power of the cross-sectional area, which means that it doubles every 4 sizes.

Ampacity numbers are based on the assumption that the wires are more-or-less out in the open.  When you bundle or enclose more that a few of them, you have to derate their ampacity.  There is a talbe for this in the National Electric Code.

[jwse30]

runtime

Do a pair of 24 gage wires = a 12 gage wire's capacity, roughly?

 

 When you run a pair of wires in parallel like you are describing, the gauge doesn't get cut in half, it gets reduced by 3 (roughly). So 2 - 24 AWG  wires in parallel will carry roughly the same as a #21 wire. Call it a #20 wire, as I don't think  they make odd sized electrical wire smaller than #3.

 

J White

 

[runtime]

Bob,

Based on the preceding, I think I need your advice again.

As I mentioned on the 'Wiring 022 switches' thread, I'm about to wire up six switches at about 20 feet from the power source. Controllers will be 1 - 2 feet from the power source.

I just bought some 4 conductor, 24 gage telephone wire. I thought I would run two conductors from the outer switch connections to the controller, and the other two conductors from constant voltage plug to 16V tap on transformer. Then a single wire from the controller center lead to transformer common (through bridging blocks).

Alternatively I'm considering splitting off the switch lamp lead, and using one 24 gage lead each for the lamp and the CV plug. Or, since it would make sense to run only one lead each for all the CVs and lamps over the 20 feet, run one 16 gage each for those, and use the 24 gage only for wiring the swithces to the controllers.

Do a pair of 24 gage wires = a 12 gage wire's capacity, roughly?

 

[lionel2]

That is very true.  But, I like to have my 022 switches on variable control, Lets me have control of turning them off and on.  Gives me more flexiability.  Thanks.

[servoguy]

 Here is another thing to consider when you load one of the transformers that has carbon rollers in it.  Based on recent measurements, the output resistance of the transformer is about 1 ohm.  This is based on a KW that I recently rebuilt.  The resistance of the roller is high enough that it can dissipate a lot of power.  Apparently, Lionel never intended for the transformer to supply all of its power through only one of the rollers.  The power dissipated is I^2*R, the square of the current times the resistance.  If you draw 4 amps through the roller, that is 16 watts which will get the roller toasty warm.  If you draw 8 amps, the roller will dissipate 64 amps which is going to get it rather hot.  The roller will survive, but the arm it is attached to will not like all the heat.  The secondary of the transformer, being copper, apparently can dissipate the heat without a problem. 

BTW, the fixed 20 volt (or is it 18 volts) output on a KW would be a lot better for 022 switches than one of the variable taps because it doesn't have the problem with the resistance of the roller.  

[lionel2]

I changed the 022 fixed voltage feeders to 14 AWG.  Thanks.

[lionelsoni]

If you're using the original lamp types, those are 1445s or 1447s, depending on whether they're bayonet or screw based.  They are the same electrically and are rated at two voltages.  At 14.4 volts they draw 135 milliamperes; and at 18 volts they draw 150 milliamperes.  So your 10-turnout group draws 2.7 amperes to 3 amperes at those voltages.  The 12-turnout group draws 3.24 to 3.6 amperes.  That's very little and would not overheat 22 AWG.  Your 18 AWG is good for about twice that current.

The resistance of your 18 AWG is about 6.3 milliohms per foot.  If the wire is 16 feet long, this is about 100 milliohms.  With a current of 3.6 amperes, the voltage drop is only 360 millivolts, which is negligible.  If you change to 14 AWG, you will not notice any difference in operation.

However, your transformers are capable of putting out 15 amperes and should not be feeding these turnouts over anything smaller than 14 AWG.  You should either change the wire to 14 AWG for safety's sake or, much easier, install a 5-ampere circuit breaker or fuse in series with your 18 AWG line.  I recommend automotive-type automatically resetting breakers.

[lionel2]

I have (10) 022 switches wired up for fixed voltage and (12) other 022 switches wired for fixed voltage.  The 10 wired to a Z and 12 wired to a ZW.  With all switches lighted up, thats 2 light bulbs per switch that are lit.  Times 10 equals, 20 light bulbs lit on the (10) 022 switches wired to the Z, will that draw a lot of power from that Z transformer??  And 24 bulbs lit for the ZW as well.  Should I use 14 AWG wire for those feeders for the fixed voltage??  I was thinking of using the wire from plug to terminal strip the same, but changing the wire that goes from terminal strip to transformer to 14 AWG to feed the 022 switches more power and better current.  Good idea??  I am using 18 AWG for the fixed voltage now all the way to transformer.  Should I get thicker wire, like 14 AWG??  Will that idea burn out my 022 switches or bulbs??  Thanks.