I went to radio shack today looking for 14 gauge wire for my common wire that is shared by all accessories, blocks, and will be connected to a ZW at each end in phase. The wire will be 80 feet long from transformer to transformer. They only had 10,12,16, and 18 gauge wire. I thought the 12 looked too thick so I grabed a roll of 16 and a roll of 18.
Can I use 16 gauge for this common bus wire or should I go back and get the 12 gauge? The rest of my bus wires are 14 gauge.
Hello John:
I am no electrical expert (as others on this board can attest), but 16 gauge is more than sufficient as a bus wire, for accessories. I am sure others will be able chime in with a more definitive answer.
Regards,
John
80 feet is a ways. I would go with 12 gauge wire. Maybe overkill, but better safe than sorry.
Jim
John- This is how I did all my buss wires. When I priced it out it was cheaper this way. I used 12 gauge “romex” wire with my ZW’s. If Iam not mistaken 14 gauge is sufficiant, but I always overkill every thing. Your wire should be sized to the amps that your transformer can put out. If you go to a store like Home depot. It comes in boxes of varying lengths. Something like 25’, 50’, 100’ and 250’. All you have to do is roll out the lenght you need. Split about a foot of the outer sheathing. grab each of the wires and pull away from each other. The sheathing should tear leaving you with just the wire that was inside. With a good pair of wire strippers you can strip it anywhere along its lenght, and sodder on your feeders. Home depot also sells rolls of project wire in a rainbow of colors ond gauges. At my local Home depot it is buy the fuses.
Jason
I think Ill take a trip to home depot and get some 12 gauge… maybe 14. I can use the 16 gauge for the control wires of the 022 switches and UCS tracks. Thanks again.
14 gauge wire will handle 15 amps. Home Depot sells 500 ft. rolls of stranded 14 gauge wire for about $35.
16 gauge is overkill for 022 switches. 18 or even 20 gauge will handle the amps of the 022 switch just fine.
Chris
PostwarMan07,
Try this from the forum archives.
http://www.trains.com/TRC/CS/search/SearchResults.aspx?q=wire+AWG&f=OTU=&u=NDA3MzE=
Thanks. I found an old post by bob nelson about wires and their amp capacity. He said that 10 gauge wire can handle a 30 amp load. Every 4 numbers smaller you divide by 2 to get the capacity so:
10 gauge: 30 amps
12 gauge: 22.5 amps
14 gauge: 15 amps
16 gauge: 11.25 amps
18 gauge: 7.5 amps
20 gauge: 5.63 amps
22 gauge: 3.75 amps
So in my case a ZW is rated at 12.5 amps. 14 gauge wire is more than enough, right? Or do I need a capacity of 25 amps since there are 2 ZWs in phase? What if I phase in a KW as well?
For runs over 50 ft, you should go up a gauge for voltage drop. This has to do with the conductor’s resistance. Solid core is good for buss wires because it is easier to strip when making T joints with feeders branching off. It also stays in place better and won’t tangle.
Since voltage drop is also a concern, courtesy of the CRC Handbook of Chemistry and Physics here’s a table of resistance verses wire gauge. The wire type is assumed to be annealed copper wire, and resistance is given in ohms per thousand feet at 20 degrees celcius(68 degrees farenheit)
Gauge…Ohms per Thousand Feet
10… .9989
12… 1.588
14… 2.525
16… 4.016
18… 6.385
So, with a length of 50 feet, 16 gauge wire would have a resistance of about .2 ohms. Since V=IR, with a current of 5 amps, the voltage drop would be just over 1 volt. If you go to 14 gauge, the voltage drop with 5 amps becomes .7 volts. Go to 12 gauge wire, and this drops to .4 volts.
Thus, with drops this long, you can see the necessity of using the largest gauge wire feasible.
By the way, if you wanted to limit voltage drop with a 5 ampere current to .01 volt, essentially zero for our purposes, you would need to use 0000 gauge wire.
Strictly speaking, if the return wire can carry a certain current, it should be sized for that current, which is the sum of the currents at which all the transformers are protected. That happens to be 15 amperes for the ZW and 10 amperes for the KW, so 40 amperes for the lot, which would require about 8 AWG. However, it is reasonable to make an allowance for “diversity”, that is, to assume that they will not all be at their maximum at the same time. I would feel comfortable with 10 AWG. You could also put an external circuit breaker in series with a 10 AWG return to protect it at 30 amperes; but I wouldn’t go that far.
Could you explain what you mean by “connected…at each end”?
When you phase transformers you connect the commons and connect a bulb from A terminal to A terminal. So I figured once the transformers are in phase you could do this:
If the ZWs are at each end of the wire will the voltage drop be cut in half. Is voltage drop as big of a concern with the common as it is with the hot?
I wondered whether that was what you meant! That’s a very good idea; and it means that the return currents will in fact be in opposite directions even though the transformers are in phase. So they will cancel rather than add; and the worst-case net current is only the 15 amperes that one of the two ZWs can supply. So 14 AWG is fine from a safety standpoint. If you might add the KW, it would be prudent to use 12 AWG however; but that should be plenty.
The voltage drop in the common is generally as important as in the other side of the circuit; but yours will never be more than if only one transformer were connected; and it will usually be less, depending on where and how large the various loads are.
Im glad that the wiring diagram will work because thats the easiest way to go about phasing 2 transformers 80 feet apart.
So 12 guage is what Ill use for the common, but is the 14 gauge ok for the hot wires Ive installed so far?
As long as both transformers are on, yes and no. It depends on what and where your loads are in physical relation to the transformers (load balance, with loads being your trains and accessories). Also, things change if one transformer is being taxed more than the other. Electricity seeks the path of least resistance and doesn’t see the physical distance. You would spend more time calculating the load balance than what the extra cost of one larger gauge is. It sounds a little confusing maybe because we are talking voltage drop over distance but that relates back to resistance and the rules change.
As far as safety is concerned, 14 AWG for the wires other than the common is just fine. Depending on the distance, you may want to use larger wire to reduce the voltage drop.
The 14 gauge wire that Im using for the hot wires is at most 45 feet from the transformer. There are 3 more blocks to be wired on the far end of the mainline: the branch to the yard and the 2 reverse loops that will be in the storage room. Seeing I dont have anymore 14 gauge anyway, Ill grab 12 gauge for them along with the common.
The only load on the mainline ZW will be the trains. I plan on running 2353 f3s on loop one and 2 single motor engines on the other with the passing siding. This totals about 180 watts.
The load on the yard/subway ZW will be the trains which would include a single motor subway train and a single motor engine for switching. This totals about 100 watts and leaves me about 80 watts for some small accessories in the yard and city scene.
So if a derailment occurs near the mainline ZW and the other trains are in that half, do I have a problem? Will a fast acting breaker solve this issue?
You cannot use watts to size conductors or breakers. Amps are what determines conductor size and breaker. 3 amps is 3 amps whether you are drawing 10 volts (30 watts) or 20 volts (60 watts) so watts is irrelevant in sizing conductors. Transformers are rated in watts because it is the combined volt/amp capacity and large numbers make good sellers.
If you have a short from a derailment, you will draw full load from the transformer, through the track feeders, until the circuit breaker opens. This is why you size your conductors to the circuit breaker rating. An inline fast blow breaker is a good idea because the breakers in old transformers are slow at opening and you risk melting insulation on your track feeders if they are sized to the train and not the transformer’s circuit breaker.
A good investment would be a Sperry clamp meter for getting amperage draw readings off your engines. These are available at Home centers and are fairly inexpensive. They have a claw that loops around one conductor, measures the magnetic field, and gives you a digital amp reading. The meters also have probes for measuring volts and ohms.
thanks for clearing that up. Ill definately be investing in fast blow breakers when the time comes.
I have to disagree with John about the usefulness of fast circuit breakers for protecting your wiring. The thermal circuit breakers in the transformers are a good match for the wiring. The circuit breaker trips when it gets too hot, just as the wire melts when it gets too hot. The greater the fault current, the faster the wire and circuit breaker heat up and the sooner the breaker trips. If you are using wire with enough ampacity for the circuit breaker’s rating (14 AWG for a 15-ampere breaker like that in a ZW), the breaker should protect the wire; and you won’t get nuisance trips for brief short circuits and other overloads.