OvermodInterestingly, in the early years of house wiring, wall switches worked this way (it is called 'four-wire'). In 1937 this was made illegal for new construction in favor of hot-side-only switching.
I was under the impression that four wire switches were only used in certain areas of the country where there was no "neutral" wire in house wiring, but two "live" wires that were out of phase, kind of the way 240 volt dryer wiring works.
As electrical code was standardized nationwide at 120 V 60 H the practice of only interrupting the "hot" wire became the way switches were constructed.
Can you imagine the time when local power providers had different voltages, frequency, and sometimes even DC supplied as house utility?
Thank goodness for the NEC.
-Kevin
Living the dream.
wjstixI'd just add that when I did this, I used a Center-Off DPDT switch. It's nice in some situations (derailment causes a short for example) to be able to cut off all power to the track, rather than just switch it from DC to DCC.
Also, using a center off DPDT toggle guarantees that the circuit "Breaks Before Makes", so there will never be a time when both DC and DCC are applied, even for a split second.
I use a DPDT Relay to switch from DCC back to DC operation. I wire the relay coil to the DC Power Pack accessory connections. Normal operation is DCC, (DC Power Pack off) when I turn on the DC power pack it powers the relay automatically switching the track from the DCC controller to the DC power pack.The DC power pack accessory output is normally AC, you can use an AC relay but an AC relay has a bit of hum, a DC relay doesn’t. I use a chip rectifier (DB107) to convert the AC output to DC to power the coil on the DC relay. Mel My Model Railroad http://melvineperry.blogspot.com/ Bakersfield, California I'm beginning to realize that aging is not for wimps.
I'd just add that when I did this, I used a Center-Off DPDT switch. It's nice in some situations (derailment causes a short for example) to be able to cut off all power to the track, rather than just switch it from DC to DCC.
The reason for 'double pole' is that you're interrupting both wires to the track, even if your layout has been wired 'common rail'. That foolproofs the connection.
As noted, the double throw part of the switch (and yes, you want a distinct position for center off "isolated") is to switch this two-wire connection between two things. Normally the center contacts would be power/data and the two switch positions would go to things drawing power. Here you have just one thing being powered (the layout main bus) and two power sources, so you wire 'backward' with the track-power outlets from the two controls connected to the outer sets of terminals and the feed to the layout in the middle... the electron flow doesn't care which way it goes through the contacts.
Interestingly, in the early years of house wiring, wall switches worked this way (it is called 'four-wire'). In 1937 this was made illegal for new construction in favor of hot-side-only switching -- cheaper to build the switches, you know. With four-wire, the fixture(s) controlled by a switch are completely isolated... with three-wire only one side is. The "logic" was that someone ASSuming four-wire without checking might get shocked if there were stray potential on the neutral (which happens all the time) and we couldn't have that, could we?
Shades of denaturing ethanol with methanol to dissuade people from that ol' demon alcoholism...
crossthedogElectrical is not my forte and will be a challenge, and I'm a spanking tyro. Lot's to learn. Any help appreciated. Thanks,
Matt, welcome to the forums! Your first posts are moderated, so they will not appear right away. After several posts, things will be normal.
I'm like you. I had to read and follow directions when working with the electrical part of the layout. Thankfully, there are a lot of helpful people on this forum.
Let us know how your layout progresses.
York1 John
I asked my doctor if I gave up delicious food and all alcohol, would I live longer? He said, "No, but it will seem longer."
You need a double pole switch. I would prefer centre off.
A single pole switch has a post for one wire in, and one wire out.
A double pole double throw has six post to attach wires to. In your use, two on one side for input, two on the other side for input, and two in the centre for output to the track.
You would also be wise to turnoff the system you don't want to use, throw the switch, and then turn on the system you want.
Hi All,
I want to run my layout as DC and DCC at different times. I keep hearing that I would need a DPDT between the track and my two controls (DC and DCC), but I've just been reading up on what DPDT means (along with SPST, SPDT and DPST) and I cannot see how the situation needs double pole instead of single pole.
I understand SPDT to mean that the switch "turns one thing off and another thing on", which seems to me exactly what's wanted -- turn the DC off and the DCC on. The DPDT is for when you want to "turn two things off and two things on". But everywhere I research setting up a layout this way the reference is always to DPDT, not SPDT. Is that because the "two things" are the two rails? If not, I don't get it.
Electrical is not my forte and will be a challenge, and I'm a spanking tyro. Lot's to learn. Any help appreciated. Thanks,
-Matt
Seattle, Washington
Modeling a pseudofictitious Pacific Northwest traversed by SP&S, GP and NP power, somewhere in the days of late steam and early diesel.
Returning to model railroading after 40 years and taking unconscionable liberties with the SP&S, Northern Pacific and Great Northern roads in the '40s and '50s.