Low Voltage Switching Mystery

[mensa]

Our home was built in the late'50s and makes use of low voltage switching.

We have a light fixture that's a complete mystery - didn't work at all for a number of months after we moved in. It then worked normally a few times, but not often. Now, when you hit the rocker switch "up" for "on", nothing happens. If you hit it "down", you can hear the magnetic relay buzz, and the light flicks on, but the connection breaks as soon as you release the switch.

I've looked into the relay box, and located the relay for this switch. It appears that this relay has been replaced previously, as it is different to all the others in this box, and looks "newer". My guess is that this switch has been an issue for previous homeowners. I'm wondering if it's possible that there's a fault in the actual wiring somewhere that could cause the relay to become faulty? Might there be other possibilities?

While I understand the theory behind the low voltage switching, I'm still a bit afraid of all things electrical. If anyone might have a couple of ideas as to where to start with this mysterious switch, while keeping in mind that I'm a complete tyro, I'd be most appreciative.

*Note: I did take off the switch plate to have a look-see, but the wires themselves appear to be wired correctly (ie - the same as all the other switches).

[bandito]

Never heard or seen this type of switch in a house.  I guess it's a sort of relay.  If you have 120 volts coming to the switch then I would just replace with a regular switch.

[mensa]

Apparently the idea behind low voltage switches was two-fold:
1) Using low voltage wires is less expensive; and
2) It eliminates the need for three way switches. We have a number of "stations", if you will where we can turn 8-10 lights on at the same switch. This is in addition to the actual switch for the fixture, placed where you would expect it.

The lights and duplexes (well, triplexes in this case, as every one has one outlet that is switched, as well as two that are not) are wired as you would expect with regular 14/2, 120v. The switches however are wired with low voltage wire (24v). You hit the switch, and the signal travels thru the low voltage to a relay box (we have 3 relay boxes in our house), which contain magnetic relays. The relay calls for the power to the fixture, which then turns on.

It's a very clunky system, but I imagine it was considered quite elegant in its day.

[bandito]

Sounds like an interesting system.

[Greg]

If I were you, I'd swap some parts in from other locations to test the parts; the relay and if that doesn't fix it, the switch.

[ritchie70]

I had a hard time even understanding what this thing was until I looked around online and realized that (my guess at least) each "switch" is really two switches - one for "ON" and one for "OFF".

When you press the "ON" button it moves the applicable relay to "ON" and leaves it there. These aren't the relays that I'm used to with a spring to move them back - the relay moves and stays there until the opposite direction is energized and it's moved back.

It's actually quite clever if you ask me (albeit quite complicated.) With a little computer you could rig up something to control all your lights from a computer or mobile device. Old/primitive home "automation" is always interesting to me, though.

If you have the "central control panels" that let you control many lights from one panel, does this fixture behave with that? If so then it's got to be the specific switch you're using.

If not, or if there is no applicable control panel for it, I would look at the wiring for the "ON" circuit for that light, and swap the "On" and "off" switches for it to see what happens. I'm going to guess that the low voltage wires aren't in conduit, so did maybe someone put a nail through it? To test that I'd disconnect all low voltage wires from that relay and carry its switch to the relay panel and wire it in with little short pieces to see if that fixes things.

If all the other relays are going strong, I just wonder what the odds are of the same relay failing twice without something else wrong.

Sorry I'm rambling, I should be in bed....

[dragoncar]

This is really cool and I'm surprised I never heard of it.  Some day someone in the future is going to be like "I have this wifi controlled light fixture but ever since Apple went out of business it's hard to emulate the all that controls it".

Sorry I have no insights - if I was there I could help but I'm a bit wary of telling you to poke around  malfunctioning electrical doodads.  24v is pretty safe, but there could be some fault causing the malfunction... I don't know how much protection there is on the 120v side.

If you really want more help, photos would help

[mensa]

I don't think the issue is with the switch  as there are two separate ones that operate this fixture. Both behave in the same way.

I did take some pictures, but due to the nature of the relay box, it's somewhat difficult to trace stuff.

The relay in question is the centre one in the attached pic, with the screws facing out. I checked to see that the connections on both sides (low voltage and higher voltage, or top/bottom in the pic) were secure, which they are, or damaged, which they are not.

I have the feeling that the fault lies elsewhere because, like ritchie70 says, it doesn't seem likely that the same relay would fail twice while all others (there are 10 in this panel, and two other panels like it elsewhere in the house) are going strong. Unfortunately, there is really no way to check to see if there's a fault in the 24v wire where it runs between floors/walls, short of tearing crap apart. I'm not likely to do that over 1 of 3 fixtures in the kitchen.

I don't really understand too much about electricity (as is likely obvious) so I'm a bit stymied.

So, I know that both switches behave the same: the relay opens when the switches are turned "off", which is backward to what should happen. Power gets to the fixture while the switch is manually held in the "off" position, and I can hear the magnetic "buzz" from the relay while holding the switch in the off position. Once the switch is released, the "buzz" stops, the relay closes and the power stops supplying the fixture. The relay appears newer, so there has (likely) been an issue previously with the same fixture/line.

If the issue is, say, a nail through the low voltage wires before they get to the relay, how could that affect both switches (supplied by different wires) equally? I can't tell where the wires for the separate switches come together to supply the relay. The fault must lie there perhaps? Does this make sense to anyone?

[Greg]

That's an impressive amount of wiring!  I still think swapping in a good known part from another fixture's relay system will help you.

It's entirely possible the relay is faulty.  It sure sounds like it from your earlier description. Replacement relays may not be of the same quality.

[mensa]

Hmmm, I've just read about the colour coding of the relay wires, elsewhere. It suggests that red is "on", black is "off" and blue is "common" (whatever common means. I suppose it's possible that whoever wired the new relay in might have attached it incorrectly?

But if that's so, my guess is that the switches NEVER would've worked as they should (ie up = on), which they have a handful of times. Argghh! So confused!

Am trying to source the relays locally. I do have a spare one which came with the house, but don't know if it works.

Greg - I'm afraid to get in there, and swap out a known good relay, in case I take out a perfectly functioning fixture elsewhere by a) screwing things up badly myself) or b) creating a fault in the swapped relay because there's something wrong with the wiring itself. Am I being a pansy-ass, or does this make sense?

[dragoncar]

That's a frickin rats nest.

From here it looks like the easiest thing to do is to swap the low voltage wires on a working relay with the non working.  It seems like that can be accomplished without a screwdriver.  That way you can tell if its the switch/wiring at fault or the relay itself.

You can also test continuity between low voltage wires with a multimeter (preferably completely detached).  You can have someone hold each switch and figure out which wires the switch shorts.  Do the same for a working set and see if the connections match.  You could be right that they just used the wrong color wire somewhere. 

[ritchie70]

Wow that's a lot of wires.

It seems likely that to turn a light on you would connect the "common" and "on" wires, and to turn it off, the "common" and "off" wires. Probably just a momentary contact if my theory about how this system works is correct. I think I'd get brave and try that on a light that works right and find out.

Assuming that's the right way to turn them on and off, I'd disconnect all the low voltage wires from the suspect relay and use the jumper wire method to try to turn the light on and off.

If it doesn't work, it's clearly the relay. If it does work, it's something in the low voltage wires between switches and relay.

Replacement relays seem to be available online if you can't get them locally.

[paddedhat]

Ritchie 70 is dead on.  Once you ring out the relay to confirm that it's operating correctly, you can ring out the wires. Pull the wires free of the switches and the relays (MARK EVERYTHING FIRST)  now take a multimeter and set it to OHMs which is a measure of resistance.  read between the wire ends to see it you get anything at all. temporarily tie two wires together on one end and read the others to see if you get a very low reading. If you get nothing, one of the wires is an "open" and broken at some point. Read each wire to ground to see if they are shorted to ground.....  Use the ohm or continuity setting on the meter to read the switches. Good luck, most relays are readily available once you identify a brand and part #.  As you have seen the system can last nearly forever with few failures. It was the hallmark of very high end construction "back in the day". Another crazy trend at the time was to install fluorescent lighting throughout the home, particularly in ceiling coves and behind translucent ceiling panels, then mount ALL the noisy, hot ballasts in a central closet. Another trend was to integrate "Despard" switches into door frames and other inconspicuous locations to maintain the clean modern lines of the home. Cool stuff. I ripped a lot of it out as an apprentice in the 80s.

BTW, hard to say if it was original "workmanship" or some later hack doing damage, but that control panel is an inexcusable mess.  It would be a lot easier to troubleshoot if the whole mess was cleaned up and the wires properly "dressed' and routed. Good luck, cool project.

[mensa]

I swapped out the relay and the damn thing works!

I found another switch that operates the fixture (that makes THREE). The newly found switch is on one of the aforementioned "central control panels", which has one switch controlling multiple lights from a dial. I am still concerned that one of the switches is the real culprit. Doubt the dialled switch is the issue though (fingers crossed).

Next up - locate new/working switch and replace that as well. We have one switchplate in the kitchen with two switches that we've never used. Thinking about using those for this project. I know for certain that the fixture that one of these unused switches operates is the yard light on the other side of the house...not sure why it would be hooked up to a switch in the kitchen (where you can't even tell if it's on or not), so I'm not opposed to getting rid of that function. The second switch in that plate doesn't appear to be hooked up to anything. Likely was for a fixture that no longer exists.

I think I'll also post on freecycle to try to locate extra switches.

Ritchie70 - yes, it is a momentary contact.

Paddedhat - yes, the relay box is a mess (as are the other two). Sadly, I'm just not up to cleaning 'em up at this time. Call me a pansy if you must :-)

[paddedhat]

Good luck on finding freebee parts for this system, wonderful if it happens, but most of this stuff is now rare as chicken lips, and few had the foresight to carefully salvage the stuff.

While you are poking around, grab a cheap mulitmeter and watch a tutorial on how to use it. In a few minutes you will be able to learn how to test switches and relays without swapping out questionable parts to learn of the may/or may not solve the problems. As for the neatness of the relay boxes, no worries. electrons are not particular, they flow through a rat's nest as easily as they would in a nice tidy install. for me it's kind of like a painter walking into a new house and seeing the cut in line between the wall and ceiling, looking like somebody did it when they were drunk. It just makes my fekin' toes curl!  Good job on the sleuthing.

[dragoncar]

It would be pretty fun to hook up an arduino to this system and control via my phone

[_JT]

I second the advice that you acquire a multimeter and begin to acquire the knowledge to use it as well. I doubt very seriously if this is your last time troubleshooting your LV lighting.

You're right to be cautious around electrical stuff, of course, but if you follow proper precautions with meter usage and (MOST IMPORTANTLY) de-energizing before you do any work (wiring/replacing components) you'll be ok.