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low-V lighting control--troubleshooting #60125
12/22/05 11:21 PM
12/22/05 11:21 PM
amp-man  Offline OP
Joined: Jun 2001
Posts: 141
Sacto, California US of A
A Merry Christmas to all!

Anybody have experience with old (like close to 50 years old) low voltage lighting control systems?

I recently got a call to troubleshoot a light fixture in a church (built in '57). There are six fixtures, switched in pairs (front, middle, and back, with the back switch also controlling several 4' lay-ins in the choir loft). One of the two back hanging fixtures doesn't work. I'm told that it gradually quit working. Jiggling the switch would get it to go on, then it wouldn't work at all.

The fixture is a huge hanging lantern, with 8 CFLs (4-pin base).

I first checked the switch, mainly because it's at ground level and the fixture is 15 feet up and the canopy about 32 feet up.

Switches for the three banks are despard-style, three in a SG box. Open it up and lo! despard switches, all right, fed by a 19-conductor, 20 gage cable (marked "Bryant control cable"). Voltage across the switch (when off) is 27 VAC. Current in the circuit for the operating banks fo fixtures with switch on is about 0.2 amps. I'm thinking that there's a good old ice cube relay somewhere that's failed.

O.K., so my mission is to find the bad relay somewhere. I look everywhere for a control panel and can't find anything.

I get the church maintenance man to move some pews and bring in the scaffolding w/tilt-up ladder w/tiny platform at top.

Up I go. No power at the fixture. So, it's up to the ceiling, at 32 feet. The platform is very moving around like a leaf in the breeze. I'm hoping that the parishoners in the church are including me in their prayers.

There's no relay in the j-box, and also no power present. As long as I'm up there, I re-make the splices of building wire to fixture wires.

Back down at the switch box, I bypass the switch for the non-functioning fixture and get no results. I re-make the splices on both sides of the switch (four conductors on the load side of the one switch, and 11 spliced together with a pigtail to each of the three switches, on the line side).

Operate switch--and lo! All fixtures come on, including the one that wasn't working!

I figure it was a bad splice, so turn off switch, turn on again, and nothing!

I figure it's a failing relay. When I get back to the site, I intend to find the circuit supplying power to the system, cut power, and use a Harris T90 (poor man's TDR)tto find length of wire from switch to relay and to power supply), and a wire tracer to try to find the relay.

I'm wondering if the relay might be in one of the other fixtures (maybe the lay-ins?), but the distance measurement ought to help sort that out.

Anyone have any experience with this sort of system?

Do you think I'm barking up the right tree?

Any suggestions?

Best regards,


Work Gear for Electricians and the Trades
Re: low-V lighting control--troubleshooting #60126
12/23/05 12:00 AM
12/23/05 12:00 AM
Larry Fine  Offline
Joined: Feb 2005
Posts: 693
Richmond, VA
Cliff, are you saying that each fixture has its own relay, or each row of fixtures has its own relay?

If it's the former, then a simple relay swap (or temporary contact bypass) will tell you.

If it's the latter, it has to be between the last operating ceiling box and the defective one's box.

Larry Fine
Fine Electric Co.
Re: low-V lighting control--troubleshooting #60127
12/23/05 12:31 AM
12/23/05 12:31 AM
amp-man  Offline OP
Joined: Jun 2001
Posts: 141
Sacto, California US of A

Well, I don't know yet. There are four leads on the load side of the switch: red, red w/white stripe, purple, and purple w/white stripe. I think each hanging fixture has it's own relay, and that there are two relays for the four banks of lay-ins.

This configuration would be consistent with the observations, and as you said, it's then a simple matter of finding the bad relay.

Escept it's not in the ceiling box above the non-working fixture, and I can't find a panel of relays. And the maintenance man and I really "tossed" the place! I mean we searched it very thoroughly.

The roof over the main chapel area (where the non-op fixture is) is a flat roof with no attic space. The banks of lay-ins are in a dropped ceiling. I suppose I ought to look there for the relays, as a last resort.

I'm banking on the distance mesurement via TDR to give me a gross indication of possible location, and then a wire tracer to led me to it. The low-v cable is in EMT, though, so I'll have to squirt signal onto the pipe and just follow the strongest signal. Or put tone on the control wiring and look for signal at outlet boxes. X-ray vision would be nice...the building is reinforced concrete.

I'm the third electrical contractor to troubleshoot this problem. First guy told the maintenance man that the problem was the splices at the ceiling box, but he never came back to check (fear of heights, eh?)

The second one said that it was the fixture ballasts, and that he was gonna come back and lower the fixture to ground level to work on it (my guess is that it weighs 70-80 pounds). He never came back.

So, finding and fixing the problem is now a challenge.

Thanks for the help. I will report back when I've revisited the site.


Re: low-V lighting control--troubleshooting #60128
12/23/05 12:44 AM
12/23/05 12:44 AM
gfretwell  Offline

Joined: Jul 2004
Posts: 9,338
One of the computer rooms I worked in had a buttload of those GE relays. each was pressed in a 1/2" KO in the first layin on each string. The coil sticks outside the enclosure with low voltage wires on it.

Greg Fretwell


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