Last week we installed some low voltage linear lighting in some display cases in a library. We removed some old fluorescent strips which were existing and used the original circuit and 2 switches that controlled the lights.

The new lights, which were supplied by the building manager, is a 24 volt system. It now consists of 2 600 watt transformers with built in circuit breakers feeding approx. 10' of lighting per transformer.

Everything fired up fine, then I get a call the lights are out. It turns out the breaker has tripped. I check the load on the circuit and each transformer is drawing about 3.5 amps, total circuit 7 amps. So I decide to change the older SqD QO bolt on breaker.

After changing the breaker I'm discovering that the circuit still trips especially when I rapidly turn the switches on and off and not 1 particular switch. Either switch being turned on and off rapidly will cause this to trip.

I need to return tomorrow morning before the library opens to dig a little deeper. I'm wondering if a problem on the neutral might be the problem however there does not seem to be a logical explanation. The wiring is BX in very good shape (the building is about 30 years old).

Any suggestions would be appreciated.

Thanks

Lee
You need to provide more info.
1 Are the transformers 120/24 volts? Are they on the same circuit?
2 "It now consists of 2 600 watt transformers with built in circuit breakers feeding approx. 10' of lighting per transformer" Is this the breaker that tripped or the line circuit breaker?
3 What size is the circuit breaker?
4 Is the amperage measured on the 120 volt side?

These types of transformer can draw large inrush currents. Sometimes 40 x FLA. If you have a good voltmeter you can measure the max current and see.

Bob, thanks for responding.

The transformers are 120v primary, 24v secondary.

Yes, they are on the same 120 volt circuit.

The 20 amp SqD bolt single pole breaker is tripping.

The "breakers" on the individual transformers have not tripped.

I measured the amperage on the primary side at the circuit breaker using a clamp on amp probe.

I think inrush current may be the problem. Square D makes some breakers called "high inrush." I've had to use these on some multiple ballast signs that tripped the breaker(s) for no detectable reason.

The stock # is QOB120HM

Good luck

Tom

I'm with Bob and Tom here.... You probhably notice a "ping", or "pong" when you flip the switch? How many watts are you running on each transformer?

Are you using a decent "lighting" Transformer, or one of those buck and boost T's with a few modifcations of adding CB's from a "Manufacturer". Some of the cheaper ones will just modify a buck and boost. That will give them a very high in-rush. (As they were designed for power, not lighting...) You can try the breaker suggested, or if possible use a dimmer to ramp up the switching current, or switch seperate.

I think you guys are right on the money with this. I'm going to try to locate that breaker tomorrow and give it a shot.

The transformer is made by the same manufacturer as the linear lighting. It is a similar system to Juno Trac 12 but the name escapes me right now.

I'll post back and let you all know how it works out.

Thanks a lot for the info!

Juno LV tansformers are buck and boost's with black paint, and a CB added...

This is good stuff, you guys amaze me with the amount of suggestions that so much collective experience makes possible. Really glad to have found this site!

Wouldn't installing one of those Maestro touch dimmers where the lights turn on and off gradually (theatre dimming) make a difference?

***Edit***

Oops...just reread the thread, I see E57 already suggested the dimmer thing. Sorry.

[This message has been edited by Sandro (edited 06-22-2005).]

I have had Meastro's fail because of a little plastic piece behind the plate. I would leary of using it in a commercial environment unless it was to be used by a soft, gentle librarian.

I don't think you can dim a transformer.

You can dim a transformer, but many dimmers don't like it.. There exist solid state dimmers that are designed to dim transformers, or you could always use a autotransformer.

I've actually used a SCR dimmer to drive an autotransformer, which was used to buck a series string of (9) 12v lamps that were used as footlights on stage for an opera production.
I did have to put an incandecent lamp (ghost load) in parallel with the autotransformer in order to stop the breaker on the SCR dimmer from tripping, but once I did, it worked just fine.

Some types of dimmers are hostile to transformers.. I've seen rainlights (6v PAR36 pinspots) burn up when connected to a dimmer.

Sure you can run a dimmer on the primary of a transformer.
You just have to make sure that the dimmer can handle the in-rush current from the transformer.

Manufacturers will usually gladly tell you if you can run transformers on their dimmers, since not all of them can. This means if theirs does you'll probably buy their product instead of someone elses. We had one manufacturer certify that their dimmer would dim a certain brand and model when we asked them and provided a sample... all for free... Well, we did buy over $6M in dimmers from them for the project...
You can usually get a written "yes" or "no" out of them though.

Well I returned to the library today and thanks to the responses I got the problem is solved!

I first tried to get my hands on the "high inrush" breaker that Mike had suggested. It would have taken at least a week to get it, so I decided to try the dimmer route.

I replaced the switches with 2 Lightolier Onset dimmers. Like the Maestro dimmers, they fade on and off. The breaker will not trip now.

Thanks again for helping me out, I owe each of you a beer!

Chimay.... Red, Blue, or Blonde