Breaker keeps tripping

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  #1  
Old 04-15-07, 05:51 PM
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Breaker keeps tripping

I just installed some Hadco LV lighting and am having a little trouble.

Here is the set-up.
Have a 20a 120v circuit from the panel to a basic Intermatic T101 timer then continues on to three on/off switches in the house with each switch controlling a seperate transformer. One switch controls the front yard lights, one controls the back yard lights....etc....

Here is the problem.
With all three switches always left on, the timer reaches the set time and turns on, the breaker trips. Reset the breaker and it works just fine, till the next evening. If I repeatedly switch the timer on/off in about 10 second intervals the breaker will trip about every 10-15 on/off cycles.
I measured the amperage with all the lights on and it pulls 9.8 amps. So, the circuit is not overloaded.
I replaced the breaker with a new one still does the same thing.
I also noticed that with the front yard lights left switched off it does not trip the breaker.
I had also added up the wattage of the bulbs and am not over the transformer rating.
Any ideas?
Thanks.
 
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  #2  
Old 04-15-07, 06:44 PM
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It sounds like the inrush current for all three transformers is too much for the circuit. It is similar to an electric motor that pulls more current starting than it does when running. You will probably have to put a delay on one of the transformers so they all are not energizing at exactly the same time.
 
  #3  
Old 04-15-07, 07:12 PM
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I had considered the same idea, but my meter when measuring the amps does jump when the timer is turned on but it measured around 16 amps for a split second before settling in at 9.8 amps.
Also, why can I switch the timer off/on for 10/15 times every couple seconds and the breaker holds till the last on/off cycle??
Thats why I didn't think that was the problem...
 
  #4  
Old 04-15-07, 07:37 PM
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The reson it dosen't trip when you cycle it is because breakers work by the expansion of a bi-metal substance, by cycling it on and off your simply not allowing enough time for it to heat up and trip . It is possibe that your 20 amp breaker is reaching it's upper limits and shutting off . Try a new 20 amp breaker. They do wear down over time and may just be deterioating.
 
  #5  
Old 04-16-07, 09:44 AM
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is this a AFCI or GFCI breaker?

either way, try to power each of the 3 sections solo for a while and see what happens. a 20a breaker should take even a 40 amp surge for a 1/2 second or so.
 
  #6  
Old 04-16-07, 11:03 AM
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I really appreciate the suggestions but I have already tried those.

I'll try to clarify a little more clearly.

Timer is off during the day, 8 p.m. rolls around the timer turns on. Just that quick the breaker trips, there is no pause between the timer turning on and the breaker tripping. Reset the breaker and all the lights work just fine all night long. Next evening same thing.
Also when I cycle the timer on/off, it sometimes trips after 2-3 cycles or sometimes 25 cycles, 10-15 cycles is the average.
I have also narrowed it down to the front yards lights, with the front yard lights left off the breaker does not trip. I am considering installing another circuit for the front yard lights and changing the timer to a STDP, but am not convinced that is the problem.
Thanks for your help.
 
  #7  
Old 04-16-07, 11:22 AM
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Is the breaker a standard type or GFCI type with TEST button?
 
  #8  
Old 04-16-07, 11:48 AM
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standard breaker,,QO120
 
  #9  
Old 04-16-07, 04:54 PM
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Does the breaker ever trip with only the front yard sub-circuit on?
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Turn off the power and get out your meter and start checking everything on your front yard light and other sub-circuits:
resistance between hot & neutral
continuity between hot & ground wire
continuity betweed hot & earth (actually stick your probe in the ground near your lights)

I'm wondering if you have a weak short.

I'm also wondering if you have a moisture related weak short. When the circuit is off for a while moisture can accumulate so when it is turned on there is a strong enough short to trip the breaker, but the act of shorting (arcing) dries out the area so it does not reliably trip the breaker any more.
 

Last edited by Pilot Dane; 04-16-07 at 05:23 PM.
  #10  
Old 04-16-07, 07:51 PM
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Yes, the breaker trips with just the front lights on. I also removed the LV wires off the transformer and the breaker held just fine.
So, your (Pilot Dane) that I may have a "weak short" in the LV wiring past the transformer? What could be the cause, damaged light or LV wire?
If thats the case I can track that down easily.
 
  #11  
Old 04-17-07, 04:31 PM
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I have a hard time beleiving that a short in the low voltage wiring is tripping your 20 amp breaker. That would be a massive short at 12 volts to pull down the high voltage breaker. I would think the transformer would fry before that.
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Well if the breaker will not trip with only the transformer connected (nothing connected to the low voltage output) then we can assume it's something in the low voltage circuit/wiring. Just make sure you tested it enough to know that it absolutely does not trip with just the transformer.

I would re-connect the LV wiring and do your on/off test to verify that the breaker tripping problem has returned. Then start disconnecting ONE thing from the low voltage circuit and re-run your on/off test. Once you've reached the point where the breaker no longer trips you've found the problem spot (at least in theory...).

Another thing you could try is to put a fuse in the low voltage wiring. You can calculate the amp draw of your lights (watts / volts = amps)(so 60 watts of lights would be 5 amps at 12 volts).
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I still suspect the problem is somewhere on the high voltage side...
 
  #12  
Old 04-17-07, 08:18 PM
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For troubleshooting sake, can you try swapping transformers, from one of the circuits that always works. Then try the one that trips the breaker, on a zone of low voltage lights that hasn't given you any trouble.

Also curious about the length and size of low voltage cable used on the front lights.
 
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