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Old 10-27-2010, 12:17 PM   #1
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Low voltage switching


I have a 200 watt Malibu outdoor transformer and want to run it through two or more outdoor switches to control different areas of the yard. Can this be done? Will the low voltage line from the transformer handle several such switches? Must the distance between the transformer and the initial junction box be +10' as required for the first lights? Many thanks.

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Old 10-27-2010, 07:23 PM   #2
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Low voltage switching


No problem having several sub-circuits each with its own switch.
Just be sure that the load of all the lights does not exceed the transformer rating (200 watts here).

There is no minimum or maximum distance except as the distance gets greater you will need fatter wires for a given number of amperes. There should be no more than one volt drop at a light at the far end of a 12 volt circuit.

The voltage drop in a given piece or length of wire is equal to the current flowing at that moment times the resistance of that wire.

Given the full 200 watts (approx. 17 amps) being used and the first junction box from the transformer is about 30 feet away and 12 gauge wiring is used, a 12 volt source will be 11 volts out at that junction box.

Depending on the thickness of the wires, you could have the lights nearer the transformer noticeably brighter than the lights at the far end of the circuit.

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Last edited by AllanJ; 10-27-2010 at 07:45 PM.
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Old 10-28-2010, 06:13 AM   #3
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Low voltage switching


Thank you for the prompt respnse. I'm using 12ga wire and 4 watt bulbs all the way around. But a second circuit will use two 50 watt and 20 watt lights for the trees.

The transformer seems to be heating up (a lot) especially if the transformer is on and the switches are all off. I suspect it's too close to the switches as they are only 2' away frm each other. The experment continues today.
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Old 10-28-2010, 08:17 AM   #4
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Low voltage switching


The transformer should not be heating up when all the lights are off. Are you sure you have the proper kind of transformer and connected it up as shown in the instructions? The fact the switches are close by does not matter.

Common reasons for overheating transformers include buying them from a surplus store instead of in a kit and not knowing the rating or capacity, or connecting the transformer backwards, or connecting it to the wrong voltage for example 240 instead of 120, or connecting the transformer into a circuit controlled by a dimmer switch.

While theoretically any transformer can be connected backwards, the input winding (winding used as the primary) has to be rated for the voltage and AC frequendcy applied to it.
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Old 10-28-2010, 09:09 AM   #5
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Low voltage switching


Thanks again,

The transformer was purchased from HD as part of a Malibu outdoor lighting kit. The circuit from the house is a dedicated 20amp line that runs only to a GFI receptical / box. Only the pond pump (4amps) and the Malibu transformer 120v and 1 A input with an out put of 88 w output (not the 200 I referenced yesterday) are pulling from the GFI box.

I'm using two 50" sections of 12 gauge wire supplied by Malibu. There are a total of 15 Malibu bulbs x 4 watts or 60 watts in total. I wanted to run each of the two segments off their own switch. When the transformer is on but the switches are off the transformer gets quite hot to the touch and hums a bit.

Steve
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