Power Flow

Lets follow the power. The power cord is plugged into a standard outlet, and goes into the gray J-Box through the rubber grommets on the left. Then it heads into the blue outlet box which is epoxied to the J-Box side. Inside the blue outlet box the power cords 3 wires are connected to Gnd (Green) Neutral (White) and Hot (Black) of a standard 3 prong outlet.

The Icon On/Off module simply plugs into the outlet. At this point you now have switched 120V AC power inside the J-Box.

You can see that out of the Icon On/Off module we routed the power to a small terminal block. This is really just a matter of convenience, and is not necessary. Our terminal block is fused at 10 amps just for good measure. If you have room, and your transformer has a plug already on it, you can just plug your transformer right into the bottom of the On/Off module.

Out of the terminal block, the 120V AC flows into the transformer through the Green/White/Black wires. The transformer turns the 120V AC into 12V AC, then to 12V DC. Keep in mind most low voltage lighting transformers produce 12V AC, NOT 12V DC. This extra step to DC is useless and is specifically why we do not recommend using the same transformer as we used. The 12V DC flows out through the Orange/Brown wires (standard color coding for 12V circuits) where a pair of orange wire nuts bind it to the low voltage wire. The low voltage wire penetrates out the bottom of the J-Box and is ready for being hooked up to whatever you want.

Calculating Amps Needed

The transformer we chose to use is far from optimum, and do not recommend using the same one we used here. All that is needed for outdoor lighting is 12V and a lot of amps. Since most power transformers are rated in amps, lets figure out how many amps you need for your circuit.

Outdoor lighting bulbs are rated in watts. Transformers are rated in amps. We need a way to go back and forth between the two numbers. Fortunately, there is a easy way to do this.

• Watts = Amps * Volts
• Amps = Watts / Volts

In the case of low voltage lighting, Volts = 12. So the above formulas become

• Watts = Amps * 12
• Amps = Watts / 12

Typical low voltage bulbs are 4 watts and 11 watts. Lets say you have 5 each 4 watt bulbs and 2 each 11 watt bulbs. Simply add the watts together: 4+4+4+4+4+11+11 = 42. Now how many amps is that?

• Amps = Watts / 12 = 42 / 12 = 3.5 Amps

So in this case you need a minimum of 3.5 Amps available from your transformer.

Many transformers are rated in mA, such as 500mA. This means "milliAmps". A milliAmp is 0.001 amp, so 500mA is only 0.5 Amps, or 1/2 Amp. In the above example you needed 3.5 Amps, so if your transformer is rated in mA, then it needs to say 3500mA.

Written by Jason Bauer

Jason Bauer is an owner and programmer for Portforward.com. He's allergic to twitter and facebook, but you can find more of his articles in the Guides section.