Electrical Safety

Some one ever gave you something that was broken and you wanted to fix it but when powering the device up it goes up in smoke?

The best and simplest device to build and use to test anything that plugs into the wall is a Dim Bulb Tester.

Costs about ten bucks if you don’t cheap out on Materials. You can also improve it by using different Bulb setups like two 40 Watt and two 60 Watt with some switches to change the Wattage range. You could also add it to an Isolation Transformer for further protection.

What the Dim Bulb Tester does is when there is a short the current will flow through the Bulb and turn on. When there is no short it will lightly glow or even not come on at all. In other words is Limits the Current.

Here is a diagram of my Tester.

I spent about ten bucks on mine. Bought just about everything from Home Depot except the Isolation Transformer, I already had the Transformer but it’s totally optional.

I used an old power cable two prong 10amp rated. Live goes to the Switch and from the switch goes into the Bulb Socket then from the Bulb Socket to the Live side of the Outlet. Neutral just runs straight through from the Line Cord to the Neutral side of the Wall Socket.

At the time when I built mine my local Home Depot had stuff on sale. I also had a few parts already on hand.

Bill of Materials
Porcelain Light Socket

2 gang electrical outlet box

Light Switch

Wall Outlet

Face Plate


Light Bulb (Only 100Watt Incandescent Bulb they had at the time)

Now take note you can only use Incandescent Bulbs with this. You can’t use LED or CFL Bulbs. If you do the in rush current will blow the light up.

If done properly you can hide all of the splices in the 2 gang box and under the Light Socket. You could use a Nema Box and use a Low Voltage 2 gang mud ring and have the Light Socket on the top of the box to completely insure everything is Isolated. If you decided to use a Metal Box then use a three prong cable and tie the Earth Ground to the Metal Box.

If you use an Isolation Transformer or Variac you plug the Dim Bulb Tester into the Secondary side.


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