Light bulb used as current limiter.
Fig. 1


Warning About Electrical Shock and How to Prevent It

Fig. 1 uses a light bulb as a current limiter and isolation transformer to prevent electrical shock from a "HOT" ground, etc. This is an example.

Some of these experiments could produce injury or death. Don't conduct any of these experiments unless qualified to do so. If under 18, proceed only under adult supervision!

The information contained in this website is for general information purposes only. I endeavor to keep the information up to date and correct. The experiments presented on this website were conducted in a college classroom under strict instructor supervision. Any reliance you place on such information is therefore strictly at your own risk.

Most of the experiments presented use 5, 12, or 24 volts D.C. and should be safe. For those using over 120 or 220 volts I recommend the following be used in the classroom:

1. Use an isolation transformer. In the case of 220 and higher voltage use a step down transformers to 120 volts.

2. Place a 40 or 25 watt incandescent bulb in series with the experiment. The will limit the current in case of a short. Be extra careful with polarized capacitors because they can explode even under voltage if connected backwards or to A.C.

The primary factor for the severity of electric shock is the electric current which passes through the body, in particular the heart. This current is of course dependent upon the voltage and the resistance of the path it follows through the body. An approximate general framework for shock effects is as follows:

To put this in everyday terms, 1 mA is .001 Amp. A 100 watt light bulb draws 100 watts divided by 120 volt equals .840 Amps or 840 mA. The current from a 25 watt bulb (.208 A 208 mA) can kill you under the right circumstances.

Also note the issue of "hot chassis" when connecting test equipment to a test circuit as shown in images below. These relates to the B&K model 1653 test equipment.

Shock hazard due to hot chassis.
Fig. 2

Hot chassis electrical shock eliminated with B&K model 1653.
Fig. 3

B&K model 1653 used as isolation transfomter.
Fig. 4

B&K model 1653 used for trouble shooting.
Fig. 5

Other Circuits

New, updated for August 2021:

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