Allegedly Defective Power Source Electrocutes Senior Design Engineer

This case involves a senior power supply design engineer that was working with an AC power source. The power source had 2 leads with alligator clips. When the engineer grabbed the leads, she was suddenly electrocuted. As a result of the incident, the engineer suffered disfiguring burns to her hands as well as severe internal injuries. It was alleged that a fault in the product’s overcurrent protection made it seem that the device had tripped. An expert in power source design and safety was sought to examine the product and determine whether or not it was defective.

Question(s) For Expert Witness

1. Please describe your experience in electrical design as it pertains to AC power sources.

2. What could potentially trip the machine making it appear off when it is still on?

3. What are some safety standards and precautions in the industry to avoid electrocution?

Expert Witness Response E-161299

I've designed AC power sources (aka inverters) professionally from scratch since about 1975. I've designed, built, and tested them in many different types and configurations, many for the US Army and US Navy. Some potential causes for such a trip that would make the device appear to be off can be electrical noise, an input power brownout, a momentary glitch on the input power, bad components, or a momentary overload or short circuit on the alligator clips. This unit is a piece of test equipment that lets the user produce a very controlled and variable AC input to AC output power for testing. Only a highly trained electrical engineer or technician should use such as device and then, only with many precautions taken. The main danger of this unit is not the fact that it has an AC output, rather it's due to the output voltage being higher than a safe level for humans (> 60 V). There are possible internal safety features in the 72-7675, like an overcurrent shut off that may have reduced the AC output voltage across the alligator clips, but it may still have been dangerous to humans between any one of the two clips to chassis ground or safety ground. This ground is the third wire in a standard AC wall plug. If the 72-7675 did not have an internal isolation transformer, then its output almost certainly would've been dangerous to humans even if the programmed AC output voltage was zero. I have extensive experience in the design, analysis, and testing of this type of AC power source.