About tapping the panel cover with the knuckles to ensure that panel is not hot

I am studying for the FHIE using InterNACHI’s materials and I have come across this question whose correct answer I consider questionable because, in my opinion, physically touching to judge the presence of electrical current is an unsafe practice, and, for that same reason, InterNACHI recommends the use of non-contact voltage detectors. Anyone can clarify why the state exam admits this practice as OK?

T/F: The electrical panel cover should first be tapped with the knuckles to ensure that the panel is not “hot” or energized before opening.
Correct Answer: YES

Source: https://www.nachi.org/my/education/practice-questions?page=6

Not the safest way but the back of the hand, instead of knuckles. Reason: Voltage will cause muscles to contract, allegedly pulling your hand away from the source.

Hope this helps


what He said …

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They are suggesting you have an alternative means. Instead of grabbing the panel.

Side note - There are many courses of action that may seem archaic but when working around electricity it means your life and others around you.

Keep on keeping on studying.

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And should be the back side of the RIGHT hand.

I use a “hot” stick or pencil and run it around all areas of the breakers and dead front to pick up indications on the dead front prior to opening. Don’t really care for the 'tongue to the 9v Battery test."…

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I really appreciate your answers and I am very grateful for that, however, my concern was about the pure theory that is assessed in the exam. I know that we all have our ancient practices that work most of the time, but, the real world sometimes differs from the books, and the state exams always go by the books.

For the exam, back side of the Right hand. The theory is if there is any “push back” shock, it’s done through an area that is the least of the other areas that could cause more harm. The left hand and arm are located CLOSER to heart than the right arm, thus allowing for a shorter path.

With that said, if you see it on a question, back side of the right hand. No fingers or anything to the left.

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Thank you Thomas

Use a non contact volt tester. :thinking:Little easier on your heart.
I use: Fluke 1AC II Volt-Alert AC Non-Contact Voltage Tester.
non contact volt tester

I got one, I was just asking for academic reasons

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Academically speaking of course, physically touching a dead front, or any other bonded conductive surface to judge the presence of electric current or voltage is unwise if/when current may exist, and a foolish practice mind you, if/when you carry a non contact volt tester.
Just my thoughts.

Excellent example, however there is no “allegedly” about it. It’s true. I have been bit a few times by 440DC doing steel work on commercial buildings. If your hand is already closed, and you use your knuckles the muscle contraction will be in your forearm and biceps, bending your arm back at you at the elbow. It’s no walk in the park, but better than not being able to let go of something.


Welcome to our forum, Michael!..Enjoy! :smile:

Lot of things you read in study material are not how done in the real world AND vice versa

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What applications used 440VDC? That is a very unusual DC Voltage (or AC Voltage for that matter). Before VFAC drives that can develop high torque at low rotating speeds were developed, DC was very common for rotating machines. I worked extensively with DC during the 1970s and 1980s. Common DC Voltages are 90, 180, 300, and 500.

DC is still the best option for motors up to about 100HP but are not the most economical option in larger motors since the advent of VFAC. There are many reasons good reasons for using DC but there are also good reasons for not using DC at 440VDC. Safety is one disadvantage of DC. DC is more deadly than AC. An encounter with 440VDC would be much less likely to have a good outcome than an encounter with 480VAC (440V is not a standard for either DC or AC).


Arch welder. Setting girders and bar joists on commercial buildings. We would weld the joists and bridging. Didn’t matter the weather, rain, snow, summer heat… Leather gloves don’t insulate too good when they are wet…


It is unlikely that the output of an arc welder would be 440VDC. The input of the welder was likely 480VAC. Arc Welders are designed to maintain constant output current. The output DC Voltage will vary as the welder maintains constant current. The output Voltage of an industrial DC welder is usually around 20VDC-35VDC. The output Voltage is constantly changing during welding. Anything above an output of 50VDC would be unusual.

I disagree with the test’s answer of using knuckles to check for Voltage being the correct answer. I found at least six questions just on Page 6 that were so seriously flawed that they make no sense, the best answer provided was not the best possible answer, or the answers the test says are the correct answer are, in fact, INCORRECT. Other pages likey have similarly flawed questions.

I went through the entire InterNACHI electrical course book and corrected dozens of errors three years ago when I was in Boulder helping Ron with the school. I don’t know what became of the edits but if the test is any indication, I’ll guess that the errors were never corrected.

IMO this back of the hand method should be removed from any type of training manual. A proximity type, non-contact tester is $15. Testing with a tester should be the primary way to determine that something is safe not using any part of the human body.


I actually recommend the lick test for this application …fast and easy with no question of accuracy…