Eliminating shocks when removing panel covers

Originally Posted By: phinsperger
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If a spring loaded circuit with a live contact was up against the panel cover then normally when the panel cover is in contact with the panel case, any current gets directed to ground. As the cover is removed, there is a moment when the cover is not in contact with the panel case but could still be in contact with a hot circuit (from the spring action of the wire). Any current would then go through you to ground


To reduce the risk of getting shocked when removing a panel cover where there might be hot circuit springing up against the panel cover, what about using two small magnetic welding clamps with a heavy multi-stranded coiled wire connecting the two clamps. Before removing the screws just put one magnetic clamp on the cover and one magnetic clamp on the case.

If, through the magnetic welding clamps and the wire the, the cover could remain bonded to the panel case until it was far enough away to be sure it was not in contact with a live circuit, then a shock could be greatly reduced and even avoided.

Would this work?

Would it be practical to do ?

How often would such a scenario actually take place?


Originally Posted By: bking
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I think the paint on the cover and the case would prevent those clamps from working very well. I believe the best thing to do is wear gloves and a face shield and even stand on a rubber mat.



www.BAKingHomeInspections.com

Originally Posted By: roconnor
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, know what you are doing, and be careful out there … one wrong move with electrical systems, roofs, etc. and your career (and possibly breathing) may be over … icon_eek.gif



Robert O’Connor, PE


Eagle Engineering ?


Eagle Eye Inspections ?


NACHI Education Committee


I am absolutely amazed sometimes by how much thought goes into doing things wrong

Originally Posted By: phinsperger
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roconnor wrote:
Here are my 2-nickels on general panel inspection safety from a topic I started a while back ...

http://www.nachi.org/bbsystem/viewtopic.php?t=1665


Excellent points Robert!


--
.


Paul Hinsperger
Hinsperger Inspection Services
Chairman - NACHI Awards Committee
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Originally Posted By: mtimpani
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Someone once asked why aren’t those covers made of plastic?



Thank you, MarkTimpani


www.pridepropertyinspections.com

Originally Posted By: mwright1
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I would also add…I was trained that if you had to touch an eletrical box, providing you don’t have a voltage sensor, to touch the box lightly with the back of your hand. That way, if you were shocked, you natural reaction would be to jerk your hand back. Hope I never have to learn the lesson.


Originally Posted By: phinsperger
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The use of the back of your hand because a shock will cause you to close your hand. If you were grabing something at the time you may find that you can’t let go even though you want to.



.



Paul Hinsperger
Hinsperger Inspection Services
Chairman - NACHI Awards Committee
Place your Award Nominations
here !

Originally Posted By: bbadger
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phinsperger wrote:
If a spring loaded circuit with a live contact was up against the panel cover then normally when the panel cover is in contact with the panel case, any current gets directed to ground. As the cover is removed, there is a moment when the cover is not in contact with the panel case but could still be in contact with a hot circuit (from the spring action of the wire). Any current would then go through you to ground


Paul if a live wire is in contact with the installed (grounded) cover that would be a short circuit and the overcurrent device would operate.

In over 20 years of removing and replacing panel covers I have never received a shock from the panel cover.

Do not take this as a statement that it can not happen, anything is possible and we all must keep that in mind.

The fear I have when opening a panel cover is not shocks, my fear is burns from arc flash.

Sometimes people leave items (tools, hardware etc.) on top or inside panels. If these items fall across live parts there can be quite an arc flash.

I have seen quite a few arc flashes when installing panel covers, the causes are varied.

*The panel cover slipping out of your hands and contacting live parts.

*Foreign objects falling into the panel

*Pinching wires between the panel and the panel cover

*Loose or broken components falling into the wrong place.

I once opened a 200 amp home type panel only to have the entire interior (breakers and bus bars) fall out of the enclosure.

This was a situation with the service conductors coming in from the bottom of the panel running up the side of the panel to the main located at the top.

There is nothing wrong with that but all the mounting points where broken the only thing holding it together was the panel cover. Once I removed the cover the weight of the service conductors pulled the guts right out at me.

I was lucky other than needing new underwear I was otherwise fine.

My point here is be aware of every move you make when handling a panel cover.


--
Bob Badger
Electrical Construction & Maintenance
Moderator at ECN

Originally Posted By: cmccann
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Mark,


I think it's fire containment is why the panel is metal.


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NACHI MAB!

Originally Posted By: gbeaumont
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Bob B wrote:
The fear I have when opening a panel cover is not shocks, my fear is burns from arc flash.


I have to agree with Bob, whilst there is always the potential for getting shocked, arc flashes are a bigger potential problem.

Having once slipped and had a dead front hit the lugs I strongly advise inspectors to use safety glasses and carry clean underwear ![icon_confused.gif](upload://qv5zppiN69qCk2Y6JzaFYhrff8S.gif)

After 4 years I am still seeing sparks when I close my eyes and the jockey shorts never came clean

Regards

Gerry


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Gerry Beaumont
NACHI Education Committee
e-mail : education@nachi.org
NACHI phone 484-429-5466

Inspection Depot Education
gbeaumont@inspectiondepot.com

"Education is a journey, not a destination"

Originally Posted By: bbadger
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Square D was selling plastic panels for a while.


I don't think the American market is read to except that yet, I know I am not ready to try to sell folks a plastic panel.

Containing arc flash / blast is possible with plastic as long as the available fault current is fairly low as it is in most houses.

Get into commercial services with high fault current levels and you may find a 3/16" thick steel enclosures and the covers held on with screws every 12" around the entire perimeter.


--
Bob Badger
Electrical Construction & Maintenance
Moderator at ECN

Originally Posted By: bbadger
This post was automatically imported from our archived forum.



gbeaumont wrote:
Having once slipped and had a dead front hit the lugs I strongly advise inspectors to use safety glasses and carry clean underwear ![icon_confused.gif](upload://qv5zppiN69qCk2Y6JzaFYhrff8S.gif)


Electricity sure can be exciting huh?

I am glad your alright and this type of accident can happen to anyone no matter how many panels you have successfully opened and closed in the past.

Long ago I was installing a panel cover on a large panel in of all things an electrical engineers office building.

It was going fine until I was tightening up the screws and pinched a wire in between the panel and the cover.

Plenty of sparks, the 30 amp branch circuit breaker tripped but so did the 400 amp main in the basement feeding this 6th floor panel. The instantaneous trip rating of breakers are very close so this tripping of both breakers can happen.

Anyway it knocked out power to two floors of an occupied office building, it also messed up the payroll Dept's. computers.

I was a much hated man that day.


--
Bob Badger
Electrical Construction & Maintenance
Moderator at ECN

Originally Posted By: ekartal
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Bob is it true that a voltage sniffer will detect energy in the circuits, therefore it is not a reliable tool for detecting a live panel?


Erol Kartal


Originally Posted By: jtedesco
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Quote:
Annex K General Categories of Electrical Hazards

This annex is not a part of the requirements of this NFPA
document but is included for informational purposes only.

K.1 General Categories. There are three general categories
of electrical hazards: electrical shock, arc-flash, and arc-blast.

K.2 Electric Shock. Approximately 30,000 nonfatal electrical
shock accidents occur each year. The National Safety
Council estimates that about 1000 fatalities each year are
due to electrocution, more than half of them while servicing
energized systems of less than 600 volts.

Electrocution is the fourth leading cause of industrial
fatalities, after traffic, homicide, and construction accidents.
The current required to light a 7-1/2 watt, 120 volt lamp, if
passed across the chest, is enough to cause a fatality. The
most damaging paths through the body are through the
lungs, heart, and brain.

K.3 Arc-Flash. When an electric current passes through
air between ungrounded conductors or between ungrounded
conductors and grounded conductors, the temperatures can
reach 35,000?F. Exposure to these extreme temperatures
both burns the skin directly and causes ignition of clothing,
which adds to the burn injury. The majority of hospital
admissions due to electrical accidents are from arc-flash
burns, not from shocks. Each year more than 2,000 people
are admitted to burn centers with severe arc-flash burns.
Arc-flashes can and do kill at distances of 10 ft.

K.4 Arc-Blast. The tremendous temperatures of the arc
cause the explosive expansion of both the surrounding air
and the metal in the arc path.

For example, copper expands by a factor of
67,000 times when it turns from a solid to a vapor.

The danger associated with this expansion is one of
high pressures, sound, and shrapnel. The high pressures can
easily exceed hundreds or even thousands of pounds per
square foot, knocking workers off ladders, rupturing eardrums,
and collapsing lungs. The sounds associated with
these pressures can exceed 160 dB. Finally, material and
molten metal is expelled away from the arc at speeds exceeding
700 miles per hour, fast enough for shrapnel to
completely penetrate the human body.



Originally Posted By: gmickes
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don’t put your hand on it if your not sure, use a voltage tester or a pen tester. you may not be able to jerk your hand under certain conditions, also what if you were in a commercial buliding were a 277 volt circuit is used? believe me you may not just pull your hand away.