How to tell if your electrical panel cover is energized

There is a long standing myth among home inspectors and others, that one should always touch the electrical panel cover with the back of your hand, specifically your right hand to see if the cover is energized.

There are some problems with this approach.  All touching it with your hand does is tell you that YOU are not grounded. You are isolated from the ground (rubber sole shoes, floor coverings, location etc). The idea is, if you were to get a shock from it, your muscles would contract pulling your hand away from the cover instead of toward it.  

Some recommend using an NCVT (non-contact voltage tester) to check the cover.  The assumption is if the NCVT is activated the cover must be energized.  But again this is not true, because there are ways to “induce” voltage on the cover without it being truly energized.  In terms of being energized, this would be more of a “false positive” indication.  Activation of the NCVT is at the very least an indication the panel is not properly grounded, but it does not “necessarily” mean it is energized.  In fact it is VERY rare the cover would actually be energized–but because it is possible we must be cautious.

So what is the best way to check to see if the panel cover is energized?

Well of course use of a multi-meter or equivalent is a good way–but finding locations to put the second lead is not always easy to do, without carrying a coil of wire to make one of the leads long enough.

There is another way to test it that is not complicated.

This method involves using both your hand and an NCVT.

In the video below, you will see a wire stuck in a receptacle that is connected to a metal box with a metal cover that symbolizes an electrical panel or ANY metal component that could be energized.  The multimeter shows the metal box at 122.5 volts (leads run from cover plate to neutral slot of nearby receptacle). 

The NCVT indicates the cover is energized and yet I can hold onto the cover without getting a shock (because I am isolated from ground). 

Watch what happens when I touch the box and touch the energized wire.  The NCVT turns “OFF.”  Surely magic, right? 

Not magic–this is just the way they work.  The NCVT cannot “see” voltage on grounded conductors (only ungrounded conductors–hot wires), and even while my body is not physically grounded, it represents enough similar characteristics to confuse the NCVT . 

As I move the NCVT away from the wire, notice how it lights up again?  This method, with one hand on the cover plate and the NCVT in the other hand, will tell you the cover is actually energized.  If it were not energized, the NCVT would simply  not activate.

Always, always, always make sure whenever you are working on any electrical component that you yourself are in no way in contact with something grounded.  And, such testing should only be done by qualified parties.

By Charles Buell Real Estate Inspections in Seattle

Grandfather gets grandfathered

Once-upon-a-time, grandpa was working on a junction box in the basement when he came in contact with the neutral of a multi-wire circuit for the dishwasher/disposal. He had shut the circuit down but because there was no handle tie–the neutral was still energized.

He got such a shock he fell off the ladder and broke his leg—already compromised by long term lead exposure.

There was no way he was going to make it up the stairs, so he thought if he could crawl to the basement bedroom he would be able to get out the window. However, the window was too high off the floor and way too small to fit through. It was not an option.

By now it was getting dark and he was beginning to panic.

The stairs loomed like a mountain in front of him, dark and ominous. There was no light switch to light up the stairs and he might not have been able to figure out a way to turn it on anyway. The missing handrail would also be of no help. So, he began the long painful slide up the stairs dragging his sorry leg behind him.

Fighting all the way, to avoid sliding back down the too steep stairs, he finally got to the top. That is when he realized he left his keys on the basement workbench. He remembered it being a bad idea when he set them down.

Without his keys he could not unlock the keyed deadbolt. It would have been excruciating to reach anyway, but after the stairs he figured he could have managed.

He thought about the back door but calling for help from there would have been useless. It had to be the front door.

He thought about the phone hanging on the kitchen wall 5 feet off the floor, but he had already ruled out being able to reach that.

He lay there listening to himself wheeze, mustering all the common sense he could.  He likely later would trade that for good sense instead.

He decided his only option was to break the very large plate glass panel next to the door to call for help.

He lifted the heavy cast iron Cherub door stop and smashed the glass with one painful blow. The non-safety-glass panel shattered into large guillotine shaped pieces that swooshed down slicing off poor grandpa’s hand.

He bled to death right there.

Charles Buell, Real Estate Inspections in Seattle

Bonding grounds and neutrals together in sub-panels

Parallel Paths, be careful

Parallel Paths

One of the most common defects I find related to remote distribution panels (sub-panels) is ground wires and neutral wires bonded together. 

This is especially true if the work has been done by homeowners or handy persons. 

In simple terms, the only place we want to bond the grounds and neutrals together is in the service equipment. Many people refer to it as the “main panel” or a variety of other terms.  

Regardless of what you may improperly call it, the point where you can disconnect all power to the building is the service equipment.  At this point, the ground and neutral are connected to the earth through a system of pipes, rebar, rods, and or wires.  The purpose of connecting the system to earth has little to do with the function of the electrical system.  This provides a layer of protection against lightning surges or static charges that would otherwise build up on the electrical system.

It is a bit like the spark you get from nose to nose when static charges build up on you and the person with the other nose.  This happens because you have no means of sending that excess energy to the earth.

The second important function of all those ground wires running in all the circuits throughout the home is to provide an emergency path back to where they are connected together in the service equipment.  In this way, if there is a short between the energized conductors and some metal component that is grounded, there will be a path back to the point of connection to trip the breaker associated with that circuit.

Circuit breakers trip on heat curves and amperage curves and a short circuit represents many times the amperage rating of the breaker tripping it instantly.  Likewise if there is a problem with the circuit that is resulting in over-amperage, the breaker will trip within the time curve of the breaker–not necessarily exactly the rating of the breaker.  A 20 amp breaker could actually not trip for a few amps above 20 amps for X amount of time without tripping.  Depending on the appliance, the appliance might finish its job before the breaker trips and we would never know it is misbehaving.

But lets get back to not connecting grounds and neutrals together in sub-panels.  Installing the green screw in this sub-panel has resulted in connecting the grounds and neutrals together.  It needs to be removed.

Improper bonding

Green screw bonds the neutral bar to the grounded metal box

When we do bond them together we create two paths back to the connection at the service equipment.  The amount of current that will flow on the two paths will be proportional to the resistance of those paths.  For example if metal conduit or a very large wire is used as the equipment grounding conductor from the sub-panel to the service equipment a large percentage of the neutral current could flow on the bare conduit or bare ground wire (or coated ground wire as the case may be) back to the service equipment.  In some cases the metal conduit might be a proportionally better path than the neutral wire feeding the sub-panel and the majority of the neutral current could then flow on the bare conduit.

I consider it best practice to always provide  a ground wire inside metal conduit but there are probably millions of installations that rely on the metal conduit as the path back to the service equipment.  As long as neutrals and grounds are not bonded together in the sub-panel this is rarely an issue. 

Now if grounds and neutrals are joined together in the sub-panel, the current of all the 120 volt circuits that are operating will travel on the metal conduit, and the neutral wire, as well as the ground wire if present.  This is multiple paths.

So in the following picture where there is no ground wire inside the conduit, but instead the only path back to the service equipment, is the metal conduit, its being disconnected is a serious problem for fire safety and ability of the breakers to trip if there is a fault to ground.  The receptacles of the circuits in this sub-panel tested as ungrounded,.  Fortunately, in this case, the neutrals and grounds were properly isolated, so there was little risk of neutral current running on the bare conduit.

Disconnected electrical conduit

Disconnected conduit feeding condo sub-panel

If they are bonded together in the sub-panel, who is going to be brave enough to grab the two ends of the pipe and stick them back together?

A competent electrician will know enough to test the metal components and/or make sure electrical circuits are turned off, but what about the handyman?  What about your Honey that works on your Honey Do list?  Most people would be unaware of the dangers present and working with the exposed metal components with bare hands could be deadly.

Here is a video demonstration done with students at Bellingham Technical College to show the effect on different size “paths” in a simulation of grounds and neutrals connected together at a sub-panel.  The “light” is the load symbolizing the sub-panel.

A big thanks to Gary Smith for his improvements to this video.

Here is a picture of the wiring diagram for the demonstration in the video:

Charles Buell Real Estate Inspections in Seattle