Grounding, Bonding and Bondage—it is important to know the difference!

In my blog I usually strive to keep things from getting too “technical”—-or too “risqué.”  I have wanted to do a post about the differences between “Service” Panels (the place where your main breaker/disconnect is) and “Remote” Distribution panels–more commonly known as “Sub-Panels.  The main difference between the two–without getting too technical is how the ground wires and neutral wires are terminated.

“Grounding” and “bonding” get thrown around casually sometimes as if there was no difference between the two.  In Residences “grounding” of the electrical system happens at the Service Panel and consists of the grounding conductor being connected to the Neutral/Ground bar.  The grounding conductor will be connected to one or more of several options:  Ground Rods, Metal Water Service Pipes, and/or Concrete Encased Electrodes (Sometimes called a UFER ground and consisting of the rebar in the foundation footings/foundation).

Other metallic systems in the home will be “bonded” (connected) to the grounding electrode system.  So if you have metal water pipes, metal heating system pipes, gas supply pipes, or cable/telephone systems in the home, these systems will all be connected mechanically (bonded) to the grounding conductor of the home.

The critical thing to keep in mind about bonding and grounding is that at the Service Panel, the Neutral Wires (white wires) and the Equipment Ground Wires (bare copper—sometimes green coated wires) join together on the Neutral/Ground bar.  So in the Service Panel you will find all of these white and bare copper wires connected to the same termination bar.

I really don’t want to get into the reasons why this is so in this post.  Just keep in mind that in a Remote Distribution Panel (sub-panel) the equipment ground wires and neutral wires cannot be joined together.  In fact even at switches and receptacles or anywhere else wires are brought together—-the equipment ground wires and neutral wires must never be connected together.

The reason for this is that there is a small amount of current that always flows on the neutral wire in the normal operation of appliances etc and you do not want that current running on the bare ground wires–these wires are connected to things you might touch and thus become a shock hazard.

So now let’s look at the electrical panel in the picture below.

This panel is a sub-panel.

On the left side of the picture we can see all the bare copper wires that are all the equipment ground wires of the individual circuits.  There is  a big copper wire connected to the ground bar that goes off to a gas pipe—out through the top of the panel.  Now aside from the fact that there are some issues with the way all of these bare ground wires are terminated in terms of the number of wires under each screw, the thing I want you to pay attention to is that they are all connected to their own little metal bar that is connected directly to the metal box itself.

Now look at the big wire with the white tape like a barber pole.  That is the Neutral wire and notice how it is connected to the vertical neutral bar on the left side (the bottom end is visible below the breakers on the left side) and that there is a Crossover Arm connected to it that goes over to the vertical bar on the right side.  This is what we look for when we talk about the ground wires and the neutral wires being isolated from each other in a sub-panel.  All of the electrical components related to the Neutral wires are separated from the metal box with pieces of plastic–so they don’t touch each other.

But wait a minute Captain–we have a problem.

Can anyone see the problem?

Take a look at that crossover arm that connects the left neutral bar to the right neutral bar.  Do you see that very pretty green screw?  That green screw is shipped with the panel, from the manufacturer, so that when the panel is going to be used as a Service Panel the Neutral bar can become a Neutral/Ground bar and the metal box is bonded with the green screw.

The green screw is meant to be discarded when the panel is being used as a sub-panel–like this one is.  So in this installation we run the risk of running some amount of current onto all of those bare copper wires and to everything they are connected to–including you if you touch them.  It is an immensely easy fix–the green screw merely needs to be removed–by the licensed electrical contractor.  But not to worry–if there is this defect, there will likely be others–to soften the electrician’s “minimum” service call.

Now for all of those that are wondering when I am going to get to the bondage part–ask Dr. Ruth–that is what Google is for.

Charles Buell, Real Estate Inspections in Seattle

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