Seattle Home Inspector's Blog

WARNING:  This post has the potential to cause one’s eyes to glaze over!

     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 “Main” Electrical Distribution Panels (the place where your main breaker is) and “Remote” Distribution panels----more commonly known as “Sub-Panels.  The main difference between the two----without getting too technical is how they are “bonded.”

     “Grounding” and “bonding” get thrown around casually sometimes as if there is no difference between the two.  In Residences “grounding” happens at the Main Electrical Distribution Panel and consists of the grounding conductor being connected to the Neutral/Ground bar and then to one or more of several options:  Ground Rods, Metal Water Pipes coming to the house, and/or Rebar in the foundation footings.

     Other metallic systems in the home will be “bonded” (connected) to these “grounded” parts of the system.  So if you have metal water pipes, or metal heating system pipes, or gas supply pipes, or cable/telephone systems in the home, these systems would 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 Main Distribution Panel, the Neutral Wires (white wires) and the Equipment Ground Wires (bare copper---sometimes coated green wires) join together on the Neutral/Ground bar.  So in the Main 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.

     Now I will change my mind and tell you that 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.

     So now let’s look at the electrical panel in the picture below.  On the left side of the picture we can see all the bare copper wires that are all the equipment ground wires.  There is one big honking one that comes in with the big black conductors from the Main Distribution Panel.  There is another big honking one that goes off to a gas pipe---out through the top of the panel.  There is a whole bunch of little ones from individual circuits.  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 main panel the Neutral bar can become a Neutral/Ground bar.  The 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 every thing they are connected to----including you if you touch them.  It is an unimaginably 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

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