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

Tin-foil Hats and Your Home’s Electrical Grounding System

Like most of my readers, I have been known to occasionally don a tin-foil hat when necessary.  I have avoided stepping on cracks and certainly tilted at windmills when necessary.

Science usually makes us give up our wishful thinking (the desire for the simplicity of tin foil) and helps us pick and choose actually conquerable windmills–or at least understand the consequences.

There will always be causes worth doing battle with as long as there are idiots to create those causes.

Often it is seemingly impossible to tell the difference. And, isn’t that what keeps us all entertained all the days of our lives?

But back to aluminum foil hats, and protecting ourselves from the unknown or seeking information from the ether. Once upon a time in a crawl space (where I have most of my epiphanies and meaningful conversations with the unknowable and the unseen), I came across an instance of where someone was clearly attempting to communicate with the void—or perhaps merely attempting to “avoid” something.

Metal piping in one’s home must be bonded and/or grounded to the house electrical grounding system. We can clearly see in the following picture that it was once connected, but now it looks more like something you might use in a search for E.T.

In this particular case this “avoidance” resulted in the house not being grounded at all at the home itself, because there were no ground rods or other means of grounding the electrical system. When this occurs grounding is achieved by the wire that runs back to the utility company transformer at the street. This condition makes it very difficult to keep static charges from building up on the house’s electrical system. 

If the ground wire at the utility pole is lost it can become even more difficult and can result in considerable damage to electronic equipment in the home.

It is now time to communicate with the electrician about repairs–they rarely tilt at windmills and I have never seen one wear a tin-foil hat!

By Charles Buell, Real Estate Inspections in Seattle

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Being well grounded is not just about one’s well being–but it could be.

There was a time, in the not so distant past, when the only way a house’s electrical system was “grounded” was by connecting the grounding conductor to the metal water pipe coming to the house. There are still a large number of such houses around the country.

While I could talk about where this wire gets connected in relation to where it is supposed to be connected, that could be another whole blog post all by itself.

Today I want to talk about how this particular means of grounding the electrical system, often gets compromised by the installation of plastic components. It is also about how plumbers are not electricians and electricians are not plumbers, so these compromises happen too often. The lowly home inspector is about the only one that is going to draw attention to the problem.

One of the most common ways these older systems get compromised is when the old galvanized pipe from the street is no longer functional (from a plumbing stand point) and gets replaced with a new plastic water line. The installation eliminates the house electrical systems grounding electrode, resulting in the loss of a proper path to ground for dissipation of static charges that might build up on metallic systems  in the home.

The ground path is not totally eliminated however. There is also a grounding path back to the ground rod at the utility transformer on the pole at the street–which could be several houses away.

For electrical safety it is important to maintain grounding redundancy.

There could also be ground rods present in addition to the water pipe grounding electrode.

Another way these systems get compromised is when the pipe is repaired with plastic components—resulting in a break in continuity of the grounding conductor.

In the following pictures we can see where the old water line has been abandoned.

Water Pipe Grounding

And while the new water line from the street is metal, plastic components have been used to connect the new pipe coming to the home to the water pipes inside the home. The grounding conductor attached to the pipe on the house side of the plastic pipe is effectively no longer connected to the incoming water line–to either of the metal pipes.  Both would still likely be required to be used as grounding electrodes for the home’s electrical system.

Repairs will not be difficult, but needs to be done to provide proper grounding of the electrical system.

By Charles Buell, Real Estate Inspections in Seattle

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