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

Do I invite the wolf in—or try to keep him out?

Do I invite the wolf in—or try to keep him out?

Everyone knows the story of the three pigs. From that story, we learned that we should all build our houses out of brick if we are to keep the wolfs at bay.

disintegrating brick columnOur houses have to deal with all kinds of wolfs. There are water-wolves, earthquake-wolves, tornado-wolves, wind-wolves and the dreaded lightening-wolves.

No matter what we build our houses out of, they all need to be maintained or the wolf WILL get in.

This house wasbuilt in 1902 and I discovered, much to my buyers chagrin, that the wolf was having his way with the brick foundation. Those pesky mortar-wolves were patiently eating away at the foundation. Almost anything after 116 years would likely show deterioration and certainly all three of the pigs are dead by now regardless of their choice of building materials. The brick foundation has done its job quite well considering the number of significant wolf-quakes it has stood up to.

But now it is likely beyond repair—or at least extensive repairs that would amount to a new foundation will be necessary. The mortar joints and bricks are crumbling and some beams are no longer supported at all.

Unsupported beam and collapsed brick

Unsupported beam and failed brick

Unsupported beam and failed brick

Unsupported beam and failed brick

Someone will have to make a decision as to whether to let the wolves have it—or to try and keep them at bay for a few more years.

By Charles Buell, Real Estate Inspections in Seattle

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Would you keep all the windows open with the heat on in your car?

Bet you didn’t know you are heating and cooling a wind tunnel!

Certainly the biggest contributors to moisture in the attic are breakdowns in the building envelope. (Of course I am assuming that water is not getting in from outside the envelope–like a leaking roof) These compromises also make the building less efficient and will empty your wallet more as you attempt to heat and cool your home/tunnel.

air bypasses To understand this problem, it is helpful to think of one’s house like a Tupperware container. Clearly if we leave the lid a little bit ajar (like an attic access that is not weather-stripped), or start drilling holes in the bottom, sides and top, the container will no longer do its job–or at least less efficiently—relative to the number of holes, the size of the holes and where they are located.

Of course, if the holes are so the snake (or whatever else the kid catches) does not die, that is another matter.  It is still important to keep the lid on though.

There are other factors–but let’s keep it simple for today.

We can build the most super-insulated house in the world but if we don’t control air movement in and out of the building our efforts at insulating can be wasted.

One of the most common, obvious, everyday sort of “by-passes” that I see in homes is dampers in fireplaces that are left open. These chimneys will pull conditioned air from the home 24/7–with an occasional pause for atmospheric inversions that can happen. The screen on the fireplace filling up with lint is the first clue that this is happening. Even closed dampers in most cases will not stop this movement entirely.

Eliminating open flame solid fuel appliances altogether is a good idea in the context of building more energy efficient homes.

I have heard people argue that this natural draft is a good way to exchange the air in the home–without a mechanical fan. The truth is that this works–but at much greater cost than running a simple exhaust fan periodically. It is the 24/7 aspect of the chimney that makes it a problem, as it vents conditioned air that we are also paying for. On a windy day the venting might be much more than on a still day. We need “control” over this air exchange if we are truly going to control energy use as well as maintain a healthy indoor environment.

I want to stress that this is a LOT more complicated than I am willing to address here. For example rates of ventilation will not always guarantee good indoor air quality. While outside air is generally of better quality than indoor air, that is not always the case and in some areas of the country, outside air is becoming worse every day. At some point the political aspects of outdoor air quality will be forced to reconcile with the private aspects of indoor air quality. Some will argue that if you want “quality” drinking water you had better be prepared to solid-block-carbon-filter the water where it comes into your home. The same thing is perhaps coming for the air we are bringing into our homes.

Welcome to the 21st Century.

Back to air by-pass issues.

As previously mentioned, the attic access hatch is a common by-pass but the list is almost endless. Here is a partial list of some common breaches: plumbing pipes running through walls and ceilings, can-lights, HVAC equipment/ductwork in attics, crawl space hatches at the interior of the home, wiring holes in top and bottom plates of walls, chimneys, b-vents, improper framing techniques, skylights, pull down stairs, drop ceilings, exhaust fans etc.

“Stack effect” is something else that affects our homes.

Stack effect is relative to temperature/pressure differences. It is relative to the fact that warm air is buoyant. It is further driven by the lowering of pressures inside the home which then allows for air to be pushed into the lower levels of the home (from outdoors and/or crawl spaces). The taller the home, the more pressure differential as the buoyant air moves to the exterior (attic) of the home, bringing with it the moisture in the air. The colder the outdoor environment and the taller the building the more that hot air will be trying to get into the roof structure or outdoors to get to that cold. Perhaps the perfect storm is to have a leaky floor system over a vented crawl space in conjunction with serious breaches in the attic floor.

In this scenario you can think of your poor heating system as attempting to heat a wind tunnel. You will have to be willing to throw a whole bunch of energy at this wind tunnel in order to feel comfortable in your home.

In a very well sealed home there will be less stratification of temperatures and less “driving” of the stack effect–even when doors at the lower level are opened. Opening and closing windows on upper and lower levels in conjunction with each other is a way to manually control stack effect to change the air in the home. This is not rocket science, but can be as expensive as rockets.

At an inspection a while back I had one of the most egregious examples of a home with a functional wind tunnel. The defect was created when part of the forced air heating system was removed. If you could zoom in on this picture, you would be able to see the furnishings in the room below. There were three of these vents into the attic. The missing insulation around the vent is not even consequential in relation to this breach.

Closet vent open to attic

Closet vent open to attic

Sealing these air by-passes, even in older inefficient homes, can drastically reduce heating and cooling costs. Remember , heat tries to get to cold and high pressure moves to areas of lower pressure. So if the attic is really hot in the summer and we are cooling the home we have made the job of the AC unit all the more difficult. Better sealed homes accounts for why the size of heating and cooling systems have halved since the 40’s–remember—back when oil was free?

Sealing and eliminating all kinds of air by-passes is perhaps the most important thing we need to do in making our houses more energy efficient. Insulation alone will not do it and in fact in many cases will only filter the air as the air moves through it. This is especially true of fiberglass insulation–even 18 inches of it. All air by-passes must be found and sealed (or otherwise eliminated) prior to insulating. Choosing types of insulation that are in themselves good air barriers is also recommended.

By Charles Buell, Real Estate Inspections in Seattle

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