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Part 4: Most Common Causes of Failure in Electrical Service Equipment

Time: Approximately 1/2 Hour

Do you know what the root causes are for most catastrophic failures in residential electrical services? 

Let's walk through a typical residential electrical system from beginning to end looking at the common failure points and failure modes along the way.

1. Service drop or service lateral

Service drop conductors are exposed to the weather, trees, animals, and even vandals who think it is fun to shoot at transformers and watch them explode.  Underground cables and conduits are subjected to movement of the earth, overhead traffic, and frost.

The wire that supports the service drop conductors is the Grounded, or Neutral conductor.  It is also called a "messenger" cable or messenger wire.  It is not a cable in the way that the word "cable" is usually defined in the electrical construction industry.  The word "cable" has different meanings even within the same industry.  In the case of a messenger cable it is used in the same way that a rope is sometimes referred to as a cable.  A messenger cable is any type of rope that supports a wire or cable that is not capable of supporting itself.  In electrical construction, messenger cables for service drops are usually stranded steel wire rope. 

Steel messenger cables are extremely strong.  They can withstand an amazing amount of abuse.  They are usually also galvanized to protect them from corrosion.  It is not impossible, however, for a steel messenger cable to fail.  When they fail the results can be catastrophic. 

In the past, the service drop conductors were owned by, and were the sole responsibility of, the electric utility company.  The home owner's responsibility started at the point where the service drop conductors attached to the service entrance conductors.  In recent years, some electric utility companies have shifted the transfer point of ownership and ultimate responsibility to the utility pole. The home owner is now ultimately responsible for something that can only be maintained by a highly trained professional.  Of course the utility companies usually continue to maintain the lines but the homeowner may have to pay for materials and labor.  In the case of underground services, many utility companies have made the service lateral conductors the sole responsibility of the home owner.

Inspecting the service lateral conductors is beyond the capabilities of even the most sophisticated home inspectors.  They are completely hidden from your view.  If you are in an area where you know that the service lateral is the responsibility of the home owner, I suggest recommending that a preventive maintenance inspection be performed once every five years.

Sometimes you can see a set of service drop conductors very clearly and sometimes you cannot.  Use your binoculars to look for evidence of damage to the conductors.  The insulation on the ungrounded (hot) conductors is a tough plastic but not tough enough to withstand constant rubbing against tree limbs.  Look for barrel splices.  Barrel splice, especially in the messenger cable, can be a weak point.  Barrel splices are allowable.  you cannot cite them as a defect or a deficiency but you should be aware that they are in wide spread use and they do fail.

I would be more concerned to see a barrel splice on a messenger cable that runs below a large tree limb than one that is clear of trees.  A lightning strike can easily take down a limb on a large tree such as a cottonwood.  I wouldn't want to have a 20" diameter cottonwood limb fall on a messenger cable with a barrel splice in it.  True, the odds are that it will pull the service completely off the house but, what if it breaks the neutral?  You will have 240V across all your 120V circuits. 

2. Service entrance conductors and point of connection to the utility company

Everyone knows to look for a proper drip loop and to check that the weather head and insulator are properly installed.  One of the most dangerous electrical deficiencies often goes unnoticed. 

Whether the service entrance conductors are in conduits from above or below are they are service entrance cables from above or below, they are subject to physical damage.  One common, and particularly dangerous, failure point that is all too often overlooked is where a service entrance cable makes tight bend to enter through the outside wall of a house.  Cables deteriorate and are abraded by movement of the house and the cable over time.  You need to look very closely at the radius and every other point along the service entrance cable.  Damaged cables can cause both fire and shock hazards.  Look at them closely.

Underground cables and conduits can be damaged by improper grading and other mechanical forces.  Look very carefully for any signs of stresses on the conduits of cables.  Sometimes they are easy to spot because the meter socket will be loose, tilted, or even pulled away from the house.  This is not merely a matter of the way it looks.  There can be potentially very serous problems in the sealed meter socket that you are not going to be able to see.  I consider these to be very serious construction defects that require repair.  You will often hear things like "Oh that, it's been that way for years".  As the home owner is telling me this, I'm thinking, "Yeah, well people are still having their legs blown off by World War 2 land mines too".  I don't know about anyone else but I surely don't want any kind of bomb in my backyard. 

3. Meter enclosure

Aside from the problem of meter sockets being moved as I described in the previous section, there are other things that you need to be aware of.  As a side note, I haven't actually counted the number of times I have encountered different types of problems but I think I am safe in saying that I have encountered far fewer serious problems with overhead services that have the service entrance conductors in conduit than any other arrangement.  I've seen the greatest number of problems with underground services.

The two most common problems with service entrance conductors are really the same; the only difference being that one is conduit and the other is cable.  The problem with cable is that the grommet that seals around the service entrance cable is rubber and over time it can become hard and brittle.  Small cracks develop allowing water to seep in.  A variety of factors will influence how long the grommet will last.  In hot dry climates such as Las Vegas and Phoenix, a meter mounted on the south side of the house in the the direct sun is likely to fail long before a similar grommet would fail on the north side of a house in the Great Lakes area.  The grommets should easily last twenty years or more but, as with anything else some fail prematurely. 

A bigger problem is with side entry conduits.  There are may right ways and many wrong ways to do almost anything.  Side entry conduits should always use a water tight threaded hub (such as a Myers Hub as shown in the drawing) or gaskets.  There should never be side entry conduits into a hole with non-gasketed reducing washers, EMT (thinwall) with a set screw connector, or either rigid or intermediate (IMC) conduit with only standard locknuts.  These are all signs of an an amateur at work.  Improper connections side entry entry of either conduits or cables can allow water into the meter socket which in turn could lead to catastrophic failure of the meter socket.  

4. Main panel

The electrical service panel is the heart of an electrical system.  An electrical system can fail at any point in the system but it is the main panel that carries the full electrical load of the entire house.  A failure in the service panel can start a fire, create a shock hazard or leave the house without electricity.  Without a properly functioning main panel the electrical system is useless at best and a downright hazard at its worst.

It might surprise you then to learn that in am not in favor of home inspectors opening electrical panels.  I know, many of you are thinking this is nothing short of heresy!  How can we possibly be home inspectors and not open the main panel!

Here's the problem.  Opening electrical panels can be very dangerous - very, very dangerous.  I spent many years opening panels and working on and around live electrical systems.  I am very comfortable getting up on a ladder and making a live changeover in a snow storm or in sleet and freezing rain.  The fact is, I'd rather be on a ladder working on a live changeover than getting into an electrical panel.  I could tell you stories of things that happened during my years as an electrician that I'm sure most you you would not even believe.  But - believe this- my worst experiences, my most frightening experiences, and the only injuries I've ever suffered in the trades have all been the result of getting into panels.   

The only reason I am alive today and the only reason I have my eyesight today is because of the training I had while working on live systems during my apprenticeship.  On one occasion, I lost my eyesight for about ten minutes.  It was the longest ten minutes of my life.  An explosion in a panel sent a screwdriver flying from my hand with such force that it landed a hundred feet away and left me temporarily blind.

On another occasion a explosion in a closed panel with the cover on burned my arm and face and was so loud that people from a city block away came running to see what had happened.  This is a long story but I am going to give you the bare essential facts.  What had happened was that I had been called to do a service call.  I turned on a molded case breaker in a panel.  The flash that burned me was the part that escaped through the very small gaps between the breakers and the cover which was securely in place.  Fortunately, I do as all electricians do when they throw a switch.  I turn to face away from the panel.  Had I not done that I would have had burns that would have left me seriously scarred.

Not only have I experienced these things myself, I have witnessed others being injured in explosions and electrocuted.  I once saw an electrical cable gently touch a man's arm.  He dropped straight down without so much as flinch or a sound.  He lived but the current shattered the bone in his arm and permanently damaged his muscles.  I once had an electrician who worked for me who was the most careful, most meticulous electrician I had ever met.  He was one of a very large crew I had on a project. I approached him one day to compliment him on his work.  I told him he set a great example for the younger electricians.  He sold me that he had not always been that careful.  After a panel exploded on him and he spent more than year in a hospital bed, he told me it gave him a whole new perspective.  He developed a respect for electricity that he had not had before.

This is a course about inspection not about safety, right?  Wrong!  It is all about safety.  It is about the safety of our clients and it is about our safety too.  I don't expect any one taking this course to stop removing panel covers during inspections.  It is part of what home inspectors do.  That does not mean that I have to agree with the practice.  Nor, do you.  What I do expect you to do is to stop for a few seconds while you are standing in front of the panel and think about it before you remove the cover.

Here is what I want you to think about and to do:

1. Inspect the main panel last, after you have inspected the other parts of the electrical system.  !  The reason is that by the time you get to the panel you will have an overall feel for the electrical system in the building.  That will help you with your assessment.

2. Look to see if there are signs of corrosion anywhere in or around the panel?

3. Look to see if there are any signs of amateur or sloppy workmanship anywhere in the electrical system.  Have you seen the types of things that could be hazardous to you if there are similar problems in the panel.

4. Look to see if there are there any screws missing from the cover or is the cover misaligned?

5.  Look at the sides to see if any wires are visible.  Amateurs and careless electricians often pinch wires between the tub and the cover.  Pinched wires can energize the electrical components or you.

6.  Look for cables or wires that are not properly enclosed in a conduit, or attached with a proper connector.  Just as with pinched conductors, you don't want to open a box with conductors that may be cut and could energize metal components or you. 

7. Ask everyone to stand back away from the panel before you remove the cover.  Ask them to turn to face away from the panel.

I have one final thing to say related to safety before we move on.  Do you know how much current can flow in an electrical fault in a typical house.  Let's say the main breaker is rated at 200 amps. Is that how much current flows.  What about the branch circuits.  They typically from 15 amps to 50 amps. How much current can flow in each of them during a fault?  What about a small commercial building?  I'm not going to give you the answers here.  I'll save the answers for our classroom or live online sessions.

Ok, so, now that we are finally in the panel, what can we learn from it.  There are a few good things I can learn about an electrical system from the panel but not as much as I can learn elsewhere in the electrical system.  the termination of grounded, ground and grounding conductors is so widely discussed on home inspection message boards that I doubt there are many inspectors who are not already aware of the rules prohibiting landing two or more grounded conductors together under a single screw, a grounded conductor and any other conductor, or two or more ground or grounding conductors.  Grounded conductors should always be terminated under a single screw and all others can have more than one where the terminal is designed and approved for the purpose.

The term inspectors usually use to describe the condition of two or more conductors terminated under a single screw is "double tapping".  Just how serious is double tapping?  It can lead to problems; serious problems.  However, double tapping in itself the real problem.

First we need to consider that double tapping can be done on either the ungrounded conductors or the grounded conductors.  There is generally more emphasis placed on the grounded conductors than the ungrounded conductors.  That is reasonable because there are generally more serious consequences to the loss of a grounded conductor in a panel than the loss of an ungrounded conductor.

The real problem though is almost always never discussed in home inspector groups of and is often completely overlooked during inspections.  It is the reason that there are rules against multiple conductors under a single screw in the first place - loose connections.  It is much more meaningful and far more beneficial to check for loose terminal screws.  Terminals screws can loosen over time with or without double tapping.  If you can turn any screw more than a quarter of a turn it was too loose.  The only way therefore, to do a meaningful inspection of the panel interior is to check the screws. 

There are a few important facts that you should know about residential electrical service panels before we move on the next section.

Electricians usually do not put thermal or vapor barriers in electrical conduits entering a house.  Panels are usually located on an outside wall with only a very short piece of conduit between the outside and the inside of the panel.  The conduit is not only a conduit for wires.  It is also a conduit for water vapor and temperature changes.  Changes in temperature, moisture, and corrosion can cause terminal connections to loosen.  Most panel failures are, therefore, caused by moisture and temperature fluctuations; either directly or indirectly.

The main breakers in all service panels are securely fastened in place to prevent them from being blown out in a fault.  Even though they are often described as being bolted in place, they are in fact usually riveted in place.  The breakers cannot be replaced if they fail.  In commercial installations it is more common to use a breaker that is bolted in place and can be replaced.  Breakers should be exercised regularly.  If they are not exercised for many years, they can fail when they are tested.  Breakers that have been tripped too many times can also become weak and fail to reset properly.  For these reasons, electricians will usually either not test a main breaker, will ask the owner to sign a release form releasing them from any responsibility if the breaker fails when it is being exercised, or will ask the home owner to test the breaker.

If you test the main breaker in a house, you are taking on some risk.  The odds are in your favor that the breaker will reset and everything will be fine but the better route to take is to recommend that the buyer ask the seller to do routine preventative maintenance on the electrical system if the seller has not done preventative maintenance within the past five years.  You should recommend that the buyer have the electrical equipment serviced once every five years.

Hourly and Daily Specials
Throughout the Holiday Season

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The Third Course in This Series:

The next course in this series is an EIGHT CEU course.  In this course you will  go a little deeper into the mysteries of electricity.  The concepts are going to be a little more complex so you are going to spend at least eight hours between self study and live online time with this course.

Electrical Basics - ELI the ICE Man

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Electrical Service Types article

http://www.bestinspectors.net/education/electrical-tutorial-service-types.htm

What is Fault Current

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Most home inspectors and many experienced electricians guess at the electrical service size requirements using rules of thumb (usually involving only square footage).  With the rapid growth in the number of electrical appliances and electronic equipment during the past few years, making a guess could be a costly mistake. 

The Residential Electrical Service Size Calculator takes the guesswork completely out of determining the electrical service size requirement.  The Calculator requires no special knowledge of electrical systems or codes.  All you do is make basic observations about the house and fill in the blanks.  The Calculator lets you enter electrical loads in either Amps or Watts.  the required information can almost always be found on the nameplates of appliances and mechanical equipment.

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The Calculator's worksheet can be filled out in about three to four minutes and can be included with any inspection in PDF format.      

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NOTE: This worksheet is intended to be used as a general guide.  It does not account for all possible factors involved in determining the size of an electrical service. Consult a qualified electrician or the NEC® for additional information.

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The calculator is essentially an Ohm's Law calculator.  The difference between the BestInspectors.Net  Voltage, Current and Power calculator and most Ohm's Law calculators is that Ohm's Law calculators are usually geared toward electronics, not power systems.  This calculator is for power distribution systems.  The calculator has a Power Factor component to it.  Most Ohm's Law calculators do not.  Calculations can be performed quickly and easily using name plate data or actual measurements.

The calculator is also a training calculator.  There is a list of relevant electrical terms and units of measure on the screen at all times.  Every time you enter a value, the related terms are highlighted.  Once you have entered the values needed to complete the calculations, the remaining input fields are blacked out so you don't inadvertently enter a conflicting value.  For example, if you have entered Voltage and Wattage values, the Current input field is blacked out so you can't insert an invalid value.  The Current in this case would be among the calculated values in the results section.

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