Inspecting Electrical Panels
By far the most dangerous part of an electrical inspection, and one of the most dangerous parts of the inspection process, is inspecting the interior components of load centers, more commonly called “electrical panels.” The hazards are electrical shock, electrocution, fire, burns and eye injury from flying debris.
Although amperages are typically higher in main panels, both main and sub panels contain energized conductors of potentially lethal amperage.
Personal Protective Equipment**
Personal protective equipment for inspecting electrical panels consists of safety glasses, footwear with rubber soles, and gloves. Electrical gloves are made of rubber and are rated according to the maximum voltage for which they will provide protection. The category most appropriate for home inspectors is 00, which provides protection up to 500 volts AC. Proper fit is important for maintaining dexterity. Leather gloves will offer some protection but are not as safe as electrical gloves. Rubber-palmed fabric gloves are the least protective.
Inspectors performing commercial inspections should consider the increased protection provided by other categories:
Class 0 - Maximum use voltage of 1,000 volts AC/proof tested to 5,000 volts AC.
Class 1 - Maximum use voltage of 7,500 volts AC/proof tested to 10,000 volts AC.
Class 2 - Maximum use voltage of 17,000 volts AC/proof tested to 20,000 volts AC.
Class 3 - Maximum use voltage of 26,500 volts AC/proof tested to 30,000 volts AC.
Class 4 - Maximum use voltage of 36,000 volts AC/proof tested to 40,000 volts AC.
The first exposure to potential danger comes from coming into contact with the metal panel, and they are all metal. It is possible for an energized conductor inside the panel to come into contact with the metal box, so that the entire panel becomes energized. When this is the case, the panel exterior surface becomes hazardous to touch. Before touching a panel an inspector should first test it with a voltage detector. These devices are inexpensive, small enough to carry conveniently and easy to use.
You may hear them called by a variety of names; voltage sensor or sniffer, or tic tracer. These devices can be used to determine whether the surface of an electrical panel has become energized.
Voltage detectors should always be checked with known live voltage when beginning an inspection. Without first confirming that the detector is working, an inspector may fail to detect an energized panel. Some types of voltage detectors will not work properly unless the person holding it is reasonably well grounded. If the detector is tested while the inspector is well grounded, but for some reason when testing the electrical panel the inspector is not well grounded, such as when they’re wearing rubber-soled shoes or standing on a rubber mat, the detector may fail to detect voltage present on the surface of the panel.
Upon finding an energized panel, an inspector should abandon the idea of inspecting the panel, post a warning tag in a conspicuous, nearby location, do their best to warn all those involved in the transaction as soon as possible that a dangerous condition exists, and recommend both in the written report and verbally that the condition be corrected immediately.
Removing Panel Screws
Once it has been determined that the panel surface is not energized, the next step in the inspection is to remove the screws securing the dead front cover. This can also be dangerous. Screws manufactured for securing dead front covers have shallow-cut, closely-spaced threads, reducing the chance that the threads will cut through insulation protecting wires as the screw is withdrawn. It’s not uncommon for the original screws to be lost and for improper types of screws to be substituted.
In the two photos above you can see the difference between the finer threads on the screw from a Square-D panel and the more deeply-cut, widely-spaced threads of a typical course-thread screw. The risk of cutting through the insulation protecting wire conductors may be greater with the threads along the shaft than with the screw point.
As a screw is withdrawn it may trap a conductor against the panel, increasing the chances that the screw threads will cut into the insulation, bringing the energized wire into contact with the grounded metal panel and causing a short. This condition can result in a bright flash and an explosion, which can send bits of metal flying through the air at high speed. Inspectors not wearing eye protection can suffer serious injury or permanent blindness. This type of accident can also result in serious burns.
The photo above shows, starting at the left, a proper dead front cover screw and three improper but commonly seen screws; a particle board screw, a gold deck screw, and a machine screw.
InterNACHI recommends that inspectors not attempt to remove improper screws, but instead, disclaim conditions inside any affected panels and recommend correction by a qualified electrical contractor. Home inspection fees are not lucrative enough for an inspector to justify taking serous risks.
Removing the Dead Front Cover
The dead front cover should be removed carefully, both to avoid contact with energized electrical components, and to avoid tripping any breakers, or knocking them loose from the main bus bar.
Tripping breakers is not necessarily a safety issue, but shutting off a circuit to the home when it’s not expected may make the occupants very unhappy, depending on what devices (such as computers with unsaved information) are connected to that circuit.
Knocking a circuit breaker out of the bus bar is a safety issue. To replace the breaker, an inspector will have to reach into the panel and in both gripping the breaker to replace it, and when pressing it into place, the inspector’s fingers will be very close to the branch circuit conductor connection points on the breaker, and to the main bus bar, both of which will be energized. There is no good choice in this type of situation. Leaving the breaker dangling from the branch circuit conductors will prevent replacement of the dead front cover and represent a dangerous condition to the home occupants. Inspectors should not do this.
Reconnecting the breaker to the bus bar means reaching into the panel, which is not a good option, but which can be made reasonably safe if the inspector is wearing gloves that will provide adequate protection if accidental contact is made with energized components. Reaching into the panel will be safer if the main disconnect is used to shut off power to the main bus bar. This may still create unhappy occupants, but replacing the breaker will be safer. If it is a sub-panel with no main disconnect there will be a circuit breaker in the main panel that can be used to shut off power to the subpanel.
It’s much better to avoid this situation by exercising care when removing the dead front panel.
Inspecting the Panel Interior
Once the cover is off the panel, many energized components are exposed to touch. Inspectors should not insert anything into the panel that will conduct electricity. This includes fingers and metal tools.
There are two reasons that inspectors may be tempted to reach into a panel. One is to move conductors aside in order to read or photograph the label that lists the amperage rating of the panel. These labels are often affixed to the sides of the panel and partially obscured by conductors.
Another reason is to confirm the size of the entrance conductors, or conductors feeding subpanels. The printing on these conductors is sometimes difficult to see due to their position on the side of the conductor away from the inspector, or because of dust accumulated on the insulation. Inspectors should resist the temptation to reach into the panel. Accidents involving contact with energized electrical components can be serious or fatal. Instead, inspectors can comment in their inspection report that they were unable to safely retrieve information such as the entrance conductor or panel amperage ratings. This is perfectly acceptable and not at all unusual.
One of the hazards of pushing conductors aside is that due to a loose connection or a break in the insulation protecting the wire conductor, moving the conductors may cause an unprotected wire to come into contact with grounded components, such as the grounding bus bar or the metal panel itself. This can cause an explosive short circuit, similar to that described in the section on removing screws.
When an inspector is accompanied by someone who may not be aware of the dangers associated with touching exposed, energized electrical components, such as a client, agent, homeowner, or occupant, that person may be tempted to point to an item in the panel that is being discussed, such as a defect of some type. Inspectors should take action to ensure the safety of anyone approaching an electrical panel. This means preventing them from approaching the panel closely, or verbally warning them not to reach toward the panel for any reason, including pointing. They may forget and reach toward the panel anyway, and inspectors should be ready to physically prevent contact. Laser pointers are inexpensive and work well for safely identifying specific components being discussed.
For the same reason, after the dead front cover has been removed, an inspector should not leave the room if there is a chance that someone unfamiliar the dangers associated with touching exposed, energized electrical components may enter the room during the inspector’s absence.
Replacing the Dead Front Cover
In replacing the dead front cover, inspectors will confront the same hazards as in removing the cover, but in addition, if pointed screws have been substituted for proper screws, which are blunt, the point of a screw may penetrate the insulation of a conductor, connecting the energized wire to a grounded component, such as the metal panel, and causing an explosive short circuit. This risk is increased when an overly long screw is used. Although some inspectors carry proper replacement screws, panels made by different manufacturers do not all use the same type of screw.