What is power surge? A power surge is a temporary unexpected increase in the voltage or current into an electrical system that can be caused, for example, by lightning or utility switching operations. Often called a transient overvoltage, a power surge occurs over a very small time interval in the form of a high or low frequency transient sinusoidal waveform that is capable of causing damage to the electrical system and any loads (components) that might be connected to (and thus draw power from) the electrical system.
Nelson was retained in a matter to determine the extent of damage at a medical outpatient facility that was reportedly caused by a power surge. At the time of Nelson’s site visit, the subject structure’s electrical system had only partial functionality.
Nelson conducted an interview with the facility operator, who reported the following: Over the weekend, lightning affected the office building’s electrical system. Over this same weekend, a painter and his assistant were painting inside the building. On Monday, only certain lights within the building worked when turned on (Figure 1). There were two light switches located on the left wall when entering the office building’s front door. The first light switch originally had a locking mechanism over it and was always in the on position. This locked light switch had never been toggled since the purchase of the building. On Monday, this subject light switch was found in the off position with the lock removed and missing. It was later determined that the painter had removed the lock to paint and had turned the switch off when leaving the building (Figure 2). The office manager turned this subject light switch on, heard a “growling” noise, then immediately turned the light switch back off. The facility operator contacted two separate electrical companies to investigate. Both electrical companies claimed the entire subject structure’s wiring needed to be brought up to code and replaced. One had quoted $50,000 for the work, while the other quoted $35,000. The office building (and thus its wiring) reportedly dated from the 1960s.
Figure 1: Interior of building with partial lighting
Figure 2: Subject light switch with lock attached
Nelson visually evaluated the disconnect and electrical panels located in the rear of the building (Figure 3). No anomalies consistent with a power surge such as burnt wiring, scorch marks, and/or melted plastic were found. These panels, consistent with having been installed in the 1960s, were functional. One of the panels was a Square D Magnetic Starter (Figure 4). A magnetic starter is an electromagnetically operated switch, used in motor applications, which provides a safe method for starting an electric motor serving a large load. Having this magnetic starter was perplexing, as there were no motors in the building associated with it.
Nelson went to the front of the building and toggled the subject light switch to “ON”. At that moment, a sound was heard at the electric panels and the lights at the front of the building turned on. Nelson went to the magnetic starter panel and noted that the light switch when toggled to “ON” supplied power to its starter coil.
This magnetic starter was comprised of a set of stationary contacts, a set of movable contacts, a solenoid coil, a stationary electromagnet, pressure springs, a set of magnetic shading coils, and a moving armature (plunger).
Figure 3: Electrical panels consisting of disconnects, circuit breakers, and magnetic starter
Figure 4: Close up of motor control magnetic starter with cover removed
When the magnetic starter’s starter coil was energized, by closing the light switch, it started the flow of alternating current through its current windings. This current flow created a magnetic field around the coil. This magnetic field created a magnetic force that pulled a moving plunger toward the stationary coil. This in turn moved a set of contacts connected to the plunger from the normally open (NO) side set of stationary contacts to the normally closed (NC) side set of contacts. When the plunger’s set of contacts contacted the NC stationary contacts, a closed circuit was created that energized three separate 20-ampere electrical branch circuits that fed power to various lights and/or receptacles throughout the building including the front (Figure 5).
Figure 5: Simplified magnetic starter circuit schematic controlled by a light switch
While on the premises, Nelson conducted a phone interview with the building’s prior owner, who reported that: He had purchased this building in 1977, selling it to the current owner (the insured) in 2013. The subject building was originally built in 1962 and used as a physician’s clinic. Inside this building, the doctors had operated heavy x-ray machinery. For safety reasons, the subject light switch had been configured to power off the x-ray equipment when the doctors left the building. It was later re-configured after the x-ray equipment was removed to power branch circuits and a lock was placed on the subject light switch so that these branch circuits remained ON.
Based on reported information and observed conditions, Nelson concluded that there was no evidence of a reported power surge and that the partial lighting outage inside the subject building was due to a modified electrical circuit controlled by a light switch being toggled to the off position.
The existing electrical system was functional and in perfectly fine condition and there was absolutely no need to outlay $35,000 to $50,000 on a new electrical system when the existing system could be “fixed” at the flip of a switch.
