Early 2022 has brought unusual electrical troubleshooting calls similar to what ERs and jails experience before or during full moons. Though scientifically unsubstantiated, many people working in such environments will tell you that behavior becomes erratic. The word “lunatic” even derives from the Latin “lunaticus,” which means “of the moon” or “moonstruck.” From lights that dim and brighten on their own to appliances that suddenly stop working, then work again with no repairs made, it has been an interesting time.

The most recent situation has likely been an issue for some time, but it made itself known to the homeowners during a full moon. It also serves as a lesson on a not-so-uncommon source of power quality problems.

The call came on a Sunday afternoon from a customer who was visiting his in-laws. They smelled something burning in the dining room, but didn’t see any visible smoke. They also had issues with the microwave over the previous week, where it would refuse to operate properly some days, yet worked on others.

He turned off the breaker that served the circuit where the microwave was plugged in, or better described as the power outlet strip that the microwave was plugged into. This was an on-the-counter microwave in a kitchen with inadequate receptacles and circuits for the kitchen appliances, hence the power strip. Although the National Electrical Code 210.23(A)(2), Utilization Equipment Fastened in Place doesn’t directly apply to this scenario since it limits fixed equipment current to 50% of a circuit shared with lighting or other equipment not fastened in place, the manufacturer’s instructions often require a dedicated circuit, according to the NEC.

Something was wrong

The receptacle the power strip was plugged into was on the same circuit that was in the dining room where the smell of smoke was noted. After verifying that the circuit was off, the receptacle’s cover plate was removed. The smell was much stronger, and a quick visual confirmed something was very wrong. Bare copper wire and melted insulation were visible on the line conductor. Carefully removing the receptacle and pulling out the connected wires revealed them to be copper pigtails to aluminum wire.

The result after removing the yellow wire nut on the junction can be seen in the picture above. Based on the damage to the insulation of the copper and aluminum wires, along with the discoloration of the wires and the tapered coiled metal insert left behind when the plastic cap was twisted off, it is clear that this connection experienced significant overheating. Fortunately, this was discovered before resulting in an electrical fire.

Power quality issues

This illustrates a source of power quality problems from improperly connected conductors. The generalized and often-quoted statistic is that approximately 70% of power quality problems originate within a facility, and of those, 25%–30% are due to improper wiring or grounding issues. One example is an improperly made connection between two conductors, which could be wires or busbar. This is part of the reason for the recommendation in NFPA 70B, Recommended Practice for Electrical Equipment Maintenance, to periodically retorque the mechanical connections of busbar and breakers (when de-energized).

Wiring problems

Improperly connected copper and aluminum wire connections result in heat being generated as the impedance of the connection goes up. When a significant level of current is conducted through the connection, the aluminum and copper wires expand differently. When the current level goes down and the wires cool, the tightness of the connection is reduced. The heat also increases oxidation (an insulator) of dissimilar metals. These further raise the connection’s impedance.

In power quality problems, the voltage drop across this connection increases, resulting in less voltage downstream for the loads. Increased voltage drops also mean more power lost in the connection from the same current level and even more heating. This cycle continues over and over again, resulting in a larger voltage drop and increased heating until the insulation starts to melt. This is the basis of the statistic that residences with older technology aluminum wire (prior to the 1980s) have a much higher risk of fire than all copper-wired structures.

In the scenario in the photo above, it is evident that there was no proper wire-splicing technique, and no UL-listed purple wire connectors used between the aluminum wires and the copper wire pigtails. Exposed wire shows below the neutral connections with a nick in the conductor from improper insulation removal. An electrician was called in to repair the damage and properly connect the wires, as well as check for and correct other such issues in the house. Fortunately, this story ended well for the homeowners.

Header image by Richard P. Bingham.