One of the old adages that applies to power quality is that a little knowledge is a dangerous thing. Sometimes, a little power quality know-how can be truly hazardous in terms of possible loss of equipment, fire and life safety.
While most electrical contractors know better than to take unnecessary risks and shortcuts, electricians often encounter problems in work done by those less knowledgeable. If any DIYers come across this article in their internet research, I hope they will take this advice to heart.
The National Electrical Code defines a qualified person as “One who has skills and knowledge related to the construction and operation of the electrical equipment and installations and has received safety training to recognize and avoid the hazards involved.”
Attempts gone wrong
A recent example of a DIYer run amok came with the addition of a piece of heavy-duty electrical equipment in a garage of a single-family residence. Without carefully reading through the installation instructions, the DIYer, who started out to become an electrician but never carried through to becoming licensed, ran the new cable off another 120V circuit from the distribution panel in the garage. Since the equipment required 240V, this wasn’t successful.
In his next attempt, he went back to the panel and attached a 12/2 cable to two separate single-pole breakers to get 240V. This posed another problem, as part of the equipment also needed 120V. Having only 12/2 cable, he just used the ground wire as the neutral and connected it to the neutral bus in the panel.
A 240V circuit is to be fed from a double-pole breaker set where both breakers are interconnected, so if one trips on overcurrent, they both trip. If only one breaker trips, someone might think the circuit is dead, as the equipment would stop functioning properly, but it would still be dangerously energized.
Grounded and grounding
There is a reason why one wire is called the grounded conductor and the other the grounding conductor. In this situation, current from the 120V circuit would now be flowing in the grounding conductor. Both are connected at one point in the main service panel at the service entrance unless there is a separately derived service. The grounded/neutral conductor is intended to carry current; the grounding conductor is not. Current flowing through a wire with resistance causes the voltage to elevate. The equipment or safety ground on equipment should not have a touch potential. With enough current and resistance, it will.
A widespread issue
This problem is also found in commercial/industrial facilities where distribution panels connect the neutral and ground busses, rather than keeping them as separate circuits back to the main service panel.
In an electronic manufacturing company, workers didn’t run a grounded conductor back to the panel, but rather connected a wire to the building steel with a nut and washer to hold it in place. The problem was that the steel beam had been painted, removing any potential of it being a solid grounding point.
Adding new loads without considering whether they will unbalance the currents is more often a commercial/industrial facility problem with three-phase circuits, but it can also apply to residential 120/240V circuits.
At another job site, the renovation required removing the heating duct to the second floor bathroom and hallway. The architect hadn’t considered that removing several walls and replacing them with beams left no place to run the duct. The proposed solution was a 2-kilowatt electric heater on a 20A circuit, which exceeds the 80% rule. The phase that it was to be connected to already had a microwave, refrigerator and one of the kitchen counter circuits. Having a significant unbalance in the currents can result in excessive neutral current. As before, current and resistance cause voltage. The neutral-to-ground at the point of utilization is generally recommended to be below 0.5V, maximum of 1.0V, for proper operation of electronic loads.
There are countless more examples of good intentions and bad judgments. Plugging computer equipment into surge-suppression outlet strips can give people the false confidence that their investments are fully protected against lightning. They should only be UL or equivalent listed devices with fuse protection, and they should never be plugged into an extension cord. In an area with frequent lightning storms, they should be replaced periodically, because each time they do their job and clamp the voltage, they lose some capabilities. All communication connections should also be protected against excessive voltages, as that is another path for lightning, especially in networked applications.
Header image: stock.adobe.com / kengmerry
About The Author
BINGHAM, a contributing editor for power quality, can be reached at 908.499.5321.