AC Power Line Problems – a Mystifying Menace, Part 2

As you may remember from Part 1, I was discussing “power line problems”. The list of disturbances listed are all transients, but what are transients? Read on…

Transient: any short-term power disturbance on the power line. All the disturbances listed in part 1 are transient by definition. Transients can either be oscillatory, varying consistently with the frequency, or they can be of the impulse variety.

Oscillatory transients are usually caused by:

            * Lightning strikes – the most common cause of spikes and surges. Lightning is most common and most severe during the summer months, though lightning has even been observed during snow storms! Lightning strikes can render sophisticated electronics in the RV useless or operationally intermittent. In either case, costly. Surprisingly, lightning does not need to strike nearby to reap havoc. A storm miles away could induce spikes that can ultimately reach your campsite pedestal. Lightning between clouds, never directly striking power lines or phone lines, will create large magnetic fields that can also cause surges and spikes in your equipment.

            * Utility grid switching – your friendly power utility company can be responsible for creating spikes and surges simply by switching high power distribution lines. Power lines can also pick up transients from power company operating equipment.

             * Campground pedestal hook-ups – even the power pedestal located in your favorite campground can be the source of transients. Many RV campgrounds and destinations sites were constructed some time ago when demand for current was not as prevalent as today. RVs of yesteryear rarely used a full 30 amps of current draw and 50-amp service was unheard of. With today’s larger RVs demanding more power to operate the modern conveniences we have come to expect, many older campgrounds are simply electrically undersized and outdated. When demand is high for current in an overloaded campground, the power sags or dips drastically. Power line transformers on the grid compensate when low voltage is sensed by raising the voltage. When the demand for power sufficiently loads that transformer, all is well, but when the load is slight, the voltage could remain at dangerously high levels.

Impulse transients are usually caused by:

       * Faulty wiring, (loose connections) – common in campground connections and from within your own RV.

        * Motor load switching

        * Improper grounding or bonding of power lines

According to some electrical industry studies, voltage transients represent 12 to 15% of all AC power line problems with only about 35% of those problems originating from outside on the utility grid. As many readers have personally experienced, and as mentioned above, problems can originate from within the campground itself or from within our very own recreation vehicle. In the campground or at a home base, transients can occur simply from a ground voltage differential between improperly bonded grounds during electrical faults. It is important to understand that given the state of the art of the technology we now employ in RV configurations, all AC power lines, campground phone, cable TV and data communication lines must all be commonly grounded or bonded together to prevent transients voltages from entering sensitive equipment.

One study shows that surges and impulse spikes can occur as frequently as twice per hour in any typical residence; some with peak values at 1,500 to 2,500 volts. In industrial applications, such as in a large campground, they can be more frequent and more severe with spikes as high as 5,600 volts as recorded during lightning storms. A study by IBM in various locations across the United States revealed an average of 50.7 voltage spikes per month. Another study showed that many locales will experience approximately twenty-five power line disturbances per year, 87% of which will probably be sags below 96-VAC. Voltages below 105-VAC can be very damaging to induction loads found in RVs such as the roof top air conditioner.

The bottom line is that electrical disturbances, the so-called “power line problems” are severe, they occur often and the damage can be substantial, which usually equates to expensive. What goes mostly unnoticed is the accumulative effect on sensitive equipment in the RV after enduring spikes, surges, dips, notches, etc. The long term performance deterioration of some delicate components may not surface until later, all the while the equipment performs at a sub-standard level until failure occurs.

So what can be done? One of the best solutions is to have a full-time spike suppressor/surge protector in your RV. A number of suppliers now provide such protective devices for the RV industry. Surge protectors act like an electrical sponge of sorts, absorbing excess voltage, thereby protecting your RV. RV surge protection should include the ability to completely shut off the incoming power before damaging transients can reach sensitive equipment. Additionally, they should have the capability to monitor and detect high voltage and low voltage conditions and to interrupt the incoming power until the system has returned to safe levels over a period of time.

Most surge protectors utilize MOVs, (Metal Oxide Varistors) to protect against transients voltages. The quality devices usually have a minimum of three MOVs in the circuitry. More sophisticated protectors, such that might be used on a computer system inside your RV have what is called sine wave tracking which actually tracks the incoming AC signal and literally cuts off the top portion of the wave. It provides better protection for highly sensitive, usually expensive equipment. The key to this technology is determined by the “clamping voltage rating” also called the “let-through voltage rating.” The lower the rating, the better the protection. Sine wave tracking protectors have a remarkably tight clamping voltage surrounding the incoming power line sine wave.

Many companies extol the Joule Rating of their surge protection device. A “joule” is a measurement of energy that indicates the amount of energy that a device is capable of absorbing. The joule rating is primarily determined by the total number of MOVs in the device. Unfortunately, there is no standard for measuring the joule rating of surge suppressors, but generally those with a higher rating are considered better. It is felt by many in the surge protection business that the joule rating of a surge suppressor is less important than the “let-through voltage” rating. Underwriters Laboratories, (UL), has, however, developed a minimum standard for spike suppressors. The surge protector you choose to install in your RV should meet or exceed the requirements of UL 1449.

You are encouraged to investigate the feasibility of adding transient voltage protection to your electrical system. If you truly value the electrical equipment in your RV and are well aware of the consequences, it can be considered cheap insurance at the very least.

And remember, RVing is more than a hobby, it’s a lifestyle!

Gary Bunzer, the RV Doctor.