AC Power Line Problems – a Mystifying Menace, Part 1

We’ve all heard the stories; a roof top air conditioner bogs down and trips the breaker; a television set image is suddenly reduced to a much smaller viewing image; your neighbor plugs his coach into the campground and your microwave oven quits in mid-cycle; reports of a lightning storm in the next county are followed by the lights inside your coach all of a sudden become very, very bright. I could go on, but I think most of you get the idea. The fact is, there are a myriad of electrical problems equally available to all RVers in virtually every corner of North America at any given time in any season. Collectively known as “power line problems,” individually they create a palette of dilemmas that we must be aware of and hopefully protect against.

Why? Quantum leaps in RV electrical technology over the years has resulted in many components in our coaches now being controlled by electronic boards and microprocessors. Additionally, the  e-mail form of communications (and blogs, obviously) have well-permeated the general RVing public. Fax/modem applications, CATV (cable TV), connections and on-board telephone connections are quite common. There exists many “smart” devices controlling everything from RV washing machines and battery chargers to VCRs and microwave ovens. Face it, we are firmly entrenched in the microprocessor and electronic age of RVing. Now with the push of a single button you can even deploy a full-length patio awning, or extend a room addition, all using electronically controlled circuitry. Power line problems are no longer just a concern for the computer industry.

The AC power line, manifested at that campground pedestal or the AC receptacle you plug into while at your home base, is the tethered life blood for all things AC and many items DC in the RV. But it can also be the pathway for a mystifying menace that can render useless many components found in the coach. Let’s take a detailed look at some of these power line enigmas and how to protect our hi-tech recreational investment from potential disaster.

Oftentimes we read in an article or hear in an electrical seminar, terms such as spike, sag, dip, surge, etc., with precious little in the way of full definition. To truly understand alternating current power problems, familiarize yourself with the following definitions.

Steady-State Voltage: normal voltage planned for a system that stays constant for ten seconds or longer. RV applications require 120-VAC at a frequency of 60-Hz, usually providing 30 amps of service for most RVs. 50-amp service simply includes another leg, or phase, of 120-VAC also at 60-Hz. (Hertz or Hz, is the unit of electromagnetic frequency for the change in cycle in alternating current. Hertz replaces the older term of “cycles per second,” or cps).

Power Failure: a zero voltage condition lasting for more than one cycle (1/60 of a second). From a power grid standpoint, it could happen on any of the three phases being delivered.

Dropout: a portion of the sine wave that has a lower value or is missing altogether, but only for a small portion of any given cycle.

Blackout: a total power failure lasting several seconds to many hours.

Brownout: a planned and usually announced region-wide reduction of available steady-state voltage. Typically associated with an impending expectation for heavy electrical consumption.

Sag: a cycle-to-cycle reduction of power line voltage of at least 10% of the average voltage for half of one cycle or longer. A sag might occur when your RVing neighbor first turns on his roof top air conditioner. Sags are detrimental to electronically controlled devices such as microwave ovens, television sets, DVD players and VCRs.

Dip: a faster sag. Dips are short decreases in the nominal line voltage, but are much quicker than a sag. Usually only visible in an incandescent light bulb.

Notch: similar to a dropout though typically too fast to see. They can be up to several milliseconds in duration and usually come in pairs. For every notch there is usually an immediate spike following behind. A notch is simply an out-of-phase impulse, (see impulse below).

Surge: the opposite of a sag, surges are cycle-to-cycle increases in the voltage on any of the three phases above the normal voltage but typically below 500 total volts. The lasting time of a surge is equal to its duration for the number of 60-Hz cycles that the power line disturbance is above normal.

Swell: basically a series of long term surges that lasts form a few seconds to several minutes.

Impulse: a very short disturbance of either polarity, (up or down), superimposed on the AC sine wave that lasts between .5 and 100 microseconds. In-phase impulses which instantaneously increase the voltage are called spikes. Out-of-phase impulses which decrease the voltage are notches.

Spike: an in-phase, over-voltage impulse ranging from 400 volts to well over 5,600 volts! Such an impulse is superimposed on top of the AC sine wave and typically lasts for less than 1/000^th of a second, (one millisecond). Any spike over 600-volts can be very damaging. Spikes contain high amounts of energy and are most detrimental to sensitive circuitry.

to be continued…

Gary Bunzer, the RV Doctor.