The Circuit Detective    -  Special Switches

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Problems With Some Automatic Home Electrical Controls


For problems with most other wiring, circuits, and connections, be sure to see my Main pages. This page is about some specific automatic home electrical controls (switches) whose features have implications for troubleshooting them or their circuits. Two similar pages address some specific Appliances and Devices.

Dimmers
Generator switches
Motion sensors
Photocells
Thermostats
Timers
X-10 switching

Dimmer switches. A dimmer saves some electricity and bulb-life. Dimmers normally produce some heat when operating. (My rule of thumb is that if you can keep your thumb on the cover-plate screw without fear of getting burned, this is normal.) Unless rated to handle more than the usual 600 watts, a dimmer controlling more than 600 watts of lighting will get hotter than it is designed for, will not last long, and could present fire hazard in some conditions. Most dimmers have electronic components that are vulnerable to surges. My experience suggests that fancier dimmers that display their setting level or that stand ready to respond to the simple touch of a finger are even more likely to be damaged, from a surge or from a light bulb burning out. Specially rated dimmers are needed for low voltage bulbs; only some are meant for use with LED bulbs or certain fluorescent bulbs/tubes/fixtures.

Generator switches =Transfer switches. These panels or switchboxes are meant to make powering some of a home by generator foolproof. Rigging your own way of interfacing the two power sources is virtually illegal. The switching setup varies with the size of generator and the number and size of circuits to be potentially run by the generator. Some even operate automatically when an outage hits, starting the generator in the process. In the cases I am aware of, either individual circuits, a subpanel of circuits, or an entire main panel are fed power through the switch(es) from either the local utility or from the generator. So even normal power on a mild day has to pass through the switch(es) to reach the circuit(s). This means that a transfer switch that is turned or knocked off unknowingly will disrupt some power on a day no one is thinking about the generator. Since people are trained to check, at the most, main-panel breakers and GFIs when they lose power somewhere in the house, the generator box gets overlooked.

Another little problem shows up if one of the circuits run by the generator has a GFCI or AFCI breaker in the main panel and there is a transfer switch for that individual circuit. When utility power comes on while the generator is still running this circuit, the GFCI or AFCI breaker, being now energized, will use its ground-fault sensitivity to notice if some load current is on the neutral wire (which is not isolated) and will notice that none is yet flowing on its hot wire (which is still isolated from the circuit). Since that would constitute an imbalance, the GFCI or AFCI breaker would trip, so that when you transferred everything back to utility power, suddenly the circuit in question would not be working and you would have to reset the breaker. But no harm done.

Motion sensors. Lights that have a motion sensor to switch them typically have the following features. Motion is sensed from the heat emitted by people, animals or cars within the field of view of the device. They also sense light so as to prevent operation during daylight (this feature can be bypassed when using a "test" mode). There are usually settings for how sensitive you want them to be (equivalent to the distance away it will sense motion, I believe). There is also a setting for how long they keep the light on after motion is sensed or after motion stops.

So when a problem arises with a motion activated light, check all these settings and of course the light bulbs themselves. One common feature is that a brief interruption of power to the sensor light (and you can do this purposely) may program it to stay on indefinitely or at least till the next dawn. To escape this mode usually involves turning power off for a longer time before restoring power.

Being electronic (and some being cheap), motion sensors die, often within five or ten years. The sensor part may be replaceable, but whole fixtures that incorporate sensors are very common, and many are cheaper than a separate sensor.

Photocells = photoelectric cells = photoelectric eyes. Some, but not all, photocells, which turn lights on at dusk and off at dawn, are rated to control quite a few lights, including fluorescent. When they fail, the result is commonly that their lights stay on all the time. Of course, if shrubbery has overgrown the area of the photocell or if paint or algae has accumulated on its "window", then the lights could be staying on or staying on later into the morning for these reasons.

Thermostats. Zonal electric heat provides thermostatic control for each heated area. Typically, these "stats" are factory calibrated so that the temperature settings stated on them correspond to the actual temperature they will maintain in the room. There will still be a lag of two or three degrees as the heater continues working before its heat has had a chance to affect the stat, or as the heater waits to come on because the coolness of the room air has not yet affected the stat to turn it on. People not familiar with such small but noticeable "swings" sometimes try to compensate for this by turning the stat way up or down, thinking the extreme settings will make things happen faster. They won't.

There are two ways that a thermostat can be inaccurate. One is that its calibration from the factory or over time has become five or even ten degrees off from the truth. Most manual stats have a small setscrew (painted in place so it won't move) that can readjust the calibration (judged by where the clicking sound occurs around the dial). However, many people are happy to ignore the strict temperatures stated on the stat and simply remember a setting that feels comfortable to them, perhaps marking this with a pencil.

The other inaccuracy of a thermostat is more extreme. This would be when its control of heat is either wildly erratic or occurs, if at all, only at the very low end of the scale -- the room definitely overheats. This tends to mean the thermostat is on its death bed.

Some large living room areas use a low-voltage thermostat in conjunction with a relay. Calibration and "swing" problems for these can usually be addressed at the stat, whereas complete loss of control will mean the relay is bad. (Good luck finding and recognizing the relay.)

The hookup of thermostats may present problems. Manufacturers of 240-volt thermostats indicate which of their wires is to attach to the incoming line wire(s) and which to the outgoing load wire(s). I am not aware that the reversing of these makes any operational difference. What can get confusing, however, is the hookup of a 2-pole thermostat, especially where it is replacing a single-pole thermostat (or vice versa). If the one or two cable-pairs of wires that go to the heater(s) are connected to the wires marked "load" and the one or two cable-pairs of wires bringing or sending on the constant incoming voltage are attached to the "line" wires, then things should work. But suppose you are replacing a single-pole stat and brought a double-pole home from the store. Yes, you might get by by attaching just one side of the double stat to the two (black) wires you unhooked the old stat from, but it matters which side of the double-pole stat you use. This is because almost all double-pole thermostats are fake. By this I mean one half is a normal single pole stat, but the other is only set up as an on/off switch, not heat related. So if you were to hook to the on/off side only, the stat would only act like a switch (always on till you clicked it off at the very bottom end).

Timers. Here I am referring to switches that mount in normal electrical boxes and control what time of day (outdoor) lights will turn on and off. Some are completely mechanical, having a motor that turns a clock past on-off trippers; these are actually the most reliable. Others are electronic and are usually more limited in the total wattage (500) and type of bulb (incandescent) they can control; some won't even work or give a read-out if they have a battery that has failed or if the bulbs total less than 40 watts or are all burned out. Electronic timers are shorter-lived, being vulnerable to surges and lightning.

X-10 switching. This high-tech type of switching is used with "smart homes", which are able (even remotely) to program lights and appliances to operate as commanded. If the people who inherit such a system are not as "smart" as it is, this technology may be not so smart after all. In any case, I have not had much call to trouble shoot these systems, but others (esp. the manufacturers' and retailers' representatives) have. If you think you have such a system, I recommend you check this site: Smarthome .


"I am the farthest thing from a DIYer that has ever lived. I had an electrical problem in my home and found your very well done website which guided me through a simple fixit." -Mark, CA

© 2005-2013 Larry Dimock

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