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A comment over on another SE got me thinking. With screw-in fuses, unscrewing it and then later screwing it back in causes negligible wear on either part of the installation. But what about modern "switch" overcurrent circuit breakers? Does manually turning them off and back on repeatedly over a period of time cause a noticeable amount of wear?

I am considering here the case of using the breakers to turn off power for example when going on vacation, so more often than only when doing things like working on the house electrical wiring but also less often than daily. Let's say on the order of ten times per year or something along the lines of that.

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Anecdotally, I worked at a garage where the large air compressor was switched off by the breaker nightly for years with no apparent issue. –  mac Dec 21 '12 at 14:50
    
In the early 1970s, I volunteered in a small theatre wired with 1960s circuit breakers which were designed to turn circuits on and off to control the lighting and lighting effects. The breakers were eventually replaced (in the late 1980s) due to obsolescence and a desire to use electronic controls, not because they wore out. –  wallyk Jun 27 at 5:17
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3 Answers

up vote 12 down vote accepted

As ChrisF mentions, any mechanical device causes some wear when it operates. With that said, let us start by checking with the National Electrical Code (NEC).

NEC 2011
404.11 Circuit Breakers as Switches. A hand-operable circuit breaker equipped with a lever or handle, or a power-operated circuit breaker capable of being opened by hand in the event of a power failure, shall be permitted to serve as a switch if it has the required number of poles.

Informational Note: See the provisions contained in 240.81 and 240.83.

So according to the NEC, circuit breakers can be used as switches with some provisions.

240.81 Indicating. Circuit breakers shall clearly indicate whether they are in the open “off” or closed “on” position. Where circuit breaker handles are operated vertically rather than rotationally or horizontally, the “up” position of the handle shall be the “on” position.

240.83 Marking. (D) Used as Switches. Circuit breakers used as switches in 120-volt and 277-volt fluorescent lighting circuits shall be listed and shall be marked SWD or HID. Circuit breakers used as switches in high-intensity discharge lighting circuits shall be listed and shall be marked as HID.

If the circuit breaker clearly indicates the "on" and "off" position ("on" being up in vertically oriented situations), and the breaker is labeled "SWD" and/or "HID". Then the circuit breaker can be used as a switch, as far as NEC is concerned.

As for whether or not using a circuit breaker in this way causes damage to the circuit breaker, we'll look to the NEC's definition of a circuit breaker.

Circuit Breaker. A device designed to open and close a circuit by nonautomatic means and to open the circuit automatically on a predetermined overcurrent without damage to itself when properly applied within its rating.

Notice it specifically mentions "without damage to itself". So in the eyes of the NEC. A device used manually or automatically to open a circuit that causes damage to itself, can not be used as a circuit breaker.

More evidence is provided in this pdf document from Schneider Electric describing the markings on a circuit breaker.

Circuit Breaker Image

4.) SWD – 15- or 20-A circuit breakers rated 347 V or less may be marked “SWD,” meaning that they are suitable for switching fluorescent lighting loads on a regular basis (NEC 240.83(D)). These circuit breakers are evaluated for high endurance use, since they will be used similar to a light switch.

5.) HID – 50 A or less circuit breakers rated 480 V or less may be marked “HID,” meaning they are suitable for switching high intensity discharge or fluorescent lighting loads on a regular basis. These circuit breakers may employ a different construction than a standard SWD circuit breaker in order to address the high inrush current resulting from the lower power factor created by the HID lighting (NEC 240.83(D)). These circuit breakers also undergo additional endurance evaluation to demonstrate their ability to perform the switching duty.


While the information presented here, is based on information that may only pertain to the United States. Other countries will have similar rule and markings, to indicate which devices can be used safely in different situations. Circuit breakers rated for this use are tested for durability similarly to switches, and can safely be used to manually open and close a circuit without too much wear and tear.

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So should "designed to open and close a circuit by nonautomatic means and to open the circuit automatically on a predetermined overcurrent without damage to itself" be read as "designed to (open and close a circuit by nonautomatic means) and to (open the circuit automatically on a predetermined overcurrent without damage to itself)", or "designed to (open and close a circuit by nonautomatic means and to open the circuit automatically on a predetermined overcurrent) without damage to itself"? Other than whether wear constitutes damage, there is a fair difference in semantics there. –  Michael Kjörling Dec 21 '12 at 13:03
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@MichaelKjörling It means the device operating in a way for which it is designed (manually opening/closing, automatically opening), should not cause damage to the device. –  Tester101 Dec 21 '12 at 13:07
    
Makes sense. (I'm not in the US, but like you say, other countries likely have very similar regulations.) So I guess at that point, if anything, it comes down more to asking about the specific model breakers in use. –  Michael Kjörling Dec 21 '12 at 13:12
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@MichaelKjörling Chances are if you live anywhere in the developed world, you shouldn't have a problem using a circuit breaker as a switch. If you don't, you probably wouldn't even be asking the question. –  Tester101 Dec 21 '12 at 13:25
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The basic answer is that as the breaker is a mechanical device there will be wear, however I'd suspect that it would be negligible over the lifetime of the breaker - unless you are turning them on and off several times a day.

They are obviously designed to be switched on and off, but the number of times this happens under normal conditions is very few. So turning them off once or twice a year (for example) to do work on the electrics isn't going to produce noticeable wear.

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It has been my experience in an industrial setting that repeated overload tripping will cause premature failure. It will eventually fail to reset or trip at a less than rated load. ` –  mikes Dec 21 '12 at 12:18
    
@mikes - I'd expect industrial breakers to trip more often than domestic ones - due to the nature of the load. –  ChrisF Dec 21 '12 at 12:24
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The point I was trying to make is that breakers we switch off frequently fail less frequently than the ones that trip due to overloads. –  mikes Dec 21 '12 at 12:29
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@mikes - I think we were agreeing with each other then! –  ChrisF Dec 21 '12 at 12:33
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Repeated overload tripping is a sign of a different problem, though. –  The Evil Greebo Dec 21 '12 at 12:54
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Generally, home circuit breakers have 10 000 or 10 000's of guaranteed operating cycles, but only 1000's of guaranteed tripping cycles. Consult the circuit breaker's datasheet for exact numbers - search for operating cycles or switching operations.

Then you can estimate the wear caused by your activities.

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