Work Shop Electrical Safety

[Ken Fitzgerald]

Bob,

If you want to use your breakers as switches....go ahead. I won't.

A quote from your reference:

While circuit breakers can be legitimately and safely used as switches, the frequency and duration of such use is very limited. Routinely circuit breakers are manually operated for service-maintenance, and repair type activities. With the preceding enhancing our understanding; we can say that circuit breakers can legitimately be used as switches, generally they are not intended for prolonged frequent or repetitive manual breaking and making type control of electrical energy utilization equipment.


Typcially they aren't designed nor meant to be used that way. That's why my air compressor has an ON/OFF switch....my DC has an ON/OFF switch and in my case a remote.

Most breakers are designed as a occasional use safety switch.


I have been working on high powered electronics equipments for over 40 years. While we have breakers on the feed for CT scanners, MR scanners, x-ray equpments, radar and other equipment used in air traffic control centers, we also have control panels to shut them off. The control panels almost always contain both a switch and in the circuit after the switch a relay (or as it is often referred to here an electromagetic switch).

I surely would NOT recommend anybody regularly use a breaker as a switch.

[Bob Riefer]

I didn't question your qualifications Ken , just pasting in a link that does a fairly nice job of explaining what my electrician told me when I asked him "Why did you tell me it's ok to cut the power to my receptacles each day when everyone else is telling me that's a big time bad thing".

Anyways, have a great day

[Keith Blaszak]

I've always been under the impression that a breaker's purpose was to protect you from a circuit overload (aka to stop such events like wires burning in your walls and setting your house on fire). I would imagine that breakers shouldn't be over used; and at some point replaced to make sure that they don't fail so such an event doesn't happen.

That being said I think we all know that breakers endure fairly thorough safety testing and can probably last a very long time if ever they would critically fail.

[Ken Fitzgerald]

Bob,

Qualifications have little to do with it. I was only trying to relate that in my 40 years of military and professional experience, that is what I have experienced.

It's also important to point out that statement from the reference you posted. They don't recommend that you do it regularly either.

I have one breaker I shut off on occasion. That's the breaker to my DC. I shut it off if I am leaving town for more than a day or two. In the event the remote control circuit failed I wouldn't want the DC running continuously.

[Chris Friesen]

Something that hasn't been mentioned here is that there is also a difference between using the breaker as a switch *under load* and turning off the breaker as a safety precaution with no load on it.

When the circuit is under load, flipping the breaker will cause arcing on the contacts and this can cause damage.

When there is no load on the circuit, flipping the breaker causes a bit of mechanical wear and cycles the spring, but it the wear is minimal.

Just as an example, a breaker I looked up at random was rated for 1000 electrical cycles, but 10000 mechanical cycles.

[Bob Riefer]

Hi Chris - What you're describing is what I'm referring to. I turn off my tools when I'm done using them. And then I cut two breakers off (no load on either of them at that point) to ensure that no one can re-start the tools. In any case, at 7 switches per week, 364 per year, it'll be about 27 years until I reach 10,000 mechanical cycles on the switch.




Bracing myself for getting told what's what on this topic again

[Ken Fitzgerald]

Okay Bob....here is an easy question for you and you don't need your electrician to answer it...

Is this a direct quote from your earlier post....it's easy now....Yes? No?

Sorry, I couldn't sleep tonight until I figured out why my electrician would have told me to use the breaker as my "off switch".

Turns out that many breakers are available as SWD (switch duty) breakers and are UL tested same as a light switch. Is it possible to wear one out? As possible as it is to wear out a light switch I guess.

Anyways, from another forum they had this link/info that may be of interest:

http://www.mikeholt.com/mojonewsarchive/NEC-HTML/HTML/ElectricalCircuitBreakers~20020419.htm

Quote:

Circuit Breakers As Switches
Both the ANSI and the NEC definitions acknowledge the potential for the legitimate use of circuit breakers as switches. Switches (pass, but do not consume electrical power) are considered as being control devices, thus one may also say that a breaker is a control device, or a controller.

To aid in the understanding of a fine point, I offer this comparative example. A gas valve and a steam pressure relief valve are both controllers, one the fuel to the burners that aids in the development steam pressure, and the pressure relief valve that opens on excessive pressure. Both are controllers, one operating (the gas valve) the other safety (the relief valve).

Likewise in a parallel manner; we say that a circuit breaker can control and protect an electrical circuit. An electrical relay is an example of an operating control; it opens and closes the circuit. Circuit breakers are not designed as replacements for relays, operating controls.

There is as you may intuitively have anticipated an exception. Some circuit breakers are manufactured for use in a specific type of application. When a circuit breaker is designed to also be routinely used as an on-off switch to control 277 volt florescent luminaires they are marked SWD, for switch duty. This does not mean that a switch duty breaker can be used to manually control a traffic signal light where it will be cycled 1,000 or more times per day. The point is; the listing for switch duty (SWD) does not mean a circuit breaker can be used as a high frequency cycling operating control, such as a relay that has a life span rated in tens, if not hundreds of thousands of duty cycles.

While circuit breakers can be legitimately and safely used as switches, the frequency and duration of such use is very limited. Routinely circuit breakers are manually operated for service-maintenance, and repair type activities. With the preceding enhancing our understanding; we can say that circuit breakers can legitimately be used as switches, generally they are not intended for prolonged frequent or repetitive manual breaking and making type control of electrical energy utilization equipment.

[Gary Radice]

I guess the question could be: is shutting off the power at the circuit breaker at the end of the day considered "prolonged or frequent repetitive use" and so an unsafe practice that should be discouraged, or a safe practice that should be encouraged?

Not weighing in on either end, just interested in the consensus if there is one. In my case, I'm the only one in my shop. I turn off the breaker only for repairs or if I'm away on vacation and we have house-sitters.

[Ken Fitzgerald]

Come on Bob...I'm waiting ...yes....or ...no ?

[Ken Fitzgerald]

Gary,

I don't believe shutting off power at the end of the day using a circuit breaker is an unsafe thing to do. It will probably cause the breaker to fail quicker.

Most breakers are general purpose breakers and as such are not intended to be used as switches. They are designed and intended to limit current and to be used as a safety disconnect for maintenance purposes as stated in the quote I made of Bob's earlier post.

SWD rated breakers are special purpose breakers and you will probably have to go to electrical supply house to get them and I will bet some of my local electrical supply houses would have to special order them.

Shutoff switch/disconnect box would would be my preferred method of disconnecting power to a panel if I was going to do it regularly and I would want it capable of having a lock applied.