Work Shop Electrical Safety

[Keith Blaszak]

Well I've been building my workshop steadily over the last year or so in my detached 2 1/2 car garage and I started to think about machine safety. We have a fair amount of kids in the neigborhood and I have alot of exposed equipment so I wanted to keep safety in mind.

I desided to install key locked push button kill switches, one for the 120v line that comes into the garage and another for the 220v. The 120v works great however I'm stuck with the 220v. I've been reading up and it looks like I might need a 2 pole relay that can handle the voltage/amperage that comes off of my 220 line.

Is anyone familiar with what im trying to do here? or perhaps has anyone else found a better way to accomplish this task?

Thanks

[Logan William]

How big is the 220V line coming in? If you want to kill the entire 220V line just get a knife throw disconnect and put it right after the 220 enters the garage, a single throw with a lock kills everything. You can get them pretty cheap, one good for up to 40 or 50 amps should be available for less then $50 bucks, look for appliance disconnects(common for AC units).

If you want to be able to kill individual machines I would just put a small knife style disconnect on every machine, you'll probably spend more on fittings and adapters then on the disconnect

[Chris Padilla]

240 V has two hot legs. Theoretically, you can stop your machine with opening one leg but to be safe, both legs should be opened.

[Bob Riefer]

I just made sure that my panel was wired so that receptacles for tools (not lights, and not receptacles for general use) were isolated on their own breakers. So I just cut the breaker at the panel each time I leave the shop. Someone would have to know where my panel is, which breakers to turn on, and would have to have time to figure that all out before I stormed in asking why the heck they're in my shop in the first place, before there was ever risk of danger.

[Rod Sheridan]

Keith, as Logan indicated, a lockable disconnect switch may be the easiest and least expensive option.

It's interesting to note that the Euro machines I've purchased all have a lockable disconnect switch built in.

regards, Rod.

[Anthony Whitesell]

I also need to address this issue. Many of my stationary tools have the switch at a height that my 3 year old can reach. It's making me more and more nervous. I will hopefully be upgrading my service from 100A to 200A and plan to use the old main panel as a subpanel after the upgrade. You're not supposed to constantly toggle breakers. They're not designed to be switches. I'm hoping to find an inexpensive 60-100A 220V disconnect between now and then.

The jointer gets unplugged due to the way the control box is wired (vampire circuit), but adding lockable or removeable switches to the other machines seems like a lot of work.

[Prashun Patel]

+1 on a lockable master disconnect.

[Keith Blaszak]

hmm my 220v line that comes into the garage is 3 wire cord (black, White, Grnd).

To Chris' point the black and the white each carry 120v; to completely cut the power wouldn't I need a knife throw disconnect for each hot leg? I thought that this was why most 220v machinery came with a magnetic switch.

[Logan William]

hmm my 220v line that comes into the garage is 3 wire cord (black, White, Grnd).

To Chris' point the black and the white each carry 120v; to completely cut the power wouldn't I need a knife throw disconnect for each hot leg? I thought that this was why most 220v machinery came with a magnetic switch.

The knife style disconnect for 220/240V single phase will throw both hot legs. You'll bring the line side of the service in the top of the box, lug both hot(generally black/white) into the top side of the switch, then the line going out to the rest of your devices(assuming a subpanel) will be hooked to the bottom of the disconnect. You can pick up a 30-40 amp AC unit disconnect for 30 or 40 bucks, most of those are waterproof as they're generally outside so if you can find one not outdoor rated it should be even cheaper.

[Ken Fitzgerald]

Chris and Keith are correct. To be safe you need to disconnect both hot legs. You can do this with a switch or a relay.

However, the biggest safety reason for magnet switches in equipment is more to prevent them from accidentally restarting in the event of a power failure and then power comes back on......

[Keith Blaszak]

Excellent. This sounds slightly cheaper then buying a seperate relay and connecting it to a pushbutton. I think a 40amp might do the trick. I'm going to have to double check what I have going out to the garage.

Ken,
I always wondered why it was a magnetic switch that actually makes alot of sense now.

Thanks for all the replies everyone!

[Bob Riefer]

Someone mentioned you're not supposed to toggle breakers like a switch.. Why not? (I honestly don't know, I'm not attempting to challenge your knowledge). If the reason is that they'll wear out... how many toggles will that take (I'm on two years worth of toggling without fail so far)? And for a $5 replacement breaker, it doesn't seem like I'd be too upset if it did need to be replaced very infrequently.

[Ken Fitzgerald]

Bob,

They are not designed to function as a switch on a regular basis. They are designed primarily to trip in over current conditions and secondarily can be used to occassionally shut off circuits for safety reasons.

There are a lot of things that can be used in manners other than their intended use....but that doesn't mean it is the right thing to do.

[Anthony Whitesell]

More than occasional use of a circuit breaker may reduce the spring tension and based on how the breaker is designed, may increase or decrease the amperage at which it trips.

Long story made short. I worked for a company that was contracted to build an economical field rating device for circuit breakers.

[Bob Riefer]

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



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.

[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 :eek:

[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 (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.