Circuit Breaker Testing

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If I remove panel cover to check circuit breaker and using a screwdriver type of tester see if light goes on when the breaker switch is on and it goes off when the switch is off...Does that mean the breaker is working or is there more involved? Thanks.
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harry manka wrote:

Yes. There is more. You are only testing that the breaker can be turned on and off. You did not test to assure that it will turn itself off when it gets and overload, nor did you test to see if it might turn off at the proper overload. Old breakers often start triggering early so they shut down the circuit under normal load.
BTW a breaker that fails to shout down the circuit with an overload is very rare.
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Joseph E. Meehan

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Yes, it's rare. I had one that shouted down so loud that I could hear it at every outlet box in the house.
(I know; typo; you meant "shut down". But it was cute.)
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Christopher A. Young
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There are circuit breaker testers made for every manufacture that I am aware. Problem is that they start out at about $5k and go up from there. When I was a field service engineer the company owned about everything that was available. The smaller test sets for plug-in breakers, residential types, were the least accurate. Check out NEMA for specs on testing breakers. That is the most stringent spec that I know.
Buying a new breaker will be easier and cheaper than testing molded case breakers below 100 amps.
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Plug in and turn on two hair driers at the same socket? Overload that breaker?
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snipped-for-privacy@yahoo.com (harry manka) wrote:

Assuming this is a 15 or 20 amp breaker, you could cause a deliberate short, and see if it trips.
I wouldn't do this on a bigger breaker, too much current there.
Shut off the breaker, connect a short piece of wire to it, turn back on, touch wire to ground (metal box), breaker should blow.
Cost $0.20 (2 ft of wire at 10/c a foot). Watch out for flying sparks.
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John Hines wrote:

If the withstand rating of the breaker is inadequate for the fault current that the fault you are creating then the breaker may fail explosively. If you look at the breaker you will find the withstand rating expressed as X AIC were X is the number of amperes of fault current that the breaker has been tested to interrupt without failure. If the transformer that supplies your home has been replaced with a larger unit to keep pace with neighborhood demand the available fault current may exceed the rating of your panel or the breakers that are installed in it. My last service upgrade was from a relatively small transformer only one span away from the drop and the available fault current was 8800 amperes. If the transformer had been on the same pole as the drop the withstand would have needed to be upgraded above the 10,000 ampere value of the stock breakers.
In other words if you don't know what the available fault current is then dead faulting a breaker is a DAMMED STUPID THING TO DO! -- Tom H
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wrote:

If a normal household breaker can't withstand a short circuit, it is bad. Create it any way you like, but that is it's job, to trip and not explode, in that situation, a short circuit.
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John Hines wrote:

John, I have to agree with Tom it "is a DAMMED STUPID THING TO DO!"
--
Joseph E. Meehan

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John Hines wrote:

A normal breaker has a maximum amount of fault current it can interrupt without damage. This is called it's withstand rating. The current it is capable of withstanding without damage is labeled right on the breaker. If there is more fault current available then the breaker is built to withstand then the breaker will fail. If the fault current is high enough it will fail explosively and bury parts of itself inside the eyes of the idiot who dead faulted it. You are welcome to continue to test your own breakers in the way you have recommended but to advise others to do so is negligent. Many breakers in homes have had there withstand ratings surpassed by the increase in available fault current caused by changes in the supply network brought on by increased demand. Faulting a breaker without knowing the available fault current is like pulling the pin on a grenade without having anywhere to throw it. You want to do that then fine but kindly stop being so reckless with the safety of others by offering such dangerous advice to people who have not the training to evaluate your competence. -- Tom H
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wrote:

Just plug in TWO 1500watt electric space heaters, turned on HIGH. A 15A breaker should trip in a few seconds. A 20A one should trip shortly, but it may take several seconds, up to one minute. That is the easiest way to test breakers without sparks. This method is ONLY for 15A and 20A 120V breakers. Dont mess with any larger ones, or 220V types.
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I'm not advocating shorting out the breaker, but how would one determine the available fault current at a service.
Also, if the available fault current exceeds the rated maximum fault current of the existing breakers, how important is it to upgrade them?
Mr. Fixit eh
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Steve Nekias wrote:

To test a fifteen or twenty ampere breaker you detach the house wiring, attach a multi outlet assembly temporarily, plug in two 1800 watt hair dryers, turn the first one on all the way, turn the second one on to succesively higher settings until the breaker trips. The breaker should trip in less than a minute at 3600 watts or 30 amperes of current flow.
If the withstand of the breakers is exceeded by say ten percent I wouldn't be in a rush to change them. If the available fault current is more than twenty percent over the breakers withstand rating I would have them changed fairly soon. If the available fault current exceeded say 150% of the withstand rating I would change them as soon as the replacements could be obtained. If breakers with a high enough withstand are not available for your equipment then a fused disconnect with appropriate fuses for the fault current could be installed ahead of it but the calculation of the series rating of such equipment combinations is beyond the skill of most electricians. In one case I asked the power company to run a new service drop from a pole on the other side of the house. The addition of over one hundred wire feet into the supply wiring from the transformer reduced the available fault current to below the rating of the equipment. -- Tom H
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I used a heat gun, toaster oven, vacuum cleaner, and a lamp. I know the lamp doesn't use much electricity, but I wanted one just so I'd have something to see. And all my old Federal Pacific breakers worked just fine.
Load testing the breakers makes much more sense then the person who said to short them out with a screwdriver. Safer too.
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Successful test! Roger that, mate.
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Christopher A. Young
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Childfree Scott wrote:

The failure mode of FPE breakers is unique enough that tripping them out on overload will not assure that they will trip under fault conditions. If you do a search of the Consumer Product Safety commission's site you can find more information. -- Tom H
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scott snipped-for-privacy@my-deja.com (Childfree Scott) wrote in message

Here's a scary thing, I have the Federal Pacific breakers in my house (built in '72 so the vintage puts them suspect) and I'm having trouble with my computer's UPS beeping (low voltage?) if I turn on my laserjet (heater inside). If I turn on the iron on that circuit it beeps steady even if the computer isn't on. Since my breakers are this goofy shape I thought I'd look on the net and see what my options were and now I'm finding out people recommend replacing the whle panel. ouch
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Such a problem is extremely unlikely to be the panel or the breakers themselves. If it was, they'd have burned out by now.
Irons and laserjets have pretty steep current requirements. If they're on the same circuit as the UPS, and your steady-state voltage is a little on the low side, an iron or laser (during periodic warm up cycles) can "draw down" the voltage on the circuit far enough for the UPS voltage alarm to go off.
Solution? Move the those things off the UPS circuit or vice-versa. Or, report it to your power company, and they can recheck the supply voltage.
There's a more dangerous possibility - do your lights flicker throughout the house when the iron goes on? Even more compelling, do any lights _brighten_?
--
Chris Lewis, Una confibula non set est
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This hairdryer setup would be a safe way to test the withstand rating of the circuit breaker. How would you go about determining what the available fault current would be at a service location?
Mr Fixit eh
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Steve Nekias wrote:

Hair dryers can be used to load test a circuit breaker but that test will tell you nothing about the withstand rating. The withstand rating is determined by testing to destruction at the electrical testing laboratory. The resultant rating is on the breakers labeling.
The available fault current is determined by calculation. You need the rating and internal impedance of the transformer as well as the type size and length of the conductors between the transformer and the terminals of the device that you are concerned about.
"Calculations can be based on the source fault current at the transformer. Unless the user has fault data for the exact circuit of interest, a conservative estimate can be achieved by starting with the fault current at the site transformer. If desired, further refinement can be done by calculating current reductions due to conductor impedance. This method is most useful for smaller electrical facilities; use at larger facilities may provide overly conservative values.
The maximum fault current available at the transformer terminals is determined by the following formula, using data from the transformer nameplate, which can be supplied by the power company or a site engineer.
Secondary full load current =     Single phase transformer kVA (Secondary kV) OR Secondary full load current =     Three phase transformer kVA (Secondary kV)(√3) THEN
Secondary fault current =     Secondary full load current x 100 Percent transformer impedance
This is the maximum fault current at the transformer, which will be reduced by conductor impedance. This reduction can be estimated using wire characteristics for various cross-sections and lengths."
The calculation of series ratings of breakers or fuses that are down stream from other Over Current Protective Devices is the kind of task that electrical engineers are paid to do. -- Tom H
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