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1200 watt microwave using 18a on 15a breaker
- Thread starter Tywaser
- Start date
First tell us how you arrived at those numbers.
How do you know what the current draw is.....did you measure it?
How do you know what the current draw is.....did you measure it?
No they arent. They are faster than any fuse. This can be especially annoying as some will trip for as much as a blown light bulb.
If this is an old breaker box say like one of those federal pacific's. It could be that the breaker is bad. They where known to burn down a few houses. But that is only a slim possibility.
Gonzo has the question that needs to be answered. How did you arrive at those numbers?
Gonzo has the question that needs to be answered. How did you arrive at those numbers?
Maybe in Scotland their circuit breakers are different, but here in US the only breakers that move that fast are ground fault breakers in our plugs in bathrooms and arc fault types, otherwise slow. I guess I should have realized we are all different parts of the world, so where are you located Tywaser?
Can't say I agree unless they are defective or outdated... I did home remodeling for many years breakers blow quite fast and some can be overly touching blowing in the wind at the slightest sudden change like a bulb suddenly popping... I just looked up the Square D breakers in my house they are rated to trip within 1/60 second aka 16.7mS...
Clamp Meter
I used a clamp ammeter and a hot/neutral separater to measure the amperage and used a multimeter for the voltage. I measured while heating a glass of water on Hi. I have tested
my meter at a different house where the microwave oven is 1200 watts and mains voltage was 109v. It used 11.2 amps. Both tests were done 3 feet away from the microwave.
Mine is an inverter type. I live in Grande Prairie, Alberta, Canada.
I used a clamp ammeter and a hot/neutral separater to measure the amperage and used a multimeter for the voltage. I measured while heating a glass of water on Hi. I have tested
my meter at a different house where the microwave oven is 1200 watts and mains voltage was 109v. It used 11.2 amps. Both tests were done 3 feet away from the microwave.
Mine is an inverter type. I live in Grande Prairie, Alberta, Canada.
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what gauge wire is installed on that complete circuit? What is the rating of the microwave? Should it be drawing 18A?
Oh never mind, I see you already said it was a 1200W microwave. Though you never did tell us the voltage. Clamp the meter only around the black wire near the breaker in the breaker panel. Then run the microwave and see what numbers you pull then. If other devices are on that circuit take a before and while it is running reading. What type of breakers are installed?
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We can agree that it takes a split second for the breaker to heat up and mechanically trip, but as coke said. This is a fraction of a second. The only kind of breaker that won't trip in less then a second on an over current condition is one that is faulty.
I am not able to get to those power box wires because I am in an apartment. Are you suggesting that the resistance in the wire is dropping the voltage to the microwave and increasing amperage demand? at a given resistance through the load wouldn't it draw less current at lower voltage?
http://ulstandardsinfonet.ul.com/scopes/scopes.asp?fn=1077.html
I do understand the need for special purpose devices. Yes, I know the UL is an american standard.
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Then how do you know it is a 15A breaker? They do make 20A breakers and 12/2 w/GND wire under 100 foot is 20A rated.
A device that is 1200W will draw so many Amps based upon the formula W/V = A. Because power is equal to voltage times the current.
Tywaser said:
Those contradict, which one is it? Code it most all areas will require the service panel be accessible in each unit for multiple safety reasons...
From my experience most 'newer' builds will indeed have 20A breakers and 12g wiring in the kitchen... They 'technically' need a 20A rated receptacle that will give it away, although as normal many contractors will cut corners if they can slip it by the inspector thus the receptacle is not always a give away... Wire gauge isn't a dead giveaway either but I doubt you will find many contractors pulling 12g for 15A circuits when code only requires them to pull 14g... Trust me from experience 12g is a $%@#$%# to pull though conduit and make connections with vs 14g, it's not only a cost increase but one of labor so contractors simply don't do it... I rewired my entire house with 20A sockets and 12g wire, and although I love the end results (and would do it again) trust me there was a lot of regret and swearing when doing the job, it just made everything harder...
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The reason a device can draw a higher current than it's rated to draw is power factor. Many devices are inductive (or very occasionally capacitive) loads and as a result a significant amount of current flows between the device and the supply just to charge and discharge the inductors (or capacitors) as the a.c. waveform varies. This current flow doesn't do actual work, it just heats up your conductors and wastes energy.
If you worked out the current that should flow based on the "real power" in watts, you would have I = P/V= 1200W / 110V = 10.91A
However as this device (and most other devices too) has a less-than-unity power factor, the equation for power is actually P=V x I x p.f, and current is I=P/(V x p.f), where p.f. will be less than one so the current flowing will be higher than the 11A we need to get 1200W of "real power"
In your case, if it's drawing 18.9A then we can see p.f. = P / (V x I) = 1200/(110x18.9) = 0.58. This is pretty poor, but as I understand it not uncommon for microwaves.
So your microwave has an "apparent" power of 110V * 18.9A = 2.079 kVA (this is what is "apparent" when you measure the current draw using a meter), but only delivers 110V * 18.9A * 0.58 = 1205W of heating to your food (the power doing "real" or useful work)
If you worked out the current that should flow based on the "real power" in watts, you would have I = P/V= 1200W / 110V = 10.91A
However as this device (and most other devices too) has a less-than-unity power factor, the equation for power is actually P=V x I x p.f, and current is I=P/(V x p.f), where p.f. will be less than one so the current flowing will be higher than the 11A we need to get 1200W of "real power"
In your case, if it's drawing 18.9A then we can see p.f. = P / (V x I) = 1200/(110x18.9) = 0.58. This is pretty poor, but as I understand it not uncommon for microwaves.
So your microwave has an "apparent" power of 110V * 18.9A = 2.079 kVA (this is what is "apparent" when you measure the current draw using a meter), but only delivers 110V * 18.9A * 0.58 = 1205W of heating to your food (the power doing "real" or useful work)
As for tripping times, a miniature circuit breaker won't trip immediately if you go over the rated current. Your conductors won't vaporise immediately, either. A small overload will be tolerated for some time before the MCB trips to protect the conductor.
See this link as an example of the time-current characteristic curve for a thermal-magnetic circuit breaker.
You can see that for small overloads, the thermal heating will eventually cause the breaker to trip, but for large ones the magnetic effect will cause an immediate trip.
Based on that curve, if you were drawing double the rated current it would still take 80s to trip. Your microwave, drawing 1.26x the rated current, would operate for some time before tripping the breaker.
See this link as an example of the time-current characteristic curve for a thermal-magnetic circuit breaker.
You can see that for small overloads, the thermal heating will eventually cause the breaker to trip, but for large ones the magnetic effect will cause an immediate trip.
Based on that curve, if you were drawing double the rated current it would still take 80s to trip. Your microwave, drawing 1.26x the rated current, would operate for some time before tripping the breaker.
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