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Old 02-01-2015, 04:37 PM   #21
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With the way people are sharing and dividing up bed rooms and living rooms in the city , to afford the rent , 1 - 20a circuit is almost not nearly enough .



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Old 02-01-2015, 05:47 PM   #22
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I do work on the old houses around the college where you have a basement and 3 floors which equals 8 people. The two people in the attic need two 20 amp circuits plus lighting. Computers, microwaves, video.
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Old 02-01-2015, 05:53 PM   #23
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Unrelated to my original case, but my condo has only two 15 amp circuits for all receptacles and overhead lights excluding kitchen receptacles. One is all lights and plugs in 2 bedrooms, bathroom, and overhead lights in the living room. The other is plugs in living room, laundry room, outside, and overhead lights in the kitchen, laundry room, hallway, and outside. There is no way to have a space heater or air conditioner AND lights on without something tripping. I hate it.
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Old 02-01-2015, 09:48 PM   #24
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What kind of lighting? could the low resistance of cold tungsten have an effect?
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Old 02-01-2015, 10:01 PM   #25
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In my original scenario? Several 4' T12 fluorescent lights.

The original breaker should have tripped when both the lights and heater were on, but it was defective, and was tripping hours later instead. The replacement breaker tripped right away.
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Old 02-01-2015, 10:12 PM   #26
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The harmonics from T12's could throw the amps off by a fair amount and the new breaker was not as tolerant as the old one, esp. if it was an older thermal one.
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Old 02-01-2015, 10:59 PM   #27
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I dont see how that would explain the random tripping in the night with everything disconnected, that has not reoccurred since the breaker was replaced.
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Old 02-01-2015, 11:03 PM   #28
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Sometimes throwing out "What If" gets other peoples creative juices flowing.

Kinda like when I lived in Wisconsin and all the guys got together we would say "what if we all pitched in and bought a tavern" then we could be pals forever.
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Old 02-02-2015, 09:09 AM   #29
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In some instances it's best to design circuits as if they were constantly in use, if the lights are on they shouldn't dim when you go to plug in your phone charger. Separating lighting and receptacle circuits is never a bad idea.
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Old 02-05-2015, 08:42 AM   #30
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Quote:
Originally Posted by xpertpc View Post
The harmonics from T12's could throw the amps off by a fair amount and the new breaker was not as tolerant as the old one, esp. if it was an older thermal one.
let's just make stuff up
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Old 02-05-2015, 02:55 PM   #31
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Quote:
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let's just make stuff up
I did't just make that up out of thin air, I read it on the internet - but seriously a standard ammeter can be skewed by harmonics, I thought it was around 5-10%.

I saw this first hand last year after replacing five T8s with T5's fixtures, the 20 amp breaker kept tripping, it was in fact a faulty breaker but while troubleshooting my RMS meter read about 2 amps higher than the non RMS meter.

I verified both meters on a known amp source to be sure the difference was real.
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Old 02-05-2015, 04:52 PM   #32
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Quote:
Originally Posted by dspiffy View Post
15 amp circuit with a space heater and some lights. Square D QO panel. Breaker never tripped with both the lights and heater on, however it would trip randomly in the night with nothing on. First step was to disconnect the lights and the heater, it still tripped the following night. With the lights and heater disconnected there was no current draw.

Replaced the breaker, and the new breaker tripped almost immediately. Turns out the lights and heater were drawing a combined total of around 22 amps.

Either the lights or heater will be moved to a different circuit.

I post because I'd never seen a breaker behave in this manner before.
A circuit that is overloaded rather than short circuited will take a while to heat up enough to trip. Could it be that the heater was turned on before bedtime and then tripped later as you slept and you just thought that it was random?
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Old 02-05-2015, 05:01 PM   #33
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Quote:
Originally Posted by xpertpc View Post
I did't just make that up out of thin air, I read it on the internet - but seriously a standard ammeter can be skewed by harmonics, I thought it was around 5-10%.

I saw this first hand last year after replacing five T8s with T5's fixtures, the 20 amp breaker kept tripping, it was in fact a faulty breaker but while troubleshooting my RMS meter read about 2 amps higher than the non RMS meter.

I verified both meters on a known amp source to be sure the difference was real.
That has to do with the sine wave distortion, at this point in time NO ELECTRICIAN should be utilizing an averaging amp clamp. TRUE RMS is the only way to go.
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Old 02-05-2015, 05:54 PM   #34
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That has to do with the sine wave distortion, at this point in time NO ELECTRICIAN should be utilizing an averaging amp clamp. TRUE RMS is the only way to go.
So TRUE -

Beer memory may preclude my expertise because I did my code class and journeymen based on the 1987 NEC. Even so, back then I thought they said harmonics could overheat a circuit even when the amps measured were within spec.

Throughout most of my career true RMS meters were kinda pricey, nowadays they are within cost of anybody in the field that requires them to be an efficient troubleshooter.
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Old 02-05-2015, 05:57 PM   #35
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A circuit that is overloaded rather than short circuited will take a while to heat up enough to trip. Could it be that the heater was turned on before bedtime and then tripped later as you slept and you just thought that it was random?
This is a workshop area, not a bedroom, and the lights and heater were all turned off during the night when the breaker tripped. After the first time, they were all unplugged rather than switched off.
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Old 02-05-2015, 09:48 PM   #36
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This is a workshop area, not a bedroom, and the lights and heater were all turned off during the night when the breaker tripped. After the first time, they were all unplugged rather than switched off.
Okay, but with my limited experience a circuit breaker will not trip if it doesn't have current running thru it.
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Old 02-05-2015, 11:29 PM   #37
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Okay, but with my limited experience a circuit breaker will not trip if it doesn't have current running thru it.
It did at the time it was supposed to trip. It was just really, really late.
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