Electrical Wimpet Wonders Why? Breaker Trip? - Page 3 - Fiberglass RV


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Old 10-16-2013, 02:39 PM   #29
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D said: I have a lot of ungrounded receptacles in my home!

The main thing to look for on those ungrounded receptacles is that the HOT / Neutral are not reversed.

If the GFCI internal breaker did not trip then it is OK.

If the circuit breaker on the AC panel is the one that tripped, then it may be the culprit.

If the wiring from the breaker panel to the receptacle is not able to carry the load then the breaker is saving you from having a fire or even worse.

Do you have a lower heat setting on the heater?
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Old 10-16-2013, 03:38 PM   #30
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In a word YES, it's time for a new breaker.
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Old 10-16-2013, 03:49 PM   #31
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Originally Posted by David Tilston View Post
I suspect that the reason that they don't want you to run on an extension cord is that a heater draws lots of power. If the cord is damaged, the heater could cause it to fail. Otherwise it is a resister in series with a load. The power cord could cause a voltage drop, but that is it. It would not cause additional current to flow to a heater. In fact exactly the opposite, less current.

A 30A service would just have a larger wire in the cord, therefor less resistance, less voltage drop. A 12/3 extension cord is all that a 15A trailer supply would require, but a 1500 W heater would be taking most of that capacity. 1500W/120VAC=12.5A
David, I'm trying to get my head around the less current when the voltage drops.
1500W/120VAC=12.5A
1500W/100VAC=15.0A I get more current when I figure it?
Not trying to hijack the thread, just get a better understanding of electron behavior.

Anyway Diane's problem probably isn't voltage drop, just likely a tired breaker as others have noted.
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Old 10-16-2013, 04:02 PM   #32
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Volts times Amps = Watts
120 x 15A = 1800W
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Old 10-16-2013, 04:07 PM   #33
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Originally Posted by ruscal View Post
David, I'm trying to get my head around the less current when the voltage drops.
1500W/120VAC=12.5A
1500W/100VAC=15.0A I get more current when I figure it?
Not trying to hijack the thread, just get a better understanding of electron behavior.


Russ
The constant here is not the 1500 watt power disspation but rather the resistance of the heater.

V/I = R. 120/12.5 = 9.6 ohms

At 100 volts the current will drop to I = V/R = 100/9.6 = 10.4 amps.

Power, P = V x I = 100 x 10.4 =1040 watts.

Since power is the rate of using energy, you would expect that rate to drop with a reduced voltage. It does, from 1500 down to 1040 watt. Physically the heater will not get as hot. Raz
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Old 10-16-2013, 04:10 PM   #34
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NEC says a breaker needs to trip at 80%. Which is 12.5 amps on a 15 amp breaker.
A breaker trips because of one of two things, heat or magnetic field.
Your equipment is working fine.
It sounds like a blood and turnip thing.
Only my opinion
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Old 10-16-2013, 04:14 PM   #35
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Opps, math mistake
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Old 10-16-2013, 04:20 PM   #36
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Raz.
I am beginning to understand this. I was thinking the heater watts was a constant value and it seemed too simple! Using the resistance at it's rated amperage in the equation makes sense. I'll have to do some exercises to get comfortable with these problems.
Thanks,
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Old 10-16-2013, 04:21 PM   #37
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Our Uhaul had a little push button breaker mounted with the one and only 110 outlet on the end of the upper cabinet. It will not run an electric heater. And as I recall the power cord that plugs into the campground electric box goes directly to that breaker. If Diane has not changed that setup, it is surely the problem. It's been awhile since I rewired our Uhaul, so I may be wrong on the wire routing, but I think everything went through that little breaker, it's not a conventional breaker as we would think of one.
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Old 10-16-2013, 04:30 PM   #38
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Think of it like water, less pressure = less flow.

The power output of the heater is not fixed. It can be considered a resister.

Ohms Law
Current (I) = Voltage (V) / Resistance (R)
V=I xR
R=V/I

R=V/I = 120/12.5 = 9.6 ohms

If the wire were also 9.6 ohms, then the current would be half, and the heater would be producing 1/4 of its rated output. This is because twice the resistance would lower the current by half. Also half the voltage, (and power) would be dropped in the wire.
I = V/R = 120/19.2 = 6.25 (half of 12.5)

Watts (P) = V x I
Subing in V = I x R (ohms law from above)

P = (I x R) x I
P = I^2 x R
P = 6.25^2 x 9.6 = 39 x 9.6 = 375 W (1/4 of the rated output)

Of course the extension cord is also making 375 W. It is going to get very hot.

Because half the total current is flowing, half the total power is being made.

I hope that I have not confused you further.
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Old 10-16-2013, 04:38 PM   #39
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Dave,
Since the heater would be half as hot you could coil the cord in bed and recover the heat.
Russ
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Old 10-16-2013, 04:41 PM   #40
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Dave,
Since the heater would be half as hot you could coil the cord in bed and recover the heat.
Russ
Yah, ummm...... if you don't mind the smell of burning plastic, (and or flesh).

And the total system would be half as hot. The heater would be 1/4 as hot.
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Old 10-16-2013, 04:42 PM   #41
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Originally Posted by mszabo View Post
NEC says a breaker needs to trip at 80%. Which is 12.5 amps on a 15 amp breaker.
A breaker trips because of one of two things, heat or magnetic field.
Your equipment is working fine.
It sounds like a blood and turnip thing.
Only my opinion
The NEC does not state that a breaker needs to trip at 80% of its rating. The NEC says a Breaker which is subject to continuous load ( Continuous load definition = 3 hours or more ) shall not be loaded past 80% of the breaker rating IE a 20 amp breaker is not to have a continuous load of more than 16 amps . A 15 amp circuit breaker's trip point is not precisely at 15 amps, being a mechanical device the trip point varies and UL standards allow for this variance. Ambient temperature and how heavily loaded the adjoining breakers in the panel also affect trip point . I've seen a 15 amp breaker in -30 Deg F ambient not trip when subject to a load of almost 30 amps. Residential circuit breakers are thermomagnetic HELP ME OUT HERE RAZ
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Old 10-16-2013, 05:12 PM   #42
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More than most will want to know about circuit breakers:
There are 3 basic types of mechanical circuit breakers - the Thermal, the Magnetic, and the Thermal/Magnetic. Each has both advantages & disadvantages, however most home and RV breaker panels use the Thermal/Magnetic type.

As its name implies, the thermal/magnetic circuit breaker can react to thermal or magnetic overloads. The thermal section trips at minot overloads (under 200%) while the magnetic trips on major overloads (400%-500% or more). Since small overloads only activate the thermal part of the breaker, this is why Steve's description of breakers holding overloads at low temperatures happens.

The reason for combining the two trip methods is economic. A pure thermal (which is often found on power tools, motor protection, etc) doesn't react fast enough at high overloads. While a pure magnetic circuit breaker is very fast, they are also very expensive. They are often used to protect sensitive electronics. The thermal/magnetic breaker has a very simple magnetic section that only works for large overloads, leaving the smaller overloads to the thermal section.
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