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Old 10-16-2013, 08:55 AM   #21
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Cord ampacity

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Originally Posted by ruscal View Post
Jim,
Shouldn't 12 ga. do 20 amps?
Russ
The ampacity for cords is listed in Art 400 of the NEC not in Art 310-16 ,which lists the ampacity of standard building wire . According to the NEC 12/3 standard cord @ listed ambient temperature has an ampacity of 20 amps .. Length of the cord and voltage drop are also issues to be considered . Using an extension cord at 100 % of ampacity usually destroys the male and female cord ends long before damaging the cord itself
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Old 10-16-2013, 09:27 AM   #22
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If Diane was running an air conditioner, I would suspect low supply voltage. Motors will draw more current under low voltage conditions. But just a heater? To me, the only possible suspect becomes the camp ground supplying too high of a voltage. Especially if the heater runs fine at home.
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Old 10-16-2013, 09:50 AM   #23
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Question for the electrical guru's.

Lets say for a moment that the trailer in question has been all rewired & has new 15 amp breakers etc and the owner had checked the issue wasnt with the campground power supply, could the problem simple be the use of an extension cord with the trailers main power 15 amp supply cord? I dont now enough about how a 15 amp trailer is normally set up (but in this case it sounds like the OP has a newer converter, so would have thought it to be the same as a 30 amp system) but I do know that most small electrical heaters have instructions indicating that they should not be used with an extension cord. If the converter is in place what happens that an appliance such as a heater would it even know there was an extension cord (with the correct amps for the heater) attached to the trailers main supply (assuming its not a real long one) & if no other power hungry appliances where in use? Would having a longer main trailer power supply cord, avoiding the use of the need for an extension cord change anything?
Enquiring minds want to know.
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Old 10-16-2013, 10:01 AM   #24
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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
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Old 10-16-2013, 10:21 AM   #25
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In acting as a resistor the 10 amp power cord could also overheat, melt insulation, short out, start a fire, you name it.

As far as the original U-Haul breaker not supporting a heater... It shouldn't be a problem
A typical small space heater is 800-1500 watts max, that's less than 15 amps in all cases and more like 10 in most.

A good 15 amp breaker should have no problems with that load, unless, as mentioned, it's original and well worn, as all original one are by now.



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Old 10-16-2013, 10:52 AM   #26
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I should have mentioned that not all power cords can support 15A A 12/3 will, but an 18/3 will not. Extended use of an 18/3 cord with a 1500W heater, could lead to a fire.
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Old 10-16-2013, 11:16 AM   #27
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it should but with a 100 foot cord it may not!
It's AC! It's 20A
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Old 10-16-2013, 02:12 PM   #28
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Okay guys, I bought the little GFCI tester, read the instructions. Man I have a lot of ungrounded receptacles in my home! Found a wired right one in the home and connected the Camper cable to it. Tested the main GFCI located at the end of the upper cabinet. It tested as being wired Okay. Then as Bob said, connected the heater...it blew the breaker in camper in 30 minutes. The heater is a 120 V 1500 watt 12.5 Ag label on the back. I did not use any extension cord. So DO YOU THINK I NEED TO REPLACE THE BREAKER AND GFCI RECEPTACLE which appears to be the original to the CT13? ALL other wiring including 12V is new.Thanks guys each and everyone of you! Have tester will travel! LOL Thanks
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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.
Russ
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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,
Russ
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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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Quote:
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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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