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Old 02-19-2012, 04:32 PM   #15
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Originally Posted by ottffss View Post
Really? I'd find a new "electrical specialist" as RV 120VAC wiring - by RVIA mandate - follows national electrical code and a xx amp outlet/circuit in that code will run xx amps all day/night/year without issue. It's corroded or poor assembly that causes the long run time overheating.

Th OP is correct in how many inverters "bypass" shore power sort-of through (not completely around) the inverter and that the inverter "bypass" current IS limited to its feed amperage (usually 20/30amps) which also must power the charger side within those feed amps.

The REAL reason to install heater OFF the inverted outlets is that in the event of a power failure while you are out you won't run the batteries down to the inverter kick-off voltage and then find you still have no shore power, your batteries are dead and you can't start the genset. Now, that's a real problem as everything starts to freeze and you have NO recourse. You might not be able to turn over the big motor without the bat boost if real cold.

There are non-inverted outlets on most rigs - garym114 has the easy way to find them. Usually, the washer, a basement plug or two, maybe an under-sink plug, a central vacuum, the engine block heater, are OFF the inverter and IDEAL elec heater outlets. (If you need an extension cord, please make a 12ga short extension cord using commercial grade plugs on both ends)

And by ALL MEANS do what

Because it is an excellent preventive issue measure!!!!!!
I agree that we wouldn't be allowed to buy RV's that don't meet the National Electric Code. I think the warnings offered by this technician are a little extreme.

There is a bypass relays in inverters, when plugged into shore power, bypass all the circuitry in the inverter (other than the relay). For the 2000W inverters, the bypass relay is generally rated at 30A.

A 30A 120V circuit delivers 3600 watts of power. That would be the 30A relay capacity.

Then there's the issue of having too much wattage on any 15A (1800 watts) or 20A (2400 watts) branch circuit to the receptacles. Overload it and the circuit breaker will pop.

Common sense prevails. I would not use a plug-in heater unattended in my home or my RV. I do use them periodically, where I can monitor their performance. For example, feel the cord. If it's hot, there's a problem. Turn it off.

The anal electrician in me does agree that a direct circuit from the auxiliary heater to the panel box bypassing the inverter is a good idea, as this bypasses any additional mechanical relays which can add resistance to the circuit. But, I also trust the National Electric Code, which our RV's are theoretically built by.

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Old 02-19-2012, 05:38 PM   #16
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Trap... good to hear your experience. I think running 750 makes a lot of sense indeed.

Don... I'm going to look into a dedicated circuit which bypasses the inverter altogether just for running a space heater. But I also agree that it "seems" reasonable to trust the circuit that runs through a recent manufactured inverter, particularly when sticking to a moderate 750 watts.

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Old 02-19-2012, 05:50 PM   #17
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One way to safely run a 1500-watt space heater would be to install a dedicated outlet near the breaker panel and run 12-gauge Romex (probably just a matter of a few feet) directly to it. In this case you should be about to draw the heaters full rated load indefinitely without excessive supply wire heating.
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Old 02-19-2012, 09:39 PM   #18
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What about the relays in the automatic transfer switch that sources power from generator or shore power. Do they heat up?
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Old 02-20-2012, 12:49 AM   #19
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I had the transfer switch inthe inverter burn up using 2 1500 watt heaters when the unit was about 7 yrs old, So to fix the problem I ran 3 new 20 amp #12 wired outlets from the main box just for my winter heater use No hot wires or outlets for past 5 years.
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Old 02-20-2012, 03:10 AM   #20
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I installed 2 small ceramic heaters in the wet bays which are via inverter. They draw 10 amps between them according to the gauge but only run for a short time because it's only a small area.
Surely if you want to forgo propane use, the easiest way would be to run an extension cord from a second outlet from the post at the camp site. I wouldn't be risking damage.
Also I mistakenly purchased a kettle that keeps the water warm. Ive regularly forgotten to turn it off on departing a campground ( disconnect shore power)
I can tell you the inverter gets angry and finally trips requiring a reset.
It's. It that hard to get to 50 Amps so a second shore power connection seems logical to me
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Old 02-20-2012, 07:15 AM   #21
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To further muddy the waters, the NEC stipulates that a circuit, unless specifically designed for full amperage use, can only be run at 80% of its rated capacity when using a 'continuous load'. Meaning that a 15 amp circuit can only be run at 12 amps and a 20 amp circuit can only be run at 16 amps, unless its just for a short duration. How long this time period is depends on the load's 'duty cycle'. Don't expect to run a 14 amp load day and night on a 15 amp circuit and not expect problems.

To clarify my earlier statement about using 750/1500W heaters in winter, I ran both at 750 continuous, one in front and one in back, and only ran one or the other at 1,500 if I had to get the place a little warmer, ie shower time.

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Old 02-20-2012, 08:03 AM   #22
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We experienced the same problem running two heaters - tripping the 30 amp breaker on the inverter panel. I have a 50amp service, and ended up connecting the second heater in the bedroom to the outlet installed for the washer/dryer (we don't have one) and problem solved.
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Old 02-20-2012, 08:24 AM   #23
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I have mentioned the 80% breaker load rating several times, but it's great that you did it again. I worked many years in product design for Square D Company and can offer this:

The National Electric Code (NEC) defines how electrical equipment is installed. Underwriters Laboratories (UL) defines how the equipment is designed and tested. UL has "Hold-in, Trip-out" tables for circuit breakers. This is the duty cycle you mentioned, and has time values for when a breaker must hold or trip at different load and overloads. A residential breaker is actually required to hold 100% of it's rating, but this is tested at 65 degrees ambient temperature. Breakers trip two ways; magnetically for short circuits, and thermally for current overloads. The internal bimetal strip that regulates thermal tripping also creates some heat. Because of this, in the real world application, breaker enclosures / loadcenters will be much hotter than 65 degrees inside the enclosure where the breakers are mounted and this is included in the UL test required for all products. This is why the recommended load is 80% - so the breakers will not thermally "nuisance trip".

Circuit breakers are not designed to protect people, they are to protect wiring and wire insulation. GFI breakers are to protect people. A breaker will trip under a short circuit, or current overload, and should be perfectly safe with a space heater on the circuit - assuming the load is within 80% of the breaker rating.

Originally Posted by trainsktg View Post
To further muddy the waters, the NEC stipulates that a circuit, unless specifically designed for full amperage use, can only be run at 80% of its rated capacity when using a 'continuous load'. Meaning that a 15 amp circuit can only be run at 12 amps and a 20 amp circuit can only be run at 16 amps, unless its just for a short duration. How long this time period is depends on the load's 'duty cycle'. Don't expect to run a 14 amp load day and night on a 15 amp circuit and not expect problems. Keith
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Old 02-20-2012, 08:57 AM   #24
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Having worked for many years as an electrical engineer, I agree with George. He has offered some excellent references and advise on AC breakers.

Winnebago owners can visit the Winnebago/Itasca web site and download the AC Electrical schematics for their coach. These drawings will show which AC outlets in your particular coach are powered via your inverter. In my case only outlets that power the entertainment electronics and one in the cockpit area are powered through the inverter. I haven't visited other manufacturer's web sites, but hopefully they offer this information to their customers as well.
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Old 02-20-2012, 09:02 AM   #25
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I've been using my space heater every year for the past 3 years with no problems.
however I only use one 1500 watt heater. If I'm on 30 amp shore power. I will use it on the low setting. If I'm hooked up to 50amp. I will use it on the high setting. I am conservative with the other appliances. If my amperage draw is getting close to the 30amp total. I will turn something off.
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Old 02-20-2012, 04:28 PM   #26
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If you don't have an inverter and just a converter, does any of that apply?
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Old 02-20-2012, 04:32 PM   #27
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Originally Posted by CharlieTwo View Post
If you don't have an inverter and just a converter, does any of that apply?
A converter does not supply 120v it uses it to convert 120VAC to 12VDC. So basically no except for all the NEC (electric code) discussions above which applies to ALL RVIA certified RVs (which is pretty much all of them).
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Old 02-21-2012, 09:13 AM   #28
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Fellows, something is wrong either with my coach or some of the information provided. I did exactly what Gary recommended i.e. turn off the inverter breaker then test all the outlets to see which outlet still has power and that will tell you it does not run off the inverter. Well, all my outlets still worked with the inverter turned off! What gives here??????? Did I do something wrong? Thanks

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