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Old 02-18-2012, 11:23 PM   #1
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Potential problems using a space heater in coach

In our last coach, we often ran one or two 1500 watt space heaters when connected to shore power in parks during cool weather to save on propane use. We ran into an inverter problem while doing so - not while inverting battery power, but while using shore power which was delivered to the power outlet THROUGH a circuit contained in the inverter.

We were told by an RV electrical specialist technician that even when plugged into shore power, most (if not all) of our electrical outlets in the coach received shore power through a circuit that ran through the inverter. Not that the outlets were being powered by inverting battery power, but that the shore power was transferred through circuits that resided IN the inverter. Apparently the connectors that this power moves through, within the inverter, are relatively fine and are more easily burned out from continuous use of high watt appliances.

He said he had seen many burned circuits in inverters due to people running 1500w space heaters (from shore power, which ran through an inverter circuit) for prolonged periods of time.

It seems the fine connection switch or circuit for this power in the inverter can handle the current heat for relatively short term runs of 1500w (like an hour or so), but for many continuous hours of running a 1500w space heater, the circuit in the inverter can fairly easily overheat and then fail.

His recommendation for running a 1500w space heater is to find an outlet in the coach which receives shore power without going through a circuit in the inverter. Such an outlet would not receive any power should one decide to use the inverter to invert battery power, but would only operate when the coach is connected to shore power - or possibly the genset.

Has anyone here had any problems frying a circuit in their inverter when using a 1500w space heater for extended periods of time WHILE CONNECTED TO SHORE POWER?

With our new coach, we're tempted again to run a 1500w space heater from park shore power to save on propane use, but are leery of doing so for fear of damaging a fine connection in the inverter.

What are your thoughts on this?
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Old 02-18-2012, 11:35 PM   #2
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I'm interested in this one. As I am writing, it is 34 degrees outside my door, snow is in the forecast, and I have two 1500w heaters running. I'm toasty warm, haven't had any problems, but I've wondered about the huge amp draw.... Looking forward to the discussion.
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Old 02-19-2012, 12:12 AM   #3
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Thanks to this forum and others this problem was brought up when I installed my 2000w inverter/charger.
Most inverters of this size are powered with a 30 amp breaker. This is used when charging and for powering all inverter loads when plugged in to shore power. My inverter is rated to pass through 30 amps AC while in this configuration. Running two 1500 watt heaters would be a problem.
When I installed the inverter AC power breaker I add a 20 amp breaker to the main breaker box and added a receptacle for a heater so it wouldn't have to go through the inverter.
How to check receptacles - With shore power connected go to your main AC breaker box and find the breaker for your inverter, it is usually 30 amps, and open it. Now check all receptacles for power. If you find one that has power it does not go through the inverter.
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Old 02-19-2012, 12:37 AM   #4
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Gary... Excellent. Thanks for your thoughts and the method for finding outlets that don't feed through the inverter! That will be my task tomorrow.
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Old 02-19-2012, 12:55 AM   #5
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Interesting. I'll be checking mine.....
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Old 02-19-2012, 09:32 AM   #6
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Yep, run 'em through non-inverted outlets. I ran two 750/1500W heaters for two seasons in central WA a few years ago. Avg. Dec./Jan. temps were 15-20F. No problems.

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Old 02-19-2012, 11:43 AM   #7
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Just a point. I use 2 electric heaters to excersize my generator once a month. The first time I did it, I blew a 25 amp breaker on my 50 amp gen after about 30 minutes. Seems both outlets were on the same breaker. This leads me to believe that these outlets don't go through the inverter from the gen. I will use the suggested test next time to see if the outlets are dead when the inverter breaker is thrown.
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Old 02-19-2012, 12:41 PM   #8
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I just shut off the 30A breaker coming from my inverter to try to find an outlet which doesn't feed through the inverter and found none. It seems every outlet in my coach is fed through the 2800 watt Magnum Inverter. I'm considering having an additional circuit installed in the coach, independent of the inverter, specifically for operating an electric space heater while connected to shore power.

This info is from the RV electrical specialist I spoke with:

"Portable electric heaters convert electricity into heat and in doing so cause a high amount of current to flow through your electric wiring in the RV. Your RV's electrical wiring system is designed to handle short duration use of high wattage appliances such as the microwave, hair dryers, and vacuums. The problem arises when a high wattage appliance is used for extended length of time (like an electric heater running overnight).

Your RV electrical system is protected by circuit breakers and GFI outlets to protect against electrical shorts, ground faults, and over current conditions.

The problem is that most circuits are protected by 15 amp circuit breakers. A 1500 watt electric heater normally pulls 12-13 amps, not enough to trip the breaker but just under its load rating. This amount of current flowing through the wiring components for an extended length of time gets them very hot, hot enough to melt wiring insulation, electrical connectors, outlets, and destroy GFI outlets (if in the circuit). This could (and has) resulted in an electrical fire from the insulation or other electrical component overheating to the point of igniting. Your circuit breaker cannot sense the danger until it is too late and a short occurs from overheating wires touching.

If your coach is equipped with a hard wired inverter and an electric heater <at 1500w> is operated for an extended period of time on one of the inverter supplied outlets, damage to the inverter or fire may very likely occur at some point. Last season alone, Sundance Custom RV was called due to 2 inverter fires and several more damaged from use of electric heaters.

The reason for the concern is that when shore power is supplied to the inverter, a set of relays (transfer switches) closes and the inverter becomes passive on the circuits it will supply power to, but the current still goes through the inverter relays. These relays are the "weakest link" in the circuit. Excessive, long-duration current on the circuit overheats the contacts on these relays until they either melt together (inverter damage) or overheat and ignite (inverter fire).

RECOMMENDATIONS
1) Utilize your RV's furnace for space heating
2) Check the manufacturer's label on the electric heater for the wattage of the unit. If it is rated at 1500 watts only - don't use it longer than a few minutes at a time. If it has a lower setting, 1000, or 750 watts, then use the lower settings, with caution.
3) Don't use an electric heater on a GFI protected circuit.
4) Never leave an electric heater unattended (this includes while sleeping)
5) Don't use an electric heater on an inverter supplied outlet.
6) Test your smoke detector regularly.
7) If you smell or see smoke when an electric heater is in operation, turn off the main circuit breaker (or park circuit breaker) and evacuate the coach immediately and call the fire department. Some fires occur inside walls and are not readily visible until too late."
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Old 02-19-2012, 01:11 PM   #9
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Scary info.... I hope others chime in. BTW, I've always been careful to secure the plugs full-in and flat against the receptacle, and I occasionally feel for heat at the receptacle and the heater cords, nothing ever detectable. Don't know how reliable this might be.

Also, why would a MH circuit rated for 15 amps be any less capable than a regular house circuit rated at 15 amps? People use electric space heaters plenty in houses.... They are both constructed to the same electrical and fire codes, are they not?
Just asking
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Old 02-19-2012, 02:08 PM   #10
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Quote:
Originally Posted by DHart View Post
.... Your RV's electrical wiring system is designed to handle short duration use of high wattage appliances such as the microwave, hair dryers, and vacuums. The problem arises when a high wattage appliance is used for extended length of time (like an electric heater running overnight).
.......
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

Quote:
Originally Posted by steelheadbluesman View Post
...BTW, I've always been careful to secure the plugs full-in and flat against the receptacle, and I occasionally feel for heat at the receptacle and the heater cords, nothing ever detectable. Don't know how reliable this might be....
Because it is an excellent preventive issue measure!!!!!!
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Old 02-19-2012, 04:14 PM   #11
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I'll have to keep looking for off-inverter outlets. There are a good number of convenience outlets in my coach, but all seem to be fed through the inverter. And one I saw in my storage basement is also off the inverter. I will continue to look for more to try.
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Old 02-19-2012, 04:32 PM   #12
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Quote:
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.
I'm inclined to agree.
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Old 02-19-2012, 04:39 PM   #13
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Not being a true expert on the subject, I won't even begin to speculate. A lot of people say a lot of things. And a lot of people are flat wrong about what they say.

I don't doubt the technician's experience with burned inverters and inverter fires due to "weak links" in an inverter's relays. Could be that older inverters, or inverters from particular makers might be more prone to this than recent production or higher end inverter makers. I really don't know for sure.

I'm looking forward to hearing what Magnum and Monaco have to say about this as they are the makers of my new inverter and new coach.

My inclination would be to err on the side of caution and if running electric space heaters, to do so on the low (750 watt) setting when running for extended periods of time. I definitely won't advise other people on what I think they should do.
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Old 02-19-2012, 05:05 PM   #14
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Quote:
Originally Posted by DHart View Post

My inclination would be to err on the side of caution and if running electric space heaters, to do so on the low (750 watt) setting when running for extended periods of time. I definitely won't advise other people on what I think they should do.

DHart that's all we ever do, your chances of an electrical fire are much higher when you run those heater's on full, vs 750. Also your heater will last a lot longer when run on 750.

I learnt a lot about these heater when we had to use them to keep our pump house warm enough no to freeze the water.

1-heater on high didn't usually last a season, when I started using two of them on seperate circuits at 1/2 high they lasted for years, in fact I still use them in our 5'er today and I know that one of them is at least 8 years old.

Personally I will never use a 1500 watt heater on high for any length of time anymore. The reduced rate should solve all your worries and not let any of the wiring get to warm.

Must safer from electrical fires too!!

Trap
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