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Old 09-26-2021, 12:37 PM   #1
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Voltage drop when water heater turned on?

I have a 50A RV that is plugged in at home into a 15A source through a dogbone adapter. My EMS shows 123V until I turn on the electric water heater. When the water heater is on, the voltage drops considerably (by 15 or more volts). Many times it drops low enough that the EMS will throw a fault for low voltage. The water heater is drawing ~ 10A.

Does it make sense that high current draw from the RV would affect the voltage supply from my home?

Also, any recommendations on a basic RV electrical training that would help me understand things like this?
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Old 09-26-2021, 12:41 PM   #2
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Makes perfect sense.


The higher the amp draw, the more voltage drop, particularly with adapters, house wiring, etc.


Reserve your 15 amp service for battery charging and other essentials. And, if a high-amp battery charger, you should limit amp use by using the "power share" or "power save" feature of your inverter/charger.
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Old 09-26-2021, 01:43 PM   #3
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The chain is only as strong as it's weakest link. In this chase the 15 amp circuit coupled with the multiple plugs, total distance from the main service panel causes the voltage to drop. It doesn't happen until there is a load.



Long term in would be better if you could install a 30 amp outlet but I that in most cases this isn't easy. Always easier to install during construction. That's why I installed 3 different 50 amp plugs when I build our house recently. One in the garage, one on the outside of the garage, and one located near where I was going to build a garage. I since have extended into the garage and have a fourth 50 amp plug.
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Old 09-26-2021, 01:53 PM   #4
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Yep - makes perfect sense. That 10 amp draw you are showing is 1200 watts (10 amps x 120 volts). The maximum you can get from 15 amps is 15x120 or 1800 watts so that load is about 70% of the capacity of the 15 amp service. A long run of wire can't handle the draw due to resistance (unless the size is sufficient) so the voltage drops when a big load is applied. The voltage will be fine so long as the load is minimal.
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Old 09-26-2021, 02:24 PM   #5
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L1
123VAC 0.4A W/O water geater ON
108VAC 0.5A with water heater ON

L2
123VAC 0.1A W/O water heater ON
108VAC 10.2A with water heater ON

L1 shouldn't change voltage as it is separate line
*0.1A change so voltage should remain at 123VAC

L2 has a 10A change with water heater on
That is accectable for an electric element
*except at 108V 10A is only a 1080W


The BIG questions are:
WHY L1 voltage dropping???
WHY size wattgae is the water heater element?
1200W s/b 10A AT 123VAC
1400W s/b 11.5A AT 123VAC
***element failing????

Need to be checking where the Hughes is 'reading' voltage on L1 and L2
*appears using same for both Hot Legs
and separate source for Amps on both Hot legs
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Old 09-26-2021, 02:37 PM   #6
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Actually, on 15 amp, there is only ONE hot, that is then connected to both hots on the 50 amp side of the adapter.


SO, voltage..... is voltage. Same, as there is only one "source".


No question, on 50 amp service the separate hots can certainly have different voltages.
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Old 09-26-2021, 04:43 PM   #7
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Your leg 1 and leg 2 share the same neutral thus the decrease in voltage in non-loaded leg
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Old 09-26-2021, 06:17 PM   #8
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Quote:
Originally Posted by wolfe10 View Post
Actually, on 15 amp, there is only ONE hot, that is then connected to both hots on the 50 amp side of the adapter.


SO, voltage..... is voltage. Same, as there is only one "source".


No question, on 50 amp service the separate hots can certainly have different voltages.
YEP....missed the part about being on 15A source


Still question what wattage the WH element is??

Is an extension cord being used?
IF YES...how long?

15VAC drop is concerning with just 10A load....
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Old 09-27-2021, 06:32 AM   #9
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Thank you for all the replies.

My literature says the water heater is a Dometic Model#94018 which is listed as 1400W.

It's currently connected as follows: House receptacle (15A circuit) - 100ft 12/3 extension cord - dogbone adapter - EMS - RV 50A cord

I don't need the water heater on when at home (it had been left on from our last trip)... and was determined to be the cause of the voltage drop. I now know that this voltage drop is expected when a high draw is placed on the circuit (I'll find some education to understand this better).
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Old 09-27-2021, 07:46 AM   #10
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It's currently connected as follows: House receptacle (15A circuit) - 100ft 12/3 extension cord - dogbone adapter - EMS - RV 50A cord

100 ft of 12/3 is too long for high currents. 50 feet may also be too long. Upgrade to 10/3 for better results.
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Old 09-27-2021, 08:26 AM   #11
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The voltage drop simply means you are trying to pull too many amps through a wire that is too long and too thin.

Ken
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Old 09-27-2021, 08:37 AM   #12
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One thing missing from these voltage drop discussions is inductance and coupling that occurs when supply cords are not properly laid out. The surest way to induce drop in a supply cord is to leave extra cord coiled up upon itself and or to have it cross over itself.
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Old 09-27-2021, 08:56 AM   #13
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Do run your 50 amp cord to your 15a plug and use a dogbone or do you run a dogbone at the camper and run a 15 amp extention cord.

If it's a 15 amp extention cord check the cord guage. I bet it is 14 or 16 guage. Use a 12 or 10 guage cord.
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Old 09-27-2021, 09:14 AM   #14
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Quote:
Originally Posted by Persistent View Post
It's currently connected as follows: House receptacle (15A circuit) - 100ft 12/3 extension cord - dogbone adapter - EMS - RV 50A cord

100 ft of 12/3 is too long for high currents. 50 feet may also be too long. Upgrade to 10/3 for better results.
About a 3% voltage drop can be expected for most 100 foot wiring runs.
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