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Old 03-22-2020, 02:30 AM   #1
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Brand: Thor Motor Coach
Model: ACE 30.1
State: Florida
Posts: 23
THOR #17950
120 volt drop

I purchased a plug in voltmeter for use while in RV parks to see if I need to buy an autoformer to control low voltage feeds. While plugged into 30 amp service at my house, I checked it and it was 121v. My wife kicked on the A/C and it dropped to 113v. Today I tried it again and started at 122v, then A/C on it went to 117v. Then I also started the microwave and it dropped to 113v. Is this normal?
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Old 03-22-2020, 02:51 AM   #2
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Model: ACE 27.1
State: Florida
Posts: 5,046
THOR #7035
When current is drawn voltage is dropped over resistance. The more current, the more voltage drop. The key is to minimize the voltage drop by minimizing the resistance. That is why you have wire sizing charts based on max current and distance from the breaker box or source. The other area where resistance is high is dirty, corroded, or loose connections. Minimize the resistance and you will minimize the voltage drop when you draw more current by running the AC and/or MW.
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Old 03-22-2020, 02:57 AM   #3
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THOR #1658
When you put on a load it can drop a little, but your numbers seem extreme to me. There is a member on here that is a retired master electrician, Iím sure that he will be chiming in soon.
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Old 03-22-2020, 01:58 PM   #4
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Brand: Thor Motor Coach
Model: Palazzo 33.3 34'bunkhouse
State: Georgia
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THOR #4735
voltage is not a constant... it does vary, but your appliances and devices are designed to use varying voltages just fine... no worries. While some will purchase devices to try to 'keep' the voltage constant, most of us do not worry about it - after 100,000+ miles across this country, including Alaska, and most of Canada, and having 'plugged in' to many, many, many rv parks, campgrounds, regular household outlets, and even 'suspect' campground sources, we've never had any issues with 'voltage'. If voltage drops, amperage increases, so it's quite possible a breaker could trip sooner than otherwise, usually the main Shore Power breaker, but that's it's job, regardless.
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Old 03-22-2020, 02:15 PM   #5
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Brand: Keystone
Model: Sprinter
State: Florida
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THOR #15553
Quote:
Originally Posted by richardehrhart View Post
I purchased a plug in voltmeter for use while in RV parks to see if I need to buy an autoformer to control low voltage feeds. While plugged into 30 amp service at my house, I checked it and it was 121v. My wife kicked on the A/C and it dropped to 113v. Today I tried it again and started at 122v, then A/C on it went to 117v. Then I also started the microwave and it dropped to 113v. Is this normal?
Yes they are all within acceptable voltage. Need need to worry below 108 volts.
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Old 03-22-2020, 09:09 PM   #6
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Brand: Thor Motor Coach
State: Missouri
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THOR #6903
Many 30 amp receptacles are wired with 10 gauge which meets most codes. If the receptacle is quite a distance from the main and transformer you will always see voltage drop that approaches the need to manage loads.

One of the huge benefits of a properly wired 50 amp receptacle and of course 50 amp RV

I encourage anyone adding a receptacle for and RV to always go 50 amp even if they currently have a 30 amp RV

Back in the day I have burnt up more than my share of 30 amp plugs in the summer time trying to stay cool and get a few other things done
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