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Low Voltage: when is it unsafe to plug in?


wiploc

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I plugged in a tester before plugging my RV. The tester showed 109 volts.

 

Is that too low? Should I ask for my money back and go on down the road?

 

If that's not too low, what is? When should I decline to plug in?

 

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Welcome to the Escapee forums! We are here to help and will do our best.

 

As a former electrical service tech, I have pretty extensive experience in electrical service work so will do my best to help. There is really no set point where the voltage suddenly becomes too low, but the design of modern electrical equipment is usually to operate on 120V-ac with a tolerance of +/- 10%, so that means from 132V to a minimum of 108V. Thus your voltage of 109V is, at least in theory OK. But the catch is that voltage is not a fixed thing and actually varies at your power plug depending upon the quality of the electrical system supplying it and the condition of all of the equipment between your RV and the power source. Even poor systems will seem fine if the loads are low but as loads increase the voltage seen at your power pedestal starts to fall, because of poor connections or small & defective wires between your power plug and the power source. In a typical park as the evening progresses more RVs arrive and turn on air conditioners and so the power load increases and that causes the supply voltage to sag. The fact that your voltage was at 109v when you tested it is an indication that there are supply system problems because otherwise you should have seen 120V or even a bit more as that is what the power company supplies at the RV park entrance. Something has already caused the voltage to begin to drop even before you connect anything to it. That is the reason that so many of us recommend that RV folks use one of the power monitors such as from Surge Guard or Progressive. Those devices would allow you to connect at the 109V but if the power drops below 108V it shuts down until the voltage returns to a level that is safe for your RV and equipment.

 

Electric equipment will tend to overheat when used with low voltage and the lower it gets the bigger the problem. Each time that happens the equipment's life span is shortened and in the worst case it can destroy the equipment. Usually that takes several times before major damage takes place and the amount of harm depends upon how low the voltage sags to. While I might connect my RV to a power plug with only 109V available, I would not operate my air conditioners on it or my more sensitive equipment, unless I had one of the two line monitor devices to protect me. Basically, connecting to that low a power supply is a bit like buying lottery tickets. How lucky do you feel? Many RV owners do connect and give it little thought, but if they use poor power long enough or often enough it will shorten the life of the equipment and often require repairs that most RV owners never realize were caused by poor electrical power.

 

To better understand the problems associated with electricity quality you may find this article published in Escapees Magazine to be helpful.

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I plugged in a tester before plugging my RV. The tester showed 109 volts. Is that too low?

 

Probably. Invest in an autoformer or voltage regulator as we've found many parks have voltage sags, especially in summer.

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I thought the standard voltage for the USA changed years ago from 120v to 110v? If this is true why would 109v be a problem?

Back in the 50's the standard voltage was 110v and 220v but it was changed on the US grid sometime in the 60's, I think.... ;)

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Wiploc- Good post but I have a question for Jim.

 

Jim,

Thanks for the link to the tester. Have you built this tester? I priced out the components from the parts list and came up with a cost of $190+ dollars and you need a degree of aptitude to assemble the tester. The Hughes Autoformer would cost you $356 to $548 and weighs 35lbs. A 50amp surge guard w/LCD display can be purchased from Camping World from $363 to $500.

 

Wiploc- Which ever way you go here you can't go wrong because I find low voltage in many parks.

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Yes, the voltages of years ago, 110v, 220v, and 440v, are no more, and have been for many years 120v, 240v, and 480v. As an electric utility lineman, we were mandated to maintain voltage to the customer at + or - 5%, so the voltages delivered would be within 7 volts above or below 120v. This allows for a voltage drop within the customer's system to still be within a safe range for his equipment.

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Edison used 110 volts as the nominal voltage for his DC lighting plants in the eastern cities. When Westinghouse replaced Edison DC power with AC distribution they kept 110 volts as their nominal end voltage so the old Edison light bulbs wouldn't burn out prematurely.

 

This gave 220 volts leg to leg on the split (single) phase feeds.

 

When utilities went to 3 phase power, a Wye connection let each hot leg give 120 volts to ground while giving 208 volts across any 2 legs. This let the utilities distribute the 120 volt loads evenly across all 3 of the available power legs.

 

Like Kirk said, the 110/120 volt dichotomy was resolved in the 1960s, with the 110/ 220 volt single phase power being raised to 120/240 volts.

 

All of this is mainly academic, what matters more is whether the campground is using single phase or 3 phase Wye transformers to feed their sites. If the campground is single phase you'll get 120 volts from each leg to ground and 240 volts leg to leg. If it provides 2 out of the 3 Wye connected legs to each site you'll still get 120 volts from each leg to ground but only 208 volts from leg to leg.

 

This is probably why 208 volt or 240 volt appliances are not code compliant in an RV. If you run a 240 volt clothes dryer on a 208 volt Wye service, it will take 20% longer to dry your clothes. Power a 208 volt stove burner from a 240 volt single phase socket and you'll get 20% more heat than you expected.

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Thanks for the link to the tester. Have you built this tester? I priced out the components from the parts list and came up with a cost of $190+ dollars and you need a degree of aptitude to assemble the tester. The Hughes Autoformer would cost you $356 to $548 and weighs 35lbs. A 50amp surge guard w/LCD display can be purchased from Camping World from $363 to $500.

I have been aware of that device, as well as another similar one around the internet RV community, for several years now and I did consider building one. The first version he shows was one I first saw and I would not trust it at all for any number of reasons, particularly his choice of those cheap, inaccurate meters. I own one of them and testing against my high-end meter has shown it to be close to accurate at 120V but loosing accuracy to only about 70% at 110V. Accurate mechanical meter movements are very expensive and also fragile, the main reason that they have mostly disappeared. The newer version is probably accurate enough and does have some good features, but................ :( It is expensive, it uses a lot of very valuable space, and it will require care & maintenance to be reliable just as any other piece of test equipment does if it is to be reliable even though it is a single purpose device that will only be used once each time you park the RV. For myself, I'll continue to carry my Fluke volt/ohm meter which is accurate, takes little space, and has many uses.

 

In addition to the price comparison that you make between the two devices, the other factor is that this monstrous testing device offers no protection at all once you connect the RV if the power should degrade. Once it has been used it is put away and you are completely vulnerable to any problem that may take place on the power source, such as voltage sag that is typical in older parks under heavy use, or to a lightning strike on power lines, also one of the more common sources of damage to electrical systems. The Surge Guard or Progressive 50a devices will give you continuing protection the entire time you are connected for only about $100 more cost and either one is also much smaller to store when not in use. That device is well thought out and looks like fun to build, but I have much better use for my limited budget.

 

All of this is mainly academic, what matters more is whether the campground is using single phase or 3 phase Wye transformers to feed their sites. If the campground is single phase you'll get 120 volts from each leg to ground and 240 volts leg to leg. If it provides 2 out of the 3 Wye connected legs to each site you'll still get 120 volts from each leg to ground but only 208 volts from leg to leg.

Do you still find the old wye connected, 208V phase to phase supplies out there? I don't believe that I have seen one in years, and I did check that at every stop with our 50a motorhome. I don't bother now as we downsized to a travel trailer that is only 30a in 2012 but I wouldn't expect to see it, unless in a very old campground.

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Do you still find the old wye connected, 208V phase to phase supplies out there? I don't believe that I have seen one in years, and I did check that at every stop with our 50a motorhome. I don't bother now as we downsized to a travel trailer that is only 30a in 2012 but I wouldn't expect to see it, unless in a very old campground.

Like you, Kirk, I test every pedestal, every time. Even though I have a whole house Progressive EMS in my rig. No sense potentially harming it ;)

 

I have never seen 208 in 16 years on the road. But it does exist....

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Wiploc,

Hope all this info has not put you into information over load. The tester would be fun to build as Kirk pointed out but it would be fragile, A solid state device would be better in the RV'ing environment. During my 15 years as an electrician in the Navy one of my assignments was as an Assistant Calibration Lab Supervisor for three years, we calibrated and certified test equipment. I worked as an electrician for over 30 years and I found that your test equipment is the most valuable tool in your tool box.

You would expect to see a voltage reading of 208VAC in a three phase application not in the traditional 120VAC single phase application which is what you should find at RV Park power. You may also see that kind of voltage reading if you have lost one leg of your three phase power. You can get this voltage from a multiple tap transformer and is used in a limited application in some equipment.

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The last 208Y/120 volt service I ran into is at the Park of the Sierras near Coarsegold, CA. The sticker at the back of our 5th wheel trailer, next to the power plug states both 120/240v and 208Y/120 are acceptable voltages, as there are no 240v loads.

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I really haven't paid much attention to 50 amp plugs since my RV is 30 amps. I do remember seeing 208 volts at Park of the Sierras.

 

When I owned a mobile home in Northern California the 50 amp single phase socket at the site had 208 volts between the hot pins. I had to re-tap the heating element in the 240 volt dryer I purchased before it would effectively dry a load of clothes. Of course, that was the same park that used 10 gauge wire protected by a pair of 30 amp breakers at the source to get from the distribution center to the nice looking 50 amp pedestals and disconnect breakers at each site.

 

I quickly learned not to dry a load of laundry while the central air conditioning was running.

 

I stopped at that park a couple of years ago and the wiring hadn't changed.

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208V is common in Ontario Canada our park has the delta transformers.

 

I asked the power provider why not 220 they said it's really cost prohibited.

 

No issues here at all. Only ones who even notice anything are the ones with a high end monitor system that reads the phases out.

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Welcome to the Escapee forums! We are here to help and will do our best.

 

As a former electrical service tech, I have pretty extensive experience in electrical service work so will do my best to help. There is really no set point where the voltage suddenly becomes too low, but the design of modern electrical equipment is usually to operate on 120V-ac with a tolerance of +/- 10%, so that means from 132V to a minimum of 108V. Thus your voltage of 109V is, at least in theory OK. But the catch is that voltage is not a fixed thing and actually varies at your power plug depending upon the quality of the electrical system supplying it and the condition of all of the equipment between your RV and the power source. Even poor systems will seem fine if the loads are low but as loads increase the voltage seen at your power pedestal starts to fall, because of poor connections or small & defective wires between your power plug and the power source. In a typical park as the evening progresses more RVs arrive and turn on air conditioners and so the power load increases and that causes the supply voltage to sag. The fact that your voltage was at 109v when you tested it is an indication that there are supply system problems because otherwise you should have seen 120V or even a bit more as that is what the power company supplies at the RV park entrance. Something has already caused the voltage to begin to drop even before you connect anything to it. That is the reason that so many of us recommend that RV folks use one of the power monitors such as from Surge Guard or Progressive. Those devices would allow you to connect at the 109V but if the power drops below 108V it shuts down until the voltage returns to a level that is safe for your RV and equipment.

 

Electric equipment will tend to overheat when used with low voltage and the lower it gets the bigger the problem. Each time that happens the equipment's life span is shortened and in the worst case it can destroy the equipment. Usually that takes several times before major damage takes place and the amount of harm depends upon how low the voltage sags to. While I might connect my RV to a power plug with only 109V available, I would not operate my air conditioners on it or my more sensitive equipment, unless I had one of the two line monitor devices to protect me. Basically, connecting to that low a power supply is a bit like buying lottery tickets. How lucky do you feel? Many RV owners do connect and give it little thought, but if they use poor power long enough or often enough it will shorten the life of the equipment and often require repairs that most RV owners never realize were caused by poor electrical power.

 

To better understand the problems associated with electricity quality you may find this article published in Escapees Magazine to be helpful.

 

Well said!!

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Good information. I've learned a lot from reading the responses and I only hope that my new rig has all the internal protection it needs. I recently took a trip to Death Valley, Ca. Given that have never experienced "bad electrical hook-up" my neighbor educated me that you get what you get......most acceptable and some not so. I didn't sleep a wink the 2 nights I was there due to power surges and my EMS going crazy. This problem, coupled with 9% downgrades and unpaved roads. I'm glad that Death Valley is off my bucket list.

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