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Old 08-06-2019, 05:06 AM   #1
Dboland9
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Extension cord Safety

The power cord for my TT is 25 feet long. I needed another 20 feet to reach the pedestal and purchased a 30 ft long extension cord made of 10G wire. I am concerned about voltage drop off over this distance and whether it is safe to use the RV air conditioner. I do have an installed surge protector from Progressive which does protect against both high and low voltages, so I expect to be ok, but thought I would ask the more experienced and knowledgeable uses of this forum. Thanks.
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Old 08-06-2019, 05:14 AM   #2
Steveo57
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You should be fine. Voltage drop should only be 2-3 volts with that extension cord. Do you have a readout on the EMS?

Just make sure the plug ends are clean and tight.
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Old 08-06-2019, 05:42 AM   #3
Dboland9
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Electrical Cord Safety

Thanks for your response. I found a chart on Calculator.net that calculates the voltage drop to be 5% for a 100 ft length of 10G wire. Is a 5% drop dangerous for the AC unit?
On another forum, I just read that the distance I need to calculate is not just the length of the extension cord itself, but also needs to include the distance from the pedestal to the circuit breaker/power source in our home. That makes sense to me. Does everyone agree?
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Old 08-06-2019, 03:06 PM   #4
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Quote:
Originally Posted by Dboland9 View Post
Thanks for your response. I found a chart on Calculator.net that calculates the voltage drop to be 5% for a 100 ft length of 10G wire. Is a 5% drop dangerous for the AC unit?
On another forum, I just read that the distance I need to calculate is not just the length of the extension cord itself, but also needs to include the distance from the pedestal to the circuit breaker/power source in our home. That makes sense to me. Does everyone agree?
Yes that makes sense but it all comes down to what you're starting with if you have 120 volts with a 5% drop then you'll end up with 114 volts or so which is not a problem. I run mine at home on a 20 amp circuit probably 50 foot of 12 gauge and the trailer cord plugged in. I can run mine as long as I am seeing at least about 112-114 volts in the trailer before starting the AC.
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Old 08-09-2019, 12:14 PM   #5
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Thanks for your thoughts. I have learned and done more since my last question. I talked to tech support at Dometic and asked what the lowest voltage that the AC should see and still be safe. They suggested anything under 109 could be problematic. I talked to an electrician who said as long as the voltage in any RV outlet did not fall more than 5% when I turned the AC on, I would be Okay. Before the AC was turned on, and with nothing else using power in the RV, I measured the voltage in an outlet in the house and compared it to an outlet in the RV and got the same value of 115V. When I turned on the AC, the outlet voltage in the RV fell to 109. That is about a 5% drop and it landed at the lower limit of what Dometic recommended.
I do not feel secure running the AC with the drop down to 109, as I fear damaging the compressor.
Any additional thoughts would be appreciated. Thanks
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Old 08-09-2019, 12:39 PM   #6
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Maybe get a soft start for the AC?
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Old 08-09-2019, 05:10 PM   #7
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A question about your 10 gauge 30 foot extension cord. Is it a "commercially manufactured 30 amp RV extension cord with 30 amp plugs on each end? Or, is it a 10 gauge extension cord with 20 amp/15 amp plugs on each end?

If it's a "RV extension cord" the 30 amp rated plugs on each end "should" carry the amperage without problem, however, if your cord has "conventional plugs" on each end, you may be overloading the plugs and that's what is causing your voltage drop/current fluctuations.

Your cord should look similar to this one
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Old 08-09-2019, 06:13 PM   #8
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Quote:
Originally Posted by Dboland9 View Post
On another forum, I just read that the distance I need to calculate is not just the length of the extension cord itself, but also needs to include the distance from the pedestal to the circuit breaker/power source in our home. That makes sense to me. Does everyone agree?
Yabut, the distance between the breaker and the pedestal is possibly wired with better than 10ga, so the calculation isn't straightforward. If you measure the voltage available at the pedestal, you can "start over" your calculations from the pedestal.
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Old 08-13-2019, 07:50 AM   #9
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Again, thanks to all for your thoughts. It is an RV 30amp, 30 ft, 10G cord with RV plugs. I do agree that if the electrician was thinking he put in a larger gauge from the house to the pedestal to minimize voltage drop off. I will be speaking to him to see if he has those records.

I am still insecure with running it as the voltage did drop to 109 and Dometic said that was the lowest voltage they were comfortable with.

I like the suggestion about the soft start and will embark on some research. Thanks
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Old 08-13-2019, 08:35 AM   #10
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You may want to attack this from a slightly different perspective, which is that 115v in the household sockets is marginal to begin with. Yeah, I'm old enough to remember when 110 was the standard, but it's been 120 for 50+ years now. If you can get your electric company to adjust your local transformer, you may finesse out of your RV problem.
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Old 08-13-2019, 09:43 AM   #11
Steveo57
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Quote:
Originally Posted by Dboland9 View Post
Again, thanks to all for your thoughts. It is an RV 30amp, 30 ft, 10G cord with RV plugs. I do agree that if the electrician was thinking he put in a larger gauge from the house to the pedestal to minimize voltage drop off. I will be speaking to him to see if he has those records.

I am still insecure with running it as the voltage did drop to 109 and Dometic said that was the lowest voltage they were comfortable with.

I like the suggestion about the soft start and will embark on some research. Thanks
I really wouldn't get too worried about running it down to 104 volts. There's tens of thousands of RVs out there every day running them at those low voltages. If you look at the AC you'll most likely see that every sticker you can find says it's rated at 115 volts.

If it was a real problem Progressive and all of the other EMS manufacturers wouldn't have a low voltage cutout at 104 volts.

On hot and muggy days when the system is stressed our household voltage typically runs 112-114 volts. And I'm sure there's millions of homes out there that run at lower voltages all the time during heavy loads.

I only worry about it if starts to get down around 105-106 as it's getting close to the 104 limit of my EMS and I don't want to start having the EMS shutting power off and on to the trailer.
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Old 08-18-2019, 07:28 AM   #12
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Here's a tip... Never leave an extension cord coiled up. Completely unwind it. Heat can build up when drawing near the max Amperage of the cord and can melt the cord. It recent happened to a fellow RVer.
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Old 08-18-2019, 08:06 AM   #13
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You might want to try one of these line regulators that protects against under or over ac voltage, in effect a voltage stabilizer:
Technology Research 10176 30 Amp Voltage Regulator
https://smile.amazon.com/dp/B00A0RANJ6/

I bought the 50A version for my Class A a few years back
https://smile.amazon.com/dp/B002YI7310/

We were staying at the only RV park up in the 1000 Islands which was anywhere near the marina where we were keeping our boat. We were there for the summer and the RV Park had serious Voltage issues. I was regularly seeing voltage on one of the 50A legs dropping to 109 and below and was worried about my A/C units on that leg. Fortunately someone suggested one of these regulators and I never had another problem. Whenever voltage would drop at the pedestal, the LED lights come on indicating the regulator, which is actually also a stabilizer, would kick in and my voltage would jump right back up to 118. Worth its weight in gold.
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Old 08-18-2019, 01:58 PM   #14
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Question: Where are you installing your EMS? If it is installed at the pedestal and then you are adding 55' of cords downstream, then you really don't know what the voltage is at the AC unit. Hopefully you have it installed downstream of your cords as close to the trailer as possible in order to get true voltage being applied to the trailer.

Most everyone will probably disagree, but if you are seeing the voltage drop to 109 at the trailer with only the AC load, that's nearly 9% drop over the "standard" of 120 and indicates to me your 30A service is significantly undersized. I wouldn't run an AC or refrigerator on this service.
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Old 08-18-2019, 02:04 PM   #15
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Quote:
Originally Posted by LHaven View Post
You may want to attack this from a slightly different perspective, which is that 115v in the household sockets is marginal to begin with. Yeah, I'm old enough to remember when 110 was the standard, but it's been 120 for 50+ years now. If you can get your electric company to adjust your local transformer, you may finesse out of your RV problem.
Most utility transformers do not come with tap changers that adjust output voltage. The utilities do have the ability to adjust the primary voltage going to the transformer, but that will only happen if the primary (high voltage) circuit is lower than what it is supposed to be. We were required to maintain voltage within 5% above or below 120 volts at the main panel, which would be 127 - 113 volts, and beyond the customer panel, it is the customer's problem, which is to install large enough wire to reduce any voltage drop.
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Old 08-19-2019, 03:02 AM   #16
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Everyone is giving you great advice. Thought I would comment from an old maintenance electrician stand point. Current increases as voltage drops so...
If voltage drops the 1st thing which may happen is the circuit breaker could trip. If you trip the breaker it could just be too much voltage drop. Everyone is giving you good advice.
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Old 08-19-2019, 07:58 AM   #17
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Amperage is the "working load that produces heat" part of electrical items.

As voltage (the pressure in the hose) goes down, the current (volume in the hose) must go up to maintain the amount of "work" the appliance performs.

As an example:
1600 watts at 120 volts carries 13.3 amps through a circuit breaker
1600 watts at 104 volts carries 15.4 amps through that same breaker...

So, in this example, if you're plugged into a campground pedestal supplying 30 amps to your trailer and the voltage is 120 VAC, your air conditioner drawing 1600 watts will run "OK" with a 15 amp breaker but will "trip" the breaker if the voltage drops to 104 VAC.....

On the "other side of that equation", most air conditioners are wired to 20 amp breakers. So, it's going to be a "happy camper" buzzing along at 120 VAC while drawing 1600 watts. With that 20 amp breaker, if the voltage drops to, say 95 VAC because of heavy useage on the campground grid, that 20 amp breaker will not protect your air conditioner (designed for 13.3 amps of current) from receiving the increased current required to maintain 1600 watts to the compressor, which will be in the 16.8-17 amp range... That will produce increased heat in the compressor, probably damaging the internal components... It may "keep on running while almost smoking" that weekend. But sooner or later, the results of being overheated will take its toll and you'll be replacing the rooftop unit.

The 20 amp breaker won't "protect your air conditioner" from low voltage or high current.... That's why an EMS is so vitally important.
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