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Old 11-15-2020, 11:53 AM   #1
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Autotransformers - electrical code ban - simple explaination

The national electrical code is said to ban RV autotransformers in the new edition. I will attempt explain autotransformers simply.

Autotransformers have been used in the electrical distribution industry for a very long time. They are used in power distribution, electronics, etc.

They are different from what you think of as conventional transformers as the primary coil is not separate from the secondary. It doesn't isolate the secondary system. The secondary system is not a "separately derived system." They are designed to provide a given boost in voltage.

The typical electrical distribution system is a "radial" distribution system with breakers protecting each feeder and branch circuit. It is a "constant" voltage system (as opposed to constant current systems used by airport runways, christmas light strings, etc). As long as you stay within the current you designed for, the voltage is relatively constant. if more current is drawn than was designed for, then the voltage begins to drop.

in an old RV park that wasn't designed for large rigs, it wasn't designed for the maximum current that will be drawn on a worst case day. Hence the park voltage will begin to reduce. Alternatively if the park is on a rural utility distribution system on a worst case day the utilities power can begin to drop. What is called a "brown-out."

The problem for you is that if your RV is plugged in an the shore power voltage drops, this can adversely affect some of your appliances or equipment. Most electronics can operate at a wide range of voltages. But motors particularly are adversely affected, like your AC units. When the voltage drops the AC unit motors will draw more current to try to operate at the same RPM. This can burn up the motor windings. motor windings have "turn-to-turn" very thin insulation.

An autotransformer can boost low voltage only by a given amount. If the shore power voltage is too low you can still damage your AC unit motors.

The argument against autotransformers is that during a brown-out if everybody reduces their usage/load then everyone will have some power. If everyone has a autotransformer and runs everything hence max load the park power system will draw too much current, then trip out and no one will have power. If only a few people have a autotransformer and draw full power, thus all the current they want, then others in the park will have further reduced voltage.

This an attempt at a simple explanation.
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Old 11-15-2020, 03:27 PM   #2
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Good explanation, but it still doesn’t explain why this is a code issue. A system incapable of supplying the needed power is the problem. Implementing code requirements that could never be enforced is not an appropriate action.
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Old 11-15-2020, 03:31 PM   #3
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And the Hughes Autoformer is not an autotransformer.
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Old 11-15-2020, 03:32 PM   #4
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Good explanation, but it still doesn’t explain why this is a code issue. A system incapable of supplying the needed power is the problem. Implementing code requirements that could never be enforced is not an appropriate action.
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Old 11-15-2020, 03:44 PM   #5
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Technically, there is no ban. NFPA says that autoformers shouldn't be used in RV parks, but they're not an enforcement agency. Usually, their decisions on electrical are used in lawsuits. Many members of the NFPA are attorneys trying to secure things that benefit them.

With that said, RV parks don't like autoformers which is fine.....but then they should upgrade their power grid so autoformers aren't needed. Now in some rural areas, the campground is limited because of local City and County infrastructure.
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Old 11-16-2020, 07:31 AM   #6
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Sometimes you have no choice but to use one.


I was staying in an older campground in northern Michigan, I was there for an extended time starting in April (yup, colder then $%!). As the campground started to fill up I started to have problems. Once my wife came in July it started to get hot and she was running 1 AC hooked to a 30 amp circuit. She had dogs and when she got back after a short trip the AC unit had quite because of low voltage. I did not have a surge protector at the time.

After checking voltage, which was extremely low, I complained to the campground owners who blamed it on the utility. Well, I was working on a project that required me to be working with the Electric Utility and had contacts so I made some calls to complain. The informed me that the campground had a known problem and that the line feeding their system was all good.

I had no choice but to buy and Autoformer to maintain decent power to the coach. We used it the whole time we were there through Sept.

This explained why when checking in back in late March the owners said that I couldn't used electric heaters and/or AC (huh???)! I said there was no way I would use the electric heaters when I got there so I offered to pay an additional $100 per month, which they happily accepted but did now explain the reason.
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Old 11-16-2020, 09:23 AM   #7
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And the Hughes Autoformer is not an autotransformer.
Very true. “Multiple input transformer with automatic ratio selection” is maybe a better term, but autoformer is a cool name!
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Old 11-17-2020, 11:49 AM   #8
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Autotransformer is a marketing term for what are commonly known as line conditioners. I have been using Oneac line conditioners for 40 years and they are designed primarily to stabilize the voltage going to any connected device. They do not change the current draw of amps from anything plugged in downstream, only the supplied voltage.

As electronic devices have become smaller they have become more vulnerable to voltage spikes which line conditioners also suppress with isolated transformers. With low voltage devices can run hotter and with digital devices the logic chips performance can become erratic or fail altogether.

A separate but even more deadly problem is stray voltage on the ground line. Electronic devices are not designed to deal with voltage on the ground connection and this is why some device that can detect this problem, either a tester or a VOM, is important.

Get quotes on replacing the circuit board for a Norcold or the cost of a new TV or a new inverter and the cost for a line conditioner and an outlet tester becomes cheap insurance.

Also the NEC covers buildings and not motor vehicles or trailers. It has been a problem with solar panel and charge converter installations as the codes are nebulous. With the solar panel and inverter installed on my house the only approvals mandated was an inspection by the fire department. This was to confirm that there was an accessible power shutoff switch and room for their people to maneuver on the roof in the event of a fire.

And there is the state of Arizona which has long dragged its feet on adopting NEC codes and still has no statewide electrical code so it can vary county by county and city by city.
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Old 11-17-2020, 04:44 PM   #9
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Autotransformer is a marketing term for what are commonly known as line conditioners. <snip>
I think you might have meant "autoformer." "Autotransformer" describes a specific electrical device, one with a single coil (vs. the two in a regular transformer) and a fixed or movable tap. One side of the autotransformer is connected to the ends of the coil, and the other to one end of the coil and the tap.

Good diagram here, but I didn't read the article:

https://en.wikipedia.org/wiki/Autotransformer
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Old 11-18-2020, 04:13 AM   #10
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Quote:
Originally Posted by Calson View Post
Autotransformer is a marketing term for what are commonly known as line conditioners. I have been using Oneac line conditioners for 40 years and they are designed primarily to stabilize the voltage going to any connected device. They do not change the current draw of amps from anything plugged in downstream, only the supplied voltage.

As electronic devices have become smaller they have become more vulnerable to voltage spikes which line conditioners also suppress with isolated transformers. With low voltage devices can run hotter and with digital devices the logic chips performance can become erratic or fail altogether.

A separate but even more deadly problem is stray voltage on the ground line. Electronic devices are not designed to deal with voltage on the ground connection and this is why some device that can detect this problem, either a tester or a VOM, is important.

Get quotes on replacing the circuit board for a Norcold or the cost of a new TV or a new inverter and the cost for a line conditioner and an outlet tester becomes cheap insurance.

Also, the NEC covers buildings and not motor vehicles or trailers. It has been a problem with solar panel and charge converter installations as the codes are nebulous. With the solar panel and inverter installed on my house the only approvals mandated was an inspection by the fire department. This was to confirm that there was an accessible power shutoff switch and room for their people to maneuver on the roof in the event of a fire.

And there is the state of Arizona which has long dragged its feet on adopting NEC codes and still has no statewide electrical code so it can vary county by county and city by city.
You need to read up on 2014 NEC 550, 551, 552 and 690 and the manufacturer's sticker on the side of your RV. RV's are covered by the NEC.
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Old 11-18-2020, 01:15 PM   #11
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And the Hughes Autoformer is not an autotransformer.
And the so-called National Electrical Code is neither "national" nor a "code". It's guidance produced by the National Fire Protection Association with input from various groups.

Each AHJ ( Authority Having Jurisdiction) such as a county, city, village, whatever, must specifically adopt any updates to the NEC. They actually must also specifically adopt the NEC itself and are free to adopt 100%, free to 100% ignore it, free to adopt sections of it, and free to change any section of it to meet their local needs.

In practice almost no one adopts updates as they come out and many jurisdictions intentionally stay one revision behind because so much local effort is required to vet very change for its local impact. Especially nowadays.

Ray
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Old 11-18-2020, 02:05 PM   #12
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More accurate name would be Voltage Regulator/Booster

Hughes, TRC/Southwire, Power Masters all market Voltage Boosters
(Autoformers, Voltage Controllers, Voltage Boosters)

NFPA publishes 'guidelines/recommendations' which can be made into a law by various governing bodies...RIVA is NOT one

A voltage booster simply converts amps to volts. Since the breaker at the pole regulates the maximum amount of power you are able to draw, it would be impossible to “take” more power than the amount the park allocated to you
Use 'em if you got'em ......damage to your RV electronics/motors will not be covered by the CG
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Old 11-18-2020, 02:34 PM   #13
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Technically, there is no ban. NFPA says that autoformers shouldn't be used in RV parks, but they're not an enforcement agency. Usually, their decisions on electrical are used in lawsuits. Many members of the NFPA are attorneys trying to secure things that benefit them.

With that said, RV parks don't like autoformers which is fine.....but then they should upgrade their power grid so autoformers aren't needed. Now in some rural areas, the campground is limited because of local City and County infrastructure.
I fundamentally disagree. I've attached the Code Panel from the 2017 NEC articles that apply to RVs and RV parks. Not a lawyer on the list.
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Old 11-18-2020, 09:43 PM   #14
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Originally Posted by NXR View Post
And the so-called National Electrical Code is neither "national" nor a "code". It's guidance produced by the National Fire Protection Association with input from various groups.

Each AHJ ( Authority Having Jurisdiction) such as a county, city, village, whatever, must specifically adopt any updates to the NEC. They actually must also specifically adopt the NEC itself and are free to adopt 100%, free to 100% ignore it, free to adopt sections of it, and free to change any section of it to meet their local needs.

In practice almost no one adopts updates as they come out and many jurisdictions intentionally stay one revision behind because so much local effort is required to vet very change for its local impact. Especially nowadays.

Ray
I agree with old-biscuit.
NFPA recommendations have been adopted as laws by some governmental units.
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