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Old 08-06-2006, 08:24 PM   #15
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Are Autotransformers allowed?

The NEC says autotransformers shall not be used.

That's all it says. No explanations, elaborations, exceptions or equivocations.

NEC 2002, Article 551 Recreational Vehicles and Recreational Vehicle Parks
Section III.
551.20 Combination Electrical Systems.
. . . .
(E) Autotransformers. Autotransformers shall not be used.

I wonder why?
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Old 08-06-2006, 08:26 PM   #16
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wire not sized for increased current?

john
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Old 08-06-2006, 08:42 PM   #17
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Originally Posted by john hd
wire not sized for increased current?

john
John,

You mean the wiring on the distribution side, ie. the Park's wiring system?
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Old 08-07-2006, 03:09 AM   #18
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yes that was my thought, each service is sized for a fixed number of watts.

if you add a transformer the wattage stays the same, the voltage drops, then the current increases to meet the demand.

what does your code book say about dry transformers in a situation such as 277/480 to 120/208? is there a provision for increased duty cycle?

i am no means an expert on this as i am involved on the delivery side not the finer details most electricians have to deal with.

i would have to think the mention is made in the code to prevent everyone from having one installed from the factory, hooking up to a service rated for 30 amps and actually drawing considerably more.

think about a campground with 100 services and everyone drew 5% more!

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Old 08-07-2006, 09:02 AM   #19
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Great point, John. But that would be asumming that everybody was trying to draw thirty amps. I think there are a lot of campgrounds out there that can't begin to deliver 30 amps at a reasonable voltage to ALL the hookups. I think the old parks that have added parking spaces and added parking spaces may be the worst of them.

It would be interesting to get a clamp-on ammeter and find out how much power I'm really using. Right now, I have the PC, the air, and the TV on. The air is the 12.5 Armstrong that came with it, and the TV is an LCD. The Univolt is running, but there's no demand on it now.

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Old 08-07-2006, 12:41 PM   #20
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Quote:
I think there are a lot of campgrounds out there that can't begin to deliver 30 amps at a reasonable voltage to ALL the hookups.
there is a formula that covers that, it is called diversity factor. the power company does not size any of our distrubution equipment for everyone to turn everything on at once.

transformers are usually sized for about 50% of maximum, and fused at 200%

make sense? in theory, everyone could turn every thing on and overload the transformer.... for a while, but not for too long. temperature of the transformer limits the time it can be run this way.

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Old 08-08-2006, 06:48 PM   #21
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John, The MOVs I work with did not explode unless they were very underated from the rating of the breaker or fuse circuit. The purpose of the MOV is not to dissipate the power of a lightning strike but to quickly limit the voltage and dissipate the power while the breaker or fuse open the circuit. Just a thought.
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Old 08-08-2006, 08:41 PM   #22
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french

that is how they work for us at the power company. i have yet to see one take a direct hit and not fragment in some way or another.

not something you want under your bed in the back of a trailer!

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Old 08-08-2006, 09:06 PM   #23
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And here I just thought it was the fireworks from the miss's kiss's

I have seen automatic variacs out. Thay are in the high end audio stores. Kind of cool, but seems a waist to me since most equiment is rated for 90 to 130 VAC that I have seen.

Wonder if those things are rated at 30 amps..................
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Old 08-08-2006, 11:10 PM   #24
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Hughes Autoformers

Due to voltage drop in rural Louisiana I purchase a Hughs Autoformer Model 430 -Yes its a new model not even on there web page you may want to wait and buy this model when available. I have noticed the current models are on sale everwhere. I got mine threw www.rvperformanceproducts.com a mobile dealer for Hughes,and yes it solved the voltage problem. Darrell
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Old 08-09-2006, 03:33 PM   #25
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You are right John, I don't know of anything that will take a direct hit of lightning and not explode. I was thinking more about voltage surge caused by the inductance in a transmission line when subjected to high variations.
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Old 09-04-2006, 11:00 PM   #26
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I believe my autoformer took a lightning hit or surge this was a new model 430 hughes. They replaced and paid postage sent new transformer before I returned mine. Also its my understanting they do not rob power from campsite neihbors and may even help from more voltage drop. This was explained that if you are runnining a 14 amp a/c on low volts it may require 16 or 17 amps to run due to low volts thus drawing more current from the park. Check with Todd Coffelt at Rv Performance Products as he's the engineer. Darrell
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Old 09-04-2006, 11:48 PM   #27
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For what its worth:
In addition to the technical details about the commercial “Hughes Autoformer,” it might be helpful to some of our forum readers to lookup (i.e., Google) the definition, operation and application of the “Autotransformer” on the Wikipedia website.
I mention this to note that the Hughes Autoformer is not exactly the same thing as an autotransformer.
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Old 09-05-2006, 01:44 AM   #28
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JSTANLEY, maybe thats why they call it an autoformer rather than an autotransformer-supposedly the 430 model has many advances over the current model I belive that to be the 2130. this model tries to achieve 117 volts unless the voltage is already avail. Darrell
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