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Author Topic: Automatic Transfer Unit (ATU) w Portable Generator?  (Read 328 times)

W4MSL

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Automatic Transfer Unit (ATU) w Portable Generator?
« on: May 27, 2020, 01:43:43 PM »

Generac SALES advised me that, though not specifically INTENDED for this purpose, that a whole-house capable ATU could be configured to accept input power from a PORTABLE generator (which obviously could NOT power an entire house). This would require that the ATU be placed in MANUAL mode, as a portable generator will not respond to a signal as would a standby unit. The unneeded house circuits would also have to be manually disengaged at the breaker box to prevent potential overload of a lower capacity generator.

Why would I want to do this? Because I want to be able, if and when needed, to use the same ATU if I decide to purchase a whole-house stby generator. I'd prefer to avoid having to purchase and then replace a manual transfer unit in that case.

Is there any reason to think that this can be done within code (Georgia) and in a manner which is reversible (if/when I need a stby generator)? And would not  compromise warranty coverage for either the ATU or the stby generator?
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KG4RUL

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Re: Automatic Transfer Unit (ATU) w Portable Generator?
« Reply #1 on: May 27, 2020, 01:54:11 PM »

Having gone through installation of a GENERAC whole-house generator system, I would STRONGLY suggest that you contact your local GENERAC installing dealer for guidance.
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KD0REQ

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Re: Automatic Transfer Unit (ATU) w Portable Generator?
« Reply #2 on: May 27, 2020, 03:14:27 PM »

a small automatic transfer system will have individual breakers for the loads it serves. a master ATU for the whole house cuts in ahead of the entrance panel and serves everything. the concern is if a breaker fails closed, like the infamous no-trip FPE ones, it will feed unwanted circuits.

the difference is thus, overload and tripping the genset, or backfeed which could kill a lineman and potentially feeding the whole neighborhood with the wrong transfer system.

it has to be done according to code and by somebody who knows what they're doing. if you upgrade from a portable generator to a whole-house rig, yeah, you're doing it all over. that's the only way to go for safety.

when we lose AC, and we've done it for 5 days, it's not a big deal to rig the canopy, tie a tarp to the canopy where the rain is coming from and anchor the bottom with two 5-gallon pails half-full, and string extention cords. if you're on the fence, heck, set up for that and save your cash for the possible whole-house job.

and contract out the big stuff. das ist fur Experten, ja.
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W4MSL

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Re: Automatic Transfer Unit (ATU) w Portable Generator?
« Reply #3 on: May 27, 2020, 05:04:11 PM »

If you're on the fence, heck, set up for that and save your cash for the possible whole-house job. and contract out the big stuff. das ist fur Experten, ja.

Ja! Sehr gut. Ich verstehe. Pretty much what I was thinking would be the case. Local Generac dealer of course had never encountered such a cockamamie idea, which is what it is.

So, yes, a transfer unit suitable for a good portable unit, and upgrade the whole thing if and when. Compared to the enormous cost of a stby generator install, the actual ATU is small potatoes.

Thanks.
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W9IQ

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Re: Automatic Transfer Unit (ATU) w Portable Generator?
« Reply #4 on: May 27, 2020, 05:17:47 PM »

The Generac ATU is easily manually switched. They provide a manual lever you can insert to affect the transfer. With a smaller generator, you will need to manually shed loads using your breakers or other means before starting your generator.

Verstehst du?

- Glenn W9IQ
« Last Edit: May 27, 2020, 05:26:50 PM by W9IQ »
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

W4MSL

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Re: Automatic Transfer Unit (ATU) w Portable Generator?
« Reply #5 on: May 27, 2020, 05:26:05 PM »

The Generac ATU is easily manually switched. They provide a manual lever you can insert to affect the transfer. With a smaller generator, you will need to manually shed loads using your breakers or other means before starting your generator.

- Glenn W9IQ

My thoughts going into this, but it sounds like getting permits to do this and meet code would be difficult. Agree, the concept sounds attractive. Getting a licensed electrician to pull permits and get it through an inspection sounds tricky.
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K6AER

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Re: Automatic Transfer Unit (ATU) w Portable Generator?
« Reply #6 on: May 27, 2020, 05:49:31 PM »

I have been installing generator input receptacles on my homes for over 40 years. Never once did pull a permit. There is a rotatable switch cover you can install in the home man breakers. When the mains are off the rotatable cover enables the split phase breaker to be turned on for the generator power cable. Harbor Freight sells 8 KW generators for about $500.00. I know it is not automatic but in a area wide blackout, simple is the best method.

Your biggest problem in a mass black out scenario is keeping enough fuel on hand for 10 days of operation.
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NA4IT

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KD4UPL

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Re: Automatic Transfer Unit (ATU) w Portable Generator?
« Reply #8 on: June 04, 2020, 06:32:39 PM »

You can absolutely feed a portable generator into an automatic transfer switch. The switch doesn't know or care where the electricity is coming from. All automatic switches have the ability to also be switched manually. You would simply start your portable generator and then manual transfer the load. You would, or course, need to manage the loads carefully.
I would strongly recommend you consider another brand besides Generac. They do have huge market share and you can buy them most anywhere but their quality is terrible. I would recommend Kohler or basically any other brand over Generac. Be careful though, lots of other "brands" are really just re-labeled Generacs. Eaton and Honeywell come to mind as 2 examples.
But, as another poster mentioned, installing an interlock on your main electrical panel cover is by far the least expensive way to be able to transfer power to a portable generator. geninterlock.com will sell you one for most any panel for about $70.
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W4MSL

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Re: Automatic Transfer Unit (ATU) w Portable Generator?
« Reply #9 on: June 04, 2020, 07:11:25 PM »

You can absolutely feed a portable generator into an automatic transfer switch. The switch doesn't know or care where the electricity is coming from...
But, as another poster mentioned, installing an interlock on your main electrical panel cover is by far the least expensive way to be able to transfer power to a portable generator. geninterlock.com will sell you one for most any panel for about $70.

Yes, thanks. There are enough viable options to make it complicated. But, at present, I'm leaning toward the interlock panel as a first step, with an exterior-rated wall-mounted receptacle on my side porch to take input from the portable. Wiring from there to the main breaker panel would go into the space between the studs of the outside wall and the interior sheetrock (after establish a safe path exists!), then terminate at the interlock. Only a few feet. An eventual automatic transfer switch would go at the mains entry point on the other side of the house, if and when I spring for a stby generator. No cost savings that way, but it at least allows me to spread out the costs and have something functional from the beginning. And, supposing the stby went on the fritz, I'd have the portable as a backup.

No preference for Generac here. My plumbing DIY work makes me favorable to Kohler as a company. But, the real factor will be a mix of cost and availability and quality of post-installation service, warranty, etc.
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K6AER

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Re: Automatic Transfer Unit (ATU) w Portable Generator?
« Reply #10 on: July 29, 2020, 06:34:33 PM »

You will need to know what loads are necessary and what can be worked around. Well pumps take about 30 amps to start and 10 to run. Air conditioners are not as bad but will take 20 amps to start and about 12 to run. Electric stoves, dryers and electric home heaters are monsters for wattage usage.
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W9FIB

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Re: Automatic Transfer Unit (ATU) w Portable Generator?
« Reply #11 on: July 30, 2020, 03:20:41 AM »

Here is some easy to understand info for a manual transfer switch which with portable generators a simpler and cheaper set up. Also have a variety of models and pricing.

https://www.electricgeneratorsdirect.com/stories/3-How-to-Pick-the-Perfect-Manual-Transfer-Switch.html
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73, Stan
Travelling the world one signal at a time.

KG4RUL

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Re: Automatic Transfer Unit (ATU) w Portable Generator?
« Reply #12 on: July 30, 2020, 05:36:48 AM »

You can absolutely feed a portable generator into an automatic transfer switch. The switch doesn't know or care where the electricity is coming from. All automatic switches have the ability to also be switched manually. You would simply start your portable generator and then manual transfer the load. You would, or course, need to manage the loads carefully.
I would strongly recommend you consider another brand besides Generac. They do have huge market share and you can buy them most anywhere but their quality is terrible. I would recommend Kohler or basically any other brand over Generac. Be careful though, lots of other "brands" are really just re-labeled Generacs. Eaton and Honeywell come to mind as 2 examples.
But, as another poster mentioned, installing an interlock on your main electrical panel cover is by far the least expensive way to be able to transfer power to a portable generator. geninterlock.com will sell you one for most any panel for about $70.

The ONLY issues I have had with my 22KW, GENERAC installation were leakage issues in the Propane system.  It has taken load on seven occasions without any problems.  I wholeheartedly recommend GENERAC.
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KB8VUL

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Re: Automatic Transfer Unit (ATU) w Portable Generator?
« Reply #13 on: August 13, 2020, 02:19:51 PM »

I understand the idea of using a full ATU now if you have the money to get one and running it with a portable generator.  But, you need to understand that you will absolutely need to shed load before starting your portable generator and transfering over.  And you need to remember that YOU might not be the only one doing it.  More than that, if you DON'T ever bother with the stationary generator, the transfer switch will lower the property value because anyone looking at it will only see a possible problem with it due to there not being a stationary generator being connected.  But I will also say this... used generators are out there for cheap.  I bought 2 60KW units for 2 grnd each.  A 60 will run two houses unless they are all electric.  And I mean tow houses with well's, electric furnace, electric stove and the whole works.  Hell I can even run the clothes dryer while baking a cake in the oven.  It's plenty of power.  Look for one with low hours, and with an engine that is common.  One of mine is a Vortec 5.7 (small block Chevy) the other one is a 351 Windor Ford motor.  I also have a 40KW diesel on a trailer to back either of the two up and it will about run the complete house. 
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