Use transfer switch to increase on-grid passthrough to 200A

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Use transfer switch to increase on-grid passthrough to 200A

Postby seanadams on Wed Oct 03, 2012 8:36 am

Unless I'm mistaken, there does not appear to be a pre-engineered solution for doing this with an Outback system. That is really surprising since this is how any proper fossil-powered automatic standby generator would be connected - why not Radian? The transfer switch also provides isolation for serviceability, a nice bonus.

See this drawing: http://i.imgur.com/fvBjB.png

The goal here is that when the grid is up, I should have the full 200 amps available in the home. But when the grid goes down I will get up to 66A from a pair of Radians, and then a load shedding controller would act to inhibit larger loads as necessary to keep the power draw within the available supply from the Radians.

Ideally, said load controller would intelligently cycle through the external loads giving each a chance to run in turn.

I don't think this would be terribly hard to engineer - certainly the transfer switch is simple enough. The Generac RTSD200A3 appears to be a simple passive device that could be controlled with just a contact closure.

The question is how to implement the load shedding control? Is there something off-the-shelf to do this or should I roll my own? I certainly know enough electronics to do that, but if there's some reasonably priced controller sold for this purpose then I'd rather use it.

Second question is where can I get the information needed to signal an overload condition. The Radian has this as one of the programmable AUX features - is this signal suitable for the exact purpose I'm contemplating here? Will it respond instantaneously if a large load tries to put the system over its limit?

Third question is what is the behavior of the Radian under overload conditions? Is there a hard shutoff or do you get a warning (sagging voltage/freq). What would be ideal is if it could drop the output frequency a little to signal that is approaching overload condition. This happens to be exactly what a gas-powered generator does intrinsically, because its rotor slows down. If the Radian could signal overload in this manner, then it could possibly allow the use the load shedding controller that comes included with the Generac ATS, without modification. (I haven't confirmed this - I don't actually have this ATS in hand to reverse engineer it).

Any other comments on this system design would be welcome.
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Re: Use transfer switch to increase on-grid passthrough to 2

Postby sparksalot on Thu Sep 01, 2016 9:18 am

Are you still out there and what did you go to?

We might share ideas, as I have been dabbling in load shedding recently. :wink:
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Re: Use transfer switch to increase on-grid passthrough to 2

Postby jslc on Tue Nov 14, 2017 6:28 pm

I'm also curious. I've been thinking about a very similar setup. Has anyone got something like this in service?
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Re: Use transfer switch to increase on-grid passthrough to 2

Postby seanadams on Tue Nov 14, 2017 8:33 pm

Yes I did use an external 200A transfer switch for my system and it worked great. I had to do some rewiring of the transfer switch controls, in order to connect an external SPST switch to control it manually (it was designed to talk to a generator control panel).

The setup I went with was to have my "critical loads" on the Radian's internal automatic transfer switch. Then to run my non-critical loads (Air conditioner etc) I would manually hit the switch which would flip the 200A contactor.

I did not attempt any kind of overload or automatic load-shedding controls. But being a manual transfer switch, I would have the opportunity to know that I'm running on backup and only run the most important things.

I no longer live there but I might have some pics and schematics I could try to dig up tomorrow.
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Re: Use transfer switch to increase on-grid passthrough to 2

Postby jslc on Tue Nov 14, 2017 9:19 pm

Thanks for the reply. I’d love any info you can provide. In particular, what transfer switch did you use and more details on the modification. Sounds like the switch was triggered manually and the Outback did not trigger it.
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Re: Use transfer switch to increase on-grid passthrough to 2

Postby blackswan555 on Tue Nov 14, 2017 10:21 pm

I suggest you have a look at your local codes first for an "approved" switch if you are connecting it to grid, Do a google for
automatic transfer switch
The big reason behind the "code" is it must have 2 methods of lockout, Mechanical & Electrical, Mechanical, A small pin in-between contractors, Electrical, the small set of contacts on end, Both to ensure that only ever one contractor can be on at any time, So you can not send "your" power to the grid and knock the linesman working down the street off his ladder,
But above taken into consideration, They are not hard to build yourself, heres a random weblink but his videos are reasonable, http://diytechandrepairs.nu/automatic-t ... ms-how-to/

Tim
My comments are based on my experience and research, They are not endorsed or checked by Outback.I am an independent British electrician living in Spain, So please take this into account when reading /acting on my post`s.
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Re: Use transfer switch to increase on-grid passthrough to 2

Postby seanadams on Tue Nov 14, 2017 10:56 pm

Tim, yes I'm aware of those NEC requirements and I believe this to be compliant. I repurposed a generator ATS, so it has all those properties mechanically - it physically can not occupy both positions. Back with more info shortly...
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Re: Use transfer switch to increase on-grid passthrough to 2

Postby seanadams on Tue Nov 14, 2017 11:37 pm

modified transfer switch wiring.pdf
(50.15 KiB) Downloaded 33 times


Attached is my schematic showing the changes I made to the transfer switch.

The attached schematic does not show the high-current side of the ATS, that is unmodified. See the manual for that part of the schematic.

It's been so long since I did this, it would take me a while to refresh my memory to be able to explain it correctly. I think two small 120V relays were added. Wish I had pics.

I misspoke earlier that this switch was completely manual. Actually it will cut in/out automatically per the availability of grid power, and the manual switch is just to force it not to go to backup (so you can prevent the big loads from being switched in if you want).

Transfer switch is Generac RTSD200A3. Technical manual: https://www.norwall.com/product_pdfs/pdf_file_39538.pdf (schematics on pp 12). The "load controller" was removed.
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