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We're researching low cost solar power systems, and we stumbled across a company out of Tx, offering a system that allows you to switch individual circuits between your service lines and solar. Sounds all well and good, but this is how they suggested to do it.

Burn baby, BURN!

I think this idea is beyond terrible, however I lack the experience and anecdotal evidence necessary to come up with a compelling argument or alternative solution.

The question:

What (low cost) solutions are there that will allow us to be able to switch individual circuits between the two power sources?

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  • Are you looking for manual or automatic transfer? – ThreePhaseEel Oct 21 '16 at 22:25
  • @threePhaseEel: Either are acceptable, but automatic is preferable. – Gabe Evans Oct 21 '16 at 22:27
  • Have you looked at existing transfer switch hardware? – ThreePhaseEel Oct 21 '16 at 22:30
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    Terrible idea generally, but even worse, all the plugs and sockets are the wrong polarity. Consumers of power use prongs because when they are unplugged and the blades are exposed, they are dead. Sources of power use recesses (female) so their always-hot parts are shielded. – Harper - Reinstate Monica Oct 22 '16 at 0:17
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    I wouldn't even buy a light bulb from these clowns. They are trying to kill you with their hot-blade male plugs. – A. I. Breveleri Oct 22 '16 at 3:28
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If you are OK with manual transfer operation, what you're after is called a "select circuit" manual transfer switch -- they're pretty readily available, for anywhere up to 12-16 circuits. Reliance and Generac both make them.

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  • This. Fits my needs like a glove. Thanks a billion! – Gabe Evans Oct 22 '16 at 16:19
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There's nothing electrically wrong with that proposal*, and it certainly is low cost - the plugs will be about $10 a pair. Wether extension-cord plugs are allowed in permanent wiring is a question for the local inspector, my guess would be no.

Would I do it? Never. The branch circuits will run through places that make inline connections rather difficult, and solid 14/2 wire won't like being handled all that often, expressing it's displeasure by eventually breaking.

Spend a bit more money and wire some proper switches in. Yes, you will need double-pole transfer switches - hardwiring the solar inverter's neutral to the house neutral is electrically possible in some cases but not others, your local code will probably say NO! Penalty for a mistake here is incineration of your solar inverter.

Personally I would make a wall panel of large knife switches, connect a couple of jacob's ladder generators and a fogger, all lit by a single 40 watt bare bulb. Find some large-dial analog volt and ammeters to monitor each circuit. And clean all the lubricant out of the door hinges. bonus points if it's in the basement and access is by a floor hatch.

  • other than the polarity of the plugs, but I'm writing that off to the company owner's daughter not knowing that detail when she did the drawing.
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That setup is terrible at so many levels, but fixable on all of them.

First it's illegal under NEC because you won't find any plugs/sockets listed for use with solid wire. Plug manufacturers will never support solid wire, since cords need to flex repeatedly and solid wire can't.

If the movable jumper had been done with proper cordage, then okay.

Second, they're using the wrong gender of plugs and sockets. They are putting the load on sockets and the supply on plugs, which makes the blades energized at all times. This was always outlawed in NEC, and was even outlawed in HEC 2015 after Ned out in Mud Creek Holler's uncle Jethro burned down his still.

So use sockets on the supply side and plugs on the load side - that works.

Third is that to greatly simplify the use of cordage, the supply (should be sockets) connectors would be better off being rendered in fixed wiring, i.e. Receptacles in junction boxes permanently mounted. Only the load side (should be plug) should move. Remember, duplex receptacles have tabs on both sides, so you can separate neutrals and use both.


Another more hardwired option is to dispense with the plugs and use DPDT switches. You must switch neutral. These fit in a standard junction box, but they are not cheap, in the $20-30 range. Also they need large/deep junction boxes since so many wires are connected to them - 20 cubic inches per switch for #14 wire and 25 c.i. For #12. A 4-11/16 box with a domed cover could support 2.


Admittedly it'd be far more elegant and likely cheaper, to have a subpanel for all the loads you might want to run on solar, and use a generator interlock (Siemens, $20) to switch the entire panel between gen and solar.


The most expensive/complex/awkward way would be using one of those generator transfer switches with like 8 switches on it. I wouldn't call them "hokey" after seeing OP, but I'm seriously not a fan of those things. When you actually know how to do electrical, you just shake your head, thinking why would they do it that way, it's wasteful, overwrought and adds a ton of complexity that just doesn't need to be there. And a bunch of failure points.

Why do these products exist? To be installed by generator installers who are not electricians and whose insurance won't let them open up a panel to do a better solution. Also it is a nice, expensive sellable unit, giving them a hefty markup/kickback.

It's important to note that reputable service equipment manufacturers like Siemens, Eaton, Schneider/Square D or General Electric refuse to make these things. Siemens lets you do the same job with a $20 strap that lets you tie together two $9 breakers and put them in a $75 main-lug panel, and all your loads go in the remaining spaces. The setup is simple, has half the wire count and uses standard parts. And that's all industrial tier stuff that'll work for 40 years.


Lastly there's the matter of AFCI/GFCI. With the subpanel solution, you provide that protection in the subpanel and it protects in all modes. All the other solutions I mention are switching downstream of the service panel, which means both sources need to independently supply AFCI/GFCI protection if/where it is required. Which is almost everywhere these days. You can't just "not provide it" in gen/solar mode. I seriously doubt a generator provides AFCI, and in fact there are length requirements to AFCI, so providing it clear out at the generator just doesn't work.

These GFCI/AFCI requirements may be the deathknell of all switched solutions and force the Siemens style subpanel solution. (All brand's panels provide generator interlocks, just Siemens' is a lovely intersection of superb in design, simple and very cheap.)

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