Stand by power transfer switch

[Pat]

After making a "mission of mercy" to help a friend with a standby generator with transfer switch arrangement I decided there must be a better way (while not going high dollar.)

A huge heavy duty multi-pole break before make switch would cost a lot more but be foolproof... I thought of an alternative...

Mount breakers in pairs with one having its OFF position on the right and the other with it on the left but the "handles" lined up so they can be physically ganged together like is done with 240VAC beakers. You can't have both breakers of a pair in the ON position at the same time. If the breaker that is ON, trips to OFF, it will not switch its "twin" to the ON position, both will remain OFF with the levers in the middle of their range of motion.

In use the "operator/home owner would just push all the handles toward the generator side or toward the grid side. NO master mechanical interlock and less confusion. The problem our friend had would not be possible since engaging a "breaker pair" in either direction automatically disengages it from the "other" source.

What I have labeled NC and NO in the accompanying sketch just shows that when one is on the other must be off. The two "wires" leaving the sketch at the bottom are just extensions of the grid and generator busses that go on to connect to the rest of the breaker pairs.

My experience/observation of breakers indicates that this mechanical arrangement would ensure break before make operation as well as ensure that you CAN'T back feed the grid and electrocute some hapless lineman.

There wouldn't be a SINGLE convenient switch to throw as you would have to separately throw each pair to go to standby power but if standby was all switches to one side and grid to the other side, a simple visual inspection would ensure you had it right. The cost would be just the breakers, enclosure, a couple terminal strips, and a few misc scraps of wire and small parts.

You would have to work out the physical breaker mounting and electrical connections as the busses in an off the shelf breaker box wold not be physically arranged to support this project. A DIY kind of person could do this.

I'm still pondering what generator (to replace my little 7 KW portable)...automatic or manual start... electric start of manual or both.. manual or automatic transfer switching...

I have settled the fuel question! DEFINITELY PROPANE!!! IT stores without degradation and burns really clean, two excellent recommendatons for standby situations. Diesels are great for power generation but on a long term basis not short runs. Gasoline is OK but is better suited for convenience with portable units. For a fixed standby generator for residential use, propane is the superior choice.

Plese forgive the crude sketch. Both the grid and generator busses should continue "off page" at the bottom of the sketch as both are required to connect with additional breaker pairs.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[GaryM]

Pat, it looks as though it would work OK.

I have a Generac unit with their transfer switch. Works fine, but only 12 circuits. I have enough capacity to run more, but there is no way to make the connections.

With your setup a person could perform power management by flipping circuits from one side to the other.

A drawback would be no automatic switching. Might be nice to have power to the freezer and refrig. if you're out of town for a long weekend. [img]/forums/images/icons/smile.gif[/img]

[Inspector507]

Yes there is Gary, add another 4-8 circuit panel next to your transfer panel. Replace or use an existing 2 pole in the transfer panel to power the extra panel. Run the new circuits to it. Let me know if I lost ya [img]/forums/images/icons/grin.gif[/img]

[GaryM]

I think I understand. Just as I replaced my 50A 220V recept. in my garage with a sub panel, I could replace a 20A breaker with say a 50A and run to a subpanel with a combo of 2-15A and a 20A. Thereby getting three circuits rather than one. Do I have the right idea? This assumes that there is a 50A breaker available for the transfer panel. I think it uses Homeline breakers.

If I want to do this, I need to find a place to mount the panel near the existing panels. Should have made the utility room larger.

[Inspector507]

You're on the right track......and yes SqD Homeline has a 50A available

[Pat]

Given the option many folks would choose a limo with driver or a private jet vs a scheduled flying cattle car but if budget considerations intrude a bicycle is still way ahead of walking in many instances and the commercial air is sometimes better than Greyhound. HUH? Say what?

My proposal for a transfer swiitch was not intended to compete with a fully automatic installation with automatic start on the generator. Some folks have manual start generators, pull rope or electric, and a manual transfer switch of varying capability and complexity. For some folks, cost is an important factor. In the cas of my friend complexity was a factor. My idea was to reduce cost and complexity without sacrificing function or safety.

Speaking to complexity, I have rethought the mechanical arrangement and have decided that a standard COTS (commercial off the shelf) breaker box would work. Using a box with two rows of breakers where the ON and OFF positions of the two rows is with the handles shoved in opposite directions, you mechanically interconnect horizontally adjacent breakers with a "pushrod", thus insuring that only one of the pair is in the ON state at a time. Other than that the wiring is the same.

To ballance the loading of the 120VAC "HALVES" of the 240VAC power, you reverse the connections on seleced loads so that for some circuits switching to the left is generator and for others switching to the right is generator. This allows load ballancing. Of course you would phisically group the breakers into two groups so that group one would all go to the left on generator and group two would all go to the right. A simple label wold end confusion.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[Pat]

Gary, Some of the boxes have DUMMY breakers available that are just used to tap/distribute power. Do you really need a breaker or just a clean way to get power to a sub or sub sub pannel?

Don't know if available in Square D Homeline but we used them in my Cutler-Hammer setup.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[GaryM]

Pat,

That might be OK, but what protects the wires going from the transfer switch to the "sub panel"? I don't seem to recall a "main breaker" on the transfer panel. There is a main breaker on the Generac unit itself. A 70A as I recall. 70A x 220V is 15KW thereabout.

[Pat]

Gary, That is 15KW for as long as it takes to trip the breaker, not very long.

Essentially the same story for the sub panels coming off my 2 ea 200 amp panels. In your case your wires could be very short and sizing them to easily take 70 amps is not a big deal. I further assume you would be placing them in conduit, a good practice.

Unless I miss your point you are concerned that an insulation failure inside the foot or so of conduit between the master and sub panels will cause a fire hazard.

What about the wires in your walls bringing power to your main breaker box. There is no breaker between the pad or pole mounted xfmr and your master breaker box. I don't know how many KW that transformer can provide in case of a short circuit but I'm willilng to speculate that it is a lot more than 15KW. If that doesn't cause you a lot of concern (or get more attention from the folks responsible for the NEC) then I fail to see the reason for your heightened concern for the previously mentioned arrangement. Are we swallowing a camel and straining at a gnat?


[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[GaryM]

Well, there's usually a breaker of some kind on the pole itself. But you're correct that the conductors from the pole to the panel don't have any protection. In my case the pole pig is feeding three houses, all with 320 A service. That's a lot of power.

I'll try and spit out that camel. Maybe start with something smaller such as a llama. [img]/forums/images/icons/smile.gif[/img]