Manual generator transfer switch(es)

junkhound

junkhound

Senior Member
Location
Renton, WA
Occupation
EE, power electronics specialty
Recent PSE power outage for 4-5 days in area due to PNW 'bomb cyclone'

Our church food bank has 8 each 600W commercial freezers and refrigerators

Member will donate an 8 kW generator, problem is how to hookup low cost (very limited funds as typical of chruches these days).

My estimate is that the permits (over $200 alone here for even a single outlet) and a subpanel with manual transfer switch would be near $500 with volunteer labor.(all refrigerators and freezers now plug into 20A outlets fed directly off 4 separate 20 A main panel breakers)

Option 1 is obviously to simply run 8 extension cords during any outage to avoid xfer switch and any code issues which would be innconvienient. .

Option 2 is my question as per code:
What if any code section would prohibit a separate box with 4 20 A outlets, 4 ea 3 way light switches used as transfer switches (common to outlet, one traveller to each of existing panel 20A breaker VIA PLUG AND CORD TO EXISTING REFIGERATO UNIT OUTLETS, the other traveller to a single extension cord via separate non NEC (aircraft surplus breaker) to generator. In case of power outage, all needed than is start generator and plug in main split 120/240 extension cord to generator, and flip 4 switches.
Code wise, I do not see any prohibitions against this, with the main extension cord disconnected at each end it is simply a switch box in the refrigeration unit cord.
 
I don't see any code violation for the switches, but kind of don't like it. But the generator side would be a violation. first it would not be listed for the application and second it would be a 30A circuit feeding 20A existing circuit wiring.

I would Start with this Transfer panel. It knocks about $200 off your estimate. Mounted right beside the panel with the breakers in. The other cost would be the material for connection between the provided generator plug and the transfer panel.
 
I would suggest Option 1, but an 8kW gen would likely have 40A output protection (not protecting 20A receptacles), so you can install a 120/240V 40A inlet receptacle to a load center, which would then feed (8) 20A circuits to (8) receptacles all to be mounted to a wall or piece of plywood, so it can be portable with the 8kW potable gen. The portable generator would be cord connected to the inlet receptacle.
 
ron said:
I would suggest Option 1, but an 8kW gen would likely have 40A output protection (not protecting 20A receptacles), so you can install a 120/240V 40A inlet receptacle to a load center, which would then feed (8) 20A circuits to (8) receptacles all to be mounted to a wall or piece of plywood, so it can be portable with the 8kW potable gen. The portable generator would be cord connected to the inlet receptacle.
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So you are saying the load center would not be tied to the building panel, and would be a stand-alone powered solely from the generator?
 
ron said:
I would suggest Option 1, but an 8kW gen would likely have 40A output protection (not protecting 20A receptacles), so you can install a 120/240V 40A inlet receptacle to a load center, which would then feed (8) 20A circuits to (8) receptacles all to be mounted to a wall or piece of plywood, so it can be portable with the 8kW potable gen. The portable generator would be cord connected to the inlet receptacle.
Click to expand...

This is my vote, as well.
 
Have rethought.

Since I'd likely be the person called to start the genset and connect or switch over, have decided that since an outage of more than a few hours only happens ever 5 or 10 years, think I will just plan to daisy chain 2 extension cord receptacle strings feeding 4 units each == since going onto 80 YO, least overall labor for me over the next 15 years or so till I'm dead <G>
 
Just make sure the cords you need are stored where they won't disappear in the meantime. These things have legs!
 
Couple other ideas:

Check out these guys and see if you can find an interlock for your panel: https://interlockkit.com/

You could install a power inlet box, a 70 amp 4 space panel, 2 20A breakers, and 2 circuits to 4 receptacles in the general area where the refer units are. It would be powered only by the generator so interlocks required.
 
jim dungar said:
General purpose 3-way switches are Listed for switching loads not switching between sources.
Click to expand...
When generator is not connected the switch is exactly the same load switching configuration as the load side switch of a 3 way switching setup
When poco power is off, the switch only switches the load.

Thus, in either case, it is switching the load, hence is listed <G>
 
It isnt the same because there are two separate power sources. There is no problem on a typical 3 way circuit if both travelers are energized at the same time. Not sure a 3 way switch is guaranteed to be break before make. This could be bad when power is restored and the generator is running. You may need to ensure generator is off before switching the 3 way back to the utility side. Can't guarantee that when on auto pilot or some trys to shut it down when you aren't there.
 
junkhound said:
When generator is not connected the switch is exactly the same load switching configuration as the load side switch of a 3 way switching setup
When poco power is off, the switch only switches the load.

Thus, in either case, it is switching the load, hence is listed <G>
Click to expand...
You kind of have a good point, though it is possible to have both sides of the 'double throw' switch energized at same time from different sources, probably has not been evaluated for that purpose.
 
junkhound said:
When generator is not connected the switch is exactly the same load switching configuration as the load side switch of a 3 way switching setup
When poco power is off, the switch only switches the load.

Thus, in either case, it is switching the load, hence is listed <G>
Click to expand...
If they remember to turn the generator off as soon as the power company returns. There is likely little to no inter-terminal insulation in those switches. I would follow the Listing of the switch.
 
jim dungar said:
If they remember to turn the generator off as soon as the power company returns. There is likely little to no inter-terminal insulation in those switches. I would follow the Listing of the switch.
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I am willing to be contrary here. I doubt there is an issue with inter-terminal insulation. However, is there a possibility that there would be more than 250 volts between "switch legs"
 
Strathead said:
I am willing to be contrary here. I doubt there is an issue with inter-terminal insulation. However, is there a possibility that there would be more than 250 volts between "switch legs"
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It depends on the voltages of the sources, one may be high and the other low, and how well in sync they are. A normal 3-way switch expects almost zero difference between poles, where did you come up 250V?
 
jim dungar said:
It depends on the voltages of the sources, one may be high and the other low, and how well in sync they are. A normal 3-way switch expects almost zero difference between poles, where did you come up 250V?
Click to expand...
Oops, from my memory , which is bad. Actual code is 300 volts

404.8 Accessibility and Grouping.
(B) Voltage Between Adjacent Devices. A snap switch shall not
be grouped or ganged in enclosures with other snap switches,
receptacles, or similar devices, unless they are arranged so that
the voltage between adjacent devices does not exceed 300 volts,
or unless they are installed in enclosures equipped with identi-
fied, securely installed barriers between adjacent devices.
 
RV’s use double throw power relays in a lot of their transferswitches, which are electrically held, and fail back to utility, but those are listed assemblies.
 
Strathead said:
Oops, from my memory , which is bad. Actual code is 300 volts

404.8 Accessibility and Grouping.
(B) Voltage Between Adjacent Devices. A snap switch shall not
be grouped or ganged in enclosures with other snap switches,
receptacles, or similar devices, unless they are arranged so that
the voltage between adjacent devices does not exceed 300 volts,
or unless they are installed in enclosures equipped with identi-
fied, securely installed barriers between adjacent devices.
Click to expand...
Yes that is the requirement for distance between external device terminals. It has nothing to do with the distance between internal switch parts.
 
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