3 way as transfer switch

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junkhound

junkhound

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Renton, WA
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EE, power electronics specialty
Not a code expert, and wondering if this is prohibited by any code section:

Small single phase genset with it's own separate 20A CB panel

Furnace, TV, microwave. lighting circuits each go to common of four separate 3 way switches. One traveler to the genset CB panel, the other traveler to the main panel.

Appears perfectly safe, but sounds like something non-code, but cannot find correct NEC reference. Or, is there a code section that allows this?
 
junkhound said:
Not a code expert, and wondering if this is prohibited by any code section:

Small single phase genset with it's own separate 20A CB panel

Furnace, TV, microwave. lighting circuits each go to common of four separate 3 way switches. One traveler to the genset CB panel, the other traveler to the main panel.

Appears perfectly safe, but sounds like something non-code, but cannot find correct NEC reference. Or, is there a code section that allows this?
Click to expand...

Garden variety 3 way switches would fall under UL Product Category WJQR. This category specifically says that they cannot be used for this purpose as they are not tested with 2 sources of supply to 1 load.
 
The switches used are probably RU registered components, allowing the whole assembly to be qualified as a transfer device.

Sent from my XT1585 using Tapatalk
 
texie said:
Garden variety 3 way switches would fall under UL Product Category WJQR. This category specifically says that they cannot be used for this purpose as they are not tested with 2 sources of supply to 1 load.
Click to expand...

Thanks for the reference. I might be getting to old to read right, but could not find the part that specifically prohibits this type use. Is it in a different section I need to link to?
 
100% doable. As long as there is OCPD protection on the gen side matching the wires (ie 15amps #14, 20amps #12) and the whole setup is treated as a non separately derived source I see no issue.
 
junkhound said:
Not a code expert, and wondering if this is prohibited by any code section:

Small single phase genset with it's own separate 20A CB panel

Furnace, TV, microwave. lighting circuits each go to common of four separate 3 way switches. One traveler to the genset CB panel, the other traveler to the main panel.

Appears perfectly safe, but sounds like something non-code, but cannot find correct NEC reference. Or, is there a code section that allows this?
Click to expand...
Don't quite understand what is being done here. By genset you mean a panel with 3 position breakers like someone posted? Or is this some kind of DIY setup. Why would you need 3-way switches.
 
A 3-way switch is a single-pole, double-throw switch, as is a transfer switch (unless it's a 2- or 3-pole T/S).

L-T-Knife-Switch-S-P-D-T-.jpg
 
Saw this in an engineer's residence.

small 1800 W 120 gas generator, has a QO 20 A breaker in standard sqD box, 1/2" emt to 4 gang regular wall outlet box. NM to furnace, dedicated microwave outlet, dedicated entertainment center outlet, and one lighting circuit. Also a 3/4" EMT to main panel with EGC, 4 black, 4 white 12 AWG THHN wires to main panel, each of those black to a 20A breaker.

In case of outage, HO switche one or 2 the 3 way at a time (all to genset ona at one time would stall genset if microwave being used) to get thru the outage. Think the HO wants to add 2 additional switches and circuits to the fridge and freezer.

My opinion to him was that I saw nothing unsafe about the setup (unless somebody got into it later and incorrectly rewired?), but was wondering about what if anything the code says about that usage of 3 way switches.
HO could always replace switches with UL fire system rated switches as implied in the UL references provided earlier.

Asto someone "in the business' having reservations, would seem like a much safer very low cost approach than suicide cords.
 
junkhound said:
Saw this in an engineer's residence.

small 1800 W 120 gas generator, has a QO 20 A breaker in standard sqD box, 1/2" emt to 4 gang regular wall outlet box. NM to furnace, dedicated microwave outlet, dedicated entertainment center outlet, and one lighting circuit. Also a 3/4" EMT to main panel with EGC, 4 black, 4 white 12 AWG THHN wires to main panel, each of those black to a 20A breaker.

In case of outage, HO switche one or 2 the 3 way at a time (all to genset ona at one time would stall genset if microwave being used) to get thru the outage. Think the HO wants to add 2 additional switches and circuits to the fridge and freezer.

My opinion to him was that I saw nothing unsafe about the setup (unless somebody got into it later and incorrectly rewired?), but was wondering about what if anything the code says about that usage of 3 way switches.
HO could always replace switches with UL fire system rated switches as implied in the UL references provided earlier.

Asto someone "in the business' having reservations, would seem like a much safer very low cost approach than suicide cords.
Click to expand...
As was noted by Texie standard 3-way switches are not listed for two feeds. Ask the engineer if he did it himself. Actually sounds like more work then doing it the right way with an interlock kit or small gentran panel. This is not supposed to be a do-it-yourself site. IMO this is an obvious DIY setup that would not be passed if inspected by an EI.
 
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