Reminder: Never connect a generator to home wiring without transfer switch

Jay Hennigan jay at
Tue Aug 31 18:13:21 UTC 2021

On 8/31/21 07:06, Mel Beckman wrote:
> Mark,
> I think you’re forgetting about the all-important blower fan in a gas-fired furnace.

We're *really* getting in the weeds here. A single note to the list 
about not backfeeding has really blown up.

> That said, the reason the code requires furnaces to be hardwired is to ensure that the blower interlock system can’t be bypassed. An electrical interlock ties a heat recover ventilator to circulation air blower operation of a forced-air furnace system. This ensure that the blower circulates supply and return air within the structure. A plug-in power source leads to the possibility that this interlock could be accidentally defeated, resulting in an overheat within the flame box.

This doesn't compute. In a conventional forced air furnace the 24V 
transformer operating the thermostat, logic, and gas valve is powered by 
the same electrical source as the blower. In the event of someone 
unplugging the furnace, or for that matter a power failure, the gas 
valve will close when the power disappears.

Yes, there are old-school pilot light thermocouple-powered gas valves in 
wall and floor heaters that require no electricity at all. They rely on 
convection to distribute the heat, not a blower.

Jay Hennigan - jay at
Network Engineering - CCIE #7880
503 897-8550 - WB6RDV

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