Special Wiring Required for Furnace/Blower?


Old 01-20-07, 09:26 AM
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Special Wiring Required for Furnace/Blower?

Hi everyone,

I'm upgrading and re-organizing the wiring in my 70-year-old house prior to some basement renovation. One of my top priorities is getting my gas HVAC unit onto a dedicated circuit. When it was installed in '94, the installer ran an armored cable from a light switch box on the unit to a junction box that also branched out to ceiling lights and a receptacle. The armored cable looks like it is the same age as the furnace (not the ancient stuff everywhere else in the house) and is strapped with wire ties to the 1/2" gas supply line.

I was planning to run 12/2 NM cable directly to the switch box, but then started wondering about that armored cable. Are there any special requirements for HVAC systems that say an armored cable or conduit must be used within x feet of the unit? It wouldn't be a big deal to run the NM to a new junction box and then tie in the existing armored cable, but this is one extra step, one more point of failure, and another temptation for a future owner to tap into the furnace's circuit again.

Thanks, as always, for your input.
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Old 01-20-07, 09:31 AM
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I always find its best to check code for where you are. Some now call for a cut off switch at the furnace . Also like another one at the top of the basement stairs
Old 01-20-07, 09:34 AM
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Wow...lightning fast response.

Would that be in the NEC, IRC, or a special code book for HVAC and other kinds of systems?

I did check the installation manual, which just said to use UL wiring that's appropriately sized.
Old 01-20-07, 10:48 AM
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Overkill is not bad. Nobody can fault you for doing more than is required. Around here we run either MC cable or put the wiring from the floor joist to the furnace in EMT (thin wall conduit). We are required to install a recepticle & switch within 6' of the furnace & within reach while working on the burner. The recepticle is wired on the "hot" side of the switch & both are mounted on the side of the furnace. There must also be an emergency switch (usually at the top of the stairs) in order to kill power to the furnace from a safe distance in case of an emergency. The emergency switch is first off the breaker & will kill power to the service switch & recepticle on the furnace.

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