Electrical cable routing

[Clay White]

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[James Duffin]

It needs to be supported. A 2x4 nailed to the rafter visible in the top of the picture would be sufficient i believe. It would need to drop down close to the cable entrance on the furnace.

[Jerry Peck]

The electrical cable to the furnace is about 4' 6-7inches - - difficult to get exact measurement. I know cables should be secured every 4.5 feet.

From the NEC.
" ... and within 300 mm (12 in.) of every cabinet, box, or fitting. "

Don't forget that last part, and, that pretty much also answers your question. ;)