Proper AC wiring not used by FR

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   The EF2400is I had last year at altitudes up to 5000 feet started the A/C every time, but there was enough voltage drop during the startup that I felt it was near its limit.  I upgraded to a Honda EU3000is for this year's trip mostly because it has a decently-sized gas tank (the Yamaha only lasted me 8 hours per fillup with the A/C temp set fairly low and the fan set to "on"), but also because this year we'll be at higher altitudes for more of the trip so I didn't want to chance it.  

I agree the NEC calls for 12 gauge, that is clearly specified.  However, doing an actual voltage drop calculation shows a difference of 0.7% vs. 1% (10 foot run, 20 amps, 12 vs. 14 gauge).  I wouldn't go to the trouble of pulling new Romex to save 0.3% when both calculated figures are well below the 5% rule.  You could even argue those numbers are lower since a 20 amp circuit is only supposed to run 16 amps continuous.  The startup surge doesn't count since it is allowed to be much higher than the continuous rating.

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techntrek Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group - pHp Joined: 29 Jul 2009 Location: MD Online Status: Offline Posts: 9059	Topic: Proper AC wiring not used by FR Posted: 21 May 2014 at 10:10am
	The EF2400is I had last year at altitudes up to 5000 feet started the A/C every time, but there was enough voltage drop during the startup that I felt it was near its limit. I upgraded to a Honda EU3000is for this year's trip mostly because it has a decently-sized gas tank (the Yamaha only lasted me 8 hours per fillup with the A/C temp set fairly low and the fan set to "on"), but also because this year we'll be at higher altitudes for more of the trip so I didn't want to chance it. I agree the NEC calls for 12 gauge, that is clearly specified. However, doing an actual voltage drop calculation shows a difference of 0.7% vs. 1% (10 foot run, 20 amps, 12 vs. 14 gauge). I wouldn't go to the trouble of pulling new Romex to save 0.3% when both calculated figures are well below the 5% rule. You could even argue those numbers are lower since a 20 amp circuit is only supposed to run 16 amps continuous. The startup surge doesn't count since it is allowed to be much higher than the continuous rating.
	Doug ~ '10 171 (2009-2015) ~ 2008 Salem ~ Pod instruction manual

Budward Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 21 Apr 2014 Location: SC/NC Online Status: Offline Posts: 438	Posted: 21 May 2014 at 5:58am
	So- Dometic says to use 12 gauge wire for the rooftop AC NEC says to use 12 gauge wire for a 20 amp breaker. FR says, screw that we are gonna use 14 gauge and save 50 cents.. I'm digging into the surge currents and voltage drop issues involved with starting a rooftop air conditioner- it sure doesn't help when FR undersizes the wiring.... For those electrically challenged, undersized wire means more resistance in the wire, that means more power dissipated as heat, which in turns mean less power actually delivered to the rooftop ac especially under high current starting conditions. Starting the air is the determining factor in what size generator and its surge capabilities is needed. A very small generator could run the air, it just can't start it up. Next step- figure out if FR secures the wiring through the ceiling to the rooftop AC or if I can yank it out and pull proper size wire in.... My Yamaha EF2400isHC is starting my air ok at 300 ft elevation although it struggles a little- I don't want to be at, say 8000 ft and find it won't, maybe just barely won't because FR undersized the wiring. I'll be at 5000 ft next week for more testing.
	2014 179 Towed by a 2015 Ford Transit Diesel Supervised by a German/Aussie mix and a Labradoodle!