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- Location
- Langley, BC
Some RVs have two AC units in a 50 amp RV except thanks to the NEC, 50 amp pedestals can be really hard to find in a campground.
Someone is now selling a mechanically interlocked transfer switch for RVs (info. http://safervpower.com/products/safe-rv-power-model-100b) so that if you have a 50 amp RV, you can plug into a 30 amp pedestal with an adapter and run a separate cord to the 20 amp recept. in the pedestal. This allows you to run two AC units both off a 50 amp pedestal or when plugged into a 30 amp pedestal using a 50 to 30 amp adapter you can switch the 2nd AC unit to power from the 20 amp pedestal receptacle. Could this be accomplished with a DPDT switch instead? The pedestal is essentially a panelboard with power from a single source. With a DPDT switch it's not like you'd have one AC unit on poco power and the other off a generator.
Besides the above, I see an issue with demand per NEC. A 30 amp pedestal requires a min. demand of 3600 watts. However, an 13.5K BTU RV AC unit draws a FLA of approx. 15 amps at 120 volts. Running 2 AC units off a 30 amp pedestal would be drawing 3600 watts before any other running loads inside an RV are included. Also, an RV AC unit will draw more current as voltage drops which can exacerbate a drop. Low voltage in campgrounds is common, especially in older ones where they didn't use loop-fed pedestals. I can also see a potential problem with inrush current (around 70 amps) and one of the branch circuit breakers (20 amps) tripping on startup. Thinking out loud, if an AC unit failed and if someone had one of these transfer switches, could an AC manufacturer potentially refuse to repair or replace it if they discovered such a transfer switch? The transfer switch itself may be UL listed, but if you consider the NEC in the picture as well, is it possibly not a good idea?
Someone is now selling a mechanically interlocked transfer switch for RVs (info. http://safervpower.com/products/safe-rv-power-model-100b) so that if you have a 50 amp RV, you can plug into a 30 amp pedestal with an adapter and run a separate cord to the 20 amp recept. in the pedestal. This allows you to run two AC units both off a 50 amp pedestal or when plugged into a 30 amp pedestal using a 50 to 30 amp adapter you can switch the 2nd AC unit to power from the 20 amp pedestal receptacle. Could this be accomplished with a DPDT switch instead? The pedestal is essentially a panelboard with power from a single source. With a DPDT switch it's not like you'd have one AC unit on poco power and the other off a generator.
Besides the above, I see an issue with demand per NEC. A 30 amp pedestal requires a min. demand of 3600 watts. However, an 13.5K BTU RV AC unit draws a FLA of approx. 15 amps at 120 volts. Running 2 AC units off a 30 amp pedestal would be drawing 3600 watts before any other running loads inside an RV are included. Also, an RV AC unit will draw more current as voltage drops which can exacerbate a drop. Low voltage in campgrounds is common, especially in older ones where they didn't use loop-fed pedestals. I can also see a potential problem with inrush current (around 70 amps) and one of the branch circuit breakers (20 amps) tripping on startup. Thinking out loud, if an AC unit failed and if someone had one of these transfer switches, could an AC manufacturer potentially refuse to repair or replace it if they discovered such a transfer switch? The transfer switch itself may be UL listed, but if you consider the NEC in the picture as well, is it possibly not a good idea?