Upgrading 30 Amp to 50 Amp Service in my Motor Home
My Motor Home has a 30 amp system in it. The previous owner had installed a second air conditioner in the rear bedroom. They installed a 3 way toggle switch to switch between the front and rear air conditioners. Could not run both at the same time without overloading the circuits. I decided to upgrade to a 50 amp service so I could run both air conditioners at the same time when hooked to shore power. I did not want to run both air conditioners with the generator, and did not want to buy a 50 amp Automatic Transfer Switch (ATS). So this is how I did it.
I already had a 50 amp 30 ft extension cable from a previous motor home. I just had to change the Cable end to match the New 50 amp Input Receptacle on the Motor Home. I purchased a Marinco 50 amp receptacle, Marinco 50 amp twist waterproof plug and cover off of Ebay for $130. The cable can be unscrewed from the motor home receptacle with a half turn. The old 30 amp receptacle was the same size so the new one fit without any modification.
I ran a 8 ft piece of #6 Cable 3 wire w/ground from the new receptacle to a 70 amp load center that I purchased along with a 30 amp and 20 amp breaker. The 30 amp breaker will feed the Automatic Transfer Switch (ATS) and the 20 amp breaker will feed the rear air conditioner. That way the 30 amp system will remain the same except there will be no Toggle switch to change AC’s from front to rear. The original 30 amp circuit from the motor home distribution panel, will feed the front AC. The rear AC will be fed by the 20 amp breaker in the 70 amp load center. Here is a explanation of what I have done and why.
In a 30 amp system you have 2 wires L-1 and Neutral, and a ground wire 120 volts between L-1 and Neutral. In a 50 amp system You have 3 wires L-1, L-2, Neutral and a ground. 120 volts between L-1 and Neutral, 120 volts between L-2 and Neutral, and 240 Volts between L-1 and L-2. So with the 50 amp service we now have 2ea 120 volt legs or circuits. One for the ATS Switch and one for the rear AC unit. The 50 amp Cable from the Input Receptacle goes to the 70 amp Load Center, the L-1 and Neutral 120 volts goes thru the 30 amp breaker in the load center, which goes to the Transfer switch. The transfer switch 30 amp, automatically transfers power between the generator and the 120 volt line to the motor home distribution panel. L-2 and neutral goes thru the 20 amp breaker in the Load Center which goes to the rear or second air conditioner.
The reason for the Load Center is for protection of the 30 amp wiring, the 30 amp Automatic Transfer Switch (ATS), and the Motor Home Distribution Panel. The 30 amp breaker in the load center protects all of 30 amp system. If you were to run the 50 amp cable direct you would not have any protection between the distribution panel and the ATS in the event of a short circuit. The switch could be damaged or the wiring could burn before the 50 amp breaker would trip in a campground pedestal. So the 30 amp breaker in the load center is necessary for protection. The rear air conditioner needs to be protected and the 20 amp breaker in the load center does that.
I removed the toggle switch and hooked the original wire from the front air conditioner circuit breaker in the motor home distribution panel to the front AC line using a metal junction box and wire nuts. This is the way it was before the second AC and the toggle switch. The line from the Second (Rear) AC is hooked direct to the 20 amp breaker in the load Center.
Finished it up today and tested it. It Works Great. Now when it is hot and we are hooked to shore power I can run both Air Conditioners at the same time.
Below is a link to pictures that I took showing some of the details.