| [GMCnet] Good article on shore power and your GMC [message #285027] |
Sat, 15 August 2015 15:57 |
glwgmc
Messages: 1014
Registered: June 2004
Karma:
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Senior Member |
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From time to time there are discussions of how the shore power works inside your GMC. Depending on who finished it, year, etc. the incoming power may be brought in via a 30 amp or a 50 amp cable and plugs, For the 50 amp versions there always is confusion as to why the power in a properly wired shore power receptacle looks like a standard 4 wire 220vac outlet but only provides 120vac into the coach. There is a very clear explanation starting on page 99 of the September 2015 issue of MotorHome magazine. I recommend it be scanned and placed into our archives so we can reference it the next time this issue comes up.
The simple answer is that the four wire 50 amp shore power cord carries two 120vac cables and inside the GMC one of those carries 120vac down the right side of your coach and the other carries 120vac down the left side of your coach. Both use the same white return line called neutral as the two 120vac lines are 180 degrees out of phase with each other IF the shore power receptacle is properly wired. No where inside your GMC are the two 120vac lines connected together to supply 220vac as you are used to in your home. Also the green ground wire and the white neutral wire are never connected together inside your GMC as they are in your home. Your stock Onan generator puts out only 120vc which it supplies to both of the 120vac lines inside your coach.
If you have a 30 amp shore power cord with which to connect to he shore power receptacle, you will have a total of 30 amps available from the wires running down both sides of your coach. The article shows a very clear diagram of how the shore power receptacle is supposed to be wired. One of the 120vac legs coming to the post supplies one side of the four wire 50 amp plug and the positive post on the 30 amp receptacle. The other 120vac legs coming to the post supplies the other side of the four wire 50 amp plug and the positive post on the 20 amp receptacle.
You can, if you want to, plug any 220vac appliance into that receptacle with a plug with the correct lug pattern, but inside your coach as it was designed you will never see 220vac, only those two 120vac lines and that is where the confusion usually starts. Hope this helps as improperly wiring inside your coach on either the hot leg side or the neutral and ground leg sides can result in a very dangerous condition so don’t deviate from the factory AC wiring unless you really know what you are doing.
Jerry
Jerry Work
The Dovetail Joint
Fine furniture designed and hand crafted in the 1907 former Masonic Temple building in historic Kerby, OR
glwork@mac.com
http://jerrywork.com
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Jerry & Sharon Work
78 Royale
Kerby, OR
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