RV Hot Skin (Exterior electrification)

CA Traveler wrote:
In the years I've been on various forums electricity is hands down the least understood topic. In 2004+ the top item was 50A RV power. It just shows how little is understood about house power which is the same except that a house us usually 100A, 200A, etc.

ie Its 120/240V 50A 3 pole 4 wire 60 Hz SINGLE PHASE and 12,000 watts.

And a 50A open ground is yet another mystery. Not being critical as there is much about a lot of things that I don't know.

Actually, 120/240 US home entrances are referred to as SPLIT PHASE, sometimes as a TWO PHASE STEP DOWN.

See HERE

"240V or split phase: For small residential buildings, the usual method is to rig up a 240V stepdown transformer (instead of 120V) in which the secondary winding is split into two 120V windings (hence the name "split phase"). The center tap is then grounded and fed to the house as if it was the neutral wire of the old 120V system, and each end is wired as a separate 120V live wire. Their waveforms have a half-cycle offset, or 180 degrees, when measured against the neutral wire. The normal 120V designed machinery does not care which live wire you use for them as long as you connect them between a live and neutral wire. Appliances in the home can be distributed on either live wire to maintain balanced loading, and when heating requires high power, the concerned appliance can be connected to both live wires to operate the heating element, providing 240V for it. "

The key here is while the PoCos transformer for residential service is only connected to one of three "phases" and the step down transformer that feeds your home service entrance actually looks like two 120V windings which for 240V are wired in series.

Because each 120V winding must be wired in series to provide 240V the center tap point is used as the Neutral creating two 120V outputs that have a 180 degree reversal in waveform when referenced via the Neutral..

Note the two bottom drawings at the link I provided..

The bad thing of 120V/240V setup like 50A RV is if you lose the neutral, 120/240 works by balancing the loads and with no Neutral your 120V loads now become part of simulating the center tap which changes the voltage potential each 120V appliance sees..

HERE is a good video explaining electrical systems "101" which may be helpful.

HERE is a video concerning main panel and Neutral/ground bond.

HERE is a video concerning sub panel separate neutral/ground wires.

On edit..

In the last video which is about sub panels it was mentioned that the NEC code was updated in 2008 to require separate isolated ground and Neutral in sub panels..

So, it IS very possible that RVs as new as 2007/2008 may have ground and Neutral connected in the panels..

But once again, OLD work is Grandfathered, you do not have to change or modify existing OLD work to match newer codes unless you change panels or make major modifications to the electrical system..

However, the last video on sub panels should very clearly give you a good reason to make the upgrade change.. I give that guy some Kudos for the video.