if you know how to use a meter:
on the 30 amp outlet the round socket is ground
the lower left is HOT
the lower right is Neutral
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on a 15 amp outlet ( like we have at home)
the U shape is ground
the short slot is HOT
the long slot is Neutral
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Hot to Neutral should be 110~125 volts
Hot to ground should be same figure as above * or up to 5 volts lower, but never higher
Neutral to ground should be less than 5 volts- 0 is better
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if you don't have a meter you can buy a test plug and use it with an adapter for 30A outlets ( also handy to test GFCI and circuit breakers)
https://www.lowes.com/pd/Kobalt-Digi...B&gclsrc=aw.ds
or
https://www.amazon.com/Receptacle-El...88&sr=8-7&th=1
I carry a meter for the AC and the DC stuff we encounter, but usually I use my test plug at campground and resort to meter if I see an anomaly
campground pedestals seem to get backed into often and campers often prop them up with rocks and drive away
cheers, Mike