While it is standard to have the ground slot on the bottom, there is no code requirement for it. There are three possible reasons for an upside down receptacle:

1. Some electricians install a receptacle that is controlled by a switch upside down, as an easy way to indicate which receptacles in a room are switched. But this is not a standard and not all electricians do it.
2.  It is the right way to do it, according some contrary thinkers, and there is a somewhat logical explanation for putting the ground slot on top. If a piece of metal drops down onto a slightly-loose cord plugged into an upside down receptacle, the metal will only contact the ground slot. But it will cause a short, with possible arcing and sparks, when the hot and neutral are on top. Hospitals install receptacles upside down, likely to avoid any arcing in a room with oxygen in use.
       Conversely, the argument against an upside down receptacle is that if the the cord is tugged out and downward (the usual way it happens), the ground can become disconnected with the cord still “live,” resulting in an ungrounded appliance that is still working.
3. The person installing the receptacle wasn’t paying attention or didn’t care that the standard installation puts the ground slot down. 

    There is no NEC (National Electric Code) violation either way. So have it flipped if it bothers you but, otherwise, you can just leave it alone.

    Also see our our blog post Why are electrical outlets and plugs polarized?

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  To learn more about electrical wiring, devices, and receptacles, see these other blog posts:

 • What is the difference between what trips a GFCI (ground fault) receptacle and a circuit breaker?

• What is the code requirement for GFCI protection for receptacles near a wet bar sink? 

• What is the requirement for a service receptacle outlet for heating, air conditioning, and refrigeration (HACR) equipment? 

• Why is an opening in the wall around the side of an electrical receptacle outlet a safety defect?  

• When was GFCI-protection for kitchen dishwasher receptacle outlet first required? 

• What is allowable voltage range at a wall receptacle outlet in a house?

• When should I replace electric receptacle outlets? 

• Does an electric receptacle outlet in a storage shed require GFCI protection? 

• What are "self-contained" electrical receptacle outlets and switches?

• When was the current receptacle/outlet spacing of 12-feet first required? 

• When was the three-slot (grounding) outlet/receptacle first required? 

• Why is there a GFCI breaker in the electric panel for the bathroom shower light and exhaust fan?

• What is a false ground, bootleg ground, or cheated ground receptacle? 

• How can adding wood paneling or a wainscot create an electrical safety hazard? 

• How do the new tamper-resistant electric outlets work?

• Why is there no bathroom electric receptacle in this old house?

• How can I tell if the electric receptacle outlets are grounded? 

• How far apart should the electrical receptacles be placed?

• What are the most common problems/defects found with electric receptacle outlets during a home inspection?

   Visit our ELECTRICAL page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.