[Grammar] Which is correct "per item" or "per an item"

[equackenbush]

A colleague consistently inserts the indefinite article a or an after per. For example "per an hour," or "per a day"
Is that correct grammar and, if so, when is that usage most acceptable?

Thanks!

 

[Chicken Sandwich]

NOT A TEACHER

No, that's wrong.

- I drink one cup of coffee per day.
- I drink one cup of coffee a day.

But 'I drink one cup of coffee per a day' is wrong.

 

[Rover_KE]

Tell your colleague that per means 'for each', so an article after it doesn't make sense.

Concise Oxford English Dictionary © 2008 Oxford University Press:
per
▶preposition

• for each: £2 per square yard.

Rover

 

[Tdol]

Yes; it's one or the other, but not both.