Custom Format Textstring (alphanumeric entry, numbers and letters)

Otto757 

Since it is a text string, you cannot use a custom number format.

You might use a formula. With the text in A2, enter the following formula in B2:

=LEFT(A2,3)&" "&MID(A2,4,2)&" "&MID(A2,6,5)&" "&RIGHT(A2,5)

This can be filled down.

Alternatively, you can use a macro to insert the spaces. This will replace the original values.

Select the ranger with the values before running the macro.

Sub InsertSpaces()
    Dim c As Range
    Application.ScreenUpdating = False
    For Each c In Selection
        If Len(c.Value) = 15 Then
            c.Value = Left(c.Value, 3) & " " & Mid(c.Value, 4, 2) & " " & _
                Mid(c.Value, 6, 5) & " " & Right(c.Value, 5)
        End If
    Next c
    Application.ScreenUpdating = True
End Sub