Ann,

Most of the manufacturer's cut sheets say more or less the same thing RE field wiring.

For example:

Q

Power Supply
1 All wiring should be made in accordance with the
National Electrical Code. Consult the local power company
to determine the availability of sufficient power to
operate the unit. Check the voltage at power supply to
make sure it corresponds to the unit’s RATED VOLTAGE
REQUIREMENT. Install a branch circuit disconnect
near the rooftop, in accordance with the N.E.C.,
C.E.C. or local codes.

- and -

Hook-Up
POWER WIRING MUST BE RUN IN CONDUIT. Conduit
must be run through the connector panel below the service
cover and attached to the bottom of the control box.
If low (extra-low in Canada) voltage control wire is run in
conduit with power supply, Class I insulation is required. If
run separate, Class II is required. Low voltage wiring may be
run through the insulated bushing provided in the 7/8 " hole
in the connector panel then routed to the control box.

EQ

http://www.mcquaybiz.com/mcquaybiz/literature/lit_ch_cu/IMOM/IM909-RCS6-7Tons.pdf

What actually happens in the field may well be a different story.