Running solar charge controllers in parallel

When sizing any PV source circuit one must first know the "short circuit amperage" or Isc. This should be on the specification tag on the back of every PV module. After one has that number multiply it by 156%. This is per UL and NEC. Thats 125% for UL and 125% on top of that for NEC or 125% X 125% = 156%.
Lets say one has 4 PV modules with an Isc of 4.5 amps each at 12 volts nominal and they are wired in parallel.
4 x 4.5 x 156% = 28 amps
Not probable, but possible. Thats the NEC for ya!
This is the  number that one would size the; wires, fuses, disconnects, and charge controller by.
I have had this happen on my system only once in 6 years and it lasted only about 2 minutes.
It was noon time, temperatures where in the low 20's, snow on the roof, and there were those certain types of clouds that cause that "edge of cloud effect' and I was equalizing the bank.
 As for paralleling multiple charge controllers...
Working with them one at a time, set the voltage set points as close as possible to the same as each other controller.
Chances are they will come on line at slightly different times in the morning and go off line at night at slightly different times.
UL - Underwriters Laboratories
NEC - National Electrical Code