cables

[plugwash]

If there is a short between phases there will be a bang just like with any other short and then provided the protective devices are correctly chosen they will trip and disconnect the fault.

Just how big a bang depends on both the protective device and the phase to phase PSCC at the point of the fault. Expect it to be considerablly bigger than on a similar single phase setup.

 

[Spark123]

so what protects a faulty motor from connecting the phases? i know most things have rcd's / fuses etc. but if it's that big a bang.. do they have different protection or is it just in the equipment's design?

It depends what type of fault - an overcurrent fault is usually dealt with by an overload in the motor control circuit whereas fault current (phase to phase or phase to earth) is dealt with by the circuit protective device such, we tend to use BS88 Gg or Gm type fuses for fault protection of motors.

 

[Spark123]

MCBs that can clear the potential short circuit fault current of the installation. I seem to remember domestic MCBs are rated to 6KA, and those used in 3ph boards are rated to 10KA or more.

Don't think it is quite that clear cut, it is up to the designer what breaking capacity fuses/MCBs to use. It is possible to fit a 6KA or less MCB to a 3 phase board, nothing wrong with that providing the PFC is less than 6KA, or they are backed up.
I think that BS3036 are only 1, 2 or 3KA. If there is backup protection (BS1361 II) then this can be considered to be higher.