Limiting Cable Temperature

The ability to limit the amount of current and heating will come from setting your protection to a lower than normal setting or increasing the wire size. Either of these options could make the installation unusable.

You need to know the maximum short circuit current available at your closest upstream location within the restricted area.

If you have current limiting circuit protective devices upstream, you need to factor in the time-current heating of the let through current, and add it to the cumulative heating, starting at the typically 90C insulation rating.

In the olden days, cable damage curves are plotted on log log paper with the time current curves of the protective devices, limited by the bolted phase fault current of the circuit.

Knowing the basis of the cable damage curves for your particular conductors will help your calculate the conductor temperature. As a check, you can use your equation while integrating the worst case current, taken assuming your primary protection failed, and your secondary protection cleared the fault.

I suspect that the limiting factors will never allow you to reach that threshold temperature, but you’ll need to do the work, taking all factors into consideration.

If the objective is protection, why not just use an approved wiring method in the area, like rigid metal conduit or type MC-HL cable? Prospective short circuit current is a function of your power system architecture. You will set up your protection system to clear the fault before the cable gets damaged.

In my view to meet and satisfy the client requirement, you may need to install temperature sensing and monitoring devices in the T3 hazardous area.. which should attaching some temperature sensors on and along the concerned cables...

In practice the actual temperature sensing /monitoring circuitries, in turn can limit or completely terminate the current flowing on the affected cables.. Implementing such scheme will definitely satisfy the client's safety requirement..