What sort of current level are you looking to sense, and how much power are you hoping to switch on or off? There are electronic techniques that operate sub-millisecond (even sub-microsecond),  but if you have a need to close a 100A contactor that response will be the limiting factor.
Also be aware of the EMC susceptibility of a fast device to fast transient currents that would normally be ignored, and most electronic devices are deliberately slugged  to emulate a mechanical one ;-)

For example the Carlo Gavazzi ones  are made in two models for each rating, one slugged (few hundred msec) and the other 'fast' a few tens of msec, and they are nothing special.

"Type Selection
Input current Reaction time Type no.
2 - 20 A AC Standard DIA53 S724 20A
5 - 50 A AC Standard DIA53 S724 50A
10 - 100 A AC Standard DIA53 S724 100A
2 - 20 A AC Fast DIA53 S724 20A F
5 - 50 A AC Fast DIA53 S724 50A F
10 - 100 A AC Fast DIA53 S724 100A F "

data sheet docs.rs-online.com/.../0900766b813e14c8.pdf

Mike.

  Many thanks for the reply. Loking to sense 32 amps. Relay will open normally closed 100 amp contactor.

I think your harder problem will be the speed of the contactor ;-)  By the time you have the typical  20msec actuation delay and a 20-30msec of arc time, your 50msec has all but gone.
Mike.

I think your harder problem will be the speed of the contactor ;-)  By the time you have the typical  20msec actuation delay and a 20-30msec of arc time, your 50msec has all but gone.
Mike.