Fast current sensing relay

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.

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.