intrinsic safety circuits

No not more. It's one of two systems for dealing with hazardous areas.

Keith Cress
kcress -

Thanks. What is the other system?

It is possible to work on I/S installations with the power on because the power's energy is limited and the installation is protected from a safe area fault putting dangerous voltage on the cabling by the I/S barrier.

Ex stuff must be powered down in order to work on it because its ability to arc or spark is not mitigated when the Ex housing is opened up.

If you didn't get it from Dan's replay the "other" is explosion proof.

Instead of limiting energy into the hazardous area to a level below that needed to ignite the environment you instead run unlimited power into the space but are then required to put everything into explosion proof enclosures. Those are designed so that if they were filled with the hazardous area worst case gas or dust mixture and an electrical fault occurred that would ignite what's in the enclosure the enclosure would be so stout as to completely contain the explosion without bursting. It would also let all the explosive gases out of the enclosure to prevent bursting but that the gas paths out are long enough to cool the gasses to a temperature below that needed to ignite the exterior hazardous environment.

Keith Cress
kcress -

IS circuit means that the Entity parameters (L/C) of the load (Transmitter) is lower than that of the barrier. So no chance of sparking due to hot working or Shorting. Technically, even the cable's entity parameter has to be considered for the length between the marshaling cabinet and the transmitter. Only L/C are considered since R does not store energy. Each loop will have to be checked individually even for same transmitter/barrier combination but for different cable length.