Dear Friends, I in my capacity as a maintenance Engineer, recently took up a Commercial installation where the local supply co. electrical power is sourced through a CUTOUT which has apart from the standard energymeter and HRC Fuses a TP MCCB also.Now downstream the CUTOUT we have a Main Switchboard comprising again an incomer TP MCCB and outgoing TP and SP MCCBs.Now these outgoing MCCBs feed to individual loads like HVAC chiller, Lighting and Power Distribution boards etc.
Now TP MCCB at CUTOUT and at the Main Switchboard has inbuilt thermal and magnetic releases but no earth fault release.Earth leakage protection is provided only at the load end ie, at the Distribution boards,starter of HVAC Compressor, Switch fuse unit of three phase burner etc - what I mean to say no earth leakage protection at main feed.
Is it o.k. to retain the same design or should I opt for a earth leakage release at either the CUTOUT TP MCCB or the TP MCCB at the Main Switchboard by way of adding a Toroid+ relay+ release combination ??
If I'm understanding you, you are wondering if Ground-Fault protection is required for protection of the equipment. This is determined by the rating of the service. If you are interested in the NEC requirements, see article 230.95.
if you are in kuwait and the installlation is is similar to the british wiring TT then the installation at origin should have an earth rod to take the fault current down to ground,
the MCCBs and RCDs should protect the appliances and cabling from over load/voltage
the standard way we wire our service from cutouts (service incomer from local PoCo) the cutout feeds the distribution board via the electric companies meter,
within the cutout would be a fuse, or fuses dependent on whether it is single or three phase, a neutral connection and or a PME (protective multile earthing connection) As you say yours is a TT system it should have an earth rod, (this should be connected directly to your distribution board together with all the main earth bonding connections.
if you need any other advice please feel free to post them her and we will try to help as there are electricians from all over the world here, and here to help.
Dear Friends, As Harrison has stated, we do have an earth rod at the start of the installation and the cutout design is same like he had mentioned. But the problem is the MCB+RCCB combination protection being just before the appliance or Distribution Board,in case of a earth leakage in the feeder cable(normally doesn't happen ,but poor installation practices may cause it to happen) from the main switch board to the Distribution board or appliance - the downstream RCCB will not sense the fault and the fault will slowly over a period of time develop into phase to phase short and if the magnitude of the fault current crosses the set limits ,the MCCB will trip ,but by then considerable damage to the installation might have occured.
My doubt/ question is there any stipulation that one should mandatorily provide and earth leakage protection at the start of installation of specification as stated in my orginal post ??