The MCC inter-compartmental wiring is defined as that wiring between the starter and the MCC central reset system and the starter and the MCC relay or programmable logic controller and is installed by the MCC manufacturer when the MCC is assembled on site.
The central reset system is designed to reset the fault relays of every starter in an MCC when power to the MCC is restored after a power failure. The purpose of the system is to minimise disruption after a local or general power failure, it does not restart the motors but enables them to be restarted. Because the reset is automatic in the event of a power failure it means that the maintenance staff do not have to manually reset every starter at its geographic location.
Should it be required that the motors restart after a power failure then the SCADA system must be suitably programmed to initiate an automatic start of each motor or group of motors on the return of power. The SCADA start sequence after power restoration must ensure that the system volt drop limits are observed. It must also be remembered that only the motors selected to be controlled via SCADA will be restarted, motors selected for control elsewhere will need to be started by manual initiation.
For each group of starters in a MCC that serve a particular function, for example an air handling unit, there should be either control and interlocking relays or programmable logic controller (PLC) located in a compartment of the MCC. The purpose of the control and interlocking relays or PLC is to provide inhibit and permissive interlocking and auto run enable signals. The control and interlocking relays or PLC must also accept and issue hard wired signals from other MCCs.
A sample of an inter-compartment wiring diagram is included in the pdf version of this article. It is based on the starter located in a compartment number 4 of cubicle 5 in MCC ident 16 with the PLC located in compartment number 3 of cubicle 4 in the same MCC.
It is a separate file entitled inter-compartment wiring diagram.pdf with an original paper size of A1 (841mm x 597mm) printing on to an A1 sheet will give a scale of 1:1, on an A2 sheet a scale of 0.707:1 and on an A3 sheet a scale of 0.5:1. To be able to read the drawing a recommended minimum paper size of A3 should be used, at the stated scaling the general text on the drawing has a minimum height of 0.9mm.