Substation and MCC lab · Level 5 of 8
Grade the incomer relay
Level 5 of 8 in the Substation and MCC lab: a free substation and MCC exercise at Advanced level. Set an IDMT relay (curve, pickup, time multiplier) so it discriminates with the MCC feeder breaker below it, and set the earth-fault element.
Free · no download. Your work is saved on this device. Updated 18 Oct 2026.
The brief
- Client
- Harlow Cold Storage
- Site
- Main LV board, substation 2
- Work order
- WO-MCC-105
- Task code
- MCC-05
- Difficulty
- Advanced
- Type of work
- Protection
Set an IDMT relay (curve, pickup, time multiplier) so it discriminates with the MCC feeder breaker below it, and set the earth-fault element.
Skills you practise
- IDMT relay curves
- Discrimination
- Grading margin
- Earth-fault protection
What the test checks
The acceptance test marks the skills this level practises.
- IDMT relay curves
- Discrimination
- Grading margin
- Earth-fault protection
In this lab
- Safe isolation: lock, tag, prove, test, earth
- Cables, breakers, relays and fault levels
- A 3D switchroom and transformer bay
Levels in the Substation and MCC lab
Previous: Commission a star-delta starterNext: Fault level and breaker check
Part of the Substation and MCC lab
Walk a small substation, isolate a motor bucket safely, grade a relay and fault-find a motor control centre.
About the Substation and MCC lab
Feeds these internships: Control Panel Design and Wiring, Commissioning and Maintenance, Electrical Design.