Level 8 of 33 · Electrical lab
Star-delta with a timer
Level 8 of 33 in the Electrical lab: a free panel wiring exercise at Intermediate level. Start a bigger motor gently: first with its windings in star, then, after a set time, in delta. Wire the star point, the delta feed and the timer that changes them over, with an interlock so both are never in.
Goal
A motor connected in star takes about a third of the starting current of one in delta.
What you do
- Lock out the board at the isolator Q1: switch OFF, apply your lock and your tag.
- Prove it dead, live-dead-live: prove the meter on the proving unit, check the board reads 0 V, prove it again.
- Wire the 27 conductors of the schedule.
- Set the timer T1 (the changeover time): long enough for the motor to get up to speed in star.
- Last. Restore power (tick the checklist, remove your tag and lock, switch Q1 ON), try every button, then run the FAT.
Done when
The factory acceptance test is marked against the panel you built.
- 27 conductors in the wiring schedule
- 4 dead checks before you touch the panel
Skills
Motor starters at Intermediate level.
Before you start
Level 7, Forward and reverse with an interlock, comes first. Do it first if the ideas are new to you.
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