Frequently Asked Questions Q1.Difficulty in racking the ACB in or out Q2.Single phasing of ACB Q3.Excessive pitting in the main contacts Q4.Overheating of main contacts Q5.Overheating of jaws and terminals Q6.ACB trips on closing Q7.ACB trips soon after closing Q8.ACB trips on closing for a motor feeder Q1.Difficulty in racking the ACB in or out ACB may not be properly mounted on telescopic rails. Withdraw ACB and check mounting. Q2.Single phasing of ACB Check lubrication of mechanism. Refer ACB Instruction Manual for greasing of mechanism. Q3.Excessive pitting in the main contacts Check adjustment of arcing contacts with filler gauge(>0.9mm and <1mm) Q4.Check adjustment of arcing contacts with filler gauge(>0.9mm and <1mm) Check whether arcing contacts are touching each other. Adjust arcing contacts as per (3) above. Q5.Overheating of jaws and terminals Occurs due to loose terminals and loose termination. Tighten terminals periodically. Q6.ACB trips on closing • Check for overcurrent release reset. • Check supply to undervoltage release. • Check whether shunt trip is getting energised. Q7.ACB trips soon after closing Check setting of overcurrent release or relay. It may be lower than current drawn by feeder. Q8.ACB trips on closing for a motor feeder Check magnetic threshold setting on overcurrent release.
Q1.Difficulty in racking the ACB in or out
Q2.Single phasing of ACB
Q3.Excessive pitting in the main contacts
Q4.Overheating of main contacts
Q5.Overheating of jaws and terminals
Q6.ACB trips on closing
Q7.ACB trips soon after closing
Q8.ACB trips on closing for a motor feeder
• Check for overcurrent release reset.
• Check supply to undervoltage release.
• Check whether shunt trip is getting energised.
Larsen & Toubro - Electrical Business Group
