Inrush — Chain Motors
Definition
Electric chain hoists draw a high inrush current when their motors start, commonly quoted at 6 to 10× the full-load current for a fraction of a second. When several motors start together, their inrush currents add up. Before any lift, the total starting current, taken from the hoist datasheets, is therefore checked against the rating of the distribution circuit.
In the field
When a motor distribution system trips its breaker at start-up, inrush current is a frequent cause. Start commands are staggered where possible, and motor circuits can be fitted with Type D breakers, whose instantaneous trip lies between 10 and 20× the rated current under IEC 60898-1, provided the fault loop impedance of the circuit still allows them to disconnect within the required time. They then ride through the inrush while still protecting against fault current.
Related lessons
Sources
- IEC 60898-1, courbe D : déclenchement instantané entre 10 et 20 In · se.com
- IEC 60364-4-41 (NF C 15-100, BS 7671) : temps de coupure en cas de défaut et impédance de boucle · electrical-installation.org
- Wikipédia (pointeur secondaire), Inrush current : courant de démarrage des moteurs à induction · en.wikipedia.org