I've recently installed 200 w induction hi bay lights in a factory. I have 12 on one contactor controlled via a switch. The lights are rated at 200 w each and I'm told they can run about 20 of them on the 20a cb so I should be well under.
The problem is when I first go to turn the lights on they trip... but every time from the rest of the day... no problem? Any ideas?

let's do some math, 200 watt fixtures X 12 fixtures = 2400 watts
If the system voltage is 120 volts then the circuit is overloaded.
If the system voltage is 277 volts then the circuit is about 50% loaded and I
would start by swapping out the circuit breaker for a new one and see what happens.

Just for fun, can you tell us what the voltage of the lights are?

I tracked them down on the web. They are from Ireland. They use either 200 V @ 50 Hz or 240 V at 60 Hz.

A string of 12 would be 2400 Watts (12 X 200 = 2400) and the amperage would be 10 Amps. (2400/240 = 10)

Inductive loads have a high in-rush of current until inductive reactance comes into play and the effective resistance goes up. Initially an inductive load has a near short circuit characteristic until the reactance comes into play. Not sure of all your details, but it sounds like it might be an issue.

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Originally Posted by Studs ad

Inductive loads have a high in-rush of current until inductive reactance comes into play and the effective resistance goes up. Initially an inductive load has a near short circuit characteristic until the reactance comes into play. Not sure of all your details, but it sounds like it might be an issue.

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I needed to clarify a bit. In a/c circuits resistance is called reactance. Same basic concept as resistance is in DC circuits, except in DC circuits the resistance in a non rotating coil is constant with the circuit. In an AC coil(ballast) the resistance of the windings are very low until an AC voltage is applied. In industry a large transformer's greatest load is when it is first energized. It takes near short circuit current at that moment. After the initial loading the reactance of the AC component makes the resistance (reactance)to designed levels and the current drops. Your ballasts are basically a transformer and the in-inrush of current can be close to 7 times the operating current.

How do you fix? If your wire size is sufficient to allow going to the next size breaker then do so. Industrial lighting can be up to a 30 amp breaker if my memory is correct.

Or or eliminate some lights and put on another circuit.