Lighting Ballast Specification

[PhaseShift]

Have a ballast specification for a 250W light that has the following:

Line Current: Operating = .63A
Open Circuit = .45A
Starting = .40A

What do the open circuit and starting current ratings mean?

 

[broadgage]

I would presume that the open circuit current, is the current drawn by the ballast from the line, if the output is open circuit, due to no lamp or a defective lamp being inserted.
I would not expect much loss to occur in an open circuited ballast, therefore this current is almost certainly at almost zero power factor and represents the current drawn by a power factor correction capacitor.

I would presume that the starting current is that current drawn from the line when the lamp has just struck and not yet run up.
Under starting conditions, the watts used are relativly low, and therefore if the ballast is power factor corrected, then the line current can be less than the running current.

 

[PhaseShift]

Do you need to fuse individual lights on a lighting branch circuit or does the ballast provide overcurrent protection for light?

I heard lighting circuits should be loaded up to 80% of circuit capacity to allow for future add-ons. Is this right?

 

[broadgage]

Most ballasts are designed for direct connection to circuits up to 20 amps, unless the manufacturer states otherwise.
Fuses may be a good design choice, in order that the other lamps remain lit, and that the faulty one may be easily located.

If the lighting is to be regarded as a continous load, as is likely, then the circuit should be loaded to more than 80% as required by the NEC.
Additional derating to allow for future additions may be a prudent design choice, but AFAIK is not a requirement.