I am having trouble finding a reference for how many circuit breakers or fuses are allowed to serve as transformer secondary protection in the absence of a secondary main device. I only have access to the 2002 Ontario code, but I would expect to find a footnote on Table 50 or some other reference to detail what secondary protection may consist of. In contrast, the US National Electric Code's transformer protection table (450.3) has a note as follows: "Where secondary overcurrent protection is required, the secondary overcurrent device shall be permitted to consist of not more than six circuit breakers or six sets of fuses grouped in one location. Where multiple overcurrent devices are utilized, the total of all the device ratings shall not exceed the allowed value of a single overcurrent device. If both breakers and fuses are utilized as the overcurrent device, the total of the device ratings shall not exceed that allowed for fuses."
We have a customer who has switchgear with nine 1200A feeder breakers and no secondary main. The nine breakers are fed from a 3000kVA, 600V transformer. The trip settings add up to nearly 8000A, or 275% of the rated secondary current. This would definitely be a violation per the US NEC. Does anybody have any information that would clear this up for me. Is there a reference in another code book?
