I have a transformer that draws more than 9 amps on the primary. When I reference 450.3(B) to size the primary protection, when primary and secondary protection are present, I see that I can size the OCPD at 250% of the primary current.
There is a "See Note 3" next to the 250%. I do not understand what note 3 is trying to get at. At first I read it as a pre-requisite to applying the 250%, but to me it now reads that in addition to 250% of primary FLA I can also size the primary OCPD at not more than 6 times rated current if I have coordinated thermal overload protection.
So, if I do not have this coordinated thermal overload protection, then I can completely ignore note 3 and size the OCPD to 250%, as long as the secondary is sized at 125% rounded up to the next standard size?
There is a "See Note 3" next to the 250%. I do not understand what note 3 is trying to get at. At first I read it as a pre-requisite to applying the 250%, but to me it now reads that in addition to 250% of primary FLA I can also size the primary OCPD at not more than 6 times rated current if I have coordinated thermal overload protection.
So, if I do not have this coordinated thermal overload protection, then I can completely ignore note 3 and size the OCPD to 250%, as long as the secondary is sized at 125% rounded up to the next standard size?
