Rule 26-256 - ECN Electrical Forums

This rule relates to overcurrent protection for dry-type transformer circuit rated at 750volts or less. 125% issued for the guide with regard to the secondary side if the primary supply is set at not more than 300 %. the rule 26-254 speaks to 9amps more or less for liquid filed units. Why does the supplieer charts list 250% of the primary FLA or the next size smallee and quotes rule 26-254 and Nec.450.3. Is the chart correct? I don't tink so.

If it's a dry transformer, the reference to CEC 26-254 is wrong or refers to a previous edition. The 250% doesn't come from our code but the manufacturer can specify a lower percentage. Maybe 250% comes from the NEC.

Originally Posted by Sparkologist

My reference to rule 26-254 with regard to sub.(5)a and b is up to date and was to show what the reference was that the Bussman catalogue used. The text from the NEC 450.3 was almost the same as the Canadian code 25th edition 2012. The are saying that if the primary and secondary do not have thermal protection use 250% and if the primary and secondary do have thermal protection and the impedance of the transformer is 6 ohms or less use 125% of the FLA. There chart shows for the primary max fuse, use 250% and for secondary use 167% or 125% depending on the more or less 9 amp rule. My point is that for dry type less than 750v the 9 amp rule does not apply and their pecentages for protecton is wrong.

26-254 once dealt with all transformers and 26-256 dealt with wire size for transformers. Or, are you saying that the Bussman catalogue refers directly to 26-254(5)? Anyway, if you don't like their catalogue, throw it away.

ok