When can you use previous code cycle?

[phil salas]

I've heard Mike say that codes will be made that can't be complied with at that time but the code panel puts it in to trigger the manufacturer's to produce the products. In those cases if the product doesn't exist you simply refer to the previous code cycle. But where is that rule written? I've also heard Mike say that there is nothing wrong with running a transformer backwards as long as the bonding jumper is installed on the proper side. I have an inspector who will not approve this even though I have a letter from Hamman (manufacture). Please Help

 

[ron]

Generally you cannot refer to a previous code cycle if the jurisdiction you are working in has adopted a particular current code cycle. If the current code cycle has required a product that is not currently available, they would have made an amendment to the adoption of that code.

You can run a transformer in reverse as long as it is marked per NEC 450.11(B) - A transformer shall be permitted to be supplied at the marked secondary voltage, provided that the installation is in accordance with the manufacturer’s instructions.
The bonding jumper location depends on whether you want to have a grounded system and if so, what kind. In many of these delta-wye transformers run in reverse, the system ends up being corner grounded on the delta coil,s and the X0 remains unbonded on the wye side.

 

[tom baker]

Please see 90.4 third paragraph to answer your question.