Step down transformer

[garyhereto]

I have a oil cooled 3 phase 480vac to 380vac and neutral step down transformer rated at 20KVA roughly 40 amps per phase to neutral. What are USA standards in Tulsa concerning the protection needed and wiring of such a system. My machine that i am supplying has an Isolator rated 40amps and i have 3 fuses rated 40 amps but i need to tell the customer what he will need to do from his side. I.E. What line protection to the Transformer and also if there must be some sort of protection on the load side before it comes into my machine ? or if the transformer is within a certain distance whether there is no need for protection? Also what about the earthing and neutral aspects as the transformer will be a delta - star configuration.


Gary de Wet
Allwerx

 

[alehman]

There are many factors to consider. The basic rule is the primary overcurrent proteciton must be less than 125% of rated primary current unless there is secondary overcurrent protection sized at less than 125% of rated secondary current. In the latter case the primary overcurrent protection may be increased to 250%.

I would strongly suggest you hire a local consulting engineer to help with this. It shouldn't cost very much and would be well worthwhile to make sure the inspector is happy and the installation is safe.

 

[eyec]

unless you are willing to take responsibility of something you are not providing, i.e. system protection, i would instead tell the customer how to best protect the equipment you are providing (the transformer).

you know your equipment and the customer knows his electrical system, each should provide guidance for the other but not the other way around as it sounds from your original post.

what requirements were contained in the PO?

just my thoughts.