SDS grounding and OCP

[commguy]

Gentlemen,
I am detailing a separately derived system power source where a single phase isolating 240:480 transformer is used to provide a feeder to another similar transformer 480:240/120 several hundred feet away (underground in HDPE conduit). I believe that I may run two conductors only (L1 and L2) between the two transformers provided that: I provide OCPD at each end of the run and provide a separate Ground at each end of the run with a separate EGC to each transformer and the enclosure containing the OCPD. I also need a Service Panel on the load side of the 240/120 transformer with appropriate OCPD and EGC to the same ground that ties to the transformer. Is all of this correct?

 

[charlie b]

There are several aspects of your description that are not correct. For starters, you appear to be using the word ?ground? and the term ?EGC? incorrectly. In addition, you speak of putting an OCPD at each end of the same set of wires, whereas overcurrent protection only takes place at the point at which the wires get their power supply.

This is the purview of a power systems engineer, so I am wondering why a communications engineer is performing this design. May I ask what this is for? Is it a home project, or something you are doing for your job? If the later, how did you get assigned this part of the design?

Oh, and by the way, we have ladies participating in this forum as well as gentlemen.

 

[erickench]

According to NEC 240.4(F) a single phase(other than 2 wire) transformer shall not be considered to be protected by the primary OCPD. Therefore the 240/120 volt transformer must has have OCPDs on both the primary and the secondary because you have three wires on the secondary. However the first transformer is permitted to be protected by a primary OCPD because it is two wire on both the primary and secondary. So I do not see the need for two OCPDs on the same run.