Article 2514, Alternating-current systems without Exterior connections, now known as Separately Derived Systems. Article 2514 was re-numbered in 1956.
This topic has always been in the Grounding Article, not in the transformer or service articles.
When this section was created, the separately derived systems,(premises wiring) were existing farm houses with generator power.
Farms with 32 volt light plants, did not require grounding even if they were separately derived systems.
The code section was created for the safety of farm houses when domestic power was installed.
Most existing separately derived systems did not have an earth connection.
Now with transformers being called separately derived systems, and being connected to earth in a second location, there is a lot of common mode current with resultant EMF.
Transformers are not separately derived systems and only need the equipment ground conductor for fault clearing.
Earth connecting the X-O of a transformer in two locations creates a ground loop, and is a violation.
This topic has always been in the Grounding Article, not in the transformer or service articles.
When this section was created, the separately derived systems,(premises wiring) were existing farm houses with generator power.
Farms with 32 volt light plants, did not require grounding even if they were separately derived systems.
The code section was created for the safety of farm houses when domestic power was installed.
Most existing separately derived systems did not have an earth connection.
Now with transformers being called separately derived systems, and being connected to earth in a second location, there is a lot of common mode current with resultant EMF.
Transformers are not separately derived systems and only need the equipment ground conductor for fault clearing.
Earth connecting the X-O of a transformer in two locations creates a ground loop, and is a violation.