CNC powering practices questioned.

[slimpickens51]

Good morning.....first time forum inquiry ....the cnc (27kva) manufacturer suggests that a 35 kva (delta wye), 3 phase transformer, 480 primary, 208 secondary transformer be installed between the 480 bus (fused bus plug 60a). The secondary wires to run directly to cnc panel, that is approximately 10 feet to cnc panel without fusing between 208 secondary and cnc panel. The cnc panel has a disconnect and fusing to protect the cnc,
A single other associated auxiliary device that should have needed 480v, 3ph at 6.5 kva has arrived and is supplied with 208v 3ph instead.
The 480v version of device is no longer available.
User considers the original 35 kva to be replaced with a 45 kva transformer. Resulting now with power for both.
Does the secondary need to be fused for both loads?

 

[don_resqcapt19]

If the primary OCPD for the transformer does not exceed 125% of the primary full load current, the secondary of the transformer does not need overcurrent protection, however the secondary conductors will require protection in accordance with one of the rules in 240.21(C).

 

[electrofelon]

I don't see any reason that the integral CNC fusing cant be the OCPD for the transformer secondary conductors if the conditions are met.

 

[GoldDigger]

I don't see any reason that the integral CNC fusing cant be the OCPD for the transformer secondary conductors if the conditions are met.

Among the conditions would be your choice of tap rules, since the OCPD is not at the source end of the conductors?

 

[electrofelon]

Among the conditions would be your choice of tap rules, since the OCPD is not at the source end of the conductors?

Right, sounds like these are transformer secondary conductors