Samardas
Member
- Location
- Los Angeles, CA, United States
- Occupation
- Electrical Engineer
Hi,
I designed a 4,000A service connection to the Main Switch Board (MS - 480/277V, 3 Phase, 4W) as follows (Also please see the Single Line Diagram attached): Each phase got two 4" conduits - with each conduit having five 600 MCM cables of the same phase in it. So, there are ten 600 MCM cables per phase run through two 4" conduits.
Inspector is saying each conduit should have all three phases run through it. I don't think this is necessary. There is no voltage drop situtation here since the entire installation is very close to the service transformer and the cable size selected totals more than 4,000 AMP (420Ax10 cables per phase) as well.
Second, do we need an 'equipment ground' running between the two panels? I have shown UFER and ground rod (grid) on the Pull box side and Ground grid and Cold water pipe for the MS. (Grounding always baffles me:?)
Can you please look at the attached diagram and suggest any changes per NEC?
I would really appreciate your early response. Thanks a LOT!!
I designed a 4,000A service connection to the Main Switch Board (MS - 480/277V, 3 Phase, 4W) as follows (Also please see the Single Line Diagram attached): Each phase got two 4" conduits - with each conduit having five 600 MCM cables of the same phase in it. So, there are ten 600 MCM cables per phase run through two 4" conduits.
Inspector is saying each conduit should have all three phases run through it. I don't think this is necessary. There is no voltage drop situtation here since the entire installation is very close to the service transformer and the cable size selected totals more than 4,000 AMP (420Ax10 cables per phase) as well.
Second, do we need an 'equipment ground' running between the two panels? I have shown UFER and ground rod (grid) on the Pull box side and Ground grid and Cold water pipe for the MS. (Grounding always baffles me:?)
Can you please look at the attached diagram and suggest any changes per NEC?
I would really appreciate your early response. Thanks a LOT!!