Mike Dolt Enterprises
Mike Dolt Enterprises
User: sgunsel, Location: New Jersey
Asked on: Wednesday, April 27, 2011 at 1:37 pm EDT
Answered on: Tuesday, May 14, 2024 at 4:41 am EDT
Question: Have an existing commercial building with 240VAC, 3 phase delta, 200 amp service (in addition to 120/240 service). Three phase motor loads are excessive now and they want to expand. Service comes in through meter to 200 amp disconnect, then to 200 amp MBP, then (via 3/0 Cu, THHN in EMT) from MBP to 600 amp MLO panel.If 240 service is increased to 400 amps and a new fused disconnect replaces the existing 200 amp disconnect, can a parallel EMT with 3/0 Cu, THHN, run from the new disconnect to the existing 600 amp MLO panel?Per 310.10(H)(2) and (3), it looks allowed, but how precisely must lengths match?Any other issues with paralleling?
Can a parallel EMT with 3/0 Cu, THHN be run from a new fused disconnect to the existing 600 amp MLO panel?
Yes, it is permissible to run a parallel EMT with 3/0 Cu, THHN from a new fused disconnect to the existing 600 amp MLO panel under the following conditions
1. Conductors Must Be Sized Appropriately:
The parallel conductors must be sized in accordance with Table 310.15(B)(6) and Table 310.15(B)(16). In this case, 3/0 Cu conductors are appropriate for a 400 amp service.2. Neutral Conductors Must Be Paralleled
If neutral conductors are required, they must be paralleled with the phase conductors.
3. Grounding Conductors Must Be Paralleled
If grounding conductors are required, they must be paralleled with the phase conductors.
4. Conductor Lengths Must Be Matched
The lengths of the parallel conductors must be matched as closely as practicable. This requirement is to ensure that the current is distributed evenly among the parallel conductors. However, there is no specific tolerance specified for the length matching.
Other Issues with Paralleling
1. Proper Connection
The parallel conductors must be properly connected at both ends to ensure a good electrical connection.
2. Protection
Each conductor in the parallel circuit must be protected against overcurrent in accordance with Article 240.
3. Fault Current Calculation
The total fault current capacity of the parallel conductors must be considered when sizing the overcurrent protective devices.
4. Accessibility
The parallel conductors must be installed in a manner that allows for inspection and maintenance.
Conclusion:
It is permissible to run a parallel EMT with 3/0 Cu, THHN from a new fused disconnect to the existing 600 amp MLO panel, provided that the conductors are sized appropriately, paralleled correctly, and the conductor lengths are matched as closely as practicable. Other factors such as proper connection, protection, fault current calculation, and accessibility should also be considered. Flag for review