Mike Dolt Enterprises
Mike Dolt Enterprises
User: Sam Moore, Location: SC
Asked on: Monday, March 21, 2011 at 10:05 pm EDT
Answered on: Tuesday, May 14, 2024 at 3:05 am EDT
Question: I do mostly residential and light commercial work, so I'm not real experienced with larger commercial services and I'd like for the more experienced guys to double checked my calc. here:1200A, 480/277v, 4-Wire, 3-Phase ServiceService will have 2, 600 Amp Services DiscosEach Disco I'm going to have Paralleled 3" RMC'sIn Each Parallel I figured 4, 350mcm THHN derated @ 80%= 560 Amps allowing for larger breaker/fuse size of 600 Amp (using Copper)I figured Electrode Conductor of 3/0 CopperThen Service Feeder to Main Distribution PanelI figured 4, Paralleled 350 Thhn's with 3/0 Copper Ground or am I allowed to use a1awg copper ground for 600amps?I figured 3" RMC for both runsI want to make sure I'm right, before I price this out,Thanks in advance for any help with this!
Service Entrance
1200A, 480/277V, 4-Wire, 3-Phase Service 2, 600A Service Disconnects Paralleled 3" RMC (4 per phase per disconnect) 4, 350 MCM THHN per phase per disconnect (560A capacity per phase, allowing for 600A breaker/fuse) Electrode conductor: 3/0 copper
Service Feeder to Main Distribution Panel
Paralleled 3" RMC 4, 350 MCM THHN per phase (560A capacity per phase) Ground conductor: 3/0 copper
Code Verification
NEC 225.26(B)(1) - Paralleling requires a minimum of 3 conductors per phase. NEC 310.15(B)(16) - 350 MCM THHN has an ampacity of 320A at 75°C. Derating for 80°C results in an ampacity of 560A. NEC 250.66 - The grounding electrode conductor must be at least 3/0 copper for a 600A service. NEC 310.15(B)(16) - 3/0 copper has an ampacity of 230A. Paralleling 4 conductors provides a total ampacity of 920A, which exceeds the required 600A.Therefore, your calculations are correct. Flag for review