An electrical contractor connecting our 2mW generator (480v 3ph 4w ) to our existing transfer switchboard is telling me he can use 5 conductors per phase of 444.4 kMCM RHW-2 to carry the 3000a output of the generator. The run is about 35 l/f from genset to swbd. The cable will be installed in ladder type cable tray. The contractor intends to use mechanical al/cu 75 degree C lugs. He tells me this is all permissible and after looking at sales literature from Mfg of the cable and reading 310.15 table in NEC, I'm not convinced. Questions: 1) is his use of the 90deg C "free air" table correct when using 75 deg C mechanical lugs on stranded RHW-2. (2) is it even permissible to use mechanical lugs on stranded cable like this? Experts, please chime in.
Ampacity of RHW-2 under 310-15
- Thread starter Genmann
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- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Table 310.15 is not a table to use so do you mean 310.15(B)(7) for free air of single conductors. I am trying to imagine 5 parallel runs in free air--
90c table is okay for de-rating but the final ampacity cannot be more than the 75C rating of the lugs.
90c table is okay for de-rating but the final ampacity cannot be more than the 75C rating of the lugs.
Welcome to the forum, Genman :thumbsup:
The way I see it, 444.4kcmil is not an NEC recognized conductor size... so the only way to be NEC compliant and establish the conductor ampacity is via 310.15(C) Engineering Supervision.
There are at least a couple other issues. As noted by Dennis, a coordinated under 110.14(C) conductor ampacity cannot exceed the terminal temperature limitation. If using 75?C rated lugs, that would be approximately 350A per conductor (the exact value must also be established under engineering supervision). There are methods of using 90?C rated transitions remote to the 75?C-rated equipment which would permit the engineering-established free air ampacity of the conductor... but likely not feasible for a 35' run, as the transitioning would take up 20', leaving only 15' at full ampacity.
The other issue is this type of cable is usually dual- or multi-rated DLO cable with fine stranded conductors. If so, the lugs will have to be identified for fine stranded conductor usage.
The way I see it, 444.4kcmil is not an NEC recognized conductor size... so the only way to be NEC compliant and establish the conductor ampacity is via 310.15(C) Engineering Supervision.
There are at least a couple other issues. As noted by Dennis, a coordinated under 110.14(C) conductor ampacity cannot exceed the terminal temperature limitation. If using 75?C rated lugs, that would be approximately 350A per conductor (the exact value must also be established under engineering supervision). There are methods of using 90?C rated transitions remote to the 75?C-rated equipment which would permit the engineering-established free air ampacity of the conductor... but likely not feasible for a 35' run, as the transitioning would take up 20', leaving only 15' at full ampacity.
The other issue is this type of cable is usually dual- or multi-rated DLO cable with fine stranded conductors. If so, the lugs will have to be identified for fine stranded conductor usage.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
444.5 kcmil sounds like a dual rated locomotive or welding cable.
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