Working on an existing generator inlet box for a 30A generator connection. The wire is currently #8 thhn/thwn-2 CU in sch 40 PVC conduit. This was sized based on NEC table 310.16 60 deg. column since the load was under 100A (it was upsized from #10 to #8 to insure adequate voltage). The inlet box is being upgraded to a 50A genset connection. With that said, the currently installed wire is good for 50A under the 75-degree column. Since the conection is under 100A, is it acceptable to use the 75 degree column and the installed wire at 50A if both the breaker and the plug terminals are rated for 75 degrees? Or is there any other determining factors before I can use the 75 degree column? The conductor is southwire simpull e51583 with insulation rated for 75 degrees when used as THWN or 90 degrees when used as THWN-2 (no oil).
upgrading outlet from 30a to 50a and keep wire.
- Thread starter mjmike
- Start date
- Status
- Location
- Illinois
- Occupation
- retired electrician
As long as the receptacle and breaker are both marked for 75°C conductors you are good to go.
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
You've mentioned "since the load was under 100A you used the 60° column".
While partly true, you only have to use the 60° column under a few conditions.
1) If the temperature rating on the equipment is not marked and the load is under 100A
2) using NM cable
These are not all inclusive but just what I could think of from memory.
To sum it up though, just because the load is under 100A doesn't automatically send you to the 60° column.
kwired
Electron manager
- Location
- NE Nebraska
It will be properly protected from overcurrent but if load has also increased you may want to double check voltage drop.
All good info, thanks. The load has increased so i will be checking the VD. At least if the conductors do need upsized to #6, the conduit and the ground are reusable. However, i have not determined if the genset inlet box receptacle is rated for 75 degree yet. It is a reliance inlet box PB30 and from what i seen, the box itself is used for both the 30A and 50A receptacle so i am investigating if the plug itself can just be changed; if reliance will sell just the plug. If so, and the plug is marked with a temp, then this will be an easy upgrade. New wire would be limited to the 6/4 soow cord and ends.
kwired
Electron manager
- Location
- NE Nebraska
Unless it is more then 20-25 years old, it probably is rated 75C.
Its brand new. The inlet power box is manufacturered by reliance controls and they use a flanged inlet (receptacle) by marinco. Reliance controls couldn't tell me the termination temp rating since it wasen't printed on the device. Sent marinco an email. Sure enough they responded noting the terminations are rated for 60 and 75 degrees but its not printed on the device. Based on that, i believe i am good with the 75 degree insulation column although i would have preferred to see the temp printed on the device.
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