I had a question regarding derating NM or UF wire for being located up in an attic as I have an application where around 5 foot is in the attic. I thought per one of Mikes videos that I could derate the NM wire starting at 90 C column but got the below email from Southwire support (blue text). Maybe this was only for derating THHN type wire as I would have to go back and watch the video. Also, do you have to derate if less than 10' or 10% of total length is in the attic so you can use the higher ampacity. See below for Southwire email on derating NM-B.
NM-B Cables are limited to the 60°C ampacity - period. The individual conductors cannot be used independently of the completed NM-B Cable. The conductor insulation is rated for 90°C max temp however that simply allows the conductors to be terminated in light fixtures that require 90°C conductors. You cannot de-rate the ampacity for NM-B Cable starting with the 90°C ampacity like you can for individual conductors. If you need to de-rate the ampacity for ambient temperature, you start with the 60°C ampacity.
I also got the following response below regarding NM vs UF to be ran from inside home breaker panel to outside Air Conditioning Disconnect. I see quite a bit of NM ran straight into the AC Disconnect where I live, but maybe UF should always be ran. I wasn't sure if you just go straight thru the wall right into disconnect there would only be a few inches or less behind the outside disconnect. I guess as they state that anything outside, even a few inches.
NM-B Cable is a dry location only product and cannot be used outdoors (even in conduit). Use UF-B Cable instead.
Also, Can you run NM-B or UF in liquid seal tight for a short distance( 6') along with should you use non metallic liquid tight vs metallic outside.
Please see the attachment for the new A/C /Heat pump that is being installed. In my mind I would use 10-2 with ground with a 40 Amp circuit breaker. But if I have to derate the wire since some is in the attic ( 5') and I go off the 90 C column, which I am not sure if that is correct I would have 40A for 10 awg at 90C X .71 factor for 140 F attic temp= 28.4 Amps. Would I then still keep my 40 Amp cirucit breaker as I know this is required per manufacturer due to startup up inrush amps.
The last thing what if I had an electric wall heater rated at 16.7 Amps and was using NM-B wiring and it was up in attic space. Per 310.15 chart 12 awg is good for 20 Amps or I could go 10 for 30 Amps with 10 awg. On this wall heaters alot of time they just list the amps and no mca or mop.
Sorry for so many questions as I appreciate the help. Thanks!
NM-B Cables are limited to the 60°C ampacity - period. The individual conductors cannot be used independently of the completed NM-B Cable. The conductor insulation is rated for 90°C max temp however that simply allows the conductors to be terminated in light fixtures that require 90°C conductors. You cannot de-rate the ampacity for NM-B Cable starting with the 90°C ampacity like you can for individual conductors. If you need to de-rate the ampacity for ambient temperature, you start with the 60°C ampacity.
I also got the following response below regarding NM vs UF to be ran from inside home breaker panel to outside Air Conditioning Disconnect. I see quite a bit of NM ran straight into the AC Disconnect where I live, but maybe UF should always be ran. I wasn't sure if you just go straight thru the wall right into disconnect there would only be a few inches or less behind the outside disconnect. I guess as they state that anything outside, even a few inches.
NM-B Cable is a dry location only product and cannot be used outdoors (even in conduit). Use UF-B Cable instead.
Also, Can you run NM-B or UF in liquid seal tight for a short distance( 6') along with should you use non metallic liquid tight vs metallic outside.
Please see the attachment for the new A/C /Heat pump that is being installed. In my mind I would use 10-2 with ground with a 40 Amp circuit breaker. But if I have to derate the wire since some is in the attic ( 5') and I go off the 90 C column, which I am not sure if that is correct I would have 40A for 10 awg at 90C X .71 factor for 140 F attic temp= 28.4 Amps. Would I then still keep my 40 Amp cirucit breaker as I know this is required per manufacturer due to startup up inrush amps.
The last thing what if I had an electric wall heater rated at 16.7 Amps and was using NM-B wiring and it was up in attic space. Per 310.15 chart 12 awg is good for 20 Amps or I could go 10 for 30 Amps with 10 awg. On this wall heaters alot of time they just list the amps and no mca or mop.
Sorry for so many questions as I appreciate the help. Thanks!