00crashtest
Senior Member
- Location
- California
- Occupation
- electrician trainee
In the 2020 Edition of the National Electric Code, in Article 100, the definition of free air says, "Open or ventilated environment that allows for heat dissipation and air flow around an installed conductor."
So, what counts as open or ventilated here? I looked at this unofficial interpretation that the interior of a cable bus (a specific type of raceway) is free air.
However, Section 310.15, titled Ampacity Tables, only distinguishes between conductors in raceway/cable/Earth and free air. A free-air cable-bus raceway is still a raceway.
1. So, do non-cable conductors in a cable-bus have to comply with the more restrictive Table 310.16, or are they allowed to comply with just Table 310.17? That is when given that there are no adjustment factors required.
2. Also, if one installs a fan at one end of a conduit and a vent at the other to let air flow through the conduit to ventilate it, it is considered free air? Of course, installing wires in HVAC ducts not for the exclusive purpose of HVAC control is prohibited by 300.22(B) due to the hazard of smoke spreading if the wire burns. However, I am not talking about that here. I am talking about a conduit that is exclusively for electrical wiring being ventilated with forced air for the exclusive purpose of active cooling.
3. Also, if one lays a liquid-cooled cable (such as in a large data centre) or an underwater cable (such as within a pond) that is labeled for such purposes, does it not have to comply with the ampacity tables because they run even cooler than bare or single-insulated conductors in free air?
4. I'm not going to touch on the topic of superconductors because it is already effectively prohibited by the NEC under the definition of conductor in Article 100, which only allows copper, "aluminum", and copper-clad "aluminum".
So, what counts as open or ventilated here? I looked at this unofficial interpretation that the interior of a cable bus (a specific type of raceway) is free air.
Article 100 Free Air (as applied to conductors).
“Free air” means an open or ventilated environment that allows for heat dissipation and air flow around an installed conductor. Conductors in cablebus are considered to be in free air.
www.electricallicenserenewal.com
However, Section 310.15, titled Ampacity Tables, only distinguishes between conductors in raceway/cable/Earth and free air. A free-air cable-bus raceway is still a raceway.
1. So, do non-cable conductors in a cable-bus have to comply with the more restrictive Table 310.16, or are they allowed to comply with just Table 310.17? That is when given that there are no adjustment factors required.
2. Also, if one installs a fan at one end of a conduit and a vent at the other to let air flow through the conduit to ventilate it, it is considered free air? Of course, installing wires in HVAC ducts not for the exclusive purpose of HVAC control is prohibited by 300.22(B) due to the hazard of smoke spreading if the wire burns. However, I am not talking about that here. I am talking about a conduit that is exclusively for electrical wiring being ventilated with forced air for the exclusive purpose of active cooling.
3. Also, if one lays a liquid-cooled cable (such as in a large data centre) or an underwater cable (such as within a pond) that is labeled for such purposes, does it not have to comply with the ampacity tables because they run even cooler than bare or single-insulated conductors in free air?
4. I'm not going to touch on the topic of superconductors because it is already effectively prohibited by the NEC under the definition of conductor in Article 100, which only allows copper, "aluminum", and copper-clad "aluminum".
