hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
I think you are mixing wiring methods and requirements of a cable to be used for a wiring purpose?
A wiring method is a complete method that meets the requirement for a given wiring purpose, the wiring method includes the conductors allowed to be used in the method, if the wiring method is a raceway, then the conductors will have the requirements of the article for that given raceway, again this includes the environment the raceway in being installed in such as dry, damp, wet, and if the conductors are to be exposed to sunlight at some point, cable systems are a manufactured system for a purpose and must meet UL's requirements of that purpose, raceways will have field installed conductors that we are given the rules on what conductors must meet to be installed in a particular location to which the wires are subject to, if we look at the list in 230.43 it includes many raceway methods, but leaves the type of conductors out of it as they are dependent only upon the location and environment they are subject to.
Conductors have four basic requirements that the NEC sets rules for, Ampacity, voltage, location, environment.
We know why we have Ampacity and voltage requirements, but location and environment can get confusing, some conductors are not allowed in certain locations such as single listed USE conductors which are not allowed inside of a building because of the harmful smoke they can produce, they must be terminated outside and another type of conductor brought in, while they do make dual listed conductors and USE is one of them that will have a USE/RHW listing, which makes it compliant to run inside.
The reason cables are listed for a purpose is because conductor selection inside of them is not field selectable, they must be manufactured for the purpose, doesn't men they can serve more then one purpose as we fined SE is allowed for many purposes, but to be use for service entrance it must have all conductors sized for that purpose, cables such as NM and UF can not be used for service entrance because the EGC is not sized by table 250.66 that service entrance cables are, the EGC in them are sized per 250.122 which will result in a smaller grounding path then the code allows, this is why you wont see a listing for conductors installed in raceways for a given purpose because the installer can chose the conductor based upon the rules in the NEC for the four given requirements I stated above which is all that is require, 230.43 will give us what wiring methods are allowed for service entrance conductors but if these methods are a wireway such as conduit, trays, or any other method where the conductors are field installed, then that is all it will say, and conductors installed in one of these raceway methods are not selected because of the purpose but are selected for the four requirements that is given above, and selected from table 310.104 for these requirements as well as other parts of 310 for voltage and current ratings.
An example would be if you have a hydraulic pump and used a conduit to supply it, would you require only conductors listed for a hydraulic pump?, no we would select the conductors based upon the four basic requirements, current, voltage, location, environment.
If we were to use a cable method we would have to look at the environment such as oil rated cables as if indoors it would have to meet the harmful smoke requirements, outdoors it would have to meet wet locations requirement, and could be required to meet all these, so this would be a special purpose cable such as SJOW or SJOW-HD where used in areas it could be damaged.
We can't just pick requirement for one method and apply them to other wiring methods or we will wind up with requirements that would be impossible to follow in an installation making the installation impossible to install.
Service entrance cables are only listed for the EGC size reason as well as the environment and location, these requirement are not a problem with a conduit method as the conductors field installed in it can be selected to meet these requirements.
Anyone who is in the position to make requirements that we must follow needs to understand what they are requiring and this may include knowing and understanding the NEC, UL and any other standard as what is available and common wiring methods, because if they require things that are just not available or can cause much more cost that doesn't provide any more safety or reliability, is just not smart rule making.
I hope this clears this up.
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