Called in our electrical contractor to give us a price on some work in several schools. I've had to call him back on a couple of projects lately and haven't been dazzled with the quality of his work. The "lowest bidder" rule in government contracting at its best.
Anyway...I want a new sub pannel installed in a school. I show him the switch gear, tell him where I want the new breaker installed, show where the EMT should go across a boiler room and into a hallway drop ceiling. I suggest that he can go to MC or greenfeld there since it will be out of site but I want EMT wherever we can see it.
He suggested switching from EMT to SO and running SO down the hallway to swith back to EMT where it becomes visable again. I told him I didn't want SO and he's going to quote greenfield but is SO even allowed?
While it sure seems like a bad idea and 400.8 seems to support what I believe. Except for two things:
1- Why is SO prohibited as a "flexible cord or cable" while NM, SE, or UF, which seem to be flexible as well, are not prohibited as building wiring?
2- This is not a "substitute for the fixed wiring of a structure" since it will be the "fixed wiring of a structure". I'm not talking about an extension cord. He wanted to use SO in the same way that romex would be used.
I've been cited for 400.8 in lots of my buildings over the years for extension cords. I didn't think 400.8 applied to other than extension cords and drop cords.
edit: trying to get the ubb codes to work.
[This message has been edited by maintenanceguy (edited 04-01-2006).]
Re: Type SO as building wiring#97826 04/01/0612:22 AM04/01/0612:22 AM
As you noted, SO cord is one of the types of cord listed in article 400, not one of the wiring methods listed in the 300's.
However I see no reason that any given cord could not be multiply rated as both one of the types listed in article 400 as well as one or more of the methods listed in the 300s, in which case that cable assembly could be used for fixed wiring exactly as described.
I don't know if any such cables are actually manufactured, nor if there are specific requirements that make such a dual rating impossible, for example permissible wire stranding. I can imagine that there are situations where a single cable, dual rated as types TC and SO would be quite useful, essentially permitting permanently installed extension cords (with suitable protection and support, of course).
Re: Type SO as building wiring#97828 04/01/0611:37 AM04/01/0611:37 AM
Maintenanceguy, your question brings up a few basic things, that I feel I ought to explain for the benefit of everyone. You probably know most of this already, but this is for those who don't.....
First of all, while the NEC tries to be written in English, some times they wander, and use a term in a manner somewhat different than the rest of the world. It is also quite confused as to whether something not mentioned is allowed or forbidden.
"Flesible cords" in the NEC are limited to what is further defined in the code; you've seen the tables. Now, there are countless other items made that are both 'flexible,' and 'cords,' but they are not "flexible cords" as the code understands the term. A prime example of this is the "festoon cable" you might see used on an overhead crane.
The other point is that UL, or anyone else, can only evaluate a product after having some idea as to its' intended use. As a result, they have various standards- one for Romex, one for UF, one for SO, etc. Strictly speaking, these are entirely different standards, and no one can say that something tested for one category is also appropriate for another category.
A great example of this is what happens when you bury S cable; it doesn't take very long for the rubber to rot away, leaving you with bare copper. UF cable buried for the same period will show almost no wear.
Another thing often overlooked in the use of SO cord is strain relief. There are different types made, varying in price from pennies to many dollars. Each is listed for use in certain circumstances, and a given method may not be adequate under all circumstances.
Re: Type SO as building wiring#97829 04/01/0611:46 AM04/01/0611:46 AM