According to 250-118 emt is an acceptable grounding conductor.250-134(a) again tells me that an emt raceway is sufficient for grounding a fixed piece of equipment as long as the race raceway can safely handle the possible fault current,250-2(d).So with this all said my question is this.In what situation is a wire conductor REQUIRED for an equipment ground. From what I've read in the '99 code I would think my pipe run would satisfy the equipment grounding requirements for anything from a subpanel to a motor. This isn't the normal procedure of course but what is wrong with my thinking? Thanks for any answers. Barry
This subject is controversial, as most of us agree that pulling a ground is always a good idea, though not required. However, bid work on larger jobs might result in the decision not to pull a ground due to cost, or the need to upsize conduits to accomodate the additional conductor. Any instance where either an isolated ground, as in some data applications, or an insulated ground, as in health-care or swimming pool type installations would require an additional ground. See a previous post for a thread on this topic.
A properly installed Metal Raceway system ( of the those permitted in 250-118 ) is adequate for an EGC.
But, I'm sure that most electricians and inspectors have seen systems where the couplings or other fittings have become pulled apart ( especially EMT systems ) or the locknuts are not properly tightened on rigid conduit systems.
I assume the design engineer(s) or the owner(s) has also seen the poorly installed metal raceway systems and do want to assure an adequate EGC system so do specify an EGC ( wire conductor ) be installed in certain metal raceway systems.
I remember seeing Code Q&A of such practices about 15 years ago in some of the "trade" magazines in which the ANSWERER did not emphasize the importance of the size of such additional EGC.
It should be sized per NEC 1999 250-122.
On two installations by the same designer, He had in the notes that all feeders in EMT over 1/0 have a number 6 AWG EGC in the raceway. In a few cases, if a properly sized EGC was to be installed the EMT size on the print(s) was not large enough. I called him and asked why he had requested a Number 6 EGC to be installed in these raceways. His answer was " In case a coupling pulls apart ". My questions to him was " What good is a Number 6 EGC in with 500 Kcmil circuit conductors if an EMT coupling pulls apart?".
My opinion again. If an (additional) EGC is specified on the prints or Spec's then it must be "full" size per 250-122.
Thank you for your answers. I'm asking these questions primarily to prepare for the upcoming Calif. test. Often what I'm taught to do in the field isn't necessarily required by code but is done for more practical reasons. Barry
Barry We all must remember that the NEC requirements are the minimum for safety. Your test will be to see if you understand that minimum. What you do in the field should always be better than the minimum. I had an instructor say in a class one time that he didn't want to put a bunch of minimum rated electricians out there in the market place. Simply passing the test wasn't good enough. I'm sure you know to study hard and do the best you can on the test, and in your endeavor as an electrician. Wishing you the very best.
Thats what I thought George, but I wasn't sure. I don't have a code book in front of me, but if I'm not mistaken, there is not even a requirement to fold it over or wrap it. It can be cut off flush with the end of the cable. Correct me if I'm wrong. I always wrap them anyway in such a way as they help hold the bushing on.
You are correct, TomBrooklyn. Has anyone noticed lots of random breaks in the 'drain' wire. I'm just wondering if that is the norm, or perhaps I just had some factory defective cable. I wouldn't think breaks in the wire would hurt much, the fault current wouldn't necessarily loop around the spiral wrap of the armor just because there was a break in the wire..only if the break gaps were several inches apart..which wasn't the case with the cable I had been using.