I worked around the computer biz for 30 years where flexible wiring methods were the standard. I think they all need a hard wire ground. I have seen far too many that have separated from the connectors. Joe Tedesco may have some of my pictures. They were in the IAEI magazine a couple times
Greg: Remind me about the images and what was included in them. I think I still have some and one with about a size 12 boot with the underfloor in a computer room.
The reason for the "flexibility" rule calling for the EGC at all times is because CMP 9 went out into the field and found that most of the compressors on roofs were with loose connections, and the flexible metal conduit that was used was not secure in many instances.
I think that the they did this around the 1981 or 1984 NEC cycle. Maybe someone can check the TCR and TCD
Steve I will say I don't see any difference between AC, FMC or LFMC in this regard. If it is not installed to 300.11 standards (secured next to the box) it should have a ground wire. Whenever you have a whip to something that can move around or where the whip can be moved around you are going to loosen a certain percentage of the connectors. At least one of the pictures I sent into IAEI shows a separated FMC connector under a computer room floor with about 4" of conductor exposed. Without a green wire ground that equipment was floating. The same can happen to T bar lights, pump motors, wall ovens or whatever you hang out on a whip. Fortunately I never had the fight when I was an inspector. Insulated EGCs were required in all state contracts, even in EMT, IMC or RMC.
I have recently noticed that furnace manurfacturers that use FMC to connect between the controls on the unit now have a insulated EGC installed in their factory assembled units.I always wondered how they got away without the ECG in the flex.
I will have to agree with gfretwell; when the appliance is likely to be physically moved (as with a dishwaser), and not simply vibrating (like a transformer), I believe that it is wise to run a grounding wire. his also applies when the flex is likely to be snagged, or tripped over, etc. I've just seen too many connectors -especially "jakes"- come loose. Indeed, I will often install liquid-tight for this reason; their connectors are more substantial.
Bob- State of Michigan requires an EGC in all flex regardles of length. There are two exceptions: One is Flexible Metal Tubing and the other is for flex 6 feet or less when used in one and two family housing subject to the Michigan Residential Code (IRC). Most contractors pull in an EGC all the time in flex regardless. I would say one of the primary reasons electricians run flex is to avoid running EMT or Conduit. The vibration issue is secondary.
I always put an EGC in all flex that I install, and make sure the fittings are tight.
Sadly, I can go up to probably 8 or 9 out of 10 flex installations I find, and take them apart barehanded, because that's the way they were installed. The same holds true for the gland nuts on LTFlex connectors. I don't like to see it that way, but it's a fact.
[This message has been edited by electure (edited 11-27-2004).]