I did two Dental remodels last year and both were as similar as apples and oranges. One was in the county and one in the city, two different inspection agencies. First according to 517-13 you must use a redundant ground for health care facilities. So not know this until starting the first remodel I used emt and pulled a bond for the various areas according to code. It was relatively easy to fiqure out where the redundant ground went and the inspector said to bond the pipe with the pulled bond wire pigtail and put on devices. Ok pretty easy. This building was framed one story with crawl space. It was the job from "hell" but fun anyway. The second was a pretty new concrete slab, steel, three story modern building. The space we were remodeling was already a Dental office but was pretty well gutted anyway. Our demo (electical) left emt runs down the middle. I had a consultation with the inspector (city now) and he determined we could use "Medical MC" this is a compo of mc and ac with both a covered bond like mc and that little thing they call a bond like ac. When asked where each went he said that the ac type bond was to be wound around the ac and then put in the connector like usual. The mc type was to be used normally bonding the box and devices. Did not agree but did not fight it. Your imput please.
tmeg46, It seems to me that the insulated ground meets the requirement of 517-13(a) and the cable armor/bonding strip combination meet 517-13(b) The "Medical MC" is necessary because the armor of standard spiral wound MC is not acceptable by itself as a gounding means, as EMT is.
[This message has been edited by Redsy (edited 01-29-2002).]
Redsy, I would agree with you on all counts but here is my thoughts. The first inspector said to bond the emt and covered ground together and terminate on the devices. the second said to spiral ac bonding strip and not bond the two together. so is the spiral wound armor cable of ac a legal bonding means. (I did not think so) and if it is why "Medical MC" if you could use AC with the bonding strip. If the NEC gives a size for bonding depending on the OCPD size how can that little bonding strip be legal. What do you think??? Lot of questions here. Thanks for the fast reply Tom
The metal jacket of AC is an equipment grounding conductor. The metal jacket of interlocking armor MC cable is not. 517 requires that the outer metallic jacket or the raceway be an EGC. It requires in addition an EGC in the raceway or cable. They will be tied together when the installion is in compliance with 517.13 (A) & (B). You might want to look at this thread: http://www.mikeholt.com/forum/Forum1/HTML/001860.html
[This message has been edited by resqcapt19 (edited 01-29-2002).]
tmeg46 I agree with you; if the second inspector stated that the metal clad cable and the insulated ground did not have to be bonded together, you could have an isolated ground and this is not what is required by 517. The code requires all grounding conductors to be bonded together except where isolation is needed for noise etc. as in the case of computer circuits. Sometimes it is best to question these people about their reasoning in a constructive way. You don't want to show them up but you must make your point about code issues.
Forgive me. I'm not exactly following. Are you saying that in the first case, you had to install a bonding jumper from the receptacle to the box (which was grounded by the EMT), but in the second case you did not? Or did you have to install bonding bushings on the EMT?
tmeg46 You did in fact bond the two grounds together at each receptacle. The jumper between the EGC splices and the box connects the two ground paths together. Health Facilities Cable is only type AC cable that contains an insulated grounding Conductor. The bonding strip from the Armored Cable is not supposed to enter the interior of the box. The connector and jacket of type AC/HFC is listed as a grounding conductor all by itself just as if the seperate insulated EGC were not there at all. That is why you are permitted to use type AC/HFC cable as the wiring means for isolated ground receptacles. The cable jacket provides the ground path for the boxes and enclosures. The insulated green copper EGC provides the grounding pathway for the grounding terminal of the receptacle. Type MC cable, of the generally available spiral interlocking metal tape variety, can only be used for circuits were only one ground path is required. The jacket of type MC cable is not listed for use as a grounding pathway except when it is ussed together with the insulted EGC. -- Tom
"This alternating current stuff is just a fad. It is much too dangerous for general use" Thomas Alva Edison
Thank you all for your responses. As usual they were very informative and right on the mark. I was told (don't use AC so did not give it a thought) that the jacket of AC was not designed to be a grounding path. So of course I got my confused on the uses of the bonding issue. I am not an AC fan and will use metal pipe or MC where necessary. Should have checked the AC art. myself. Can now put the orginal question in the "embarrassing moments" thread. but thanks to you guys I learned something and that was worth it. Thanks again. Tom