Are there any code requirements regarding the grounding of residential interior steel studs(that often use plastic boxes)?On commercial jobs I use steel grounded boxes screwed to the steel studs with FMC and MC cable or EMT.
Chris
Grounding of the metal studs themselves is not an issue.
However, your ground wires still need to comply to 250.148(A) for metal boxes and
250.148(b) for nonmetallic boxes.
Avoiding Electrical Shocks and Fire Hazards from Ungrounded Steel Studs
In Ontario . . .
The Electrical Safety Authority has been informed a homeowner received a serious electrical shock when attempting to check
for a blown fuse in the electrical panel where the steel studs framing his fuse panel had not been bonded to ground. During the
renovation of the homeowner’s basement, metal stud framing was used with non-metallic sheathed cable (NMD-90) wiring and
non-metallic or PVC boxes. When the drywall was installed one of the screws penetrated a switch leg, energizing the complete
metal stud assembly at 120 volts when the power was turned on.
The use of non-metallic or PVC boxes together with no physical connection between the bonding conductor of the cable and the
metal stud assembly energized the entire wall system for weeks before the homeowner checked the blown fuse.
CAUTION:
The Ontario Electrical Safety Code requires that metal stud partitions be bonded to
ground so that the branch circuit over current device will operate in the event the studs become energized.
Precautions should be taken to ensure that wall assemblies are at the same potential to ground as the electrical service box.
Metal or steel boxes can be secured to the studs in compliance with the Ontario Electrical Safety Code or the metal frame can be separately bonded by a conductor to connect each isolated section, ensuring good electrical contact with all framing members.
Rule: 10-002 of the Ontario Electrical Safety Code requires that grounding and bonding shall be done in such a manner as to
serve the following purposes:
(a) To protect life from the danger of electric shock, and property from damage by bonding to ground non-current-carrying
metal systems;
Experience has shown that metallic wall assemblies using non-metallic wire and boxes are susceptible to electrical faults,
resulting in a potential exposure of persons to electrical shock.
The bonding requirements of Rule 10-400: Exposed, non-current carrying metal parts of fixed equipment shall be bonded to
ground if equipment is:
(g) in electrical contact with metal, metal foil, or metal lathe; supports the general concept of bonding metal studs.
From this point of view, ESA will require metal studs assembled to form a steel building frame or wall assembly, which is not
intentionally bonded to ground and may become energized, to be bonded to the service equipment enclosure. The bonding
conductor shall be sized in accordance with Table 16.
Tony Moscioni
Electrical Inspector
Electrical Safety Authority
Tony,
Thank you for your report and it illustrated the situation that I was thinking about.
Chris
See 250.4(A)(4), 2002 Code.
"Materials" is not a defined term in the Code however this section has been construed to include metal studding for just the reason mentioned in Tony M's post.
Joe T might have a comment on this....
I've had similar concerns specifically in a situation where there is a Hot Tub and Metal studded walls were within reach and a suspended ceiling above. Walls would have Sheetrock covering them, but who among us has not seen a screwhead showing on a wall like this. As far as the ceiling goes I was thinking that the Ts (within 5 feet) should be screwed or riveted together and bonded to the tub.
Bill
I recall a rule in the Massachusetts admendments that did in fact call for bonding in the same manner described by Tony.
I can't seem to find it though, and have posted the link to that code here so someone could read it through to see if the rule can be found.
www.joetedesco.com/masscode.pdf I believe that someone in Massachusetts was electrocuted by an energized metal stud.
PS; That's also one of the reasons why the temporary wiring rules were changed to require cords to be used on construction sites, because someone back a few years in Pennsylvania was also electrocuted when a hot leg energized metal studs.
I'm probably in over my head here with the heavyweights,but if you think about it, we have to bond metal water water lines that have 1 energizing possibility at the WH.And gas lines that have in some cases no direct energizing possibility. Then It sounds very practical to bond metal studs that have mc or romex pulled through them. Russell
Now that I read Tony's, Bill's and Joe T's replys, I have to say that maybe this should be presented as a "Code Change"
On a personal note, I feel that MNC does not belong in a metal stud job. Bushings do fall out, screws can "hit". Someone will say "Same for MC", specially the Al jacketed stuff. I can't remember an instance where we had a "problem" with MC.
Maybe Caddy (Erico) will come up with a solution to bond the studs??
John
300.4(B)(1) was put into the code to address the possibility of the grommet falling out of the metal stud as the NM is installed.
Don
I would have to agree. I have wired metal stud houses both ways with romex and bushing and emt and mc. However, I always used metal
boxes that were properly bonded. When using romex I would use listed bushings for that purpose but, I still had alot of trouble with them. Metal boxes SHOULD be required for metal studs and metal sheathing for wire
protection should also be a serious consideration.
There's a Fine Print Note on 250.116.
(Of course it's not enforceable, but still a good idea)...S
Hey, how would you bond it?
[This message has been edited by electure (edited 02-12-2003).]