NEC 314.3 - Nonmetallic Boxes

[Machiavelli999]

I was recently asked whether nonmetallic boxes are allowed for receptacle installations. Obviously they are in homes, but what about in commercial settings? Certain medical imaging rooms do not allow ferrous materials and so we wanted to install PVC boxes with PVC conduit going to them.

314.3 seems to allow nonmetallic boxes as long as nonmetallic raceways are used. Is the installation allowed if we use PVC conduit?

An electrical inspector questioned whether this would work due to grounding concerns. I am not really sure what he meant as I don't think the PVC box needs to be grounded. We are providing an equipment grounding conductor for the outlet and therefore the component that plugs into the outlet will be grounded as well.

 

[Little Bill]

I think a grounding/bonding means is required where metal raceway is used with non-metallic boxes in certain cases that's allowed. But with all PVC conduit and box, only need to connect the EGC to the device and anything downstream that might be fed from this.

 

[roger]

I have never heard of any medical imaging rooms not allowing metallic boxes and raceways, this includes MRI's. I always used EMT and steel boxes and if supported correctly within walls and ceilings there is no problem.
Although all that I was involved with used copper for the room envelope I hear some are done with steel.

Using PVC or plastic would not comply with 517.13(A)

 

[Fred B]

I have never heard of any medical imaging rooms not allowing metallic boxes and raceways, this includes MRI's. I always used EMT and steel boxes and if supported correctly within walls and ceilings there is no problem.
Although all that I was involved with used copper for the room envelope I hear some are done with steel.

Using PVC or plastic would not comply with 517.13(A)

Don't think the ferrous metal is an issue for in wall in an xray room as a result of the lead wall covering required. Including how focused the new equipment is for the radiation being used in an exam. Not familiar with any wall construction requirements for an imaging room that uses MRI. Big concern with MRI is loose metal objects that can be displaced during operation and damaging equipment, conduit in a wall not going to rip thru the wall. Any disruptions of electrical current quality as a result of EM in the imaging room not sure if there is an issue or level of issue, but might actually be benefited by the use of EMT. (I know noncontact voltage tester and even cheap locators will not pick up signal through EMT or MC cable.)

 

[kwired]

Never worked in an MRI room, but my understanding is ferrous metals in the room are ok, but need proper securing. Any change to what metal is in the room also will require recalibrating the equipment AFAIK.

Chances are in many cases you dealing with steel framing members in that area as well. Even if wood framing, will still have metallic fasteners as a general rule. The equipment gets calibrated to whatever effects are there in the general construction and the operators of the imaging equipment avoid bringing in any objects that will have any impact.

 

[roger]

Never worked in an MRI room, but my understanding is ferrous metals in the room are ok, but need proper securing.

Hmmm, where did you hear that?

 

[Strathead]

I have never heard of any medical imaging rooms not allowing metallic boxes and raceways, this includes MRI's. I always used EMT and steel boxes and if supported correctly within walls and ceilings there is no problem.
Although all that I was involved with used copper for the room envelope I hear some are done with steel.

Using PVC or plastic would not comply with 517.13(A)

He didn't say, non metallic he said non ferrous

 

[Strathead]

I was recently asked whether nonmetallic boxes are allowed for receptacle installations. Obviously they are in homes, but what about in commercial settings? Certain medical imaging rooms do not allow ferrous materials and so we wanted to install PVC boxes with PVC conduit going to them.

314.3 seems to allow nonmetallic boxes as long as nonmetallic raceways are used. Is the installation allowed if we use PVC conduit?

An electrical inspector questioned whether this would work due to grounding concerns. I am not really sure what he meant as I don't think the PVC box needs to be grounded. We are providing an equipment grounding conductor for the outlet and therefore the component that plugs into the outlet will be grounded as well.

Without looking it up, I assume 517.13 cited by Roger is the requirement of redundant grounding on critical circuits, so you will have to have a conduit path that acts as a ground along with a green ground wire, so no PVC conduit and boxes.

 

[roger]

He didn't say, non metallic he said non ferrous

No, besides the title of the thread he said "do not allow ferrous materials" and ferrous materials would be metallic.

 

[kwired]

Hmmm, where did you hear that?

I really don't have an answer and don't want anyone to take anything I say here as how it works in these spaces. I do find it hard to believe no ferrous items are allowed in the room at all, I can see them needing to be properly secured and accounted for in the design and calibration of the equipment. Question also becomes how close to the room can you have ferrous objects or how do you shield adjacent objects from being an issue? The room or an adjacent room may have metal studs or ferrous drywall screws holding the wall covering and would be pretty typical. Again I have no experience in wiring or construction of MRI rooms have been involved with X ray/ CT rooms though. A little bit of information I have involving MRI came from equipment people in conversations with the X ray/CT equipment people while on those jobs, but certainly not detailed enough I am confident in saying this is how it is either. I kind of did gather that calibration to the room still factors in room content even of non ferrous items and their effect on the scanning process and that room contents typically should remain constant as possible for better results.

Maybe I am totally wrong? I really don't know.

 

[Barney B]

NFPA70-2020 Article 517.13(A) prohibits the use of non-metallic raceways or cables with non-metallic jackets for all branch circuits serving patient care spaces, which certainly includes imaging rooms. You might also benefit from access to a copy of NFPA 99.

 

[JoeStillman]

PVC is not the only type of non-ferrous raceway. You could use aluminum conduits and boxes.

 

[Strathead]

No, besides the title of the thread he said "do not allow ferrous materials" and ferrous materials would be metallic.

No, besides the title of the thread he said "do not allow ferrous materials" and ferrous materials would be metallic.

Stainless steel (even though somewhat magnetic) brass, aluminum are allowed and generally required for critical and emergency circuits.

 

[roger]

PVC is not the only type of non-ferrous raceway. You could use aluminum conduits and boxes.

Correct and we used aluminum FMC in the ceilings but aluminum conduit is a lot more labor intensive in the walls verses EMT

 

[roger]

Stainless steel (even though somewhat magnetic) brass, aluminum are allowed and generally required for critical and emergency circuits.

Also correct but unnecessary and where do you see they are required for EM circuits? Are you referring to 517.30 mechanical protection? If so EMT has that covered.

 

[Strathead]

Also correct but unnecessary and where do you see they are required for EM circuits? Are you referring to 517.30 mechanical protection? If so EMT has that covered.

This discussion is for MRI rooms, which fall under the manufacturers requirements along with the NEC. I didn't feel it necessary to start over, as EMT it ferrous and not allowed in MRI rooms, nor is PVC. So, aluminum, brass and stainless are generally your fallbacks.

 

[Strathead]

Correct and we used aluminum FMC in the ceilings but aluminum conduit is a lot more labor intensive in the walls verses EMT

Aluminum FMC over 6' would not be allowed in the MRI room either.

 

[roger]

This discussion is for MRI rooms, which fall under the manufacturers requirements along with the NEC. I didn't feel it necessary to start over, as EMT it ferrous and not allowed in MRI rooms, nor is PVC. So, aluminum, brass and stainless are generally your fallbacks.

As I said in post #3, both the manufacturers and the NEC allow EMT. I have done GE, Mitsubishi,(open and closed now) Phillips, and Siemens units and all allowed EMT (ferrous materials).

 

[roger]

Aluminum FMC over 6' would not be allowed in the MRI room either.

We only used it for the fixtures whips connected to 4X4 steel boxes, most of which were DC except for Phillips which allowed AC lighting with 130V incandescent lamps

 

[roger]

Here are a couple old threads that show EMT in MRI's.

MRI Exam Room Wiring

Looking for a little help finding suitable boxes for concealed work inside of the RF shielding. Can't seem to find any stainless steel products. Has anyone out there done one of these rooms recently?

forums.mikeholt.com

MRI wiring

Contractor is installing a new MRI in the local hospital. demo of existing MRI shows equipment wiring done in smurf tube. Manufaturer rep says that this is the way it is typically done. anyone have any experience with this, thanks.

forums.mikeholt.com