PVC conduit for critical branch circuits

[mshields]

I've got a contractor who installed PVC conduit for the 24VDC lighting circuits within an MRI room.

He did this on the advice of the MRI technician in order to avoid installing Ferrous, Steel, EMT. He should have installed non-Ferris Aluminum conduit both because the circuit needs to be shielded (and that by the way is the big problem) BUT also because the mechanical protection of branch circuits serving patient care areas (that are part of the EES) may not be non-metallic.

To solve the shielding issue I'm considering allowing the contractor to copper tape the PVC conduit. I am left with the code issue. My question is, might there be a lieu pole here given that the branch circuit feeds a 24VDC power supply. Are the 24VDC conductors still a branch circuit? And if they are, does the fact that they are low voltage and either a Class 2 or Class 3 circuit, have any bearing?

Thanks,

Mike

 

[GoldDigger]

Being Class 2 or 3 does make a difference in allowed wiring methods, but IMHO the copper tape shielding would only be allowed if the wires could have been legally run without metallic protection in the first place.
But a large part of the problem in a MRI room will be the magnetic field resulting, and the best way to reduce that effect is to use tightly twisted pairs for the wiring. No net field at a distance keeps pulsed fields in the MRI from affecting the lights and will keep the light current from affecting the MRI machine.
The twisted pair wiring will be necessary regardless of any non- ferrous raceway, since aluminum or copper will not block the magnetic field.
Wrapping the PVC in mu-metal foil would work, but would be incredibly expensive.

 

[fmtjfw]

I've got a contractor who installed PVC conduit for the 24VDC lighting circuits within an MRI room.

He did this on the advice of the MRI technician in order to avoid installing Ferrous, Steel, EMT. He should have installed non-Ferris Aluminum conduit both because the circuit needs to be shielded (and that by the way is the big problem) BUT also because the mechanical protection of branch circuits serving patient care areas (that are part of the EES) may not be non-metallic.

To solve the shielding issue I'm considering allowing the contractor to copper tape the PVC conduit. I am left with the code issue. My question is, might there be a lieu pole here given that the branch circuit feeds a 24VDC power supply. Are the 24VDC conductors still a branch circuit? And if they are, does the fact that they are low voltage and either a Class 2 or Class 3 circuit, have any bearing?

Thanks,

Mike

Once the PVC Conduit is installed as a complete system, I don't believe the Code says much of anything about what goes on the outside of the conduit. You can paint it pink or tape it with copper tape (or Duct Tape). The only concern would be insulation that would overheat the conductors which is unlikely from your description. Does the conduit(s) contain control circuits or feed to power for them?

 

[Pharon]

Once the PVC Conduit is installed as a complete system, I don't believe the Code says much of anything about what goes on the outside of the conduit. You can paint it pink or tape it with copper tape (or Duct Tape). The only concern would be insulation that would overheat the conductors which is unlikely from your description. Does the conduit(s) contain control circuits or feed to power for them?

517.30 prohibits PVC for EPSS circuits. Stupid rule, though.

 

[steve66]

IMO, if its 24VDC, its not a branch circuit, so I don't see any code violations.