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Class 1 circuit for Mini-Split

M

Michael Brown

SAWHORSE
Joined
Mar 27, 2017
Messages
38
Location
Covington, GA
We have a multi-story apartment building in Charlotte, NC where we have 20 mini-splits serving various areas. We pulled a 14-4 TC-ER cable as the control wire for these units, taping them along the lineset as we do any other control wire and we have installed this type of wire for years in this area. The new electrical inspector wants an MC cable, not the wire we installed. We haven't been able to get an explanation as to why the cable we installed is incorrect. 2 of the four conductors will carry 208v with a third carrying a DC control signal. 725.24 seems to support the way we have this wire installed. We're not necessarily looking to argue with the inspector, we just want to understand the requirement and the inspector has not been forthcoming. Can anyone offer any insight?
 

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Michael Brown said:
We have a multi-story apartment building in Charlotte, NC where we have 20 mini-splits serving various areas. We pulled a 14-4 TC-ER cable as the control wire for these units, taping them along the lineset as we do any other control wire and we have installed this type of wire for years in this area. The new electrical inspector wants an MC cable, not the wire we installed. We haven't been able to get an explanation as to why the cable we installed is incorrect. 2 of the four conductors will carry 208v with a third carrying a DC control signal. 725.24 seems to support the way we have this wire installed. We're not necessarily looking to argue with the inspector, we just want to understand the requirement and the inspector has not been forthcoming. Can anyone offer any insight?
Click to expand...
Look at 334.10 for prohibited uses of nm wiring methods. determine what building classification in NFPA 220 table 3-11 and that might give you your answer. When rejected AHJ should quote code violation for you.
 
First of all, he needs to cite a code section and not just write it up. Please ask him for a code section or ask his boss for a code section.

Secondly, I can only take a complete guess that he is relying on this:

336.12 Uses Not Permitted.
Type TC tray cable shall not be installed or used as follows:
  • (1) Installed where it will be exposed to physical damage
 
jar546 said:
Secondly, I can only take a complete guess that he is relying on this:

336.12 Uses Not Permitted.
Type TC tray cable shall not be installed or used as follows:
  • (1) Installed where it will be exposed to physical damage
Click to expand...
Yet 330.12(1) for MC cable is identical. So as the inspector is asking for MC cable, we can conclude that the installation will not be "exposed to physical damage."

Cheers, Wayne
 
wwhitney said:
Yet 330.12(1) for MC cable is identical. So as the inspector is asking for MC cable, we can conclude that the installation will not be "exposed to physical damage."

Cheers, Wayne
Click to expand...
Correct however, there are degrees of severity that can be applied to potential physical damage. That which can damage TC tray cable might not harm MC cable given that TC tray cable has a nonmetallic sheath whereas MC cable is metal clad.

Could it be that the inspector has determined that MC cable can withstand the environment but TC tray cable can not?
 
ICE said:
Correct however, there are degrees of severity that can be applied to potential physical damage. That which can damage TC tray cable might not harm MC cable given that TC tray cable has a nonmetallic sheath whereas MC cable is metal clad.
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That's a perfectly reasonable theory, but (a) there's no language in the NEC that would support making that distinction and (b) TC-ER cable is subject to the same crush and impact tests as MC cable, which suggests it is as durable as MC cable.

Cheers, Wayne
 
wwhitney said:
(b) TC-ER cable is subject to the same crush and impact tests as MC cable, which suggests it is as durable as MC cable.
Click to expand...
Correct again however, odds are great that inspectors, me included, are not aware of the Stnd. applied to the cables and judging by appearance, MC beats TC hands down. I would expect MC to outperform TC in a test of abrasion. I have no knowledge of the environment that the OP is dealing with. Might there be a spec sheet involved?
 
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