Where can I find Disconnect requirements for DC circuits in MC cable?

I

Installer

Senior Member
Location
DesMoines, Washington
We have an equipment rack fed by 20 A 120 VAC. The equipment rack has an inverter which will feed 4 touch displays screen with speakers 4 floors up with DC voltage.
6930.31 D requires the DC wiring to be placed in MC cable.
Some of the DC wiring guidance in the NEC Code is for photovoltaic installations and may not apply to this installation
Where do I find guidance for a Disconnect Switch for the DC circuits?
Does the inverter in the rack serve as a Disconnect?
Do we require a disconnect 4 floors up where the Displays are?
Thank you in advance
Installer
 
An inverter does not supply DC. 😉

As you said, article 690 does not apply. I think you made a typo referring to 690.31(D). You do not have to follow that rule in your application.

As Ron said, many of the rules here are not different than for AC. Whether disconnects are required arguably depends on what article, if any, applies to your screens. For example maybe Article 645, Information Technology. But maybe some other article, or maybe it's just not clear.

If you have a readily accessible disconnect (which could be the breaker) for the AC circuit supplying your DC supplie(s), I'm not sure in this case if there is any additional requirement for disconnects in the DC wiring.
 
Installer said:
The DC circuits are similar to DC adapters that you plug into the wall and are low amperage. However they are 48 VDC.
Click to expand...
The key here is what class these power supplies are. Just because the power is 48 volts is irrelevant. (Phones run on 48VDC.)

As with all low voltage, you have to look at the label on the power supplies to determine what is required to connect them to their load. If it says Class 2 or Class 3 you look to Art 725 and it's safe to assume that a disconnect is no way required. If there is nothing on the label about class or wiring, you have to assume Class 1 which means a chapter 3 wiring method. But here again, a disconnect is not something that I would imagine would be required given the application.

Much of this kind of stuff is being connected and powered by POE (power over ethernet) these days. One simple CAT5e cable does it all. What are the touch screens and system for and what does the manufacturer have to say in the instructions? That is what I would look at first.

-Hal
 
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