Article 690 question. Is MC cable required for 48 VDC running from 2nd floor to 7th floor Observation Deck?

I

Installer

Senior Member
Location
DesMoines, Washington
We are installing an equipment rack on the second floor of Building powered by two 30 Amp Single Ø 120 VAC circuits.

The equipment rack has a power distribution unit which provides 48 VDC power through cables in a Cable chase to Touch Screen equipment on an Observation Deck on the top of the building 5 floors up.

I believe the 48 VDC power cabling should be in MC cable. However because the NEC Code doesn’t directly point to this guidance, I can’t get people to listen.

Starting with Article 720 “Circuits and equipment Operating at less than 50 VDC”, if you’re not an Electrical, you really have to dig into the code to find this guidance (look at the tree below; it isn’t easy.)

The requirement for MC cable isn’t easy to find in the NEC Code. Its buried under Photovoltaic PV systems. I’m probably going to get pushback because it’s under Photovoltaic Systems. Can I get some concurrence that this requirement for MC cable applies for a non PV application?

Thank you in Advance

Respectfully

RC on behalf of JP and AA

(G) Photovoltaic System Direct Current Circuits on or in a Building. Where PV system dc circuits run inside a building,
they shall be contained in metal raceways, Type MC metal-clad cable that complies with 250.118(10), or metal enclosures from
the point of penetration of the surface of the building to the first readily accessible disconnecting means. The disconnecting
means shall comply with 690.13(B) and (C) and 690.15(A) and(B). The wiring methods shall comply with the additional
installation requirements in 690.31(G)(1) through (4).
​
MC cable.png
 
Note that Article 720 was deleted from the 2023 code as unneeded. In the previous codes, Article 720 did not specify wiring methods so the wiring methods in Chapter 3 are required. The limitations of what Chapter 3 wiring method can be used will be based on the building construction.
 
Installer said:
The equipment rack has a power distribution unit which provides 48 VDC power through cables in a Cable chase to Touch Screen equipment on an Observation Deck on the top of the building 5 floors up.
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What you have to look at is what Class of wiring is required, not your seat of the pants guess. The requirements will be on a label on the power distribution unit as well as the installation instructions. It will say Class 2 or Class 3 wiring required on maybe Class 1 or maybe nothing. If nothing, Class 1 is implied and Class 1 is a chapter 3 wiring method like MC.

But, I suspect that with everything going PoE, all that you will need is CAT 6 Ethernet wiring.

This question and installation sound very familiar, was it you? I left off that one asking what kind of touch screen equipment is it? Directories or something else? Never got an answer.

-Hal
 
hbiss said:
What you have to look at is what Class of wiring is required, not your seat of the pants guess. The requirements will be on a label on the power distribution unit as well as the installation instructions. It will say Class 2 or Class 3 wiring required on maybe Class 1 or maybe nothing. If nothing, Class 1 is implied and Class 1 is a chapter 3 wiring method like MC.

But, I suspect that with everything going PoE, all that you will need is CAT 6 Ethernet wiring.

This question and installation sound very familiar, was it you? I left off that one asking what kind of touch screen equipment is it? Directories or something else? Never got an answer.

-Hal
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Thanks for answering and heading me in the right direction. (No I didn't post this question previously)
Let me do my homework on Class 1 , 2 and 3 remote-control, signaling, and power-limited circuits
Its not POE wiring. The PDU's in the rack are powering 400 watt processors up on the Observation deck which feed the Touchscreens.
We don't have the equipment in hand yet--its made in Europe- and we're awaiting documentation so we have no label on the PDU to consult .
We're providing the vendors with the US NEC Code requirements for there equipment, so that's why this question has arisen.
The reason I jumped to the PV section instead of Remote control, signaling and power limited sections was because of the 48 VDC 400 watt processors, it wasn't seat of pants.
 
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Installer said:
The PDU's in the rack are powering 400 watt processors up on the Observation deck which feed the Touchscreens.
We don't have the equipment in hand yet--its made in Europe- and we're awaiting documentation so we have no label on the PDU to consult .
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I question why they are sending 48VDC @ 400W up to the touchscreens rather than just powering them directly with local 125VAC at their locations. FYI for 48VDC @ 400W you would use any Chapter 3 wiring method which MC cable is one of. That would be found in Art 725. 720 covers photovoltaic not what you are asking about.

If it's made in Europe it's not likely to conform to our standards. It's not just a matter of reading the Code book, you have to understand it. Also, there are other safety related design areas that we take seriously here that they must satisfy that have nothing to do with the Code. They will require UL or other recognized testing laboratory approval and listing after they make it conform.

Installer said:
(No I didn't post this question previously)
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Well, those "vendors" apparently had somebody else working on this maybe six months ago.

-Hal
 
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Since you are in WA, is this install subject to OSHA or WSHA inspections? If so, anything electric needs to be NRTL listed (e.g. UL, ETL, or a host of others). A CE mark won't cut it. If not listed by a NRTL, you can use a Field Evaluation Body (FEB) to approve equipment. WA has a list of specific FEBs that can approve thins in WA state.

With a 400W load, you are most likely past the CL2/CL3 power limits so you'd need a chapter 3 wiring method. MC cable could be used, but it needs to be protected from damage. You could also perhaps use SE cable or some of the other cable methods, Flex metal conduit and pull individual conductors, EMT conduit, and other choices.

What type or wire or cable do the "others" want to install? Hopefully they are not thinking zip, SO, or SJ cord...
 
Installer said:
Thanks for answering and heading me in the right direction. (No I didn't post this question previously)
Let me do my homework on Class 1 , 2 and 3 remote-control, signaling, and power-limited circuits
Its not POE wiring. The PDU's in the rack are powering 400 watt processors up on the Observation deck which feed the Touchscreens.
We don't have the equipment in hand yet--its made in Europe- and we're awaiting documentation so we have no label on the PDU to consult .
We're providing the vendors with the US NEC Code requirements for there equipment, so that's why this question has arisen.
The reason I jumped to the PV section instead of Remote control, signaling and power limited sections was because of the 48 VDC 400 watt processors, it wasn't seat of pants.
Click to expand...
That is well outside the maximum power for a Class 2 or 3 circuit. It remains my opinion this is a power circuit and the fact that the voltage is 48VDC does not change anything. These circuits need Chapter 3 wiring methods. The type of wiring method may be limited by the building construction.
 
Its interesting how many things are marked for '48VDC' for example the sticker on a Square D QO breaker states its listed for 48VDC.
 
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