In this question, someone has a desk lamp with power totally exposed on metal parts. You also have installed overhead lighting on open rails doing the same thing.

What does NEC say about the maximum voltage permitted on such installations?

I am interested in fixed installations (not cord-and-plug) which are readily accessible, e.g. Low hanging low-voltage lighting that you could reach out and touch.

I am also interested in the outdoor rules, because my nefarious plan is to use the racks which hold up solar panels to carry the current from the panels, so the racks become massive feeder wire that lets me keep voltage low. Some of the panels will be on the ground.

Is the maximum voltage different for AC versus DC? If AC, does it mean RMS (the normal way AC is measured) or peak (1.4x more)?

  • WHOA. I don't know what the NEC says about the LV stuff, but unless I'm really confused it will be a big NO-NO to use the rails for carrying PV. I have a large PV system on my house and the DC voltage into the inverters is about 400 volts. Warning labels all over the place saying it's a solar circuit. Remember you can't "turn off" the panels, the rails will always be hot except at night! – George Anderson Feb 18 '20 at 19:43
  • Looks like NEC 411 covers various aspects of low voltage wiring including exposed conductors. Maximum voltages are different for AC and DC as well as whether in a potentially wet location. In other words, "it depends". – George Anderson Feb 18 '20 at 20:13
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    @because your setup chose a series connection to get the least voltage drop, but at the expense of high system voltages that open numerous cans of worms in the Rapid Shutdown arena. My aim is to sidestep Rapid Shutdown altogether, by keeping system voltage below RS minimums. That requires fat conductors, and that favors using the mounting racks as conductors. – Harper - Reinstate Monica Feb 18 '20 at 21:08
  • So even a single panel, say this one: lg-solar.com/downloads/spec-sheet/DS_NeON2_60cells.pdf is capable of 40V at 9A. Under the right circumstances that could be lethal. I'm not clear how low voltage is going to help you with your rapid shutdown. The inverter is going to take care of that for you, right? Either that or I'm unclear on your mode of operation here. – jwh20 Feb 18 '20 at 22:17
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    @jwh20 this isn't an XY problem so I am looking for a general answer, not a solve on the solar use-case. That particular panel is a quote-24V panel, with double the voltage across the board compared to a traditional bog-standard quote-12V panel, which is 19ish volts open circuit. Rapid Shutdown is a big regulatory mess that starts caring about voltages at 30V, so if I stay at 19V I'm OK. But I also want to use open rails in other applications. – Harper - Reinstate Monica Feb 18 '20 at 22:36

690.31(A) nixes your diabolical plan

Unfortunately, unless you could find a racking system specifically listed to connect the contained panels in parallel as you describe, you can't do what you're after, as 690.31(A) requires a Chapter 3 wiring method, or a wiring method explicitly listed for use with PV panels, for all PV system wiring:

690.31 Methods Permitted.

(A) Wiring Systems. All raceway and cable wiring methods included in this Code, other wiring systems and fittings specifically listed for use on PV arrays, and wiring as part of a listed system shall be permitted. Where wiring devices with integral enclosures are used, sufficient length of cable shall be provided to facilitate replacement.

(1) Identification. PV system circuit conductors shall be identified at all accessible points of termination, connection, and splices.

Where PV source and output circuits operating at voltages greater than 30 volts are installed in readily accessible locations, circuit conductors shall be guarded or installed in Type MC cable or in raceway. For ambient temperatures exceeding 30°C (86°F), conductor ampacities shall be corrected in accordance with Table 690.31(A).


I quoted the low voltage contact limits in that post with the lamp As per 680.2 15 vac 30vdc there are additional non sine ac values and pulsing dc but special test equipment would be needed so I did not add those. There is additional information in the notes for table 11-a&b in chapter 9. Pv has separate rules as listed in 690 doesn’t follow the same rules as the lighting systems discussed in the light sparking example.

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