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I'm trying to figure out regulatory requirements for residential electrical installations. Specifically, when is a licensed electrician required by code to perform an installation? Obviously you don't need one to install speaker wire. What about 120VAC line? Is there a voltage cut-off where low-voltage is less regulated than high voltage? If so, what is the cutoff? I should say that I'm only interested in installations up to 120VAC.

The reason for this question is that we are designing an electronic product to be installed in homes and would like to make installation require as little professional work as possible. Ideally this product could be installed by someone at the audio/video level of skill/licensing. We will run off a DC power (power supply would connect to 120VAC and likely be installed by a licensed electrician) but have a choice about what voltage to use. Higher voltage is better for electrical reasons but we don't want to trigger all kinds of complications with the installation.

I understand that codes vary by geography, and ideally the answer to this question would cover the differences in every region across the US but that's a long shot. If you only know your local code, then it is still helpful to me as long as you tell me your region.

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Some jurisdictions (e.g, NYC) require that every line voltage installation be done by a licensed electrician. While low voltage, such as 24 volt HVAC lines, may not be strictly controlled, anything more is likely to run afoul of some regulation. – bib Dec 20 '13 at 0:14
Probably the more relevant question is "when is a permit/inspection required?". Many jurisdictions will let a homeowner do whatever work they want as long as it's properly permitted and inspected. – Henry Jackson Dec 20 '13 at 2:18
It's unclear exactly what you're asking. Is your device attached to the electrical system via a plug? Would the device require a special branch circuit to supply it with power? Does your device require additional conductors to be installed in the home for it to operate? – Tester101 Dec 20 '13 at 12:44
Thanks for the feedback. Actually it's been pretty helpful already, even just to instruct me how to better ask this question. To clarify: The device will likely be installed inside the wall. It will be supplied DC power by an off-the shelf power supply, also residing in the wall. That power supply will be connected to mains power, not through a special branch but probably spliced off the nearest line. What we're concerned about is any trait that might trigger a more complicated installation. Any trait could be current or voltage max, and complicated could be requiring inspection or licence. – Dave Dec 27 '13 at 23:38

I'm not sure this is a great question for this site; you seem to be asking what are all the possible code requirements. There isn't really an answer to that. You also haven't specify if this is running in-wall or not, and what kind of current you're talking about.

You might be better off consulting the UL or your insurance / liability lawyer. In practice if you're developing a product you'll probably be limited by what your insurance company will sign off on.

The UL has a definition of "low voltage" that's either under 20V or under 42V, depending on the current. I don't believe NEC defines "low voltage"

However if you're looking for other comparison points: most thermostats are 24 volt, and power-over-ethernet devices run at around 50 VDC.

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NEC defines anything below 480 volts as "low voltage". – wallyk Dec 20 '13 at 0:36
Actually, the NEC has no requirements for who does the work or their qualifications, it is limited to how the work is to be done. Any voltage is capable of starting a fire, so voltage is not the criteria. License requirements are decided by the authority having jurisdiction (building department), not the NEC. As with any bureaucracy, there may not be any logical reasoning for their requirements. – bcworkz Dec 20 '13 at 0:51
Power-over-Ethernet is a good comparison in terms of the voltage and power we're seeking. In most districts, can anyone install PoE lines (in wall)? Do they require city inspection? What are the restrictions an installer would need to consider? – Dave Dec 27 '13 at 23:41
48 Volts is a great number to use as a max voltage. It is the voltage of the telephone system. – Some Guy Mar 19 '15 at 9:14

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