What exactly is High Voltage

[Morte615]

A question came up recently which was what actually constitutes high voltage?

I know 12v is considered low voltage, I use it for control, led, and other items all the time. But I also routinely run 70v audio lines through walls and in ceilings and have never had issues, from others or from AHJ. But I have been told on more than one occasion that 100v audio lines are high voltage and have to be in conduit, and I know 120 is always considered high voltage.

So is there a code list or something that specifies what high and low voltage is? Or is it on a case by case basis.

 

[JD]

Used to be CV circuits were wired with zip cord. Times have changed! All speaker lines in a permanent install pretty much have to be up to regular electrical code regarding materials (fire) and voltage breakdown. In most cases, CV can still be run using #16, but it has to be class II. If it's in a plenum space, then conduit or plenum rated cable is a must. Regular sound equipment is even worse! Modern amps easily generate line voltage output and with quite a bit of current too! Gone are the days of the old 30 watt system.
Now, as for what is considered "High Voltage"? Well, that is subjective, but the rule of thumb is when you get anywhere nears line voltage, treat it as if it were. That includes 70 v CV systems.
Something to consider at home too, if you have a powerful system. Although you won't get inspected, home fires caused by audio are becoming a factor.

 

[Chris15]

It all depends who you are talking to.
In technical terms, mains voltages are all low voltage, tens of of kV are medium voltage and hundreds of kV are high voltage...

But what's technically defined as extra low voltage is probably the more germane consideration here.
Up to 50V ac or 120V dc is one accepted delineation point...

 

[porkchop]

I'm not sure that the question you've asked will really give you the answers you're looking for. "High Voltage" is poorly defined, mostly because it's a pretty pointless moniker as far as safety goes. OSHA defines anything <50V (AC or DC) as non-hazardous, but all that means is that you can work on it live without additional protection from electrical arcs. That doesn't have any relevance to the fire or physical hazards that are guarded from by running cable through conduit. The NEC and OSHA both use 600V as a cutoff for increased risk and the need for additional protections so a person could reasonably call that high voltage, but that's not very satisfying given the rarity of a person in our industry ever encountering a voltage that high. I could go on, but you get the point.
In my experiance voltage (at least in the ranges we deal with) rarely has much to do with wiring going through conduit or being open air. It has a lot more to do with the show being temporary or not. If I need 480VAC for a two day event in an arena I'm going to run feeder cable from the generator outside along the normal path for that building and not even think twice about additional guarding or permanent cable runs. Alternatively if I'm working at a resident show that operates for years on end and I want more runs of ethernet cable I'm going to call a licensed electrician to come in and pull it through conduit. And those basics are just for a generic building. For any specific facility there are likely to be standards of practice developed between the building labor, insurance company, management, and the AHJ that could further complicate the question of how a specific service needs to be run. I think you've got the right idea, know how you stuff operates, work smart and safe, talk to the people who decide what is safe for the building you're working in, and be flexible. Arguing rarely gets you very far.

 

[Morte615]

Actually so far this is giving me exactly what I wanted to hear (or expected to hear at least.)

Pretty much there is no clear limit in code or elsewhere that says over this voltage (or current, or ...) is considered High Voltage and needs to have different procedures in place.

I have seen the terms High and Low voltage used in code but never a definition so that's what I was looking for.

Though if someone does have a code somewhere please speak up so I know whether I am correct on that or not.

 

[n1ist]

As said, it all depends. On my digital projects, 3.3V is low voltage and 12V or 24V is high voltage. For some electricians, 120V and 208V is low and 480/277V high. For my friend who is into plasma physics, low voltage is anything below 100kV...

Most codes seems to break things into <50V, <600V, and above, though the solar guys are routinely running into >1000V DC.

And you need to be careful even with "low" voltage - just ask anyone who works with 48v battery banks or even 12V car batteries.

/mike

 

[JD]

As said, it all depends. On my digital projects, 3.3V is low voltage and 12V or 24V is high voltage. For some electricians, 120V and 208V is low and 480/277V high. For my friend who is into plasma physics, low voltage is anything below 100kV...

Most codes seems to break things into <50V, <600V, and above, though the solar guys are routinely running into >1000V DC.

And you need to be careful even with "low" voltage - just ask anyone who works with 48v battery banks or even 12V car batteries.

/mike

Yes, Arc Flash doesn't care about "low voltage." Just ask anyone who has worked around 10,000 amp submarine batteries.

 

[Jay Ashworth]

Very very roughly, in the context of building wiring, the break point is 50V, and the distinction is that code controls what you do with non-LV circuits much more tightly.

In the context of industrial electricity, high voltage is everything above 480VAC.

And, as Chris says, the breaks in power distribution/transmission are around 4300 and 23-60kV, depending on how froggy a guy you're talking to. Most of the building delivery I see -- and I look, though I don't do that for a living -- is at 240 'split-phase', and three phase at 480, 4300, and 13200ish.

Those interested in such things might want to join the Facebook group "I Take Pictures Of Power Systems" where such froggy guys hang out.

 

[MNicolai]

Low-voltage cabling is something of a generic term. Tends to refer to wiring for which delivery of power is the not the primary purpose or for <50V, low-current power supplies. Different sections of code deal with specific instances of low-voltage cabling differently depending on what the purpose and application is. All cabling must comply with codes and regulations for the manner in which it is installed (plenum, non-plenum, supported every x' in free air, cannot be supported by other trades' equipment or supports, cannot be supported by support wires for ceiling grid, can be supported by additional wires added to ceiling grid not required for structural support of ceiling, abandoned cables must be removed, etc).

Data cabling, which may have 48v PoE has no special requirements over general low voltage cabling. However, bundles of cables with PoE may require heat dissipation be taken into consideration so a large bundle of cables, each dissipating heat do not damage the cable or cause data transmission performance issues.

In practice, a 70V audio line is generally accepted as not requiring an electrical permit or being a licensed electrical contractor to install but may require a low-voltage permit in certain jurisdictions. However, a 100v audio line may require an electrical permit or a licensed electrical contractor to install. Most people will not encounter any issue because AHJ will not inquire or put this under scrutiny. I have seen it put under much finer scrutiny on office towers, in large cities, or areas where labor unions are highly active.

If you want some light reading, register at the NFPA website and you can log in and view the NFPA 70 electrical code in its entirety for free. Chapter 3: Wiring Methods & Materials, and Chapter 8: Communications Systems, refer most specifically to what you are asking about. Local jurisdictions will differ, but NFPA 70 is generally the baseline.

 

[RickR]

By code: look to the definitions in that code. NFPA 70 has different specs than OSHA than others, etc.

How high is up? How low is evil? These are relative terms that must be defined...