NEC definition of Low Voltage

[tdl12v]

Can someone please provide me with the NEC reference that defines Low Voltage. I have heard that the definition can be found as a limitation to the max. voltage allowable (i.e. 30v)for a "low voltage" product. I am trying to reconcile the apparent disconnect between the NEC definition of Low Voltage and the UL 1838 Listing for Low Voltage Landscape Lighting, which limits transformers to a max. output of 15v.

 

[hbiss]

Re: NEC definition of Low Voltage

The NEC does not specifically define low voltage. Generally it is 50 volts or less but installation requirements depend also on the current and current limiting capability of the supply.

As far as differences between UL and the NEC, UL does not necessarily follow the NEC and creates their own requirements as they feel necessary.

-Hal

 

[tom baker]

Re: NEC definition of Low Voltage

The mother of all low volage articles is Art 725, but the title is Class 1, Class 2, and Class 3 Remote-Control, Signaling, and Power-Limited Circuits. The nec does not use the term low voltage. Circuits in Art 725 per the FPN are:
FPN: The circuits described herein are characterized by usage and electrical power limitations that differentiate them from electric light and power circuits; therefore, alternative requirements to those of Chapters 1 through 4 are given with regard to minimum wire sizes, derating factors, overcurrent protection, insulation requirements, and wiring methods and materials.

Once a circuit exceeds the limits in Art 725 it becomes a fire hazard or shock hazard and is wired per the rules in Chapter 3. For example a 1,000 VA 12 v transformer for landscape lighting could be low voltage, but not limited energy, as it could cause a fire. A car battery is low voltage but there is enoght energy that they can and have started fires.

Also 30 volts is often considered the voltage below which no protection is required.

 

[charlie b]

Re: NEC definition of Low Voltage

The phrase ?low voltage? has no meaning, unless it is used in some context that describes the equipment under consideration. In my type of work (power systems engineering), I use the terms ?High Voltage? to mean ?over 25,000 volts,? and ?Medium Voltage? to mean ?more than 600 volts and less than 25,000 volts,? and finally ?Low Voltage? to mean ?600 volts or below.? On the other hand, to people who work on security, fire alarm, and communications systems, the phrase ?Low Voltage? would certainly mean less than 120 volts, but can mean different numbers to different people.

So I just suggest that you always take care to verify that the person you are talking to will interpret the phrase ?Low Voltage? in the same context as you.

 

[tom baker]

Re: NEC definition of Low Voltage

Right Charlie. The NEC itself is not clear on the boundaries between voltages. I consider anything over 600 V to be high voltage, a fire alarm person may consider 120V to be high voltage.

 

[a.wayne3@verizon.net]

Re: NEC definition of Low Voltage

I have used 50 volts as the cut off point.Over that Nec guidelines,common scence also.Now com. cables do have some of the same rules look at 800 for protection 300.4 D is there so why not other articles that pertain to low 50 + volt systems.Get enough ringers on a phone line and get in the middle OUCH !!!!!

 

[pierre]

Re: NEC definition of Low Voltage

Low voltage is such a variable term, that we all have to be very careful (as mentioned above) that the person(s) we are discussing the subject with has a very good understanding of what we are saying.
From the IEEE 100
The AUTHORITATIVE DICTIONARY Of IEEE Standards Terms 7th edition

Low Voltage - An electromotive force rated nominal 24 volts, nominal or less, supplied from a transformer, converter, or battery.

Low-Voltage System (electric power) - An electric system having a maximum root-mean-square alternating-current voltage of 1000 volts or less.

As these two definitions show us, we have to take the term 'low voltage' in context as to the type of installation that is being discussed.


I hope this adds to your confusion - oops I mean helps clear up your confusion