"All Others" Lighting Load Demand Factor

Hi, all.

I have always seen the general lighting load demand factor (not dwelling units, hospitals, hotels, or warehouses) set at 125% on projects on different companies. However, NEC table 220.42 states that "all others" lighting loads are to be demanded at 100%. There's an asterisk note there, but it refers only to hospital and hotel loads, not the "all others".

I have asked this to coworkers and they have said this 125% is in response to articles 210.20(A) and/or 215.2(A)(1)(a). Problem is (to me, anyway) is that those articles are specific to branch OCPD and feeders, not demand factors.

Does anyone have a better explanation to the use of this 125% for demand factor for general lighting loads? Or perhaps the use of 125% is not really required by NEC?

Thanks in advance,


  • Hi Edgar,

    I presume, due to you references to NEC, that you are in the USA, or another place that wires using the USA codes ?

    Here in the UK, and indeed 230V/400V land generally,  load diversity factors are calculated a bit differently, and although the physics is the same, the language used and the final circuit layouts in use end up being rather different.

    There are a few folk who pop up on here from time to time who are familiar with US practice, and the rest of us can discuss the ideas in principle, but you may get a faster and better defined  answer by asking on a US-centric forum as well - and if you do, please come back and tell us the answer..

    And I'm sorry,  have no idea why American hospital lights are special cases - here they would not be except in terms of perhaps needing unusual levels of emergency and task specific lighting, but the cable sizing maths etc would be as per standard.


  • Thank you very much, Mike.

    I was hoping this site would be it, but you're right, I indeed work I the US and need a forum where most of the users are also not only working here, but familiar with the NEC.

    Thank you so much for clarifying. Going to look for a US-based EE forum now Grin



  • Do let us know how you get on. It is always informative to know what other places do and why they do it.


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