How where the clearances for 110.26 originally determined? Does anyone know?

[gdstewar]

I know this goes back awhile, however a student asked the question of me the other day " How where the clearances established? Did they just throw out a number or what?"

 

[Volta]

I think they just tried to figure out how much room a person needed to work on the equipment safely, and over the years we've been getting fatter. :roll:

 

[kwired]

Moses came back from the mountain with a third stone not mentioned in the Bible, it had the first version of NEC on it:lol:

 

[GoldDigger]

Moses came back from the mountain with a third stone not mentioned in the Bible, it had the first version of NEC on it:lol:

Which was much shorter that the present one, since it only had lightning protection to worry about, and that was done primarily through prayer.

 

[mgookin]

The NEC is a NFPA publication. In Fire College we were shown movies about how the NFPA comes up with the metrics used in their standards. I'll use exit capacity as an example (because that's one particular movie clip I particularly remember). They set up cameras in a stadium, an arena, a theater, etc. and watch people coming and going, what happens during alarm conditions, etc. They monitor hallways, stairs, doors, etc. That's how they came up with 0.2" exit width capacity per person on a stair and 0.3" per person through a door (or vice versa; it's been a while).

So I would suspect they set up a camera (or just stood there) and watched an electrician working on some electrical equipment, gave consideration for the height & width of most electricians, the amount of space he needs to work safely, and went from there.

 

[480sparky]

110.26 started out as Rule 1111 in the 1940 NEC.

2? and 4' were used then.