ECN Electrical Forum
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per the 2008 NEC how many steps need to be present to justify a 3-way system,,, example 2, 4, 6,

210.70 (a)(2)(c) provides the answer...

"(c) Where one or more lighting outlet(s) are installed for interior stairways, there shall be a wall switch at each floor level, and landing level that includes an entryway, to control the lighting outlet(s) where the stairway between floor levels has six risers or more. "

your local building code may have more to say on the switching requirements

A lot of what I am seeing these days is not actual switches, but PIR switching on stairwells.
Where as a given flight of stairs might have a sensor on it, it will trigger on movement at the bottom of the stairs and also trigger a delay timer at the top of that set of stairs, that energises the next PIR (and lights) and turns off the lower lighting.
If it saves lights being left on all night,, I'm all for it.

Having said that, in fire situations, it's all lights on.

I like motion lights. The light follows you around my house, inside and out.

My wife follows me round the house switching them off, which is nearly the same but with added mutterings about utility bills ! Seriously, you could lose all the cost saving advantages of low-energy lights if the switch timers are of too short a duration. They don't like short runs.

I thought that was true but I have CFLs in the motion lights in my garage, the post light out front and one of the lights inside. They seem to be holding up OK.

Do you really need a 3 way switch at the top and bottom of the stairs when the stairway goes into an attic?

Harold:
It will depend on the definition/use of the 'attic'.

Pull down stairs for access to the space I would say only a switch at the entry, walk-up stairs to a space that could be 'occupied' may require a 3-way. Intent and design fall into the discussion at that point.

PIR switches are nice but they have to have regular switching. So as not to leave anyone in darkness.

3 steps in Michigan...

IRC requires switches even if a PIR is used. Because they can and do fail

That is the code run amok.
I suppose someone should point out, switches break and lamps burn out too.

Multi bulb lamps, extra lamps, multiple motion detectors, and a bank of switches. Oh wait, also an emergency break-in box with a flashlight, and extra batteries. That should cover lots of breakage :-)

Do they have a wattage requirement, or can I use 4 watt bulb.

What about permanent step lights? Can I get by with just those?

I didn't see where it said 3-way. Can I use on/off contactors?