Richard,

I don't know the US rules, but this is from a UK perspective...

On Mon, 15 Jan 2007 15:38:04 -0800, Richard J. Pytelewski wrote:

> Alan:
> 
> This is not for personal use only but for a product - for residential ac
> control. 

Ah, so I imagine you won't have to just comply with the NEC but also the regulations for consumer products, which will include the spec. for isolating 
live from "touchable" items within the unit, including extra-low-voltage (ELV, in the UK this is < 50VDC) circuits.  Running mains and ELV in the same 
trunking is certainly not allowed here - there must be a physical, insulating barrier between them (not just the cables' insulation).  In places like 
under floors where they may be running "free", there must be at least 50mm (2") between them.  Also don't forget the induction problem - running 
them too close will cause AC to be induced in your control wires, and if they have high impedance at the ends, you can get a surprisingly high 
voltage.

> There are always ways to separate low and line voltage and I'm
> trying to ascertain the requirements.  In most home installations, the low
> and line voltages are in separate "boxes" or in the case of TV cable,
> Ethernet wiring and bell wire, it's OK to have no "box", just a frame to
> mount the faceplate.

Right, but there will be some distance between them and anything live.  The key words are: "Creepage & Clearance Distances".

>  In my application, I am trying to avoid costly
> wireless or less than 100% reliable line carrier technologies (X-10, for
> example).

As long as you keep the two sides of the thing separated by the appropriate distance and/or barriers, and use opto-isolation when they have to 
interact, I'd say it's doable.

> I'm at an early stage but I am sure that the product (like everything else)
> is going to be price sensitive.

As usual!  :-)  I think you need to get hold of the appropriate specs for the inside of the device (UL perhaps?) because if the NEC is anything like the 
UK wiring regulations, it will only deal with connecting things together, not what's inside them.

Cheers,


Howard Winter
St.Albans, England


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