New to Relays and also trying not to start fires

[archstenton]

Recently got to lights with the Elk M1.
 
Regards to relays and controlling lights that I want to also MAINTAIN THE CURRENT ROCKER SWITCH as a manual over-ride to the Elk control,  is it as simple as tapping say an Elk 912  AC output into the switched leg of the light wiring?.  For instance if I had a string of lights along the wall, do I just splice the relay's AC output anywhere along the switched wire section?  i.e. switch and Relay can be "ON" at the same time  illuminating the light?
 
Rudimentary
 
AC power------|-------------$------------|---------Light
                       l------------Relay------ |

 
Now, the AC input power to the Relay on a different AC circuit than the manual switch?  I'd imagine that's a no-no, two different circuits feeding the same light, different circuit neutrals connected downstream from Main Electric Panel type of stuff.

 

[RAL]

If you put the relay in parallel with the existing switch, if either one is on, the light will be on, and the other device won't be able to turn it off.
 
One way this could be solved is to wire the light for a 3-way switch circuit, and use a SPDT relay.  But that gets confusing for the Elk, because at one time, turning the relay on will turn the light on, but if someone throws the manual switch, then the M1 would need to turn the relay off in order to turn the light on.  The M1 won't know the status of the manual switch, so it can't know whether the relay should be on or off for the light to be on. 
 
You need to be careful in wiring relays to 120VAC wiring, and use relays that are UL approved for the purpose, such as a Functional Devices RIB relay.  Still, you'd have the same problem with putting a relay in parallel with a switch.  The Elk 912 isn't appropriate since it is rated for only 10A and your lighting circuit would be 15 or 20A.  You would have  to make sure any relay is properly enclosed and keep high and low voltage wiring properly separated to meet the electrical code.  The RIB relays do that for you.
 
The way most people solve this sort of problem is with switches that are designed for home automation, and an appropriate HA interface on the Elk M1.

 

[archstenton]

Thanks for the info.
 
On the parallel setup, I'm not too worried about functionality as the use of these would be occupancy type needs like outdoor lighting and the Elk command would be on a timer and eventually lights goes off in minutes measurement. Also, the user of the Manual switch won't be Home automation literate and figures they always need to turn the light OFF since "they" turned it ON.
 
Yeah, don't know why ELK has all this stuff showing use but not UL listings for it?.  To be UL rated does a relay need to be enclosed & not a "board"?  I can't imagine with what I have in mind, any relay would be more than feeding 1.5 amp at AC level.
 
On the separation, I've been going off of NEC 725.136 and maintaining 1/4" gap but basically got them on opposite sides of the box until where the relay board would be and used CL3 wire too and of course <150 volt circuit.

 

[RAL]

Thanks for the info.
 
On the parallel setup, I'm not too worried about functionality as the use of these would be occupancy type needs like outdoor lighting and the Elk command would be on a timer and eventually lights goes off in minutes measurement. Also, the user of the Manual switch won't be Home automation literate and figures they always need to turn the light OFF since "they" turned it ON.
 
Yeah, don't know why ELK has all this stuff showing use but not UL listings for it?.  To be UL rated does a relay need to be enclosed & not a "board"?  I can't imagine with what I have in mind, any relay would be more than feeding 1.5 amp at AC level.
 
On the separation, I've been going off of NEC 725.136 and maintaining 1/4" gap but basically got them on opposite sides of the box until where the relay board would be and used CL3 wire too and of course <150 volt circuit.

 
There are different types of UL labels, which have different meanings.  Components, such as relays, can be "UL Recognized" which is indicated by a RU mark (with the R backwards) on the component.  This means that the part meets UL standards.   Companies that use those parts in larger systems (such as an alarm panel) care about that sort of thing.  But because the part has the RU mark does not mean the system it is eventually included in does.
 
Another type of UL mark is the "UL Listed" mark, which is applied to standalone products.  The symbol is the letters "UL" enclosed in a circle, with the word "Listed" underneath. It means the product has been tested to UL standards for a specific purpose, and at a higher level than an individual component would be tested.
 
If you look at a photo of the Elk 912 relay, you can see the RU mark on the relay itself.  But the overall board does not have a marking.  There's not much else on it, except a diode and a terminal strip.  I can understand why Elk didn't want to bother with any higher level of testing of such a simple product.
 
You can take a component, such as a bare relay, and use it for a purpose such as controlling lights, but then it is up to you to make sure it meets the necessary requirements, for fire safety and electrical safety.   At a minimum, you would have to convince an electrical inspector that what you have done is safe.  Some AHJs might give their approval, others might not.  And your insurance company might care in the event of a fire.
 
Overall, it's just easier to use something like a RIB relay which has been tested and shown to meet UL standards for that purpose and avoid the argument with the AHJ and anyone else.