wiring in smoke detector...?....

Hello Forum,

simple question about wiring a house smoke detector. It operates at 120 V.
Two wires, the black (hot) and white (neutral) are enough. 
There is a 3rd wire, red, to interconnect multiple alarms: if one alarm
rings all the others ring too. The connection between the different alarms
is in parallel (I guess).

That said, I am not clear what the red wire does. Is it a hot or neutral
wire?

I am trying to envision a circuit with, say 2, smoke alarms represented as
two switches connected in parallel. When one switch is closed the other one
must close too.....but I am still wondering how the red wire comes into
play.

Are the red and white connected together?

thanks,
fisico32

On Mar 21, 1:39&#4294967295;am, "fisico32" <marcoscipioni1@n_o_s_p_a_m.gmail.com>
wrote:
> Hello Forum,
>
> simple question about wiring a house smoke detector. It operates at 120 V.
> Two wires, the black (hot) and white (neutral) are enough.
> There is a 3rd wire, red, to interconnect multiple alarms: if one alarm
> rings all the others ring too. The connection between the different alarms
> is in parallel (I guess).
>
> That said, I am not clear what the red wire does. Is it a hot or neutral
> wire?
>
> I am trying to envision a circuit with, say 2, smoke alarms represented as
> two switches connected in parallel. When one switch is closed the other one
> must close too.....but I am still wondering how the red wire comes into
> play.
>
> Are the red and white connected together?
>
> thanks,
> fisico32

This is a DSP group. The electrical technician group is elsewhere...

You are right, my bad.

fisico32 schrieb:
> Hello Forum,
>
> simple question about wiring a house smoke detector. It operates at 120 V.
> Two wires, the black (hot) and white (neutral) are enough.
> There is a 3rd wire, red, to interconnect multiple alarms: if one alarm
> rings all the others ring too. The connection between the different alarms
> is in parallel (I guess).
>
> That said, I am not clear what the red wire does. Is it a hot or neutral
> wire?
>
> I am trying to envision a circuit with, say 2, smoke alarms represented as
> two switches connected in parallel. When one switch is closed the other one
> must close too.....but I am still wondering how the red wire comes into
> play.
>
> Are the red and white connected together?
>
> thanks,
> fisico32

Check the manual I am no electrician and playing around with 120V is no fun.
There are 2 possibilities:

1. The sensor has an extra pin out of which a switched voltage comes
    carrying the alarm state.
2. The current which flows through the sensor changes when the alarm is
    turned on. Then you can put a relay between the neutral port of the
    sensor and the neutral line using the red and white cables which
    switches other alarms on.

But be careful and try to check the datasheet first before using the red 
cable for anything.

Greetz,
Sebastian

On Mar 20, 8:50&#4294967295;am, HardySpicer <gyansor...@gmail.com> wrote:
> On Mar 21, 1:39&#4294967295;am, "fisico32" <marcoscipioni1@n_o_s_p_a_m.gmail.com>
> wrote:
>
>
>
> > Hello Forum,
>
> > simple question about wiring a house smoke detector. It operates at 120 V.
> > Two wires, the black (hot) and white (neutral) are enough.
> > There is a 3rd wire, red, to interconnect multiple alarms: if one alarm
> > rings all the others ring too. The connection between the different alarms
> > is in parallel (I guess).
>
> > That said, I am not clear what the red wire does. Is it a hot or neutral
> > wire?
>
> > I am trying to envision a circuit with, say 2, smoke alarms represented as
> > two switches connected in parallel. When one switch is closed the other one
> > must close too.....but I am still wondering how the red wire comes into
> > play.
>
> > Are the red and white connected together?
>
> > thanks,
> > fisico32
>
> This is a DSP group. The electrical technician group is elsewhere...

Actuallly, this is a group where people who are interested in DSP
meet.  It is also an unmoderated group, so pretty much any one can
post topics here if they choose to.  I appreciate some posts such as
this from regulars to the group.

If you want the reliable time, you don't stand on the street corner and ask a passer-by, but that's often the best you can easily do and often good enough.

The equivalent of tuning in WWV (or getting time from your cell phone) is consulting the wiring diagram that came packed with the detector. I know what I would guess if I had to, but not having to, I won't. 

Does the alarm work if the power is turned off? My battery alarms do. Never trust the power to remain on in an emergency. Think of Fukushima Daiichi.

Jerry
-- 
Engineering is the art of making what you want from things you can get.

fisico32 <marcoscipioni1@n_o_s_p_a_m.gmail.com> wrote:
(snip on smoke detector outputs)

> You are right, my bad.

But it is a digital signal (yes smoke, no smoke) and he
would like to know how to process it.

I believe connect all the red wires together.

-- glen

As I supposed: http://tinyurl.com/4vskoo9

Jerry
-- 
Engineering is the art of making what you want from things you can get.

Jerry Avins schrieb:
> If you want the reliable time, you don't stand on the street corner and ask a passer-by, but that's often the best you can easily do and often good enough.
>
> The equivalent of tuning in WWV (or getting time from your cell phone) is consulting the wiring diagram that came packed with the detector. I know what I would guess if I had to, but not having to, I won't.
>
> Does the alarm work if the power is turned off? My battery alarms do. Never trust the power to remain on in an emergency. Think of Fukushima Daiichi.
>
> Jerry

That was what I was wondering also. The typical smoke detectors I know 
are battery powerd and not connected to 120/230V AC. Usually with an own 
warning sound for battery low.

Sebastian,

Smoke detectors here in the US cone in atleast two varieties: self-contained battery-powered (either 9- or 3-volt) and line powered. The line-powered detectors are required for new construction in many places. They have the advantage that all of them sound if a problem is detected by any of them. Our domestic power distribution standard is approximately 120 volts. One wire -- usually black -- is "hot" or "live". It is at 120 V with respect to any ground (such as a water pipe) and is the only wire that is fused. The other power conductor -- usually white -- is designated "neutral" and is physically connected to ground (earth) at one point in the system. In addition, a third wire, usually green, is also connected to ground and is used to ground the outsides of appliances, rendering them relatively safe in the presence of internal insulation failures. In normal operation, all current in the hot wire returns via the neutral. An insulation failure that could shock someone implied that the hot and neutral currents differ. A device called a "ground-fault interrupter" can detect the difference and trip a circuit breaker. Putting your finger into a light-bulb socket and touching both contacts will give you a shock, but if the lamp is protected by a GFI, and you touch the center contact while a foot is in a full bathtub, the breaker will trip so fast you will probably feel nothing. For higher-powered appliances (big motors, cookstoves, etc.) we usually use 240-V feed, which has two hot wires (red and black) and a neutral, plus ground. Each hot wire is 120 volts to ground; essential a pair of ordinary residential circuits with a common neutral. (Three-phase systems that deliver 120 volts to neutral have 208 volts from phase to phase. 208 volts is also used for high-power single phase devices.)

Back to fire detectors. They are connected *on the same circuit* black to hot, white to neutral, and red to an interconnect wire. When any alarm activates itself, it puts 9 volts with respect to neutral on the red wire. When an inactive alarm sees 9 volts on its red terminal, it sounds as if activated. Some have a stand-by 9-volt battery for safety during power outages. (That's why the interconnect signal is 9 volts.)

Jerry

P.S. For screw terminals, brass plating on screws define "black", nickel plating defines "white", and other colors of importance (primarily green for the ground wire) are indicated by paint.
-- 
Engineering is the art of making what you want from things you can get.