Hi folks! Hope this is the right forum for my question.

I am trying to replace 2 interconnected smoke alarms - a basement on and another on the main floor of the house. The old alarms had 5 wires in them (Black, White, Brown, Blue, and Green). The new type only has 3 wires (Black, White, and Red).

The problem is that the old outlet boxes have way too many wires and not sure which ones to bundle together and which ones to cap off. The basement box has 2 Black and 2 White wires - as in the picture. The main floor box has 3 Black and 3 White wires and the old alarm is still connected. As per one of the pictures you will notice that the two whites from the box are connected to the white from the alarm, the 3rd white is connected to the blue from the alarm, the two blacks are connected to the black from the alarm, the 3rd black is connected to the brown from the alarm. The green is just grounding.
Thanks in advance.

 

Normally two blacks and two whites would be power in and power out.

I don't see any interconnect wire in the house wiring, normally a red.

 

Thanks for the response forum pcboss. It appears that one of the black wires was being used to interconnect the two devices. Too bad I did not test their connectivity before removing the basement smoke alarm. I could have activated one of them and checked if both would ring.

 

How many cables are in the round box?

 

The basement box has 4 cables: 2 black and 2 white
The upstairs box has 6 cables: 3 black and 3 white

I was suspecting that one of the black cables is an interconnecting wire. The upstairs box still has the old smoke alarm connected to it and one of the three black wires is connected to the brown wire from the alarm. Suspecting the brown wire is on the old smoke alarm was the interconnecting wire.

 

You have two cables in one box and three in the other. What you are calling cables are wires or conductors.

I can't say I have ever seen smoke wired that way.

 

My apologies, they are wires and not cables.

 

Solved!

Thank you to all who have taken time to brainstorm my problem. I figured things out and thought I would provide my solution in case anyone else might run into such a problem:

First thing to do is make sure you take pictures of the connected wires before removing an old smoke alarm. I made the mistake of not doing so with my basement alarm. Luckily the basement outlet box only had 2 black wires and two white wires. so one of the black wires had to be a connecting wire. Probably the person who originally installed these smoke alarms was too lazy to go and grab a different color wire for the interconnect and just used the same black wire used for hot. So I bundled the 2 whites and connected them to the alarm's white, connected one black to the alarm's black, and connected the other black to the alarm's red wire. How did I know which black wire is for what? Lucky guess - and if it did not work I would switch them around.

As for the upstairs box with six wires (3 black and 3 white), I naturally assumed that the black connected to the brown wire from the old alarm was the interconnecting wire. I then bundled the remaining two blacks and connected them to the new alarm's black. I bundled 2 white wires and connected them to the new alarm's white. I just capped off the 3rd white.

Turn the breaker back on and it did not trip. Both alarms turned on. Tested if both alarms were communicating with each other by introducing smoke to the basement one - both went off.

 

That goes with ANY wiring job including replacing receptacles, switches, lights and fans.


REAL lucky guess...... if you put 120v on the interconnect (red) lead you'll blow out the detector.

Your smoke detectors were not wired to normal standards. A three wire cable is normally used for interconnected smoke alarms.