Electrical box in ceiling has too three cables coming in. How do we know which ones to use for hook-up?
Figure Out What You Have First
The instructions below are based on a typical configuration. This is very likely to be the case if:

The 2 Black/White cables are currently connected together
Power is coming in on one (and if you disconnect them, only one, of the black wires). You need a tester to verify this before continuing.


If these 3 cables are all sitting capped (wire nuts) in the box then this will be tough to figure out. More typically though, one set is &quot;in&quot;, another is &quot;out&quot; (to other devices sharing power) and the third is &quot;switched&quot;. All grounds go together, so they can be ignored for purposes of figuring this out. A typical configuration is:
In - Black, White

Black = Hot
White = Neutral

Out - Black, White

Black = Hot
White = Neutral

Switched - Black, White, Red

Black = Hot
Red = Switched Hot 1
White = Switched Hot 2 (note, this one of the rare situations where White is not Neutral) or Neutral in the Switch Box (required in most places in new installations)

If that's the setup, it is designed for a combination ceiling fan + light with separate switches for fan &amp; light. That used to be very common. Now with inexpensive remote controls it is less common.
New Fan

Black = Hot or Switched Hot
White = Neutral

Connections - Using a Single Wall Switch

All Cable Hots (Black from all 3 cables) together
All Cable Neutrals (White from In &amp; Out) together plus white wire from fan
Switch connects to Hot (Black) and Switched Hot (Red)
Cap the Switched Cable White wire on both ends - you're not using it right now.
Red (Switched hot) to Fan Black wire.