New Circuit

Ran a new 12/3 wire from the box to the atic to supply 2 ceiling fans I installed. Everything looks good as far as connections. Installed new 15A breaker and turned it on and got instant flash and smoke. Removed it right away. I have a Murray 150A service box and the breaker was a Siemens breaker. Does this matter?
If not, what else can I look at? Thanks

 

We need more details to diagnose this. You ran the 12/3 from where to where? What is "the box"? Is there a switch or two involved? What did you connect it to and where? How did you make all the connections at the switches (if any) and fans? Do your fan's have lights?

Clearly you shorted this out. If you draw out your whole diagram including where the power was tapped from and what you did, you'll probably see that you have a direct short from hot to neutral, either all the time or when the switch is on. What some people don't realize is that not all white wires are neutral wires, and if you use one as such, you will have this problem.

Please provide more details.

 

The house did not have ceiling boxes so I cut in two new metal boxes on hangers. I then ran the wire from the breaker box to the attic thru the wall to a single metal junction box and spliced a 12/3 line from there to each fan. There are no switches. One is on a remote and the other is a pull chain.

 

Thanks. That was more information, but still not enough.

From your panel to the junction box, you ran what? 12/2 or 12/3? I'll assume you ran 12/2, because if you ran 12/3 then I have no idea how you connected the red wire in the panel. So now I still don't know what you did with the red wire in the junction box or at the fans.

Please describe all the connections in the junction box. Then describe all the connections at the fans.

 

My mistake. Everything was 12/2 Not 12/3. Sorry

 

And the connections? Is everything just matched by color? If so, then you just have an accidental short somewhere. Double-check all your connections to make sure they are clean and tight with no wire exposed past the wire nut.

 

Thanks. I'll try that. All connections are wired and taped. How about the new breaker. Does it have to match the box? The rest are Murray MP-T single pole. The one that blew was a Siemens Type QP single pole.

 

Wired and taped? Do they also have wire nuts under the tape? I sure hope so. If not, upgrade your fire insurance ASAP.

Yes, your breaker must match your panel. Many Siemens breakers are approved for use in a Murray panel, but I'm not sure about the exact panel and breaker you quoted. If you compare the two breakers side by side, do they look identical? When you got that flash and smoke, did the breaker trip? You might try disconnecting the wire from the breaker, turning it on and measuring voltage with a voltmeter.

 

Yes. They have wire nuts also. The breakers look the same and it did trip.