Short circuit wiring problem - how to find it.

[simsd]

We have a project that is a dormitory with 225 rooms. There is a thermostat with a window and door contact that shuts off the A/C when they are left open.

The issue is that some of the window sensor wiring is showing closed even when the window is open and the sensor is physically removed.

This is a wood structure and the wire was not put in conduit because the structural engineer wouldn't allow penetrations in the wood.

Our issue is that we think the wires for the sensors have been hit with drywall screws. Since this has hard lid ceilings and drywall walls, does any one know of a way that we might be able to trace out where the fault might be to minimize the drywall damage?

[skwsproul]

No penetrations in the wood. Does that mean the wire is sandwiched between the studs and the sheet rock? How about running new in wire mold?

[simsd]

Brand new building still under construction. We are just getting into the start up phase. So "No' on the miremold.

The wire goes up the wall and runs length wise with the ceiling joists. There is metal furring runs along the ceiling and walls and the drywall is attached to that (I don't remember term for that type furring).

I'm also a little frustrated because I just found out that my senior technician that was working on this, didn't actually check it out himself and had some newbies do it - so now I'm not sure how many or if it's really a problem.

[jeffk91467]

Never used this tool, but it sounds like it would do what you are looking for.

http://www.idealindustries.com/products/test_measurement/circuit_analyzers/suretest_circuit_tracers.jsp

[simsd]

Thanks Jeff,

That's what I was talking about. I thought Ideal mght make something. I just wasn;t sure what it was. I'll check it out.

[skwsproul]

Never used this tool, but it sounds like it would do what you are looking for.

http://www.idealindustries.com/products/test_measurement/circuit_analyzers/suretest_circuit_tracers.jsp
Cool. I did not know they made one for spotting shorts. Have to add that to the bag o tricks.

[berg2666]

We have a project that is a dormitory with 225 rooms. There is a thermostat with a window and door contact that shuts off the A/C when they are left open.

The issue is that some of the window sensor wiring is showing closed even when the window is open and the sensor is physically removed.

This is a wood structure and the wire was not put in conduit because the structural engineer wouldn't allow penetrations in the wood.

Our issue is that we think the wires for the sensors have been hit with drywall screws. Since this has hard lid ceilings and drywall walls, does any one know of a way that we might be able to trace out where the fault might be to minimize the drywall damage?

OK so you start at one of the defective windows sensors and check continuity in the wiring from the room back to the controls. Take the wires off the control and see if they show an open circuit after you disconnect then from the wiring and eliminate if it the wiring.

If so can you replace the wiring? If not then I would just go ahead and eliminate that from the AC control circuit. Or the customer would have to allow for some other way for this to happen.

Is it just one system or multiple systems?

[berg2666]

Brand new building still under construction. We are just getting into the start up phase. So "No' on the miremold.

The wire goes up the wall and runs length wise with the ceiling joists. There is metal furring runs along the ceiling and walls and the drywall is attached to that (I don't remember term for that type furring).

I'm also a little frustrated because I just found out that my senior technician that was working on this, didn't actually check it out himself and had some newbies do it - so now I'm not sure how many or if it's really a problem.

If is still under construction then someone is responsible for the damage and it should be repaired.

Will the referenced ideal device check wiring through sheet rock?

[berg2666]

Brand new building still under construction. We are just getting into the start up phase. So "No' on the miremold.

The wire goes up the wall and runs length wise with the ceiling joists. There is metal furring runs along the ceiling and walls and the drywall is attached to that (I don't remember term for that type furring).

I'm also a little frustrated because I just found out that my senior technician that was working on this, didn't actually check it out himself and had some newbies do it - so now I'm not sure how many or if it's really a problem.

Was your buisness involved from the begining or brought in midway through?

[WhoIsThat?]

If there is one short somewhere in a series string of 225 windows, you'll find it faster if you look at window #112, open the circuit and decide if the short is upstream or downstream.

If it's upstream you look at window #56.

Still upstream? Look at window #28. Downstream? Look at window #84.

Each time you halve the number of possibilities.

This "binary search" routine or "binary chop" routine is the quickest way to find a problem like this.

[hotrod53]

I have seen a demo of one of those units, it was pretty impressive on a roll of wire. Never saw one used in the real world.

I agree with WhoIsThat, process of elimination.

Can you say backcharge? That is if the Professional stands up for you and doesn't hang you out to dry.

They do make wireless sensors like that, the batteries are supposed to last to 6 years. That many points may be costly though but hey, no wires!

[WhoIsThat?]

I know electricians have these, they're $xxx and up.
http://en.wikipedia.org/wiki/Time-domain_reflectometer
Maybe you can rent one.

The readout may tell you that "the short [or open] is 34.6 feet from where you are standing."

In the 70s we made our own with a fast o'scope and a very fast pulse generator.