Opinions

No benefit. You could actually "weld" reed contacts shut using this method. Inadvisable in any case. Measuring resistance is a much more reliable and indicative way of testing circuits.

Panels don't see resistance. They see voltage. The difference in resistance is what changes the value of the voltage, or simply put, the tolerances between the two determine the status of the loop (as the panel sees it -open/closed/short). There is no benefit, just another means of testing a circuit. Where it would make a difference is if you were hunting for a ground fault on a circuit.

Jack

By placing a voltmeter across the loop? js

I wouldn't say better, but rather another way. For a while back in the 80's when I called Radionic's tech support, they generally had me check the zones for voltages, as it's what the panel ultimately looked at, as do all panels. Europlex is about the only panel I can think of that lets you go through diagnostic's and the panel will actually tell you the resistance level in ohms. Most will tell you the status ie: open/closed/short without even pulling out your meter. Seems though 99 times out of 100, you'll be using an ohm meter to find the actual problem.

Jack

Thats was my reasoning as well. Ive had a few techs say that its better to test the voltage while the zone is connected to the panel. My argument was also that as relating to Ohms law, resistance, voltage and current are all related and if one changes then there are changes elsewere. Ive been servicing and fault finding for years using the testing of the circuit and checking the resistance method with great results, but im always willing to listen to better methods.

Paul

I believe hes talking about putting a voltmeter across the zone terminals with the field wiring still connected.

Doug L

By applying 12 volts dc to the loop. (I'm assuming he's talking about using a battery to texst the loop)

A really **big** voltmeter? :^)

That could certainly do damage but I don't know anyone who would test voltage across a loop that way. Put a hefty alarm backup battery across the typical loop and you might just start a fire.

Well if it doesn't ........ how come they call it a leaky capacitor an ....n nnn why does current leak and why did they call vacuum tubes .... valves and what are outboad transistors and howcome there's wave soldering, an n n n how .....how come they call it a damping signal .....n-n-n ... a saturated circuit an-n-n what does a motorboating circuit float in ..... a wave? and does the wave have ripple or leakage and a current? And wadabout floating grounds and floating circuits and overflow circuits and whats a tap and a port, for?....an what does a heat sink .......sink in? Annn n nnn where does a kilostream flow?

And here you always wondered why your meter probes got rusty.

Oh and also, I just thought you should know that the people in this group only work on the best. No class B circuits for this group .......... we're class A ......all the way.

Dang young wippersnappers ......... think they know everything!

It's easy to discover the weak spot in a large window foil loop by applying 120VAC. The high-resistance "swinger" would blow off the window, literally.

It's easy to discover the weak spot in a large window foil loop by applying 120VAC. The high-resistance "swinger" would blow off the window, literally.

I've seen a few dumbass contractors (even an electrician who claimed to "know alarm systems") do it this way when testing a prewire. One was using a batt & siren to test loops, and fried a few wires in a McMansion. Luckily, he didn't start a fire, but we did have to go in and rewire several windows. (On the "expert's" dime, of course)

Exactly Paul,

Since resistance drops voltage (from the control panel zone) the reading is equally reliable as pulling the loop and using a resistance check but the "Benefit" is that the tech does not have to remove the loop.

When providing tech support in the past, it has amazed me that many long time Pros don't know that there is a voltage drop accross a Class B circuit.

Yeh sure and also weaken anything else that would not have failed if you hadn't done that. If you'd ever done that once you'd know that it only makes the foil job fail more often in the future. The window always has to ultimately be re-foiled after it's been "flashed"

True, but it's a lot of fun! Is foil even installed anymore?

I've been in the industry for about 35 years, so I've still got some foil jobs out there. When I heard that the Brooklyn Foil Co, was closing down, I bought six rolls of regular foil and a couple of UL rolls. I wrapped them up and keep all but one of each in my freezer. I very rarely foil anymore but when necessary, I can repair or replace the foil, if it will maintain the "look" of a job. The hardest thing is keeping the varnish from drying up. I open up a can and then don't use it for a year .... next time, it's all dried up or got a one inch skin on it. One or two uses and throw it away. The foil blocks are starting to get a little yellow looking too. :-)

Unfortunately, no one makes UL listed foil any more. :(

No. The reading will be the same whether other zones are open or shorted.

Either method will work fine. On a related note, I get a kick out of installers who remove fuses to check them. :^)