Resistor on the high or low side

[88keys]

Okay...I'm a dummy - Can someone please explain to me in plain redneck english what the difference is between the high and low side of the zone terminals and why it matters to which side the resistor is tied to. Thanks

[itsbeebingfornoreason]

one of the answers ive got was that because all the commons on the panel are shared and on the super rare occasion  an alarm might not be from that particular zone. ive never asked the engineer department from Honeywell whats the real answer is.

[Repairguy]

High low = +/-.  Resistor location m akes no difference for operation.  The +/- is extreme low dc voltage, but it is there.  You have to have a current to sense continuity.  You can actually use the low as the neg. power for a powered device in a worst case scenario and run a motion w/ just 3 wires.    (Just an example, not to be used as standard or recommended practice)

[OldGrouchy]

After reading this article in SDM I put all of mine on the low side.

 




Edit to fix link

[Old EW Tech]

I've read similar recommendations in the past.  In my opinion the conclusion is based on several incorrect assumptions:

• Of the four manufacturers systems that we currently have on our bench, none have zone common terminals tied to Earth ground.

• The failure mode assumes that the short will be to Earth ground; this seems unlikely.  The metal doorframe used in their example would probably not be bonded to Unified Earth Ground.

• To assume this particular failure condition (zone high shorted after the EOLR) and that the short is to a part of the structure that happens to be at Earth Ground potential and that all of this occurs on a system that has zone common tied to Earth Ground is quite a stretch.

While I don't share the authors opinion regarding the number of security zones "out there that will not work", it doesn't take any longer or cost any more to wire as suggested.

Even if the benefits were overstated, I don't see any reason for not doing it as described.  If it detects only one failure out of 500,000, that and the step towards standardization seems sufficient justification.   

[OldGrouchy]

Old EW Tech, I agree completely. The chance of that particular problem is probably 1 in 500,000.  As you said, some kind of standardization would be nice.

[Radiotrack1]

Another problem with Lees design is if the positive side grounds to earth ground and it is not a dead short to ground the connection may also mimic the value of the EOL and you still would not get an alarm. Because the high side is what is looking for a change to ground not the common or low side.

[rrauenza]

Updating the link to the referenced article -- original is gone now.  But there's a copy in the internet archive "way back machine":

http://web.archive.org/web/20081120201827/http://www.sdmmag.com/CDA/Articles/Kinks_and_Hints/BNP_GUID_9-5-2006_A_10000000000000067022