Re: Can't Mix Smoke Models....really?

[Nomen Nescio <nobody@xxxxxxxxx>]

mbbaker said:

>Each test is conducted using one
>make and model of smoke detector.  They don't mix makes and models on
>the same circuit, therefore, the manufacturer isn't making any
>warrantees as to the reliability of mixing different types of smoke
>detectors on the same circuit.
>
>The test is described in UL 864 8th edition:

The tests you quoted have nothing to do with compatibility.  Operating
voltage doesn't mean compatibility.  It has more to do with the current
draw of the two-wire smoke in alarm condition, and whether that increased
current from a particular smoke is sufficient to cause an alarm on a
particular control panel's circuitry.

I've looked at a couple of panel instruction manuals, and although they all
list which two-wire smokes are approved for use with those panels, I don't
see anything that prohibits mixing those approved smokes on the same
circuit.  I don't see any logical reason why it should make any difference.

When multiple two-wire smokes are connected on the same zone, the only one
that counts is the first smoke to go into alarm.  When that first smoke
trips, it places the entire zone into alarm until manually reset:  the
other smokes no longer do anything useful at that point.  So, if there are
three different brands of two-wire smokes on the same zone, and all are
approved for use with that panel, then any one of those smokes is capable
of causing an alarm.  Once it does, the other two smokes no longer matter.
In fact, they probably don't even do anything, since many two-wire smoke
zones can only supply enough current to power one smoke detector in alarm
condition.

Finally, if there were any problems with mixing different brands on the
same zone, it would become obvious during testing.  I'll bet no one has
ever seen a smoke fail to operate as a result of mixing approved smokes on
the same zone.

- badenov