FA Class A&B

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mstrlucky74

Senior Member
Location
NJ
Some questions.
Class A will not have an EOL but class B will?
class A has 2 cables run the to each device then back to panel... both notification and initiating?

thanks.
 

luckylerado

Senior Member
Some questions.
Class A will not have an EOL but class B will?
class A has 2 cables run the to each device then back to panel... both notification and initiating?

thanks.

Correct. Class B has EOL and can end the circuit at the last device. Class A has no EOL and the circuit must end at the device it started from.

There are other important differences that determine the class of the circuit so this is not 100% true 100% of the time. For example, You could have a circuit that returns to the panel but does not maintain proper separation along the run and could therefore not be considered a class A circuit.
 

mstrlucky74

Senior Member
Location
NJ
Correct. Class B has EOL and can end the circuit at the last device. Class A has no EOL and the circuit must end at the device it started from.

There are other important differences that determine the class of the circuit so this is not 100% true 100% of the time. For example, You could have a circuit that returns to the panel but does not maintain proper separation along the run and could therefore not be considered a class A circuit.

so really since class A is 4 wire you could not run a 2 pair cable as it would not maintain the separation. you'd have to run 2-1 pair wires? even if it was run "free air"?
 

luckylerado

Senior Member
so really since class A is 4 wire you could not run a 2 pair cable as it would not maintain the separation. you'd have to run 2-1 pair wires? even if it was run "free air"?
With a few exceptions.

2013 NFPA 72 12.3.7
...The outgoing and return (redundant) circuit conductors shall be permitted in
the same cable assembly (i.e., multi-conductor cable), enclosure,
or raceway only under the following conditions:
(1) For a distance not to exceed 10 ft (3.0 m) where the outgoing and return conductors enter or exit the initiatingdevice, notification appliance, or control unit enclosures
(2) For single raceway drops to individual devices or appliances
(3) For single raceway drops to multiple devices or appliancesinstalled within a single room not exceeding 1000 ft2(93 m2) in area
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
Also note that the classification applies to each type of circuit. So, you can have a class A specified for initiation devices, but class B wiring specified for your NAC circuits.
 

GrayHair

Senior Member
Location
Nashville, TN
It was also possible for a Class A Circuit to use a inside-the-panel EOL resistor, although the EOL device was usually a relay, as long as McCullough conditioning was available at the "far" end. Not usually observed since it was "hidden" in the guts of the panel.
 

luckylerado

Senior Member
It was also possible for a Class A Circuit to use a inside-the-panel EOL resistor, although the EOL device was usually a relay, as long as McCullough conditioning was available at the "far" end. Not usually observed since it was "hidden" in the guts of the panel.

I do not see how this can be true. You cannot meet the operational requirements of a Class A system with EOL relays or resistors regardless of their location. Some class B EOL circuits may continue to function during a single ground fault but not an open fault.

12.3.1*ClassA. A pathway shall be designated as Class A when
it performs as follows:
(1) It includes a redundant path.
(2) Operational capability continues past a single open, and
the single open fault shall result in the annunciation of a
trouble signal.

(3) Conditions that affect the intended operation of the path
are annunciated as a trouble signal.
(4) Operational capability is maintained during the application of a single ground fault.(5) A single ground condition shall result in the annunciation of a trouble signal.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
I do not see how this can be true. You cannot meet the operational requirements of a Class A system with EOL relays or resistors regardless of their location. Some class B EOL circuits may continue to function during a single ground fault but not an open fault.

12.3.1*ClassA. A pathway shall be designated as Class A when
it performs as follows:
(1) It includes a redundant path.
(2) Operational capability continues past a single open, and
the single open fault shall result in the annunciation of a
trouble signal.

(3) Conditions that affect the intended operation of the path
are annunciated as a trouble signal.
(4) Operational capability is maintained during the application of a single ground fault.(5) A single ground condition shall result in the annunciation of a trouble signal.

Note that he said the EOL was at the panel. The Pyrotronics/Siemens System 3 had this arrangement. See page 5 of the IOM for details.
 
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