I am building a control panel where the incoming power is 120VAC, however, the majority of this equipment is powered from a 24VDC UPS fed from the 120VAC within the panel.
The 24VDC feeds a couple of external actuators, provides supply power to 24VDC components within the panel, and provides power for what I would typically label control circuits.
The UPS is UL60950-1 listed, and the battery bank is UL1989 listed so according to 44.1.4, 43.1.1, and 43.1.2 everything downstream of the UPS in the circuit can be classified as a low-voltage limited energy/class 2.
The confusion comes in when looking at the definitions in UL508A for "Low-Voltage Limited Energy Circuit" and "Class 2 Circuit". Both definitions describe these circuits as control circuits. "A control circuit...".
The definition for a control circuit is "A circuit that carries the electric signals directing the performance of a controller, and which does not carry the main power circuit..."
but the definition for a power circuit is "Conductors and components of branch and feeder circuits."
but the definition for a branch circuit is "The conductors and components following the last overcurrent protective device protecting a load"
and the definition for a load is "A device external to the industrial control panel that is connected to the power circuit"
It seems according to the rules above almost my whole panel can be considered a low-voltage limited energy/class 2 "control circuit" meaning that I no longer have any "power circuits" downstream of the UPS and the devices that I am powering externally are no longer considered "loads" since they are fed by control circuits only?
Essentially if this is the case almost anything fed from a 24V supply is considered a control circuit, and supplementary protectors can be used everywhere downstream of the power supply.
Something doesn't seem quite right here.
Is it possible to still have "power circuits" within Low-voltage limited energy/ class 2 circuits?
The 24VDC feeds a couple of external actuators, provides supply power to 24VDC components within the panel, and provides power for what I would typically label control circuits.
The UPS is UL60950-1 listed, and the battery bank is UL1989 listed so according to 44.1.4, 43.1.1, and 43.1.2 everything downstream of the UPS in the circuit can be classified as a low-voltage limited energy/class 2.
The confusion comes in when looking at the definitions in UL508A for "Low-Voltage Limited Energy Circuit" and "Class 2 Circuit". Both definitions describe these circuits as control circuits. "A control circuit...".
The definition for a control circuit is "A circuit that carries the electric signals directing the performance of a controller, and which does not carry the main power circuit..."
but the definition for a power circuit is "Conductors and components of branch and feeder circuits."
but the definition for a branch circuit is "The conductors and components following the last overcurrent protective device protecting a load"
and the definition for a load is "A device external to the industrial control panel that is connected to the power circuit"
It seems according to the rules above almost my whole panel can be considered a low-voltage limited energy/class 2 "control circuit" meaning that I no longer have any "power circuits" downstream of the UPS and the devices that I am powering externally are no longer considered "loads" since they are fed by control circuits only?
Essentially if this is the case almost anything fed from a 24V supply is considered a control circuit, and supplementary protectors can be used everywhere downstream of the power supply.
Something doesn't seem quite right here.
Is it possible to still have "power circuits" within Low-voltage limited energy/ class 2 circuits?
