P-K MACH
®
Gas Fired Boiler
Technical Service 1.877.728.5351
Revised: January 3, 2020
Released: January 3, 2020
Patterson-Kelley 2020
All Rights Reserved.
1004905981 P-K MACH C1500H-C4000 Installation and
Owners Manual (Rev F Jan-2020).docx
Page 24
Relay C
– User-configurable relay output #3. The normally-open contacts on this relay have a
maximum voltage rating of 240VAC and maximum current capacity of 1/2 Amp.
Relay D
– User-configurable relay output #4. The normally-open contacts on this relay have a
maximum voltage rating of 240VAC and maximum current capacity of 1/2 Amp.
Master Alarm Relay
– The Master Alarm Relay terminals are normally-open dry contacts that close in
the event of an alarm output from the boiler control.
3.3.6 Low Voltage (TB1) Terminal Block
Enable/Disable
–TB1-1 and TB1-2 can be used to remotely enable or disable the boiler. The
functionality of these terminals is user-configurable through the NURO controls, but generally closure of
the Enable/Disable circuit provides a call for heat to the boiler. Opening this circuit prevents the boiler
from running.
The boiler ships with a factory-installed jumper across the Enable/Disable terminals. This circuit is
energized with a 24VAC potential, so the contacts on any remote enable devices must be rated for
minimum 24VAC.
4-20mA Analog Input
– TB1-3 and TB1-4 can be used to provide a remote analog 4-20mA control
signal to the boiler.
This analog signal can be used to change the boiler’s operating setpoint or firing
rate.
Spare Analog Input
– TB1-5 and TB1-6 are reserved for future use.
HDR Temp Sensor
– TB1-7 and TB1-8 can be used to connect a remote header temperature sensor,
installed in the primary hydronic system piping, downstream of all the boilers. This temperature sensor
must be a 2-
wire 12kΩ NTC thermistor. This circuit is energized by the boiler with a 5VDC potential.
DHW Stat/Sensor
– TB1-9 and TB1-10 can be used to connect either an aquastat or remote DHW
temperature sensor installed in a domestic hot water storage tank. If using an aquastat, use a SPST
normally-closed, break on rise type with either a fixed or adjustable deadband above and below the
setpoint.
Alternatively, if using a temperature sensor, it must be a 2-
wire 12kΩ NTC thermistor and be of
sufficient length to measure an accurate storage tank temperature. This circuit is energized by the
boiler with a 5VDC potential.
Outdoor Temp Sensor
– TB1-11 and TB1-12 can be used to connect an outdoor air temperature
sensor which allows the NURO control to be programmed to run an outdoor air schedule. The outdoor air
temperature sensor must be a 2-
wire 12kΩ NTC thermistor and should be installed on the North face of
the building and shielded from direct sunlight exposure. This circuit is energized by the boiler with a
5VDC potential.
Night Setback
– TB1-13 and TB1-14 can be used to connect a day/night or occupancy timer. Closure
of the Night Setback circuit enables the Night Setback mode which reduces the boiler’s operating
setpoint. Opening this circuit resumes normal operation. This circuit is energized by the boiler with a
5VDC potential, so the contacts on the day/night timer must be rated for minimum 5VDC.
4-20mA Analog Output
– TB1-15 and TB1-16 provide a 4-20mA analog output signal which tracks the
boiler’s firing rate. When operating at full power (maximum firing rate), the boiler will provide a 20mA
output. When operating at minimum power (minimum firing rate), the boiler will provide a 4mA output.
Ground
– TB1-17 provides an equipment (frame) ground connection for input, output, or
communication connections. For independently powered control devices, it may be necessary to
create a common ground.
