HTP EL-399NVWH - Manual (Page 47)

47
LP- 346 REV. 3.20.14
NOTE: If sensor wires are located in an area with sources of
potential electromagnetic interference (EMI), the sensor wires
should be shielded, or the wires routed in a grounded metal
conduit. If using shielded cable, the shielding should be
connected to the common ground of the heater.
H. SYSTEM / PIPE SENSOR
The system/pipe sensor can be used to control the temperature
of the storage tank when a tank sensor or mechanical control
cannot be mounted. The system/pipe sensor would be wired into
the terminals of the low voltage terminal strip as shown on Figure
26. It is important to note that when a system/pipe sensor is
used, the circulating pump must be wired to operate
continuously; otherwise the heater will short cycle.
The system/pipe sensor can also be used in a cascade system
when the sensor is placed on the supply line of multiple heaters
that feed the storage tank. This will control the temperature and
modulate the firing rate of the connected heaters. The
system/pipe sensor would then be wired into the master heater
terminals on the low voltage strip as shown on Figure 29.
NOTE: If sensor wires are located in an area with sources of
potential electromagnetic interference (EMI), the sensor wires
should be shielded, or the wires routed in a grounded metal
conduit. If using shielded cable, the shielding should be
connected to the common ground of the heater.
I. OPTIONAL 0-10 VOLT BUILDING CONTROL SIGNAL
1. A signal from a building management system may be
connected to the heater to enable remote control. This signal
should be a 0-10 volt positive-going DC signal. When this input is
enabled using the installer menu, a building control system can
be used to control the set point temperature of the heater. The
control interprets the 0-10 volt signal as follows; when the signal
is between 0 and 1.5 volts, the heater will be in standby mode,
not firing. When the signal rises above 1.5 volts, the heater will
ignite. As the signal continues to rise towards its maximum of 10
volts, the heater will increase in set point temperature. See Part
10 for details on the setting of function 16.
2. Connect a building management system or other auxiliary
control signal to the terminals marked 16, 0-10 VOLT + and 17,
0-10 VOLT
– in the electrical junction box (shown in Figure 26).
Caution should be used to ensure that the 0-10 VOLT +
connection does not become connected to ground.
J. OPTIONAL UL353 LOW WATER CUT-OFF
INTERFACE KIT
If an optional UL 353 Low Water Cut-Off (LWCO) Interface Kit is
used, the control box of the kit should be mounted to the left side
of the heater cabinet near the low water cut-off probe, which is
located on the outlet nipple of the heater.
Follow the complete instructions included in the kit for proper installation.
K. WIRING OF CASCADE SYSTEM COMMUNICATION BUS
1. A Cascade Bus Termination Plug has been installed on the customer connection board of this boiler. The purpose of this plug is to
stabilize communication between multiple boilers and reduce electrical “noise”. See Figures 28 and 29 for Cascade Bus Termination
Plug installation detail.
2. Use standard CAT3 or CAT5 computer network patch cables to connect the communication bus between each of the boilers. These
cables are readily available at any office supply, computer, electronic, department or discount home supply store in varying lengths. If
you possess the skills you can also construct custom length cables.
Figure 26 - VWH Control