LAARS Mighty Therm LO-NOx PW (Sizes 500-1825) - Install and Operating Manual - Manual (Page 8)

LAARS HEATING SYSTEMS Page 8
2.5 Electrical Wiring
WARNING
The heater must be electrically grounded in
accordance with the most recent edition of the
National Electrical Code, ANSI/NFPA 70. In
Canada, all electrical wiring to the boiler should
be in accordance with the latest edition of CSA
C22.1 Canadian Electrical Code, Part 1. Do not
rely on the gas or water piping to ground the
metal parts of the boiler. Plastic pipe or
dielectric unions often isolate the heater
electrically. Service and maintenance
personnel who work on or around the heater
may be standing on wet floors and could be
electrocuted by an ungrounded heater.
Wiring diagrams are included in the information
packet provided with each unit.
1.
All Laars heaters need 115V 60Hz supply
voltage unless specifically ordered otherwise.
Check heater wiring and pump for correct
voltage, frequency and phase. Consult the
National Electrical Code or the Canadian
Electrical Code regarding branch circuit
requirements for equipment with these motors.
2. The heater should be wired exactly as shown in
the wiring diagram.
3. All field installed electrical safety devices and
all field installed controllers (valve end switches,
draft switches, relays, timers) can be connected
to the heater control to the terminals shown in
the wiring diagram designated “Field Interlock.”
4. Where the heater is installed with a draft fan
refer to the fan manufacturer's wiring diagram.
The draft switch should be wired across the field
interlock terminals in the heater control panel.
SECTION 3.
Water Piping Instruction
3.1 General Piping Practice
1. Be sure to provide valves at the inlet and outlet
of the heater so it can be readily isolated for
service. A butterfly, ball type or similar type of
valve is recommended.
2. The pressure relief valve installed in the tapped
opening provided in the outlet header (see Figure
7), must be piped, but not fastened, to a drain or
floor sink. The drain pipe must be the same size
as the valve outlet and must pitch downward
from the valve. Pay special attention to relief
valve settings in installations where the heater is
located on the ground floor of a tall building, or
where the operating temperature of the heater is
Figure 7. Pressure Relief Valve Location.
above 210°F (99°C). In both instances, the static
pressure of the system is elevated and could
cause the relief valve to leak and bring
considerable raw water into the system.
3. Where no special setting of the relief valve is
ordered, the factory will furnish a 75 psi setting
for heating boilers (PH models), and 125 psi for
water heaters (PW models).
4. The pressure relief valve lever must be tripped at
least once a year to insure that waterways are
clean. When manually operating lever, water
will discharge through the drain line. Precautions
must be taken to avoid contact with hot water
and water damage.
3.2 Heating Boiler (PH Model)
3.2.1 Variable Water Flow System
Heating systems using zone valves, zone pumps
or 3-way valves can experience reduced water flow
through the boiler. This can result in an excessive
water temperature rise and unstable boiler operation.
If the system water flow is variable, the boiler's
temperature sensor must be installed in the outlet
water. Laars recommends primary-secondary pumping
for all variable flow systems (see Figure 9). Primary-
secondary pumping is mandatory for variable flow
systems. The boiler pump in a primary-secondary
system maintains constant flow through the boiler
even though the system flow is variable. In a primary-
secondary system the pressure drop of the boiler is not
added to the system.
3.2.2 System Pressure Requirements
The boilers are designed to operate on closed,
pressurized systems. Maintain a minimum of 12 psi
(81.8 kPa) on the system where boiler supply water
temperature is 200°F (93°C) or less. If higher
temperatures are required, the minimum system