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Gas Supply Pressure
A minimum of 4.0 in. WC upstream gas pressure under full
load and a maximum gas supply pressure setpoint of 10.5
in. WC under load and no-load conditions for natural gas.
A minimum of 4.0 in. WC upstream gas pressure under
full load and a maximum gas supply pressure setpoint of
13.0 in. WC is required for propane gas. The gas pressure
regulator(s) supplied on the heater is for low-pressure
service. If upstream pressure exceeds 1/2 psi at any
time, an intermediate gas pressure regulator, of the lockup
type, must be installed. This regulator should be placed a
minimum distance of 10 times the pipe diameter upstream
of the heater gas controls.
When connecting additional gas utilization equipment to
the gas piping system, the existing piping must be checked
to determine if it has adequate capacity for the combined
load.
A
CAUTION: For proper operation, no more than a
30% drop in gas supply pressure from no-load to full-
load conditions is acceptable. Under no circumstances
should the pressure be outside the listed operational
range.
NOTE: During normal operation, carbon dioxide should
be 9.0% ± 0.2% at full fire for natural gas and 10.2% ± 0.2%
for propane gas. Carbon monoxide should be ‹100ppm
at all firing rates, measured at the test port, 12" (305 mm)
above the flue collar.
Electrical Power Connections
Installations must follow these codes:
•
National Electrical Code and any other national,
state, provincial or local codes or regulations having
jurisdiction.
•
Safety wiring must be NEC Class 1.
•
Heater must be electrically grounded as required by
the NEC.
•
In Canada, CSA C22. 1 C.E.C. Part 1.
The MVB 503A-1503A heaters are wired for 120 VAC, 12
amps while the MVB 1753A & 2003A heaters are wired for
120 VAC, 18 amps. Consult the wiring diagram shipped
with the heater. Before starting the heater, check to ensure
proper voltage to the heater and pump.
Pumps larger than 3/4 HP must use a separate power
supply and run the power through the pump contractor,
which is located in the rear wiring box. Use appropriately-
sized wire as defined by NEC, CSA and/or local codes. All
primary wiring should be 125% of minimum rating.
If any of the original wire as supplied with the heater must
be replaced, it must be replaced with 105°C wire or its
equivalent.
All high voltage wiring connections to the MVB heater are
made inside the rear wiring box as shown in Figure 18.
20
Power for an indirect DHW pump not exceeding 5 amps
should be taken from terminals 4 (Hot), 5 (Com), and 6
(Gnd). Power for a system pump not exceeding 5 amps
should be taken from terminals 7 (Hot), 8 (Com), and 9
(Gnd). Power for boiler pumps 3/4 HP and smaller should
be taken from terminals 1 (Hot), 2 (Com), and 3 (Gnd), and
must be routed through the pump contactor; 30A supply is
required. Power to the MVB heater should be connected to
Terminals 1, 2, and 3 as noted in Figure 18. All low voltage
wiring, including sensors, interlocks, enable/disable, and
various options are wired into terminals 1–24 on the front
wiring panel as noted in Figure 22.
FIELD WIRING
SYSTEM
SUPPLY
PUMP
5A MAX
DHW
PUMP
5A MAX
GROUND
COMMON
HOT
(120V)
P/N 902062 REV 1
F10688
Figure 18. Wiring Electrical Connections
Field-Connected Controllers
It is strongly recommended that all individually-powered
control modules and the heater should be supplied from
the same power source.
NOTE: Field-supplied isolation relays should be
installed when field-connected controllers are mounted
more than 50 equivalent feet (18 AWG) from heater. See
wiring diagrams.
NOTE: Minimum 18 AWG, 105°C, stranded wire must
be used for all low voltage (less than 30 volts) external
connections to the unit. Solid conductors should not
be used because they can cause excessive tension on
contact points. Install conduit as appropriate. All high
voltage wires must be the same size (105°C, stranded
wire) as the ones on the unit or larger.
Check the Power Source
A
WARNING: Using a multi-meter, check the following
voltages at the circuit breaker panel prior to connecting
any equipment. Make sure proper polarity is followed
and house ground is proven. (See Figure 19.)
GND
9
COM
8
HOT
7
(120V)
6
GND
COM
5
HOT
4
(120V)
3
2
1
FACTORY WIRING
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