22
The MVB 504A-1504A heaters are wired for 120 VAC,
12 amps while the MVB 2004A 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 must use a separate power supply and run the
power through the pump contactor, 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
Fig. 20. Power for indirect DHW pump not exceeding
5 amps should be taken from terminals 4 (Hot), 5
(Com), and 6 (Gnd). Power for 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 for pumps larger than 3/4 HP must be a sepa-
rate circuit wired through the pump contactor. Power
to the MVB heater should be connected to terminals 1,
2, and 3 as noted in Fig. 20. All low voltage wiring,
including sensors, interlocks, enable/disable, and var-
ious options are wired into terminals 1–24 on the front
wiring panel as noted in Fig. 25.
Electrical Power Connections
Installations must follow these codes:
• National Electrical Code and any other national,
state, provincial or local codes or regulations hav-
ing 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.
Natural Gas – 1,000 BTU/ft
3
, 0.60 specific gravity at 0.5 in. WC pressure drop •
Propane Gas – 2,500 BTU/ft
3
, 1.53 specific gravity at 0.6 in. WC pressure drop•
Table I: Maximum Equivalent Pipe Length
NOTE: Manifold pressures should be ±0.2 in. WC.
Table J: Manifold Gas Pressure Settings
Model
N
o.
1 in. NPT 1-1/4 in. NPT 1-1/2 in. NPT 2 in. NPT 2-1/2 in. NPT
N P N P N P N P N P
504A 15 35 65 150 130 360
7
54A
5 1
5
6
5
1
00
7
5
1
80
2
50
1104A 35 55 35 90 125 300 300
1504A 10 15 15 25 60 150 150 275
2004A 35 90 85 210
Model
Manifold Gas Pressure Setting
High Fire Values (in. WC)
Natural Gas Propane Gas
504A -4.1 -4.4
754A -4.6 -5.8
1104A -4.6 -7.2
1504A -7.0 -9.2
2004A -4.4 -8.1
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