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• 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 503-1503 heaters are wired for 120 VAC, 12
amps while the MVB 1753 & 2003 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.
Boiler mounted pumps (up to
3
⁄4 hp) get their power
supply directly from the boiler power supply (connec-
tions in rear wiring box). Install a circuit breaker sized
sufficiently for both the heater and the pump. Pumps
larger than
3
⁄4 hp must use a separate power supply
and run the power through the optional pump contac-
tor 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.
18. Pump power should be taken from terminals 2
(Com), 3 (GND) and 6 (Hot) –
3
⁄4 hp and smaller ONLY.
Power to the MVB heater should be connected to ter-
minals 1, 2, and 3 as noted in Fig. 18. All low voltage
wiring, including sensors, interlocks, enable/disable,
and various options are wired into terminals 1–20 on
the front wiring panel as noted in Fig. 18.
The gas valve pressure regulator on the heater is
nominally preset as noted in Table J.
During normal operation, carbon dioxide should be 8.5
to 9.0% at full fire for natural gas and between 9.5 and
10.0% for propane gas. Carbon monoxide should be
‹100ppm.
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.
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
Manifold Gas Pressure
(High Fire Values)
Model
No.
Natural Gas Propane Gas
503 -0.1 -0.1
753 -0.4
-0.1
1003 -0.8 -0.2
1253 -1.6
-0.2
1503 -2.4 -0.6
1753 -0.4
-0.1
2003 -1.0
-0.5
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
503 15 35 65 150 130 360
7
53
5 1
5
6
5
1
00
7
5
1
80
2
50
1103 35 55 35 90 125 300 300
1253 15 25 25 60 85 225 200 300
1503 10 15 15 25 60 150 150 275
1753 45 110 115 230
2003 35 90 85 210
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.