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and disconnect switch. The water heater should be grounded in
accordance with national and local codes.
Voltage applied to the heater should not vary more than +5% to -10%
of the model and rating plate marking for satisfactory operation.
DO NOT ENERGIZE THE BRANCH CIRCUIT FOR ANY REASON
BEFORE THE HEATER TANK IS FILLED WITH WATER. DOING SO
WILL CAUSE THE HEATING ELEMENTS TO BURN OUT AND VOID
WARRANTY.
The factory wiring is attached to a terminal block within the external
junction box unit. The branch circuit is connected to the terminal
block within this junction box. The water heater should be connected
to a separate, grounded, branch circuit with over-current protection
and disconnect switch. The water heater should be grounded in
accordance with national and local codes.
BRANCH CIRCUIT
The branch circuit wire size should be established through reference
to the current edition of NFPA-70, the National Electrical Code
or other locally approved source in conjunction with the heater
amperage rating. For convenience, portions of the wire size tables
from the Code are reproduced here. The branch circuit should be
sized at 125 percent of the heater rating and further increase wire
size as necessary to compensate for voltage drop in long runs.
CALCULATING AMPERAGE/OVER-CURRENT PROTECTION
The heaters come from the factory in two configurations:
1.
Two wire C-2 circuit for single element heater equipped with a
high limit control, single phase power input.
2.
Four wire A-8 circuit for dual element heater equipped with two
high limit controls, single phase or three phase power input.
The heater with dual elements is factory wired for connection to
a three wire, three-phase delta branch circuit, non-simultaneous
operation. In addition a ground conductor is required.
Element connection is for non-simultaneous operation. This means
only one element at a time operates. The wiring diagram shows the
heater may be field converted to simultaneous element operation by
moving the red wire on "J" terminal to L1. See Wiring Diagram (page
23). It is then possible for both elements to operate at once as
determined by the thermostats. Regardless of element connection
the heater operates in an "unbalanced" fashion.
The heater may be field converted to single-phase operation by
moving the wire on L3 of the terminal block to L2. L3 is not used.
See Wiring Diagram (page 23).
The heater, now in single-phase non-simultaneous operation, may
be field-converted to single phase simultaneous operation by moving
the red wire on terminal "J" to L1. See Wiring Diagram (page 23).
This is an example of calculating heater amperage for both types
of element operation. From this, the branch circuit conductor and
over-current protection sizing can be established.
The example is of a three-phase 240 volt unit with two, 6 kw elements.
The notations are for units field converted to single-phase. Check the
heater model and rating plate for actual specifications and substitute
those values in the following.
Table 3. Example Calculation
Non-simultaneous:
(Factory wired)
3000 : 240 = 12.5 amps*
*NOTE: as a single-phase non-
simultaneous unit.
The rating of the over-current protection should be computed on
the basis of 125 percent of the total connected load amperage.
Where the standard ratings and settings do not correspond with
this computation, the next higher standard rating or setting should
be selected.
PORTION OF TABLE 310-16 (NFPA-70) FOLLOWS:
Allowable Ampacities of Insulated Copper Conductors. Not more
than three conductors in Raceway or Cable or Direct Burial (Based
on Ambient Temperature of 30° C, 86° F).
These ampacities relate only to conductors described in Table 310-13
in Code.
For ambient temperatures over 30° C (86° F), see Correction Factors,
Note 13 in Code.
Portion of Table 310-16 (NFPA-70)
Size
AMG
MCM
RUW, (14-2), T, TW, UF
18
16
14
12
10
8
6
4
3
PORTION OF TABLE 310-18 FOLLOWS:
Allowable Ampacities of Insulated Aluminum and Copper -Clad
Aluminum Conductors.
Not more than three conductors in Raceway or Cable or Direct Burial
(Based on Ambient Temperature of 30° C, 86° F. These ampacities
relate only to conductors described in Table 310-13 in Code.
For ambient temperatures over 30° C (86° F), see Correction Factors,
Note 13 in Code.
Portion of Table 310-18 (NFPA-70)
Temperature Rating of Conductor
Size
AMG
60°C
MCM
(140°F)
Types:
RUW, (14-2), T, TW, UF
12
10
8
6
4
3
2
1
14
Simultaneous:
(Field conversion)
3000 : 240 = 12.5 amps*
12.5 x 1.73 = 21.6 amps
*NOTE: as a single-phase simultane-
ous unit the total is: 12.5 x 2 = 25
amps
Temperature Rating of Conductor
See Table 310-13 in Code
60°C
75°C
(140°F)
(167°F)
Types:
Types:
RH, RHW, RUH, (14-2),
THW, THWN, XHHW, USE
- - -
- - -
- - -
- - -
15
15
20
20
30
30
40
45
55
65
70
85
80
100
See Table 310-13 in Code
75°C
(167°F)
Types:
RH, RHW, RUH, (14-2),
THW, THWN, XHHW, USE
15
15
25
25
30
40
40
50
55
65
65
75
75
90
85
100
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