Electrical; General; Branch Circuit; Calculating Amperage/Overcurrent Protection - A.O. Smith DEL-6 Instruction Manual

General

The installation must conform with these instructions and the local
code authority having jurisdiction and the requirements of the power
company. In the absence of local codes, the installation must comply
with the current editions of the National Electrical Code, NFPA 70 or
the Canadian Electrical Code CSA C22.1.
An electrical ground is required to reduce risk of electrical shock
or possible electrocution. 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.
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 overcurrent 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/oVercurrent 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, on page
12, shows the heater may be field converted to simultaneous
element operation by moving the red wire on "J" terminal to L1. 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 page 12.
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 page 12.

electrIcal

This is an example of calculating heater amperage for both types
of element operation. From this, the branch circuit conductor and
overcurrent 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.
Non-simultaneous:
(as factory wired)
3000 : 240 = 12.5 amps*
*NOTE: as a single-phase non-
simultaneous unit.
The rating of the overcurrent 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.
For ambient temperatures over 30° C (86° F), see Correction
Factors, Note 13 in Code.
Size
AMG
MCM
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.
Size
AMG
MCM
12
10
8
6
4
3
2
1
11
table 3
Simultaneous:
(Field conversion)
3000 : 240 = 12.5 amps*
12.5 x 1.73 = 21.6 amps
* N O T E : a s a s i n g l e - p h a s e
simultaneous unit the total is:
12.5 x 2 = 25 amps
table 4
Temperature Rating of Conductor
See Table 310-13 in Code
60°C
(140°F)
Types:
RH, RHW, RUH, (14-2),
RUW, (14-2), T, TW, UF
THW, THWN, XHHW, USE
- - -
- - -
15
20
30
40
55
70
80
table 5
Temperature Rating of Conductor
See Table 310-13 in Code
60°C
(140°F)
Types:
RH, RHW, RUH, (12-2),
RUW, (12-2), T, TW, UF
THW, THWN, XHHW, USE
15
25
30
40
55
65
75
85
75°C
(167°F)
Types:
- - -
- - -
15
20
30
45
65
85
100
75°C
(167°F)
Types:
15
25
40
50
65
75
90
100