Three Phase Unbalanced Circuit - State Water Heaters RESIDENTIAL ELECTRIC WATER HEATER Service Handbook

Note: For simplicity, the thermostats are not shown.
UNBALANCED 3 PHASE LOAD
Three phase power delivers power
with 3 legs to the water heater. The
water heater must be specially wired
to accept three phase power. Since
there are only two elements with two
wire terminals each in the water
heater, power from a three leg power
supply cannot be divided evenly.
One leg will have a higher amperage
draw than the other two.
In the diagram at right the connection
to power leg L2 will have the higher
amperage draw. The chart below
gives the amperage draw for L1, L2,
and L3. The maximum amperage
draw per leg is never allowed to
exceed 48 Amps in accordance with
the National Electric Code. The
chart only applies when elements
are wired for simultaneous
operation.
Element
Wattage
Upper/Lower
3000/3000
4000/4000
4500/4500
5000/5000
6000/6000
Formula: L2 Amps = wattage* x 1.73 / volts
*Wattage = ½ of total wattage.
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Technical Training Department
Ashland City, Tennessee ©2004
RESIDENTIAL ELECTRIC WATER HEATER
SERVICE HANDBOOK
THREE-PHASE UN-BALANCED CIRCUIT
SIMULTANEOUS DUAL ELEMENTS
(both elements 'on' when entire tank is cold)
Full Load Current in Amperes
Connected to Three Phase Power
(Terminal L2/ Terminals L1 & L3
208V
25.0/14.4
33.3/19.2
37.5/21.6
N/A
N/A
20 of 36
240V 480V
21.7/12.5 10.8/6.3
28.9/16.7 14.4/8.3
32.5/18.8 16.2/9.4
36.1/20.8 18.0/10.4
N/A 21.7/12.5
Residential Electric Svc Handbook
STC082