A.O. Smith TC-049-R2, Service Handbook

Page: 46 / 61

RESIDENTIAL GAS AND ELECTRIC WATER HEATER
SERVICE HANDBOOK
A.O. Smith Water Products Company Training Department
©
2002 Ashland City, Tennessee
45
Miscellaneous Residential Electric Water Heater Service Items:
•
Watts divided by Volts = Amps
Supply wire gauge and fuse (breaker) protection must be at least 125% of the expected
Amperage draw of the water heater.
•
Volts times Amps = Watts
Replace elements with elements rated at the same wattage and voltage indicated on the
heater model and rating plate. Installing an element with a
higher
voltage rating or wattage
output may create a safety hazard by overloading the heater wiring or supply wiring or
fusing. Installing an element with a
lower
wattage or voltage rating will reduce performance.
•
Normally, a residential electric water heater with two elements will have
only one
element
operate at a time. If the upper element or thermostat fails, the customer will be out of hot
water. If the lower element or thermostat fails, the customer
should still
have 1/3 of the
tank with hot water.
•
With two element heaters, the
lower element and thermostat
will
cycle more
frequently
than the upper element and thermostat. For this reason, the lower element will normally
accumulate lime faster and fail more often than the upper element. Lower thermostats will
fail more often than upper thermostats.
•
Replacement elements:
Replace elements with an element having the
most surface area
(low watt density)
available for your water heater. By spreading the heat of the element over a greater area,
lime (calcium) buildup rate should be reduced.
Elements constructed of
Incoloy
are much more durable than elements made of copper
with zinc coating.
•
Many electric
utilities
offer discounts if you do not use electricity during certain times of the
day.
Contact them
– by purchasing a larger storage water heater, with special wiring (see
A-7 wiring circuit) for time clocks or “off peak meters”, you may save on monthly operating
costs.
Element with Links
Resistance of Element in Ohms (± 7.5%)
Rated Wattage Rated
Voltage
600 750 1000 1250 1500 2000 2500
120 23.2 18.6 13.9 11.1 9.28 6.96 5.57
208 72.1 57.7 43.3 34.6 28.8 21.6 17.3
240 92.8 74.3 55.7 44.6 37.1 27.8 22.3
277 128 102 76.7 61.4 51.2 38.4 30.7
Rated Wattage Rated
Voltage
3000 3500 4000 4500 5000 5500 6000
120 4.64
208 14.4 12.4 10.8 9.61 8.65 7.85* 7.2
240 18.6 15.9 13.9 12.4 11.1 10.1* 9.28
277 25.6 21.9 19.2 17.1 15.3 14.0 12.8
480 76.8 65.7 57.5 51.1 45.7 41.8 38.4