POSITIVE TEMPERATURE COEFFICIENT (PTC2) HEATER MANUAL
PTC2 Heater Systems are manufactured and distributed by Waukesha
®
Service & Components, a division of SPX Transformer Solutions, Inc.
PTC2-Manual Rev. 1.3, 04/2013
3
Chart 1 – Heater Output
Wattage at Corresponding
Ambient Temperatures
SELECTION (continued)
TO SELECT A HEATER
1)
Calculate the power (watts) needed for your particular enclosure size.
For estimation of enclosure heat needed (based upon natural convection air moving less than 5 m/s),
use this equation:
Joules/Second =
Watts
= h x A x T
Where
h
= overall heat transfer coefficient
W/(m^2K)
– The value of
h
is difficult to calculate and is different for virtually
every application; however, for rectangular outdoor enclosures with small amounts of venting and mounted to a vertical
support, the typical value is between
5
and
10.
Using 10 will represent a “worst case” scenario in a more windy environment.
A
= Exposed surface area of enclosure
(m^2)
T
= Temperature difference desired
(K)
– For anti-condensation purposes, typical value is equal to
5.
A higher value may be
used for particularly humid applications.
EXAMPLE: A 3.5 foot wide, 4 foot tall and 1 foot deep cabinet mounted to a flat wall would have exposed surfaces
equaling 29 ft^2 or 2.7 m^2. Watts = h x A x T = 10 x 2.7 x 5 = 135
2)
Draw a corresponding horizontal line on the selection chart (see Chart 1 below) based upon wattage
calculated in Step 1 above.
3)
Determine the highest ambient temperature condition for the enclosure application and draw a
corresponding vertical line at the bottom of the chart.
EXAMPLE: The same cabinet in the example above is in a location where the higher air temperatures often reach
45°C. The vertical line should be drawn at 45°C and intersect with the 135 watt horizontal line in Step 2.
4)
Select the closest heater that intersects
above and to the right
of the drawn intersecting lines.
EXAMPLE: The 200 watt heater would be selected for this application. NOTE – If high temperature operation would
have been 65°C or higher, the 300 watt heater would have been appropriate for the application.
Wattage vs Heater Inlet Temperature
0
50
100
150
200
250
300
350
400
450
500
-10
0
10
20
30
40
50
60
70
Degrees C
W
atts
200 Watt
300 Watt
400 Watt
