IM-P402-62 AB Issue 5
6
1
2
3
10
11
12
Termination
box
Screen
Brown
Red
Orange
Black
*
*
See PA20 Installation and Maintenance Instructions
for sensitivity selection
LT2010
Transmitter
+
IN
Common
Flying leads supplied
with PA20
(
approximately 300 mm [12"]
)
Wiring diagram UL version
PA20 preamplifier and LP20 capacitance probe
(see PA20 and LP20 Installation and Maintenance Instructions)
Screen connection
An earth current loop is created if a wire or screen is connected between two earth points, which
are at different potential (voltage). If the instructions are followed correctly, then the preamplifier and
transmitter screen will only be connected to earth at one end.
Note: The PA20 earth terminal is a functional earth rather than a protective earth.
A protective earth provides protection from electric shock under a single fault condition. This
product has double insulation and therefore does not require a protective earth.
A functional earth is used in order for the product to operate. In this application, the earth
(tank/ boiler shell) is used as the common of the probe/ preamplifier. It also provides a sink/ drain
for any electrical interference.
Ensure that the screen is connected to the earth terminal of the PA20 and to the common terminal
of the transmitter.
Ensure the common terminal of the transmitter is not internally earthed. (All Spirax Sarco boiler
controls are internally isolated from earth).
The common terminal of the transmitter must only be earthed via the PA20.
CAUTION:
Do not connect the common terminal to an earth local to the transmitter. To do so may
induce an earth current loop, which may reduce the performance or damage the product.
5. Wiring diagrams
Fig. 4
See CAUTION above
Ensure resistance from probe body to
pipework /boiler shell is less than 1
W
.
