PC5 SERIES WATT TRANSDUCER CALIBRATION MANUAL
Page 18
USING CURRENT AND POTENTIAL TRANSFORMERS WITH
WATT TRANSDUCERS
TECHNICAL BULLETIN NO. 101
CONNECTIONS
One of the most commonly overlooked
connections is that between the watt
transducer and the current transformers.
Power measuring transducers and meters are
polarity sensitive.
Current transformers are marked with both
primary and secondary polarity marks. The
“H1” on the body of the current transformer
is for the primary current through the
opening. The “H1” must face the line or the
source of the current. The secondary leads
or terminals are labeled with an “X1” and an
“X2.” The “X1” corresponds to the polarity
“H1” of the primary.
Current transformers supplied as part of OSI
watt transducers have white and black
secondary leads. The white lead is the X1
lead and the Black is the X2 lead.
In OSI connection diagrams the dots in the
diagrams refer to the H1 for the primary and
the X1 for the secondary.
H1
LINE
White
Black
X1
X2
LOAD
To watt transducer
Figure 1 Current Transformer with
Polarity Marks.
X1
X1
H1
H1
To watt transducer
LINE
LOAD
Figure 2 Current Transformer and
Potential Transformer with Polarity
Marks.
EXTENDING SECONDARY LEADS OF CURRENT TRANSFORMERS
It is very important to keep the electrical resistance in the secondary circuit of current
transformers to a minimum. The following chart gives the maximum secondary lead length for
typical current transformers.
CT CURRENT RATIO
10 GAUGE WIRE
12 GAUGE WIRE
14 GAUGE WIRE
100:5
20 feet
15 feet
10 feet
200:5 through 400:5
40 feet
30 feet
20 feet
600:5 and higher
80 feet
60 feet
40 feet
TB101.12.98
