25 – 7
25.4 Achieving Correct External Neutral Sensor Polarity
(for air-core sensors WLNCT2 and WLNCT3)
The polarity of the neutral sensor must be observed when installing the neutral sensors in the apparatus. The "dot" side of the sensor, iden-
tified as P2 in the drawing below, must face in the same direction as the bottom stabs on the breaker. The schematics and elevation drawing
identify the P2 side with a "dot" because that is the label side of the sensor, and most installers and service technicians are accustomed to
the label side of the sensor being the 'dot' side. There is also a P2 in a circle on the face of the sensor.
For a top-fed breaker (line on top and load on bottom), the P2 must go towards the load (away from the neutral bus).
For a bottom-fed breaker (line on the bottom and load on the top), the P2 must go towards the neutral bus (away from the load).
As long as the X8-9 and X8-10 leads are connected to the correct terminals on the breaker, the polarity relationship between the internal
breaker sensors and the external neutral sensor will be correct for the rules given above.
Figure 9
The correct neutral sensor polarization is achieved when the P1 mark on the neutral sensor is oriented on the neutral bus so that it matches
the upper stabs of the breaker (normally the line side). Even if the breaker is bottom fed, the load flow must be such that the lower stabs of
the breaker and the P2 mark on the neutral sensor are matched (both line or both load).
The wires from the neutral sensor are color coded as follows:
- BLACK => X8.9 = P1
- BLUE => X8.10 = P2
These wires terminate in a plastic 2-pin connector which is usually connected to a black twisted pair. At the far end of the twisted pair, the
two wires are labeled. These wires are usually connected to a shielded, twisted pair which brings the signal to the secondary disconnects
(X8.9 & X8.10). If incorrect polarity is detected at the ETU in spite of what appears to be a correctly mounted neutral sensor, then the wires
crossing between shipping splits should be inspected carefully.
Upper Breaker Stab
Lower Breaker Stab
Breaker Internal CT
P1
P2
External Neutral CT
P1
P2
Neutral Bus
X8.9
X8.10
Polarity must match
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