
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
Summary of Contents for UL 489
Page 36: ...5 21 Frame size II 3000 A Frame size III 1 Holes 14 mm 0720 1 0721_nu ...
Page 63: ...7 2 Horizontal connectors 0733_nu top view ...
Page 64: ...7 3 Rear vertical connectors 0734_nu top view rear view ...
Page 65: ...7 4 Front connectors 0736_nu front view top view ...
Page 66: ...7 5 Front connectors and pressure wire terminals 0737_nu top view front view ...
Page 67: ...7 6 7 2 Frame size II fixed mounted version 0494 3_nu ...
Page 68: ...7 7 Class C always 0494 5_nu top view rear view ...
Page 69: ...7 8 2500 0738_nu LH side view front view ...
Page 71: ...7 10 7 4 Frame size III fixed mounted version 0495 1_nu LH side view ...
Page 72: ...7 11 0495 2_nu top view top view ...
Page 73: ...7 12 0495 3_nu top view rear view ...
Page 75: ...7 14 7 5 Door cut outs fixed mounted circuit breaker Frame size I 0735_nu ...
Page 76: ...7 15 Frame size II III 0496_nu ...
Page 77: ...7 16 7 6 Frame size I draw out version 0745_nu ...
Page 78: ...7 17 0746_nu rear view top view ...
Page 79: ...7 18 0747_nu bottom view ...
Page 80: ...7 19 0748_nu ...
Page 81: ...7 20 0749_nu ...
Page 82: ...7 21 7 7 Frame size II draw out version 0490 1_ul ...
Page 86: ...7 25 7 8 Frame size III draw out version ...
Page 87: ...7 26 ...
Page 88: ...7 27 ...
Page 89: ...7 28 7 9 Door cut outs for draw out circuit breakers Frame size I 0750_nu ...
Page 91: ...7 30 7 11 External sensor for neutral conductor WLNCT2 ...
Page 92: ...7 31 WLNCT3 ...
Page 107: ...9 5 I tripping Ground fault tripping ...
Page 351: ......