Electrical Test Instruments MAC-21
Section III
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MAC-21
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Copyright(C) 1994-2004 Electrical Test Instruments, LLC All Rights Reserved
Page III-3
takes the unit out of PRESET ADJUST mode.
MAINTAIN key:
This key toggle the MAINTAIN mode for initiation; its LED indicates
that this mode is enabled. When in MAINTAIN mode, the INITIATE key need only be
pressed briefly to turn output on. MAINTAIN must be set in order to read pulse
current when output is initiated by means other than the MAC-21.
For test sets with motorized vernier, the MAINTAIN key may be pressed while output
is ON to provide automatic current hold. The LED in the MAINTAIN key will blink while
this mode is set, and the vernier motor will be activated whenever the current varies
more than 5 amperes from the value displayed when the key was pressed. The key
may be pressed again to return to normal mode. STOP or RESET will also discontinue
current hold.
N.O. key:
This key is used to set the Normally Open contacts mode. In this mode, lack
of continuity on the CONTACTS binding posts indicates that the protective device
under test is in its normal (non-tripped) mode, and ready to accept current. In N.O.
mode, after the INITIATE key is pressed, the timer starts when current (about 3% of
range) is detected. The timer stops when the STOP key is pressed, or continuity is
sensed at the CONTACTS binding posts. Timing accuracy in this mode is typ/-
0.01 seconds.
N.C. key:
This key is used to set the Normally Closed contacts mode. In this mode,
continuity on the CONTACTS binding posts indicates that the protective device under
test is in its normal (non-tripped) mode, and ready to accept current. This mode may
be used for testing multi-pole breakers by connecting the CONTACTS binding posts
to an unused pole. In N.C. mode, the timer starts as soon as current (about 3% of
range) is detected after the INITIATE key is pressed and stops when the STOP key is
pressed or a break in continuity is sensed at the CONTACTS binding posts. Timing
accuracy in this mode is typ/- 0.01 seconds.
C.L. key combination:
When the N.O. and N.C. keys are pressed simultaneously, both
LEDs light, indicating C.L. mode (Current Latch). This is the normal power-up default
mode for the test set, and is recommended for all tests, unless there is a good reason
for using contacts to sense trip. In this mode, current is continuously sampled, and
when it exceeds approximately 10% of the current range value, the timer starts, and
calculation of pulse current begins. When current stops (or drops below a dynamically
determined threshold value), the timer stops running, and the final value for pulse
current is calculated and displayed. If the output was initiated by the MAC-21, it is
turned OFF. NOTE: in C.L. mode only, the contacts jacks may be used for remote
initiation (see below).
PRESET key:
This key toggle the PRESET ADJUST mode, indicated by illumination of
its LED. When PRESET ADJUST is active, the adjacent SECONDS and CYCLES keys
respectively lower and raise the preset time in seconds or cycles, depending on the
time base that was selected. Both keys may be pressed simultaneously to reset the
time limit to zero, which disables the time limit function. When not in PRESET mode,
the LED will flash if the displayed time exceeds the preset limit.
