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Fig. 8-Four Coil Attachment
rod which is pushed up against the tripping lever.
The calibration is varied by changing the air gap
between the moving and stationary cores by raising
or lowering the calibration screw. The lock bolts
must be drawn tight after changing the calibration.
The calibration setting is indicated by figures on
the tube and a line on the calibration plate. The
setting thus indicated corresponds to the amperes
in the secondary winding of the current trans
former.
If the opening of the circuit breaker is not de
sired unless the overload continues, an oil dashpot
delaying device is attached to the end of the moving
core. The calibration is inscribed on the dashpot
and is varied by screwing the pot into the cover.
Time is varied by changing the number of holes in
the bottom of the piston uncovered by the dia
phragm. Instantaneous tripping is possible because
the check valve action of the washer at the time of
tripping varies inversely with the amount of over
load and directly with the viscosity of the oil.
Figure 10, page
12,
shows approximate variations
of the time with the variations of the overload and
the effect of the two grades of oil. The values
shown by these curves are approximate and will
vary considerably with changes in temperature and
changes in the viscosity of the oil. Where a definite
time delay is required it is recommended that suit
able relays be used.
11
Corg
l:kl5h Pot
Fig. 9-0verload Release
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