GEH- 1 81 4
the other two phases are g rounded, the relay voltage i ncreases to rated voltage and the
left-hand contacts close in approxi mately 1 0 seconds.
The IAV53D relay is si mi lar to the Type IAV538 relay except that it has a shorter time cu rve.
Time/voltage characteristics are shown in Figure 1 4.
The Type IAV53K is si milar to the Type IAV53A, IAV53L to IAV538, IAV53M to IAV53C and
IAV53N to IAV53D.
While the IAV53A,B,C,
&
D are in sing le-end cases, the IAV53K, L, M, and N relays are in the
double-end case, with contacts con nected between the u pper and lowe r blocks a n d
coils con nected to both blocks. The pu rpose of this is to avoid false tri pping of
the
if the con necti ng plugs are removed and subsequently reinserted with the
relay in the reset position, i .e., ci rcu it-opening contacts closed . Inse rtion of either p l u g
causes t h e relay to pick u p ; both plugs must be i n place before t h e contact ci rcu its a re
completed . See i nternal con nections Figures 1 - 8 for coi l and contact ci rcu its, and Fig u res
1 0 and 1 1 for external con nections.
CONSTRUCTION
These relays are of the induction-disk construction. The d isk is actuated by a potential
operating coi l on a lami nated U-mag net. The d isk shaft carries the movi ng contact, wh ich
com pletes the tri p or alarm circu it when it touches the stationary contact or contacts. The
d isk shaft is restrained by a spi ral spri ng to g ive the proper contact-closi ng voltage, and its
motion is retarded by permanent magnets acti ng on the d isk to g ive the correct ti me delay.
There is a sea l-i n u nit mou nted to the left of the shaft of all but the IAV538, D, L and M
models , as shown i n
1 5 . This u n it has its coi l i n series and its contacts i n para l l el with
the main contacts,
that when the mai n contacts close, the seal-in u n it picks u p and
seals i n . When the sea l-i n u n it picks up, it ra ises a target i nto view, wh ich latches u p and
remains exposed unti l released by pressi ng a button beneath the lower-left corner of the
cover.
The case is su itable for either su rface or semi-flush panel
and an assortment of
hardware is provided for either mounti ng. The cover attaches to
case, and carries the
reset mechan ism when one is req u i red. Two of the cover screws have provision for a
sea l i n g wi re.
The case has studs or screw con nections at both ends (IAV53 K, L. M, or N) or at the bottom
only (IAV5 1 and 52A, and IAV53A, B, C, and D) for the external con nections. The electrical
con nections between the relay u n its and the case studs are made through spri ng-backed
contact fingers mounted in stationary molded i n ner and outer blocks, between which nests
a removable connecting p l u g (two pl ugs for the IAV53 K, L, M , and N models) t h at
completes the ci rcu its. The outer blocks, attached to the case, have the studs fo r t h e
external con nections, a n d t h e i n ner blocks have the termi nals fo r t h e i nternal con nections.
The
mechan ism is mou nted in a steel framework cal led the crad le and is a com p l ete
u n it,
all leads
terminated at the i n ner block. This cradle is held firmly i n the case
by a latch at the top
bottom and by a g u ide pin at the back of the case. The cases and
crad les are so constructed that the relay cannot be i nserted i n the case u pside d own. The
plug, besides making the electrical con nections between the respective blocks
of the
and case, a lso locks the latch in place. The cover, which is fastened to the case
by th u mbscrews, holds the connecting plug i n place.
To d raw out the crad le from a sing le-ended case, the cover must first be removed . Then the
con necting plug can be d rawn out. I n so doing, the trip ci rcu it is fi rst opened, then the
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