Application Note For General Purpose Relays

Issued June, 2013
13C9136

Venting of Sealed (washable) Relays (that have vents provided)
Introduction:

Why sealed washable relays should be vented:

Unless specifically advised otherwise by TE Engineering, allsealed relays (that have a venting means provided by themanufacturer) must be vented after PCB assembly andcleaning, but before use electrically, in order for publishedratings to remain applicable.

There are two main effects/conditions that may occur if sealed
relays are not properly vented before electrical use): 1)
possible insulation failure and 2) reduced contact switchinglife.

There are several types of relays that have no venting means
provided by the manufacturer. This Application Note does not
apply to those types.
For additional relay processing information, see related
Application Note “Mounting, Termination and Cleaning ofPrinted Circuit Board Relays”.
Identification, location and removal of the vent covering:(See figures following) Vents may be either a small hole covered by a tape seal or asmall cylindrical plastic pin (called a “vent nib”).
 Tape vents can be located anywhere except on the PCB
mounting surface and should be opened after processing by
peeling off the tape.
 Pin/nib-type vents are usually located inside a small
depression – typically on the top of the relay opposite themounting surface -- but can be located anywhere.
 Pin-type vents are removed by cutting the pin with a sharpknife blade or by breaking it off using a small sharp-edged
tool like a screwdriver. Deflecting the pin sideways will resultin fracture of the pin leaving the small vent hole.
 Care should be used to avoid extruding the plastic into thehole or smearing into the hole any coating or othercontaminant that might be on the relay surface which would
result in constriction of air-flow through the vent.

“Rated” life of the relay takes these effects into account, soneither condition should occur during the rated life at a
specified loading. However, if the sealed relay is not vented or
if it is operated beyond rated life to actual failure, either
condition can occur.
• Insulation failure:
When relay contacts switch a voltage and current sufficientto generate an arc, arcing of the contacts results in formationof metal vapor, ozone, carbon and other contaminants. This
increases with higher load current, voltage and temperature.
These contaminants then fall or condense upon internalsurfaces of the relay. Because these contaminants may beslightly conductive, they can result in formation of a leakage
current path between electrically live parts inside the relay.
This is especially critical if such a path forms on the plastic
surface between relay contacts or terminals.
The continued build-up of these contaminants can result inincreasing current flow across insulated surfaces – which
may form a carbon track of decreasing resistance over time.
Eventually this path may conduct sufficient current to cause
the plastic to melt or ultimately char, which may result in
structural impairment of relay function and, in severe
instances, fire.
• Reduced contact life:
Arcing of contacts as described above also results in acontaminated, ion-rich environment inside the relay which
increases the length of the switching arc. This results inaccelerated contact erosion and generation of morecontaminants.
Eventually, the relay contact will erode until it no longer
makes contact, which can result in an open circuit (failure tomake) or in contact force so low that the contact welds when
it makes the load current (failure to break).
Contact life can be reduced to 20 to 50% of the rated value
for some relays. This effect is largely dependent on thepercent of rated current being switched along with ambient
temperature conditions.
Venting a sealed relay allows natural “breathing” of the relay,
helping to reduce contaminant build-up which leads toreduction/elimination of the accelerated failure modes
mentioned above.
Notably, most Agency testing and internal reliability testing
on sealed relays is conducted with the relay properly vented.
Conditions where sealed relays are not vented:
Under special conditions for specific applications, it may berecommended that sealed relays not be vented. Such
conditions include (but are not limited to): Much less than full rated contact current.
 Low level contact voltages and/or currents
 Low ambient temperatures© 2013 Tyco Electronics Corporation, a TE Connectivity Ltd. company
All Rights Reserved.
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 Low switching rate and low number of lifetime switching
operations expected in the application.
 The need for low contact resistance at low voltage andcurrent – especially in very contaminated environments.
 Operation at low to medium contact loads in a dirty
environment (dust, grease, salt air, urban pollution, etc.)
 The application of spray or dip conformal coating on PCB
mounted relays where the relay vent nib area is not masked
offCaution - TE Engineering should always be consulted toreview the application prior to using sealed relays in thesealed, unvented condition during service.

Disclaimer:
TE has made every reasonable effort to confirm the accuracyof the information set forth herein; however, TE does notguarantee that it is error-free nor does TE make any otherrepresentation, warranty, or guarantee that the information isaccurate, correct, reliable or current. TE EXPRESSLYDISCLAIMS ALL WARRANTIES REGARDING THE
INFORMATIONCONTAINEDHEREIN,WHETHER
EXPRESS, IMPLIED OR STATUTORY, INCLUDING ANYIMPLIED WARRANTIES OR MERCHANTABILITY OR
FITNESS FOR A PARTICULAR PURPOSE. In no event will
TE be liable for any direct, indirect, incidental, special orconsequential damages arising from or related to Recipient’s
use of the information.

Venting of Sealed (washable) Relays (that have vents provided)

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