Relays with forcibly guided contacts...
Relays with forcibly guided contacts are specified wherever
the logic of an application wants to detect the state of the
contacts of a relay and use it for control purposes. Such
relays enable the implementation of self-monitoring
systems.
Typical applications in the safety market are:
• Emergency-off devices
•
Monitoring devices for protective doors
•
Robot controls
•
Light curtains
•
Light barriers for safety purposes
•
Two-hand switching devices
•
Step mat controls
•
Elevator controls
•
Signals engineering, railway controls etc.
Because these relays are used in safety critical
applications, relays with forcibly guided contacts are
subject to special requirements, which are summarized in
the standard EN50205. This standard specifies that the
switching relays must feature at least one NC and one NO
contact.
The contacts are mechanically interlocked in such a way
that the NC contact and the NO contact can never be
closed at the same time.
This applies over the entire life span for contacts under
load and no load conditions. Apart from this it must be
guaranteed that open contact distances of at least 0.5mm
exist over the full life in normal operation as well as in any
case of relay failure. All newly developed relays of ELESTA
relays GmbH have gained TÜV approval for compliance
with this standard, i.e. they meet the latest requirements
applicable to relays with forcibly guided contacts.
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At this time the range of ELESTA relays GmbH comprises:
• 36 different styles of safety relays with up to 10 forcibly
guided contacts.
Insulation of different voltage potentials
In power installations, relays are used for galvanic
separation of different voltage potentials. In addition to
this isolation, relays with forcibly guided contacts must
guarantee mechanical interlocking of the contacts. In
corresponding applications at least one contact is used for
control, and further contacts serve for either control or
load switching purposes. In normal power relays, galvanic
separation is usually only effected between coil and
contact block, in the case of relays with forcibly guided
contacts, isolation of different voltage potentials must also
be guaranteed within the contact block.
Galvanic separation within the contact block
Relays with forcibly guided contacts are used in
applications relying upon a high degree of safety. Thanks
to the forcibly guided contacts and high voltage isolation
characteristics, they guarantee the protection of people
and equipment over the full life span of the relay including
fault conditions.
The separation of the power circuits is achieved with
suitably dimensioned insulation between live components
(basic insulation, extra insulation, reinforced insulation,
EEx insulation). The creepage distances and clearances are
defined in accordance with the insulation voltage. The
control side of the relay to the output contacts and also the
output contacts among themselves are spaced with the
required isolation distances. With the products of ELESTA
relays GmbH, an isolation voltage of >250V specified for
many applications can even be guaranteed for the case of
"safe separation".
ELESTA relays GmbH produces its relays under the motto
"Safety without compromise"
This is why the dimensioning of the creepage distance
within the relay is steadfastly based on pollution degree 3
which the applicable standards define for conductive
pollution. The detailed layout of insulation/isolation
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barriers can be found in the specifications.
Pollution degree 3
Insulation strength (basic insulation, additional insulation,
double insulation, reinforced insulation, EEx insulation)
depends on the safety levels demanded of the equipment
in which the relay is used. Insulation dimensioning is
based on pollution degree 3, which is the level required by
the EN50205 standard for relays with forcibly guided
contacts. ELESTA relays comply rigorously with the
standard, because relays with forcibly guided contacts find
uses in highly safety-conscious applications. The result is
added safety for personnel and plant.
Maximum insulation strength
ELESTA relays GmbH offers relays with the highest degree
of insulation. The control side of the relay is separated
from the output contacts, and similarly, the output
contacts are separated from each other by double or
reinforced insulation. In this way "protective separation"
for an insulation voltage of > 250V is reached.
EEx protection
In the standards relating to electronic components for
areas where a danger of explosion exists, a creepage
distance of > 10 mm is defined for the insulation voltage
of < 375V for separating conductive parts. All ELESTA
relays GmbH products meet this demand between the
control side and the output side of a relay (intrinsically
safe electrical circuits in categories "ia" and "ib"; the
requirements of the PTB Parts Certificate or relevante EEx
protection regulations must be observed).
Standards and directives relating to relays with
forcibly guided contacts
The main purpose behind the applicable standards is to
establish minimum requirements for measuring and
manufacturing industrial electronic control gear, and afford
protection against electric shock.
The minimum requirements set out by the standards
reflect professional experience in achieving given technical
levels of safety and reliability.
The major standards are:
prEN50178 Electronic equipment for use in power
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installations
DIN
VDE0160
Electronic equipment for use in power
installations
DIN
VDE0106
Protection against electric shock
IEC664
Insulation coordination for equipment within
low-voltage systems
DIN
VDE0110
Insulation coordination for equipment within
low-voltage systems
DIN
VDE0700
Safety of household and similar electrical
appliances
DIN
VDE0730
Automatic electrical controls for household
and similar use
DIN
VDE0631
Automatic electrical controls for household
and similar use
VDE0860
Safety requirements for electronic and
related apparatus for household and similar
general uses
VDE0804
Particular safety requirements for equipment
to be connected to telecommunication
networks
IEC255
All-or-nothing electrical relays
EN50205
Relays with forcibly guided (linked) contacts
EN50020
Electrical apparatus for potentially explosive
atmospheres
350 Milford Point Rd. Milford, CT 06460
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P.203-878-0400 F.203-878-0458
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