RTBD-NB Brochure RTB-NB/RTBD-NB
No Break Bypass / Isolation Switches
05-074 RTB_RTBD-NB Brochure 6/28/05 12:06 PM Page 1 Russelectric Inc.
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www.russelectric.com
99 Industrial Park Road
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Hingham,MA 02043
TEL: 781 749-6000
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FAX: 781 749-4205
Form RTB-NB/RTBD-NB
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©1997 Russelectric Inc.
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Printed in USA
RTB-NB/RTBD-NB
No Break Bypass / Isolation Switches
Russelectric RTB-NB and RTBD-NB No
Break Bypass/Isolation Switches combine
all the functions of an Automatic Transfer
Switch (ATS) plus a method for manually
bypassing power from a dead source to a
live source in the event the transfer switch
is disabled. They also allow the transfer
switch to be isolated and deenergized for
maintenance, testing, or repair without
interrupting power to the load. The ATS is
a standard open transition Russelectric
Model RMT or RMTD. RTB-NB and
RTBD-NB switches are identical in size and
carry the same closing and withstanding
ratings as Russelectric Standard RTB
and RTBD Bypass/Isolation Switches.
The Industrys Highest 3-Cycle Closing
and Withstand Ratings
Russelectric RTB-NB and RTBD-NB
Bypass/Isolation Switches have the
same closing and withstand ratings as
the ATS, which are the highest 3-cycle
closing and withstand ratings of any
switches available today (see chart).
These 3-cycle ratings mean that
Russelectric switches are not restricted to
specific manufacturers circuit breakers,
but are fully rated and labeled for use
with any manufacturers circuit breaker
with instantaneous trip. These unrestricted
ratings are extremely important, since they
allow engineers to apply switches without
problems of coordination with different
breaker types.
Underwriters Laboratories, Inc. requires
a transfer switch to be able to close in on
the same amount of fault current as it can
withstand before they allow it to be listed
with a short circuit rating. In view of this,
fuse protection becomes mandatory
where extremely high short circuit current
is available. All Russelectric switches
have closing and withstand ratings of
200,000 amperes when coordinated with
current limiting fuses.
Operation
To bypass normal to load, emergency to
load, or to return from either bypassed
position, the bypass switch must parallel
the source to which the ATS is connected.
When the ATS is connected to the normal
source, bypass normal to load may be
accomplished. When the ATS is connected
to the emergency source, bypass
emergency to load may be accomplished.
A solenoid interlock prevents bypassing
to a source that is not connected.
Bypass
Pushing the solenoid interlock button
and moving the bypass handle to the
Bypass position closes the bypass
contacts (BP), paralleling them with the
ATS contacts (see figure). After the BP
contacts are closed, mechanical interlocks
immediately open the load break contacts
(LB), disconnecting the load from the
transfer switch while maintaining power to
the load through the BP contacts. Coming
out of bypass reverses this procedure,
closing the LB contacts before opening the
BP contacts, restoring power flow through
the ATS without power interruption.
Test
After bypassing the ATS as described
above, power is no longer flowing
through the ATS, but control power is still
maintained to the ATS controls. Complete
operational testing capability is available,
including transferring the ATS from source
to source, without disturbing the load.
Isolate
After bypassing the ATS as described
above, moving the isolation handle to
the Isolate position simultaneously
disconnects primary power and control
power from the ATS. This operation
physically releases the transfer switch
base, which is equipped with casters so
that it may be removed from the enclosure
for inspection, maintenance, and repair.
When reinserting the switch base, moving
the isolation handle to the Normal position
draws the switch base into the connected
position, reconnecting both primary
power and control power while maintaining
power flow through the bypass contacts.
The transfer switch is now ready to come
out of bypass.
Switching Between Bypassed Sources
The bypass/isolation switch is designed
to operate as a manually operated backup
transfer switch when the transfer switch is
in the Isolate position. Moving the
bypass handle from the Bypass position
of the connected source to the Auto
position and then moving it again to the
Bypass position of the alternate source
manually transfers the load from the initially
connected source to the alternate source.
This transfer is done open transition.
3-Cycle Closing and Withstand Ratings
RMS Symmetrical Amperes 480 VAC
Based on Testing Under UL-1008
Switch Rating
Amperes
100 - 400
600 - 800
1000 - 1200
1600 - 4000
Closing and
Withstand
42,000
65,000
85,000
100,000
For further information or a specification on RTB-NB and RTBD-NB switches, consult factory.
NORMAL
SOURCE
EMERGENCY
SOURCE
LOAD
BPN
BPE
ATS
NORMAL
(CONNECTED)
AUTO
BPN BPE
LB
ISOLATE
05-074 RTB_RTBD-NB Brochure 6/28/05 12:08 PM Page 2