Specifications

February 2007
CA08101001E For more information visit: www.eaton.com
16-3
Transfer Switches
16
Transfer Switch Equipment
Automatic Transfer Switches
Generator — Generator
Transfer switches are sometimes
applied between two generator sets
for prime power use, often in remote
installations. In such applications,
source power is periodically alternated
between the generator sets to equally
share run-time.
Service Entrance Rated Transfer Switches
Modifying the molded case switch in
the transfer switch by adding trip units
and optional ground fault, along with
adding the service entrance option
eliminates the need for separate
upstream disconnect devices and their
respective power interconnections.
This means the Automatic Transfer
Switch (ATS) is installed directly at
the point of service entrance, saving
valuable space and cost.
Built-in Protection
All Eaton Molded Case Switches are
“self protected,” such that under
extreme fault conditions, the switch
will open before destroying itself. This
feature allows Eaton to offer “Mainte-
nance Free Contacts” on the molded
case transfer switch. The molded case
switches have instantaneous magnetic
trip units installed in each switch.
These trips are not accessible once
installed by the factory to eliminate
field tapering. The trips are set to a
minimum of 12 to 15 times the rated
current of the molded case device,
well above any coordination set
points. This means they will not inter-
fere with the normal operation of the
distribution system and will only trip
if something is very wrong.
Figure 16-2. Standard Application Generator — Generator
Figure 16-3. Service Entrance Rated Transfer Switches
Figure 16-4. Built-in Protection

Magnetic Trip 12 x frame rating.
G
Ge
n
e
r
ator
Br
ea
k
er
G
Ge
n
e
r
ato
r
Br
ea
k
er
L
oad
AT
S
Generator
Breaker
G
Load
Service
Disconnect
ATS
Utility Service
G
Generator
Breaker
Load
ATS
Service
Disconnect
Utility Service
Typical Transfer Switch Installation
Transfer Switch Installation Rated
For Service Entrance
400 FLA x 1.25 = 500 Ampere Breaker
Compare 400 Ampere ATS and 500 Ampere LD Breaker
Time
(Min.)
5
1 2 3 4 5 6 7 8 9 10
Breaker Ok
400 ATS
햲
Will Only Trip at
7200 Amperes 100% Rated
Device per UL 1008
Breaker Trips
ATS Ok
ATS Trips
500 Ampere
HLD Breaker
Current x 1000
Misconception: Breaker
Type Switches Susceptible
to Nuisance Tripping.
Example: 400 Ampere ATS With 500 Ampere T/M Breaker
Reality: Upstream Breaker
Will Trip Before ATS MCS
Trips When Overcurrent
is <7200 A