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In-Phase
Monitors
Q. Dan,
Your publication Healthcare Emergency
Power Supply Systems (which we have
purchased), was highly recommended by an
advisor to JACHO. We are using your
Monthly Testing Log form. As a result of
a major construction-renovation project,
we have a new Emergency Power System
which consists of two Generac 375 KW
480/277 volt generators in parallel,
synchronized to a main buss and
distributed to the three branches
through Asco transfer switches.
On page 177, 4.10.11 you recommend using
the start button on the transfer switch
to start the generators and then record
the time from cold start to transfer. On
page 176, 4.10.10.9, you recommend not
opening the normal feed breaker to the
transfer switch to simulate a power
outage as that is causing one, which
makes sense. However, when we use the
transfer switch to initiate the test we
have a transfer time of over 10 seconds
because the generators see the normal
power available and synchronize with it
before transferring to generator power.
If normal power is not available as in a
normal power outage, the synchronizing
will not have to take effect. The
synchronizing takes approximately 7
seconds. The Generac technician feels
that this amount of time is necessary to
prevent events that could be
electrically detrimental to the
equipment served and also to the
transfer equipment itself.
The Normal circuit breakers feeding the
transfer switches for the Critical and
Life Safety are 400 amp and 125
respectively. The only solution that I
can see is to alternately (monthly) open
the Normal respective circuit breaker to
create an outage to reach the maximum 10
second limit; providing the circuit
breakers can be documented as capable of
being used on a regular basis for this
purpose.
We are wondering if you have encountered
this situation previously and could
advise us on this matter. Thank you, D.F.
A. Age old problem….having
in-phase monitors in the ATS, and then
having to explain to a surveyor how they
work!
As you stated the only way you can
“prove” your EPSS can supply voltage to
the load side of an Emergency (LS an CB)
ATS is by opening a normal feed breaker
to an ATS, or by disabling the in-phase
monitor prior to the test.
Note that neither NFPA 99 nor 110 state
that you have to “prove” the “10 second
or less” time frame on any frequent
basis. Therefore, I would not be
inclined to use the normal feed breaker
as a “test button” unless an AHJ
demanded it, and took responsibility for
a failure, or you thought there was a
problem somewhere in the EPSS.
Reply: Thank you for your quick
response. I guess that I assumed that
since the “cold start to power” item was
on the Testing Log form that we was
required to prove the 10 second test
each month. We are going to take your
advice and use the test button on the
transfer switch for our monthly tests
and record the time even though the time
is above the 10 seconds. Once a year we
will open each normal feed breaker to
the Critical and Life Safety and verify
the 10 second test. However, if we
notice an abnormality in the monthly
test time, we will then proceed to open
the power to the transfer switches to
further investigate.
Response: Cool. |
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Diesel Exhaust Systems
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