3300 ACM Installation and Operation Manual Power Measurement Ltd.
Installation 2-3
2.4 CHASSIS GROUND
CONNECTION
The ground terminal, G, of the 3300 ACM serves as the zero
voltage reference point for voltage measurements, as well as
the chassis ground connection for the meter. This terminal
must be connected to earth ground.
A good, low impedance chassis ground connection is
essential for accurate measuements and proper protection.
It should be made to the switchgear earth ground using a
dedicated 14 AWG (2.7mm
2
) gauge (or larger) wire to a
point where there will be no voltage error due to distribution
voltage drops. Do not rely on metal door hinges as a
ground path. Ensure that the screw has been tightened
down securely onto the ground wire.
CAUTION
The G terminal of the 3300 ACM must be
connected properly in order for the noise
and surge protection circuitry to function
correctly. Failure to do so will void the
warranty.
2.5 PHASE VOLTAGE AND PHASE
CURRENT INPUT CONNECTIONS
2.5.1 PHASE VOLTAGE INPUTS
V1 Input Connection
The 3300 ACM uses the V1 input as the reference for
maintaining phase relationships for all power and energy
related measurements. For any system configuration, the V1
input must be connected to ensure accurate readings and
the correct operation of the 3300 ACM.
Direct Connection
Whether or not potential transformers (PTs) are required
depends on the nature of the system being monitored, the
voltage levels to be monitored, and the input option of the
3300 ACM.
BASIC MODEL
The basic model can be used for direct connection to Wye
systems up to 347 VAC line-to-neutral/600 VAC line-to-
line or Single Phase systems up to 347/694 VAC. These
can also include 120/208 VAC Wye, 120/240 VAC Single
Phase, 277/480 VAC Wye, and 277/554 VAC Single Phase
systems.
HIACC OPTIONS
The HIACC options provide higher measurement accuracies
than the basic model. A guaranteed 0.25% accuracy is
provided on phase voltage and phase current measure-
ments, rather than the 0.5% accuracy of the basic model (see
Appendix C for complete specifications).
Devices equipped with any one of the HIACC options are
designed to be used with the specific system voltage defined
by the option. For example, a 3300 ACM - HIACC: 120
should be used with a 120/208 VAC Wye or 120/240 VAC
Single Phase system. Other HIACC options include
HIACC:277 and HIACC:347.
If a device equipped with a HIACC option is used at any
voltage lower than what it is rated for, the accuracy of the
voltage measurements must be derated accordingly. Please
consult your local Power Measurement sales representative
or contact Power Measurement directly for more informa-
tion.
Using Potential Transformers
If Wye system voltages are over 347/600 VAC, Single Phase
system voltages are over 347/694 VAC, or the system is a
Delta configuration, PTs are required.
CAUTION
PTs are always required for Delta
systems.
PTs are used to scale down the line-to-neutral voltage of a
Wye or Single Phase system, or the line-to-line voltage of a
Delta system to within the rated input scale of the 3300
ACM. The basic 3300 ACM can be used with PTs that have
secondaries rated at 347 VAC or less. This can include 100/
√3, 110/√3, 100, 110, 120, or 220 VAC secondaries.
Devices equipped with any one of the HIACC options are
designed to be used with PTs with secondary ratings equal
to the specific system voltage defined by the option (e.g. 120,
277, or 347). Using PTs with other secondary ratings not
equal to the option rating requires that the voltage accuracy
be derated accordingly (see HIACC Options section above).
For proper monitoring, correct selection of PTs is critical. For
Wye systems, the PT primary rating should equal the system
line-to-neutral voltage or nearest higher standard size. For
Delta systems, the PT primary rating should equal the
system line-to-line voltage. For all system configurations,
the PT secondary rating must be within the rated full scale
range of the 3300 ACM voltage inputs.
PT quality directly affects system accuracy. The PTs must
provide good linearity and maintain the proper phase
relationship between voltage and current in order for the
voltage, kW, and power factor readings to be valid. Instru-
ment accuracy Class 1 or better is recommended.
Courtesy of NationalSwitchgear.com
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