Appendix B 385
In general, the finer the level at which the precision criterion is
imposed, the greater the data collection requirement. If the primary
goal is to ensure savings accuracy for a project or group of projects as a
whole, it is not necessary to impose the same precision requirement on
each subset. In fact, a uniform relative precision target for each subset
is in conflict with the goal of obtaining the best precision possible for
the project as a whole.
Appendix C
Measurement Techniques
ELECTRICITY
The most common way of sensing alternating electrical current
(AC) for energy efficiency and savings applications is with a current
transformer or current transducer (CT). CTs are placed on wires con-
nected to specific loads such as motors, pumps or lights and then con-
nected to an ammeter or power meter. CTs are available in split core
and solid torroid configuration. Torroids are usually more economical
than split-core CTs, but require a load to be disconnected for a short
period while they are installed. Split-core CTs allow installation without
disconnecting the load. Both types of CTs are typically offered with ac-
curacies better than one percent.
Voltage is sensed by a direct connection to the power source. Some
voltmeters and power measuring equipment directly connect voltage
leads, while others utilize an intermediate device, a potential transducer
(PT), to lower the voltage to safer levels at the meter.
Though electrical load is the product of voltage and current, sepa-
rate voltage and current measurements should not be used for inductive
loads such as motors or magnetic ballasts. True RMS power digital sam-
pling meters should be used. Such meters are particularly important if
variable frequency drives or other harmonic-producing devices are on the
same circuit, resulting in the likelihood of ham-ionic voltages at the motor
terminals. True RMS power and energy metering technology, based on
digital sampling principles, is recommended due to its ability to accu-
rately measure distorted waveforms and properly record load shapes.