Monitoring power usage: five reasons to log power and energy use

Paul Boughton

Electricians are often required to conduct a load study before adding  a new electrical load to an existing panel or service. Why?

The requirements come from the electrical inspector, the electrical engineer who  designed the  project, or the  customer adding the  new  load and  the reason is to determine if there is sufficient  capacity  to add  new loads.

A load study involves using a logger to document existing load levels  (three phase current draw) over time. That’s where safety comes in. On the positive side, a load study can be used  to ensure adherence to local safety regulations. On the negative side, failure to perform  a load study before  adding new loads can result in overloading an existing electrical  source, creating electrical safety and reliability hazards.

Manage energy costs

While energy expenditures are a significant portion of overall operational cost, many companies do not really know where their energy dollars are being  spent, since all they get is one overall monthly bill, with no indication of whether that use was  standard or excessive compared to operations that month.

By logging power use at the  main service entrance and then at large loads and  secondary supplies, facilities can see how much power is being used  when, by what,  and at what  hourly cost. Without fail, the data  will turn up several energy  wastes that  can be rectified by operational changes alone,  such  as turning  off certain loads, reducing loads during peak rate  periods, or adjusting the schedule so that loads operate during  non-peak rate  periods.

Accuracy of electrical bill

Owners of large and medium sized facilities often install electrical sub metering to bill tenants for their specific electricity usage. However,  these sub meters are commonly installed improperly, putting that billing into question. Installation issues vary, from current transducers installed backwards, current transducers on the wrong phase, and errors in configuring  the  sub meter.

A good business practice is to double check the reading with a portable energy logger. Logger data provides a rough order of magnitude comparison of what  is being billed versus what is actually used. A significant deviation between the amount charged for electricity usage and the logger data would  signal the need to investigate the sub meter set-up.

Rebates and financial incentives

Utility companies offer incentives and rebates as a way to encourage their  customers to decrease energy use. The goal is to serve more customers with  the same existing power supply, since building  new  power  generation plants is prohibitive.

Many incentives and rebates are available for retrofitting existing buildings, such as energy efficient lighting and high  efficiency motors, as well as replacing motor starters with variable frequency drives.

In order to receive the financial incentive, the utility company will often require verification of the energy savings — an ideal scenario for a load study.

A pre-retrofit load study will document the existing energy use to provide  baseline data, while a post-retrofit load study verifies the energy savings achieved upon completion of the modifications.


There are many times when the only way to troubleshoot a problem is to capture and analyse data over an extended period of time. For these advanced troubleshooting scenarios, energy loggers  are invaluable—and they are much more affordable and easier to use than a more complex power analyser. A good example is when a circuit breaker trips randomly. Obvious events, like a large motor starting up, may not be the cause.

In fact, what causes the trips might appear to be totally random or may occur when technicians are not around to observe it (like the middle of the  night). Because it’s impractical for a maintenance technician to monitor  the load until the circuit breaker trips, connecting an energy logger
to the load side of the circuit breaker to record the current draw over time can help troubleshoot the trip.

Fluke Europe BV is based in Eindhoven, The Netherlands.