Four Wire Delta Circuits

Four Wire Delta Circuits A four-wire delta (4WD) electrical service is a three-phase delta service with a center-tap on one of the transformer windings to create a neutral for single-phase loads. Motors loads are commonly connected to phases A, B, and C, while single-phase loads are connected to either phase A or C and to […]

Energy (kWh) vs. Power (kW)

Energy (kWh) vs. Power (kW) There is sometimes confusion about the difference between “electrical power” and “electrical energy”. The following article should help clear up the differences. Power Power is measured in watts (W), kilo-watts (kW), mega-watts (MW), and giga-watts (GW). The power of a load can change quickly, especially if the load is turning […]

Electrical Measurement Math

Electrical Measurement Math Overview This page discusses a variety of questions concerning math on quantities related to power measurement. Math on certain electrical quantities doesn’t work the way you might expect because some electrical measurements are vector or phasor quantities, so adding or subtracting the amplitudes doesn’t work correctly. Math with Power Quantities Can I […]

Electrical Service Types and Voltages

Electrical Service Types and Voltages This page describes various types of utility electrical services and supply voltages. The nominal system supply voltages listed below can vary by ±10% or more. WattNode® meter models are available in seven different versions that cover the full range of electrical services types and voltages. Meters and current transformers are [...]

Electrical Terminology

Electrical Terminology CT – Current transformer – CTs measure the AC (sometimes DC) current in a wire by transforming the current to a lower current or voltage. CCS CTs are voltage output, generally 0.333 Vac at full-scale, eliminating any shock hazard. Three-phase – Refers to electrical services where there are three AC line conductors with […]

Inverter Power Factor

Inverter Power Factor What is the power factor of an PV or wind power inverter? Overview Inverters are generally designed to generate power at unity power factor, particularly at full power. The actual requirements vary, but one example is: The power factor must be greater than 0.90 for generated power greater than or equal to […]

Reactive Power

Reactive Power Overview Reactive power (Q) is a term for the imaginary (non-real) power from inductive loads like motor or capacitive loads (less common). It is generally measured in units of VARs (volt-amps reactive). Sometimes reactive power is reported in units of watts; this isn't exactly correct, but not all devices or software offer units [...]

Measurement Categories (CAT III)

Measurement Categories (CAT III) Measurement categories are defined by the CE and UL safety standard IEC 61010-1 and are used to indicate the ability of an instrument (like the WattNode® meter) to withstand voltage spikes without posing a shock hazard to the operator. An instrument should only be used at or below its rated measurement […]

Corner-Grounded Delta Circuits

Corner-Grounded Delta Circuits Occasionally, (especially in older facilities or in oil well and irrigation applications), you may encounter a three-phase delta service with one phase (leg) connected to ground, called a “corner grounded delta” or “grounded leg service”. You can determine if you have a corner grounded delta service by using a multimeter (DMM) to […]

Two-Phase Electrical Service

Two-Phase Electrical Service What is two-phase electrical service? Residential electric service in the United States (120/240 VAC) is sometimes called two-phase service but this is NOT correct. It is only single-phase, since both line voltages are derived from a single phase of a distribution transformer with a center tapped neutral and are 180° out of […]