Power Quality Assessment
What is a Power Quality Assessment?
A power quality assessment at a customer's location is a service offered by UL in which a series of tests are performed to assess the electrical power distribution quality. This service surveys the power supply to a test area including source transformer ratings and test circuit performance for voltage, current, frequency and total harmonic distortion over a period of time under specified load conditions.
Tests include:
- Independence of Test Circuits
- Line, Neutral, and Ground Voltage Measurement Test
- Electrical Regulation / Circuit Capacity Test
- Total harmonic distortion
Each representative test bench outlet receptacle/test power connection point is checked by measuring the open circuit voltage between Line to
Neutral (L-N), Line to Ground (L-G), and Neutral to Ground (N-G). The other tests are completed at the outlet with the longest wire length for each circuit.
Outlets or Power Test Sources requiring a power quality assessment:
- 120 Volt AC, 60 Hertz, single-phase, 20 Amps
- 230 Volt AC, 50 Hertz, single-phase, 16 Amps
- 240 Volt AC, 60 Hertz, single-phase, 15 Amps
UL's Data Acceptance Program requires all labs that generate data to be used for a certification decision are required to comply with our Power Quality document (00-OP-C0036). If a product is to be connected to a branch circuit in the field at one of the voltages and current ranges listed above, and UL will be utilizing this data to make a certification decision, then a Power Quality Assessment must be conducted regardless of the actual current rating of the supply the client is using. When clients use a variac, UL will need to also consider the output of the variac at the voltages and current ranges listed above to determine if a Power Quality Assessment is required.
Circuits that have current ratings higher than above but are used for testing at voltage and currents within the above ranges also need to have a power quality assessment. For circuits outside the above parameters, a power quality assessment is not required, but power quality must be monitored whenever testing is being conducted and recorded for use by UL.
Preparing for a UL power quality Assessment
A customer will need to provide UL with a single line drawing showing the electrical connection from the test outlet(s) or test connection point(s) back to the source transformer(s). The drawing should include the source transformer, switchboards, panel boards, approximate wire distances and conductor's sizes wiring method. Sample line drawings are available below under Additional Resources.
When UL conducts a power quality assessment, it is unnecessary to shut down a plant or laboratory. UL will connect to a circuit to test and load it, but a customer should be able to work around that single circuit by using alternative circuits. Thus, the plant/laboratory should be running normally.
What type of report do customers receive?
A technical report is provided to the customer without any engineering judgments. If a customer needs assistance in improving their power quality, they can request a quote for a technical consultation by clicking the banner above. The final decision regarding compliance resides with an appropriately qualified UL Engineer within the specific industry discipline and/or the DAP/MTL Lead Auditor.
Why choose UL for Power Quality Assessment
This new service offering supports our public safety mission by helping to confirm there is a suitable environment for testing products. Clients are required to conduct a power quality assessment if they wish to participate in UL's Data Acceptance Program (DAP) or Manufacturer Test Laboratories (MTL) programs. Customers may conduct testing themselves or use an outside source. Using UL for this service is optional. UL utilizes calibrated equipment and a knowledgeable, experienced staff in performing power quality studies. UL clients may save time and money by having UL perform this service as opposed to outsourcing the work to another service provider or conducting the tests themselves.
Additional Resources
- DAP power quality job aid (00-OP-C0036)
- MTL procedure for measuring laboratory power (CTL-OP-110)
- Power Quality Assessment Sell Sheet
- Line drawing example #1
- Layout drawing example #2
