Mike Dolt Enterprises
Mike Dolt Enterprises
User: DetroitEE, Location: Detroit, MI
Asked on: Monday, March 14, 2011 at 9:28 am EDT
Answered on: Tuesday, May 14, 2024 at 2:46 am EDT
Question: Recently at a meeting among engineers at my firm, the topic of 200% neutrals came up. Common practice seems to be that you provide a 200% neutral for panelboards that serve a majority of non-linear loads, such as computer power supplies. However, one person made a comment that computer power supply technology has advanced over the years, and that they do not produce as many harmonics as they once did.The main point of our discussion was to determine if we still feel it is necessary to provide 200% neutrals for large computer loads. Does any one know if there's any truth to computer power supply harmonics being less of an issue now? When do you guys typically use a 200% neutral?
Truth to Computer Power Supply Harmonics Being Less of an Issue
Yes, there is some truth to the claim that computer power supply harmonics have decreased over the years. Advancements in power supply design, such as the use of active power factor correction (PFC), have significantly reduced harmonic distortion. This is due to: PFC circuits
They shape the current waveform to make it more sinusoidal, reducing harmonic content.
Higher switching frequencies
Modern power supplies operate at higher frequencies, which reduces the magnitude of harmonics.
Improved filtering
Advanced filtering techniques remove unwanted harmonics from the output waveform.As a result, modern computer power supplies typically have THD (total harmonic distortion) values below 20%, and some may even meet the 10% THD limit set by IEEE 519.
When to Use 200% Neutrals
Despite the improvements in computer power supply harmonics, 200% neutrals are still recommended in certain cases: Large, concentrated computer loads
When a significant number of computers are concentrated in a single location, the harmonic currents can still add up and cause problems.
Sensitive loads
If the panelboard also serves sensitive loads that are susceptible to harmonics, such as lighting or audio equipment, a 200% neutral may be necessary to mitigate harmonic interference.
Code requirements
In some jurisdictions, electrical codes may still require 200% neutrals for panelboards serving computer loads.
Typical Uses of 200% Neutrals200% neutrals are typically used in the following situations: Data centers and computer rooms Office buildings with high computer usage Server rooms Medical facilities with sensitive electronic equipmentConclusion
While computer power supply harmonics have decreased, it is still prudent to consider 200% neutrals for large computer loads, especially where they are concentrated or code requirements dictate. The decision should be made on a case-by-case basis, taking into account the specific load profile, sensitivity of other equipment, and any applicable regulations. Flag for review