Tips for Choosing 3-Phase Line Filter

3-Phase Power System
In electrical engineering, 3-phase electric power systems have at least three conductors carrying alternating voltages that are offset in time by one-third of the period (Each phase is set at the same frequency and voltage amplitude but phase shifted by 120° allowing for constant power transfer during electrical cycles). Fig.1, below, shows the typical waveforms of instantaneous voltages in a 3-phase system in one cycle’s time domain.

Fig.1 Time Domain Waveforms in a 3-phase system

In the circuit connection, these are called phases and are usually denoted as A, B and C or L1, L2 and L3. A 3-phase system may be in delta (∆) or wye (Y) (also denoted as the star in some areas) connection. Fig 2 shows the typical circuit connection of delta (∆) and wye (Y) respectively.

Fig.2 Circuit Connection of Delta (left image) and Wye (right image) 3-phase system

3-Phase Power Line Filters
A 3-Phase filter is able to reduce unwanted electromagnetic interference (EMI) noise within the conducted area of electromagnetic susceptibility for such applications as frequency converters, motor drives and machine tools. The range of operating frequencies is around 47-400Hz. When placed at the point of power entry to equipment, these filters prevent line noise from entering the equipment. However, EMI filters can also prevent noise generated by the equipment from exiting and entering the power lines.

Regulations such as CISPR 32 (EN 55032) and the FCC Emissions Limit specify the maximum permissible noise levels (in dB) allowed back on power lines. The general requirements for a 3-Phase EMI filter design include input currents, line voltage, size limitation, and required insertion loss. In addition to this, the configuration of a 3-Phase filter plays an important role in the design.

CISPR 32 (EN 55032) Emissions Limit:

According to CISPR 32, the limit is 40 dBuV/m from 30-230 MHz and 47 dBuV/m from 230-1000 MHz when making measurements at 10 meters for class A commercial environment, or 3 meters for class B residential environment. This corresponds to a level of 100 microvolts per meter of electric field strength at say 100 MHz.

FCC Emissions Limit:

According to Part 15 of CFR 47, the limit is 100uV/m from 30-88 MHz, 150uV/m from 88-216 MHz, 200uV/m from 216-960 MHz and 500uV/m above 960MHz. That gives the following 3-meter limits and their approximate respective source powers.

Fig 3. The maximum permissible noise level (CISPR (dBuV/m) and FCC (uV/M) limits) in different frequency ranges.

Wye Filter Type (Y or Star):
Wye Filters are typically used in switch mode power conversion devices and other applications that require a neutral connection. Wye Type utilizes a star or “Y” configuration, with all three hot wires connected at a single neutral point. One neutral wire (N) makes for a total of four wires in 3-phase Wye systems (3-Phase, 4-Wires). It allows both line-to-neutral (single-phase) and line-to-line (2/3 phase) connections, such as the TY Series Power Line Wye Filter from Delta Electronics.

Fig.4 20TYS9, TY series from Delta

Fig 5. Application Schematic of 20TYS9 ( sources by Delta Electronics )

Delta Filter Type (Δ):
Delta 3-Phase Filters are designed to reduce the electromagnetic interference in devices connected to 3-phase delta power. The Delta Type has three phases connected like a triangle, where the connection is made from one end of winding to the starting end of the other, forming a closed circuit. Delta configuration requires only three wires for transmission (3-Phase, 3-Wires). The power load is the same at any instant because of the three single-phase circuits that consistently deliver power such as the FN3026 Series Power Line Delta Filter from Schaffner EMC.

Fig.6 FN3026HP-20-71, FN3026 series of Schaffner EMC

Fig 7. Application Schematic of FN3026HP-20-71 ( sources by Schaffner EMC)

The following is two examples to compare two system filters –

Difference / Part Number TY series from Delta FN3026 Series from Schaffner EMC
Filter Type 3-Phase (Wye) 3-Phase (Delta)
Rated Current 10-20A 10-50A
Configuration Single Stage1 Single Stage1
Voltage – Rated AC 440V 300 VAC (Phase to Ground/Neutral) & 520V (Phase to Phase)
Approval Agency cURus, ENEC, SEMKO CSA, ENEC, UR
Mounting Type Chassis Mount Chassis Mount
Termination Style Quick Connect Terminal Block

Table 1 – TY Series and FN3026 Series filters comparison

Stage1 refer to the number of circuits repetitions (put in series) inside the filter. The single-stage filter has one circuit. If the circuit is repeated it becomes a dual-stage filter and so on. Increasing the number of stages improves filter performance while optimizing the filter package (size). It also helps in lowering the cut-off frequency.

Advantages of Wye and Delta configurations:


  • The design is suitable for systems that need a neutral connection
  • Feasible design for loading – using Line to Line (high voltage) or Line to Neutral (Low voltage)
  • Easy to implement individual isolation for the same voltage support


  • For power transmission, lower cost than Wye because it uses three wires only (if the neutral line can be omitted/grounded)
  • It offers higher starting torque
  • Allow higher current rating than wye
  • Better performance in the same dimension as wye

See Also: A note on using 3 Phase power with an AC/DC converter