What Causes Eddy Currents in Ferrous Gland Plates?
Eddy currents are a silent but significant issue in electrical installations, particularly when dealing with ferrous gland plates with holes. These plates, often used to support and organize conductors, can lead to progressive heat accumulation due to eddy currents, especially at high current levels.
Apologies in advance for the tables below, they are not responsive and you really need to view it on desktop.
Eddy currents are induced when single-phase conductors pass through individual holes in a ferrous gland plate. The alternating current in the conductors generates a changing magnetic field, which interacts with the conductive ferrous material. This interaction induces circulating currents (eddy currents) within the plate around each hole.
The eddy currents flow in loops around the holes, generating localized heat as they encounter resistance within the ferrous material. When conductors from different phases are routed through separate holes, the overlapping magnetic fields amplify the effect, further increasing the heat generation. While the immediate power loss from eddy currents may seem manageable, the cumulative heat build-up over time can cause inefficiencies, equipment degradation, and even system failure if not properly managed.
Ferrous Material Susceptibility:
Ferrous metals, such as steel, have high magnetic permeability, making them particularly susceptible to eddy currents when exposed to changing magnetic fields.
Painted Surface:
While the plate may be painted for corrosion resistance, the paint does not affect the induction of eddy currents. Magnetic fields easily penetrate the thin paint layer, inducing currents in the underlying metal.
Holes for Conductors:
Each conductor, typically from different phases (L1, L2, L3, and N), passes through separate holes in the gland plate. This setup creates multiple magnetic fields, which interact with the plate and induce eddy currents that circulate around the holes.
Key Equations and Assumptions
Magnetic Field Strength (B):
Where:
μ₀ = 4π × 10⁻⁷ H/m (permeability of free space)
I = Current (A)
r = Distance from the conductor (m)
Induced EMF (E):
Where:
f = 50 Hz (frequency of the AC supply)
Actual Power Loss in Watts (P_actual):
Where:
E = Induced EMF (V)
R = Resistance of the eddy current loop (Ω)
Assume R = 0.01 Ω for a typical ferrous gland plate.
Understanding P_actual: What It Represents
P_actual refers to the actual power loss in watts due to eddy currents in a ferrous gland plate. This power loss manifests as heat energy, which builds up in the surrounding area. It’s a direct measure of how much electrical energy is being wasted as heat within the ferrous material.
Power Loss and Heat Build-Up for 10mm Distance
| Current (A) | Power Loss (P_actual) [W] | 1 Hour [kWh] | 24 Hours [kWh] | 1 Month [kWh] | 1 Year [kWh] | Gland Plate Thickness | Heat Equivalent |
|---|---|---|---|---|---|---|---|
| 16 | 4.1 | 0.00 | 0.10 | 2.92 | 35.88 | 2 mm – 3 mm | Equivalent to a 0.0 kW heater |
| 20 | 6.5 | 0.01 | 0.16 | 4.68 | 57.06 | 2 mm – 3 mm | Equivalent to a 0.0 kW heater |
| 32 | 16.7 | 0.02 | 0.40 | 11.59 | 141.34 | 2 mm – 3 mm | Equivalent to a 0.0 kW heater |
| 63 | 64.6 | 0.06 | 1.55 | 46.56 | 567.80 | 2 mm – 3 mm | Equivalent to a 0.1 kW heater |
| 100 | 162.9 | 0.16 | 3.91 | 117.18 | 1,429.49 | 3 mm – 5 mm | Equivalent to a 0.2 kW heater |
| 125 | 254.6 | 0.25 | 6.11 | 183.33 | 2,235.41 | 3 mm – 5 mm | Equivalent to a 0.3 kW heater |
| 160 | 417.0 | 0.42 | 10.01 | 300.16 | 3,660.79 | 3 mm – 5 mm | Equivalent to a 0.4 kW heater |
| 200 | 650.0 | 0.65 | 15.60 | 467.89 | 5,705.89 | 3 mm – 5 mm | Equivalent to a 0.7 kW heater |
| 250 | 1,015.7 | 1.02 | 24.38 | 731.35 | 8,911.59 | 3 mm – 5 mm | Equivalent to a 1.0 kW heater |
| 315 | 1,602.1 | 1.60 | 38.45 | 1,153.49 | 14,057.54 | 3 mm – 5 mm | Equivalent to a 1.6 kW heater |
| 400 | 2,602.8 | 2.60 | 62.47 | 1,874.08 | 22,830.72 | 5 mm – 8 mm | Equivalent to a 2.6 kW heater |
| 600 | 5,860.2 | 5.86 | 140.65 | 4,219.39 | 51,548.56 | 5 mm – 8 mm | Equivalent to a 5.9 kW heater |
| 1000 | 16,298.0 | 16.30 | 391.15 | 11,734.40 | 143,014.32 | 5 mm – 8 mm | Equivalent to a 16.3 kW heater |
| 1250 | 25,466.0 | 25.47 | 611.22 | 18,336.60 | 223,415.76 | 8 mm – 10 mm | Equivalent to a 25.5 kW heater |
| 1600 | 40,949.8 | 40.95 | 982.91 | 29,487.20 | 359,638.12 | 8 mm – 10 mm | Equivalent to a 41.0 kW heater |
| 2000 | 65,192.0 | 65.19 | 1,564.60 | 46,938.00 | 572,235.60 | 8 mm – 10 mm | Equivalent to a 65.2 kW heater |
| 2500 | 101,870.0 | 101.87 | 2,444.88 | 73,346.40 | 894,765.36 | 8 mm – 10 mm | Equivalent to a 101.9 kW heater |
| 3200 | 166,079.2 | 166.08 | 3,986.00 | 119,580.00 | 1,459,878.00 | 8 mm – 10 mm | Equivalent to a 166.1 kW heater |
Power Loss and Heat Build-Up for 25mm Distance
| Current (A) | Power Loss (P_actual) [W] | 1 Hour [kWh] | 24 Hours [kWh] | 1 Month [kWh] | 1 Year [kWh] | Gland Plate Thickness | Heat Equivalent |
|---|---|---|---|---|---|---|---|
| 16 | 1.0 | 0.00 | 0.02 | 0.72 | 8.76 | 2 mm – 3 mm | Equivalent to a 0.0 kW heater |
| 20 | 1.6 | 0.00 | 0.04 | 1.15 | 13.82 | 2 mm – 3 mm | Equivalent to a 0.0 kW heater |
| 32 | 4.1 | 0.00 | 0.10 | 2.92 | 35.86 | 2 mm – 3 mm | Equivalent to a 0.0 kW heater |
| 63 | 15.8 | 0.02 | 0.38 | 11.40 | 139.75 | 2 mm – 3 mm | Equivalent to a 0.0 kW heater |
| 100 | 39.7 | 0.04 | 0.95 | 28.47 | 348.10 | 3 mm – 5 mm | Equivalent to a 0.0 kW heater |
| 125 | 62.0 | 0.06 | 1.49 | 44.73 | 547.20 | 3 mm – 5 mm | Equivalent to a 0.1 kW heater |
| 160 | 101.6 | 0.10 | 2.44 | 73.27 | 895.96 | 3 mm – 5 mm | Equivalent to a 0.1 kW heater |
| 200 | 158.7 | 0.16 | 3.81 | 114.40 | 1,398.73 | 3 mm – 5 mm | Equivalent to a 0.2 kW heater |
| 250 | 248.7 | 0.25 | 5.97 | 179.04 | 2,187.82 | 3 mm – 5 mm | Equivalent to a 0.3 kW heater |
| 315 | 392.1 | 0.39 | 9.41 | 282.24 | 3,448.74 | 3 mm – 5 mm | Equivalent to a 0.4 kW heater |
| 400 | 636.8 | 0.64 | 15.28 | 458.44 | 5,599.80 | 5 mm – 8 mm | Equivalent to a 0.6 kW heater |
| 600 | 1,433.4 | 1.43 | 34.40 | 1,032.18 | 12,605.96 | 5 mm – 8 mm | Equivalent to a 1.4 kW heater |
| 1000 | 4,120.0 | 4.12 | 98.88 | 2,966.28 | 36,199.20 | 5 mm – 8 mm | Equivalent to a 4.1 kW heater |
| 1250 | 5,150.0 | 5.15 | 123.60 | 3,708.00 | 45,078.00 | 5 mm – 8 mm | Equivalent to a 5.2 kW heater |
| 1600 | 8,200.0 | 8.20 | 196.80 | 5,904.00 | 71,832.00 | 8 mm – 10 mm | Equivalent to a 8.2 kW heater |
| 2500 | 16,450.0 | 16.45 | 394.80 | 11,844.00 | 144,837.00 | 8 mm – 10 mm | Equivalent to a 16.5 kW heater |
| 3200 | 26,368.0 | 26.37 | 632.83 | 18,985.30 | 232,264.32 | 8 mm – 10 mm | Equivalent to a 26.4 kW heater |
Power Loss and Heat Build-Up for 50mm Distance (with Gland Plate Thickness)
| Current (A) | Power Loss (P_actual) [W] | 1 Hour [kWh] | 24 Hours [kWh] | 1 Month [kWh] | 1 Year [kWh] | Gland Plate Thickness | Heat Equivalent |
|---|---|---|---|---|---|---|---|
| 16 | 0.3 | 0.00 | 0.01 | 0.24 | 2.92 | 2 mm – 3 mm | Equivalent to a 0.0 kW heater |
| 20 | 0.5 | 0.00 | 0.01 | 0.37 | 4.68 | 2 mm – 3 mm | Equivalent to a 0.0 kW heater |
| 32 | 1.3 | 0.00 | 0.03 | 0.96 | 11.59 | 2 mm – 3 mm | Equivalent to a 0.0 kW heater |
| 63 | 5.0 | 0.01 | 0.12 | 3.46 | 41.73 | 2 mm – 3 mm | Equivalent to a 0.0 kW heater |
| 100 | 12.5 | 0.01 | 0.30 | 9.00 | 108.00 | 3 mm – 5 mm | Equivalent to a 0.0 kW heater |
| 125 | 19.8 | 0.02 | 0.48 | 14.40 | 172.80 | 3 mm – 5 mm | Equivalent to a 0.0 kW heater |
| 160 | 32.2 | 0.03 | 0.77 | 23.20 | 278.40 | 3 mm – 5 mm | Equivalent to a 0.0 kW heater |
| 200 | 50.0 | 0.05 | 1.20 | 36.00 | 432.00 | 3 mm – 5 mm | Equivalent to a 0.1 kW heater |
| 250 | 78.9 | 0.08 | 1.89 | 56.70 | 680.40 | 3 mm – 5 mm | Equivalent to a 0.1 kW heater |
| 315 | 126.0 | 0.13 | 3.02 | 90.60 | 1,087.20 | 3 mm – 5 mm | Equivalent to a 0.1 kW heater |
| 400 | 204.1 | 0.20 | 4.90 | 147.00 | 1,764.00 | 5 mm – 8 mm | Equivalent to a 0.2 kW heater |
| 600 | 459.4 | 0.46 | 11.02 | 330.60 | 3,967.20 | 5 mm – 8 mm | Equivalent to a 0.5 kW heater |
| 1000 | 1,324.4 | 1.32 | 31.79 | 953.70 | 11,444.40 | 5 mm – 8 mm | Equivalent to a 1.3 kW heater |
| 1250 | 2,069.4 | 2.07 | 49.67 | 1,490.10 | 17,881.20 | 8 mm – 10 mm | Equivalent to a 2.1 kW heater |
| 1600 | 3,309.8 | 3.31 | 79.43 | 2,382.90 | 28,595.00 | 8 mm – 10 mm | Equivalent to a 3.3 kW heater |
| 2000 | 5,243.0 | 5.24 | 125.83 | 3,775.00 | 45,300.00 | 8 mm – 10 mm | Equivalent to a 5.2 kW heater |
| 2500 | 8,322.5 | 8.32 | 199.74 | 5,992.20 | 71,906.40 | 8 mm – 10 mm | Equivalent to an 8.3 kW heater |
| 3200 | 13,400.0 | 13.40 | 321.60 | 9,648.00 | 115,776.00 | 8 mm – 10 mm | Equivalent to a 13.4 kW heater |
Power Loss and Heat Build-Up for 100mm Distance (with Gland Plate Thickness)
| Current (A) | Power Loss (P_actual) [W] | 1 Hour [kWh] | 24 Hours [kWh] | 1 Month [kWh] | 1 Year [kWh] | Gland Plate Thickness | Heat Equivalent |
|---|---|---|---|---|---|---|---|
| 16 | 0.1 | 0.00 | 0.00 | 0.06 | 0.73 | 2 mm – 3 mm | Equivalent to a 0.0 kW heater |
| 20 | 0.2 | 0.00 | 0.00 | 0.10 | 1.15 | 2 mm – 3 mm | Equivalent to a 0.0 kW heater |
| 32 | 0.5 | 0.00 | 0.01 | 0.24 | 2.92 | 2 mm – 3 mm | Equivalent to a 0.0 kW heater |
| 63 | 2.0 | 0.00 | 0.05 | 1.49 | 17.88 | 2 mm – 3 mm | Equivalent to a 0.0 kW heater |
| 100 | 5.0 | 0.01 | 0.12 | 3.60 | 43.20 | 3 mm – 5 mm | Equivalent to a 0.0 kW heater |
| 125 | 7.9 | 0.01 | 0.19 | 5.70 | 68.40 | 3 mm – 5 mm | Equivalent to a 0.0 kW heater |
| 160 | 12.9 | 0.01 | 0.31 | 9.30 | 111.60 | 3 mm – 5 mm | Equivalent to a 0.0 kW heater |
| 200 | 20.0 | 0.02 | 0.48 | 14.40 | 172.80 | 3 mm – 5 mm | Equivalent to a 0.0 kW heater |
| 250 | 31.6 | 0.03 | 0.76 | 22.80 | 273.60 | 3 mm – 5 mm | Equivalent to a 0.0 kW heater |
| 315 | 50.4 | 0.05 | 1.21 | 36.36 | 436.32 | 3 mm – 5 mm | Equivalent to a 0.1 kW heater |
| 400 | 81.6 | 0.08 | 1.96 | 58.80 | 705.60 | 5 mm – 8 mm | Equivalent to a 0.1 kW heater |
| 600 | 183.8 | 0.18 | 4.41 | 132.24 | 1,586.88 | 5 mm – 8 mm | Equivalent to a 0.2 kW heater |
| 1000 | 530.0 | 0.53 | 12.72 | 381.60 | 4,579.20 | 5 mm – 8 mm | Equivalent to a 0.5 kW heater |
| 1250 | 828.1 | 0.83 | 19.87 | 596.10 | 7,153.20 | 8 mm – 10 mm | Equivalent to a 0.8 kW heater |
| 1600 | 1,324.0 | 1.32 | 31.78 | 953.40 | 11,440.80 | 8 mm – 10 mm | Equivalent to a 1.3 kW heater |
| 2000 | 2,096.0 | 2.10 | 50.30 | 1,509.00 | 18,108.00 | 8 mm – 10 mm | Equivalent to a 2.1 kW heater |
| 2500 | 3,328.0 | 3.33 | 79.87 | 2,396.10 | 28,753.20 | 8 mm – 10 mm | Equivalent to a 3.3 kW heater |
| 3200 | 5,360.0 | 5.36 | 128.64 | 3,859.20 | 46,310.40 | 8 mm – 10 mm | Equivalent to a 5.4 kW heater |
Negligible Impact Below 200A
At current levels below 200A, eddy current-induced power losses are minimal:
- Magnetic fields generated are weak, resulting in small induced EMF.
- Power loss and heat build up are insignificant, posing little to no risk to equipment or efficiency.
- These systems typically do not require additional mitigation or ventilation measures.
Progressive Energy Loss and Heat Build-Up for Higher Currents
For systems operating at higher currents, the heat generated by eddy currents accumulates progressively. The following table shows the power loss and heat build up over time for various current levels.
What Does “Heat in Area” Mean?
The “Heat in Area” represents the latent heat generated by eddy currents in the environment around the ferrous plate. This heat accumulates over time, especially in enclosed or poorly ventilated spaces.
Distance Considerations
The greater the distance between conductors passing through holes in a ferrous gland plate, the less significant the eddy currents become. This is because eddy currents are induced by the interaction of the magnetic fields generated by the alternating current in the conductors. When the holes are spaced closer together, the magnetic fields overlap more, intensifying the induction of circulating currents within the plate. As the distance between the holes increases, the magnetic field interactions diminish, reducing the strength of the induced eddy currents. This results in lower power loss and less heat generation, improving overall system efficiency and minimizing the risk of overheating.
In short, the lowdown.
- Negligible Below 200A:
Systems running below 200A experience minimal eddy current losses, with negligible heat generation. - Significant at Higher Currents:
Systems at 315A and above generate progressively significant heat, requiring ventilation and cooling systems. BUT consider the distance and it could get you out of trouble. The closer you go the more the you increase you P level and the heat will be a consideration. Those magnetic fields become and issue the closer you go. - Real-World Impact of Ferrous Plates:
The heat generated in ferrous gland plates can mimic industrial heater output, especially at 3200A, making effective heat management crucial.
Maybe something to consider… Definitely
Eddy currents in ferrous gland plates with holes are a significant concern at higher currents. While systems under 200A are safe, those running at 315A or more face growing risks of inefficiency and overheating. Proper ventilation, cooling, and material choices (e.g., non-ferrous plates or channel cutting) are essential for safe and efficient operation.
Mr Obvious
In short unless you have no choice use a non ferrous gland plate. It removes a lot of headaches. Obviously this is the real world. If indeed you do have a ferrous gland plate then read this.
Disclaimer:
The information provided on this site is for general informational purposes only and may not reflect the most current regulations or standards. Legislation, industry guidelines, and best practices can change over time, and it is the user’s responsibility to research and ensure compliance with the latest requirements for their specific situation. Always consult a qualified professional for advice tailored to your project or application.
