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Seeking K Coefficient Values for WT-3 gG/gL 80A Fuse Links - Calculation Query

anet870 40194 15
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  • #1 17668644
    anet870
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    Hello. Does anyone of you have or know where to find the K coefficient values for WT-3 gG/gL 80A inserts? I found a value of 11.8 in the Eti table for a switch-off time of 0.2 s, but after calculating 80x11.8 = 944 230/944 = 0.24 Ohm. The permissible resistance value is very low and the value measured in the connector is 0.29 Ohm. In this case, the quick shutdown condition is not met. I wonder if I calculated it correctly and, above all, if I have good data on the K coefficient? Additionally, the table shows switch-off times of 0.4 s. and 5 s. with lower factors. Where can I find information on what conditions to use a given shutdown time?
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  • #2 17668690
    opornik7
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    anet870 wrote:
    Does anyone of you have or know where to find the K coefficient values for WT-3 gG/gL 80A inserts?

    Are you sure it`s an 80A fuse and type 3? In my opinion, type 3 contains fuses from 315-630A.
    80A falls into type 2 (63-630A) and for 80A the k factor is 11.1 at a time of 0.2s.
  • #3 17668729
    anet870
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    Inserts installed in the ars630a switch disconnector in the ZK-4 connector. If I substitute coefficient 11.1, the result is 0.26 Ohm. Can I use the 4 s time factor for calculations? according to the table I have, it is K = 8.6, then the permissible value is about 0.33 Ohm. If so, how can I justify it?
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  • #4 17668748
    Strumien swiadomosci swia
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    anet870 wrote:
    Can I use the 4 s time factor for calculations? according to the table I have, it is K = 8.6, then the permissible value is about 0.33 Ohm. If so, how can I justify it?
    anet870 wrote:
    The permissible resistance value is very low and the value measured in the connector is 0.29 Ohm


    So what should we do, either modernize the cable or go down to 63A/
  • #5 17668762
    opornik7
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    anet870 wrote:
    If so, how can I justify it?

    What does this fuse protect? Why did you adopt 0.2s?
  • #6 17668765
    anet870
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    The project includes 80A protection. New investment. YAKY cable 4x35mm2 between the cable connector and the connector with sockets for powering stage devices, etc. I don`t really want to modernize it because that`s what the project assumes. Before the ZK-4 connector, there is also a measuring system with a 63A power limiter for 40 kW, but increasing the power allocation is not a problem, especially since the set of connectors is next to the pole. Maybe I`m worrying too much?
  • #7 17668773
    Strumien swiadomosci swia
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    anet870 wrote:
    New investment. YAKY cable 4x35mm2

    If it doesn`t work, get one with a larger cross-section.
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    #8 17668774
    opornik7
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    anet870 wrote:
    The project includes 80A protection.

    Are SWZ calculations included in the project?
    anet870 wrote:
    connector with sockets for powering stage devices

    Is this connector class I?
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  • #9 17668794
    anet870
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    Replacing the cable with a thicker one is not a good idea as it will be very time-consuming...
    I did not receive any calculations for the designed installation, only diagrams with descriptions.
    The connector is made of thermoset fiber.

    Added after 4 [minutes]:

    Quote:

    Is this connector class I?


    He is in the 2nd grade
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    #10 17670441
    Miniax
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    anet870 wrote:
    The project includes 80A protection. New investment. YAKY cable 4x35mm2 between the cable connector and the connector with sockets for powering stage devices, etc. I don`t really want to modernize it because that`s what the project assumes. Before the ZK-4 connector, there is also a measuring system with a 63A power limiter for 40 kW, but increasing the power allocation is not a problem, especially since the set of connectors is next to the pole. Maybe I`m worrying too much?


    If this connector with sockets is made in the form of a switchboard: it has its own protections for all sockets and, additionally, it is a permanent connector, not a portable one, and it works in normal environmental conditions, in principle, a time of <= 5 s can be assumed. It all depends on the classification of the device.

    I recommend the study (although I disagree with it on some points):

    https://sep.com.pl/opracowania/opracowania_wykonowanie_pomiarow.pdf
  • #11 17680317
    anet870
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    I reached an agreement with the designer and will use the coefficient K = 5.4 for the calculations for a switch-off time of 5 seconds. The explanation is the same as in the post above by Miniax.
    I have one more question, if I understand correctly. If I calculate the permissible IPZ in the L1-N circuit, I use 230V for the calculations, and if I calculate the IPZ between L1-L2, then 400V?
    The difference is that for 230V the IPZ is 0.53 Ohm and for 400V it is 0.92 Ohm.
  • #12 17680798
    opornik7
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    anet870 wrote:
    If I calculate the permissible IPZ in the L1-N circuit, I use 230V for the calculations, and if I calculate the IPZ between L1-L2, then 400V?

    Buddy, take it slow. Why are you writing about IPZ for L1-N?
  • #13 17681291
    anet870
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    Because there may be a short circuit between L1-N and I want to know the permissible resistance of the short circuit loop for such a case
  • #14 17681312
    opornik7
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    I still don`t understand why N and not PE.
  • #15 17681339
    anet870
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    I made the measurement for a Yaky 4x35mm2 cable and there is no PE there, only in the connector with the sockets there is a division into PE and N and it is connected to the earth electrode.
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    #16 17681342
    kkas12
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    So N`s not there either. So not L1-N but L1-PEN.
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Topic summary

✨ The discussion revolves around the K coefficient values for WT-3 gG/gL 80A fuse links, specifically addressing the calculation of permissible resistance values in relation to switch-off times. The original poster found a K value of 11.8 for a 0.2s switch-off time, leading to a calculated resistance of 0.24 Ohm, which is below the measured value of 0.29 Ohm, raising concerns about compliance with quick shutdown conditions. Responses clarify that the 80A fuse may actually belong to type 2, with a K factor of 11.1 for 0.2s. The poster considers using a K value of 8.6 for a 4s switch-off time, resulting in a permissible resistance of 0.33 Ohm. The discussion also touches on the implications of using different K values based on the classification of the connector and the project's requirements, with suggestions to avoid modernizing the cable unless necessary. The poster ultimately agrees to use a K value of 5.4 for a 5s switch-off time and seeks clarification on permissible resistance calculations for different voltage scenarios.
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FAQ

TL;DR: For fixed connector switchboards, a disconnection time of E5 s can be acceptable; "It all depends on the classification of the device." Choose the K factor accordingly, then verify Zs against your measured loop. [Elektroda, Miniax, post #17670441]

Why it matters: This FAQ helps site electricians and designers choose K and check Zs so WT gG/gL 80A fuses meet disconnection times.

Quick Facts

What K coefficient should I use for an 80A gG/gL fuse at 0.2 s?

Use K = 11.1 for an 80A insert at 0.2 s. 80A belongs to the WT type 2 group, not type 3. "For 80A the k factor is 11.1 at a time of 0.2s." [Elektroda, opornik7, post #17668690]

When is a 5 s disconnection time acceptable for socket boards?

Use E5 s for a permanent connector switchboard with its own protective devices and normal conditions. Classification drives the choice. "It all depends on the classification of the device." Document the device class and environment. [Elektroda, Miniax, post #17670441]

For 5 s, what K value did the designer accept for the 80A case here?

The designer agreed to use K = 5.4 for a 5 s disconnection time. They referenced the same rationale about classification and permanence. [Elektroda, anet870, post #17680317]

My measured Zs is 0.29Ω; does that meet the 0.2 s requirement?

In this thread, no. With K = 11.8 at 0.2 s, Zs_max was 0.24Ω for 80A at 230 V. The measured 0.29Ω exceeded the limit, so quick shutdown was not met. [Elektroda, anet870, post #17668644]

How do I calculate the maximum permissible Zs using K and In?

Follow this three-step check:
  1. Select the target disconnection time and K from the fuse table.
  2. Compute Zs_max = 230 V F (K × In).
  3. Compare with your measured Zs; if Zs > Zs_max, adjust design. Example from the thread: 230 F (11.8 × 80) ≈ 0.24Ω. [Elektroda, anet870, post #17668644]

On a 4×35 mm² YAKY feeder without a separate PE, which loop do I evaluate?

Treat the upstream conductor as PEN until the split to PE and N. Calculate and test the L–PEN loop, not L–N. "So not L1-N but L1-PEN." [Elektroda, kkas12, post #17681342]

For Zs checks, should I use 230 V or 400 V in calculations?

The thread compared both. Using 230 V gave Zs_max ≈ 0.53Ω, while 400 V gave ≈ 0.92Ω. These figures came from the same installation example. Confirm the applicable fault path before choosing the voltage. [Elektroda, anet870, post #17680317]

Is an 80A WT insert “type 3” or “type 2”?

A contributor advised that 80A belongs in type 2, not type 3. They also provided the K value for 0.2 s at 80A. This affects which table row you use. [Elektroda, opornik7, post #17668690]

If quick disconnection at 0.2 s is not met, what should I change?

One recommendation was to redesign the cable or reduce the fuse rating. "Either modernize the cable or go down to 63A." This action avoids non-compliant Zs. [Elektroda, Strumien swiadomosci swia, post #17668748]

Does the connector’s class (I or II) change the disconnection time choice?

Yes, classification influences time selection. A fixed board with its own protections can use E5 s if conditions match. "It all depends on the classification of the device." Document the class in your report. [Elektroda, Miniax, post #17670441]

Where can I find K coefficients for WT gG/gL inserts?

Use the manufacturer’s fuse tables. In this thread, the ETI table informed K for time-based checks. The OP cited K = 11.8 for 0.2 s as an example. [Elektroda, anet870, post #17668644]

Would increasing cable cross-section help meet Zs limits?

A participant suggested upgrading the conductor if the design fails the Zs check. "If it doesn’t work, get one with a larger cross-section." This lowers loop resistance and improves disconnection. [Elektroda, Strumien swiadomosci swia, post #17668773]
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