What Is The Maximum Permitted Zs

December 05, 2021 Post a Comment

Solution 1 Z test max Zs F From Table 41B1 the maximum permitted value of Z s 889 ohms From Table 1C of GN3 F 120 1 Z test max x 889 120 74 ohms. Take a Zs on the busbar terminal of RCBO and one on the L Load of RCBO and you will see what it is adding.

Https Www Electricalsafetyfirst Org Uk Media 1627 Master Earthfaultlooptable Pdf

Option 1 is the most preferred route option 4 the least.

What is the maximum permitted zs. Certainly the maximum Zs for a 30mA RCD protected circuit is nominally 1667 Ohms but it would be unwise to approach this figure in the same way as TT earth electrode resistances. BS 3036 and BS 1362 The other fuse standards in Tables 412 and 414 BS 3036 and BS 1362 remain at the same values as in BS76712008 so the corresponding values of maximum Zs are also unchanged. Calculate the maximum acceptable Z s value of the circuit having adjusted it to take account of temperature.

If you cannot meet the Max Zs then you will need to install additional protection of a 30 mAmp RCD which will protect the circuit from Earth fault condition but not an overload. It all depends on the RCD in use ie from a 30mA 1667 ohms to a 500mA 100 ohms. Nominal Rating A Fuses Circuit-breakers to BS 3871 or BS EN 60898 or RCB0s to BS EN 61009 BS 88 gG Parts 2 and 6 BS 1361 or BS 1362 BS 3036 BS 88-2 Fuse systems E bolted and G clip in BS88-3 Fuse System C Type 1 Type 2 Type B.

For instance when conducting a PIR the Maximum permitted Zs for a 32A MCB would be 144Ω yet a circuit would fail if the measured Zs is greater than 1152Ω. For types and rated currents of general purpose gG fuses other than those mentioned in. The maximum permitted Zs values for 60947-2 protective devices vary between different manufacturers for instance 60947-2 Merlin Gerin Zs values are different to 60974-2 Eaton Zs values and 60947-2 Square D max Zs values are different to 60947-2 Dorman Smith max Zs values.

BS7671 Max Zs and Maximum Measure ZsIve asked 3 of my lectures but have yet to get an answer to this question. If it is the unit adding it to your reading then make a note on cert and put 1667 as maximum Zs for that circuit only. Maximum measured values of earth fault loop impedance Zs The values of maximum earth fault loop impedance Zs given in Tables 412 413 and 414 in Chapter 41 of BS 7671.

We then give the Report to the customer who then struggles to understand why a circuit has failed due to high Zs when the schedule clearly shows that the measured Zs are below the maximum permitted. MAXIMUM EARTH FAULT LOOP IMPEDANCE VALUES FOR OVERCURRENT PROTECTIVE DEVICES IN COMMON USE FOR FAULT PROTECTION For fault protection the limiting values of earth fault loop impedances Z s are given in Tables 412 413 and 414 of BS 7671 for many commonly-used overcurrent protective devices. To satisfy the requirements of Chapter 41 of BS 7671 for the earth loop impedance the measured value of Zs as described in the above examples should not exceed 80 of the required values as given in Table s 412 to 414.

The question is why is the maximum permitted measured Zs BS7671 Max Zs x 08 appendix 3 page 363. In the 2391 as you do not have the regs you use the 75 rule. Here we find that the maximum Zs value for 20 A BS 88-3 fuses is 204 ohms.

The Max values in 41B1 41B12 and 41D. If you have TNCS TNS system check that the Ze is below the required limit as said 035 08 ohms. From Table B8 of the OSG the correction factor is 106.

Maximum measured values of earth fault loop impedance Z s The table below provides maximum values of Zs for fuses and circuit breakers. 41146 Where a fuse is used to satisfy the requirements of Regulation 411322 maximum values of earth fault loop impedance Zs corresponding to a disconnection time of 04 s are stated in 2 for a nominal voltage UI of 230 V. Table 2 Maximum measured values of Zs for circuit-breakers or the overcurrent characteristic of RCBOs Based on information as at January 2015 Maximum measured values of earth fault loop impedance Zs Rated current A 04 sto 5 Type 1 Type 2 Type B Type 3 and C Type D Circuit-breakers to BS 3871 or BS EN 60898 or RCBOs to BS EN 61009.

Hope this helps CJS 0. May 21 2016. Therefore the maximum measured 175 Ω 104.

I have my own theory but would like to ask if Im on the right track or not. 2008 for commonly-used overcurrent protective devices should not be exceeded when. It then warns you in a note below the table that the rod resistance shouldnt be above 200 ohms because it could be unstable.

From Table B6 of the OSG the maximum measured Z s value is175 Ω at an ambient temperature of 10 o C. If you go table 415 in the regs it gives you the values of Zs for a TT. There is no 80 rule the appdx 2 values happen to be approx 80 so the NICEIC use that as their rule.

Really this column is only there to make sure that the Zs has been checked for the circuit for whatever CPD is fitted.

60947 2 Max Zs Charts Mccb Zs Tables Pro Certs Software