What if the earth loop impedance be too high? However should the resistance is too high, the circuit protection may not operate at all. As a user of electrical items you may not notice any issues, however over a period of time your equipment around you my start to deteriorate (stop working or catch fire).
What is the possible problem if the earth loop impedance exceeds the requirement?
Consequences when performing earth loop impedance tests
Inadvertent disconnection of a circuit, group of circuits, distribution board or even a whole installation could occur if an RCD operates when an earth fault loop impedance test is carried out.
What does high earth loop impedance mean?
The higher the impedance, the lower the fault current will be and the longer it will take for the circuit protection to operate. So in short it is the impedance of the earth fault current loop starting and ending at the point of earth fault.
How can earth fault loop impedance be improved?
Increase the size of the PE or PEN conductors and/or the phase conductors, to reduce the loop impedance.
What do I do if my Zs is too high?
If a Zs value is high, then you need to establish whether it is due to circuit conditions, supply conditions, or a fault. You can then descide the appropriate course of action. Just installing an RCD or RCBO may not be the solution in a deteriorating installation.
What is maximum earth loop impedance?
Tables of maximum earth fault loop impedance
3 gives the maximum Zs value of 1.37 ohms at a nominal voltage (U0) of 230 V. This compares with 1.44 ohms in the same table of the previous version of BS 7671.
What is the purpose of earth fault loop impedance?
Should there be a fault in an electrical circuit, an earth loop impedance test is conducted to ensure the fault current will be strong enough to set off the circuit protection. If a fault current is undetected or not disconnected fast enough, circuits can overheat and catch fire.
What is the acceptable earth resistance value?
Ideally a ground should be of zero ohms resistance. There is not one standard ground resistance threshold that is recognized by all agencies. However, the NFPA and IEEE have recommended a ground resistance value of 5.0 ohms or less.
How do you test an earth loop impedance?
The total earth fault loop impedance is measured by plugging a loop tester into a socket outlet, or in some cases with an external earth probe. The value of the earth fault loop impedance is the sum of the resistances.
What does a successful ZS test prove?
A Zs test is not to prove an earth connection exists, although it would do so, but to prove that the CPD would operate within the time required by BS7671. Smpling should be of circuits, not equipment of a circuit that is being tested.
How do you reduce Ze?
Zs can be reduced by reducing cable length or increasing cable size but Ze is in a TN system set by the supplier not the consumer in which case the supplier should be contacted with TT system i.e. you have an earth rod. Then adding more metal should improve the reading.
What should my Ze be?
We all know the 17th edition states that the maximum ZE should be 0.35 ohms. That figure is for TNCS, you said your supply is TNS which should be a max. of 0.80 ohms.
What is the acceptable earth resistance value in South Africa?
The system is not recommended for use in South Africa. 8.6. 5.2 Where a Neutral conductor is provided, test the Neutral loop impedance for all low voltage distribution systems.
8.6 Testing – SANS 10142-1 :2020 Edition 3.
| 1 | 2 |
|---|---|
| Rated current of protective device | Maximum resistance of earth continuity path |
| 50 | 0,184 |
| 63 | 0,146 |
Should ZS be higher than Ze?
So, would you fill in the forms as follows Zs 39 ohms and Zs for sockets 0.79 ohms, or would you say Zs is 39.41 ohms given that Zs strictly speaking is the sum of Ze and R1+R2?
See Also:
| Technical discussion forums | |
|---|---|
| · | Wiring and the regulations |
| · | Other and general engineering discussions |
| Archived categories |
What does a high Ze reading mean?
High ZE readings essentially refer to earthing arrangements in the property. High readings could be due to a wiring fault on the earth cable.
What is a good earth fault loop impedance reading?
The value of external earth loop impedance (Ze) measured or otherwise determined in accordance with Regulation 313.1 may differ from the applicable typical maximum value declared by the electricity distributor, which is usually: 0.8 Ω for TN-S system. 0.35 Ω for a TN-C-S system.
What is a good earth loop reading?
It is generally accepted that, where the measured earth fault loop impedance of a circuit is not greater than 80% of the relevant limit specified in BS 7671, the impedance can be expected to be sufficiently low under earth fault conditions to meet the relevant limit specified in BS 7671, and for the protective device
How does earth fault loop impedance affect disconnection times?
If the earth fault loop impedance is too high then disconnection of the protective device will take too long due to the earth fault current not being high enough for the protective device to meet its maximum disconnection time.
What is a Ze reading?
`Ze` is a measurement of the external earth fault impedance of the installation. It is the measured resistance of the supply transformer winding, the supply phase conductor, and the erath return path of the supply. `Ze` can be obtained by enquiry to the electricity supplier or by direct measurement at the supply.
What can cause an earth fault?
Common causes of ground faults
- Water, which is a conductor of electricity, leaks into an electrical box.
- Worn or damaged wires.
- Loose connections, for instance, a hot wire not being properly secured in a terminal.
- Miswiring can cause the flow of electrical charge to connect with another pathway to ground.
What is maximum value beyond which the earth resistance should not be increased?
However, the NFPA and IEEE have recommended a ground resistance value of 5.0 ohms or less. The NEC has stated to “Make sure that system impedance to ground is less than 25 ohms specified in NEC 250.56. In facilities with sensitive equipment it should be 5.0 ohms or less.”
