The following table lists the recommended minimum sizes of earthing conductors.
Note: This serves only as a guide, calculations are still required for verification.
| Nominal size of active conductor mm² | Nominal size of copper earthing conductor | |
|---|---|---|
| mm² | ||
| With copper active conductors | With aluminium active conductors | |
| 1 | 1* | - |
| 1.5 | 1.5* | - |
| 2.5 | 2.5 | - |
| 4 | 2.5 | - |
| 6 | 2.5 | - |
| 10 | 4 | - |
| 16 | 6 | 4 |
| 25 | 6 | 6 |
| 35 | 10 | 6 |
| 50 | 16 | 10 |
| 70 | 25 | 10 |
| 95 | 25 | 16 |
| 120 | 35 | 25 |
| 150 | 50 | 25 |
| 185 | 70 | 35 |
| 240 | 95 | 50 |
| 300 | 120 | 70 |
| 400 | ≥120+ | ≥95+ |
| 500 | ≥120+ | ≥95+ |
| 630 | ≥120+ | ≥120+ |
| >630 | ≥25% of active size+ | ≥25% of active size+ |
* - May be used only when incorporated in a multicore cable
+ - A larger conductor may be required.
Source: AS/NZ 3000-2007, Table 5.1
Update (29-Jan-2011):
Calculating the fault loop impedance of a circuit will provide a more precise selection of the size of the earth conductor. See the article on fault loop impedance for more details.
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Can you please mention the source(Standard) behind this Table.
If not a Standard, might be calculations.Can you please share it.
Thanks & Regards
Hi, Shams-ul-Hassan,
I have added the source as requested. Thank you for visiting my blog.
thanks for the blog but i am still having problem with my water heater.
when earth conductor is connected to the heater earth terminal i feel a slight shoking sensation. when the earth conductor is disconnected i dont get the feelings. pls what does that suggest. i feel very uncomfortable putting it into use.
pls could you assist me with possible solution to the problem.
thanks
You need to verify the integrity of the earth conductor. A qualified technician may be able to do it.
thanks for the blog but i am still having problem with my water heater.when earth conductor is connected to the heater earth terminal i feel a slight shoking sensation. when the earth conductor is disconnected i dont get the feelings. pls what does that suggest. i feel very uncomfortable putting it into use.
+1
can u pls help me getting those formulas for designing earthing conductors.
There is no single formula in calculating earthing conductors. You need to know the earth fault currents, touch and step potentials and earth resistivity.
However, if you refer to local standards in your area, there will be a recommended minimum size of earthing conductors. It will save you some calculations.
Dear Ver,
I have an Earthing Design calculation & I would like to share the same with you to clarify my doubts. Pls provide me your maiID
@Balamurali Dev
Please send it to this address
spa102000-contact@yahoo.com. Thanks. Verver thanks for your so important details.I am Rizwan ,Electrical engineer.Though I am not design engineer,but some times to verify design calculations.I need to calculate the earthing conductor size for A.C equipment Air Handling Unit(30KW motor) fixed on roof, open area. It has metallic body & can be used as lightning protector.
Dear VER
Can you tell the method of selection for the earhting wire for the MDP or SMP in the multy storey buildings . What we have to follow ? your table will help for this
Hi BASAVARAJ,
In IEC 60364-5-54:2002, Article 543 Protective conductors
543.1 Minimum cross-sectional areas
543.1.1 The cross-sectional area of every protective conductor shall satisfy the conditions for automatic disconnection of supply required in clause 413.1 of IEC 60364-4-41 and be capable of withstanding the prospective fault current.
The cross-sectional area of the protective conductor shall either be calculated in accordance with 543.1.2, or selected in accordance with table 54.3. In either case, the requirements of 543.1.3 shall be taken into account.
I have a 3MVA Transformer rated 13.80kv primary/380V secondary 3-phase. The %impedance is 8%. What would be the short-circuit current and the size of secondary earthing conductor.?
@ray: your question is difficult to answer with that data you provided. The size of your earthing conductor depends on the standard you are using, the type of load you have and the type of installation. A cable installed on cable ladder will have different current-carrying capacity to a cable inside a conduit or a direct-buried cable.