Earthing Line Current

Hello Guest,

Please advise the following:

1. Equipment (Motors/Starters etc) Voltage
2. Equipment (Motors/Starters etc) age
3. Type of Cables to Equipment (Motors/Starters etc)
4. Size in kW of connected equipment.(Motors/Starters etc).
5. Were Power Factor correction Capacitors used at the motor/s? - Advise size/s in kVAR please.
6. Advise Make/model of Frequency Inverter.
7. Type of Power Supply network: MEN (Multiple Earthed Neutral) - other - advise please.
8. Resistivity of local ground (Gravel, clay, swamp bottom, river bank etc) - advise please.
9. Other relevant information - Advise please.

It is normal to have earth Currents flowing in many Industrial installations.

Capacitance and leakage in older equipment is the main cause of Earth Current.

What type of meter did you measure the Earth Current with? (Digital instruments often give incorrect readings).

Reply here, with

Kind Regards....

Hi Sparkstation,

Here is the information that i still remember;

1. Equipment voltage is 380Vac for case 1, 415Vac for case 2

2. Equipments are new (during that time commissioning)

3.Type of Cable, actually not very clear.

4. Size of kW, there have 4kW, 15kW, 22kW

5. PF (dont know)

6. Frequency Inverter is Commander, 11kW

7. Type of Power supply network (dont know because not in my scope, as customer just supply the 3 phases supply to us)

8. Resistivity of local ground, for case 1 the site at Bangladesh i think should consider as gravel, for case 2 the site at malaysia but i dont know how to category it, but nearby got plantation.

Actually both case commissioned quite some time, so many things just try to recall back, sorry for any information that i can't provide in detail.

The meter i used to measure the earth current is digital clamp amp meter.

Hope those information will help. Thank you very much

Vince

your doubt has two dimensions .

1. its possible that these is continious leakage current in system beacause of hiegher earth resistance and surely it may damage the life of equipment if operated for more length of time .

2.Additionaly it may crease a cause of accedent because if there is continious earth leakage more than set value and equipments are in operation bypassing the protection this bound the give detoriation in system insulation level and any time it may give short or trip the system from next level co-ordination.

2 nd aspect may be there are earth leakage current due to unballance load in system , this leakage current too is allowed to certain level that will depent on system design and system insulation level and this will not harm the system even if continious for long time if with in limit.

hope i have cleared your doubt .do wtrite back.

regards

veer

Hi veer,

Thanks for your reply.

1. If the system has balance load, low earth resistance <5 ohms. Can i say that, leakage current will not exist? All equipment work well

2. If the system has balance load, high earth resistance >5 ohms. Can i say that leakage current will generate? All equipment life cycle shorter?

3. If the system has un-balance load, low earth resistance <5 ohms. Leakage current generate and all equipment work well in normal condition?

4. If the system has un-balance load, high earth resistance >5 ohms. Worst case.

How can i judge that the system is balance load in proper way?My understanding is use clamp amp meter measure each phase current, if each phases got similar amp reading, consider balance?

Thank you very much

With regards,

Vince

"With this two cases, everything is working properly. My doubt is other than the current is danger to human, who touch the earth bar, what is the other danger effect? Does this current damage the equipment slowly and the life cycle of the motor will become shorter?"

Danger?

Until earth wire of right Resistance is there, and earthed properly, its not a big danger.Because for human body, its potential difference that matter not a current that flow in cable. even if the earth resistance is as worst as 5 Ohms, that can only drop 35 Volts across it. at a current of 7amps,

Second point is it hurting any of your equipments? may be yes or may be no. and for that you need to know why such a high current is there in you earth line. it may be capacitive current that is formed between stator of a motor and its winding, or may be due to winding shorting to it stator.

Lets say you have 1000 Motors and transformers there, each have an average Leakage capacitive current of 1 mA, that can lead to a total current of 1Amps, In that case it is not going to hurt your equipments, But if the current is due to any short circuit of winding with body, then its certainly going to hurt equipment life,

Below pics can help you somewhat

Hi Rakesh semwal,

Thanks for your explaination.

Regarding " even if the earth resistance is as worst as 5 Ohms, that can only drop 35 Volts across it. at a current of 7amps", my understanding is with voltage drop of 35 volt in earthing line, with high resistive of human body even human touch it, it would not harm to us. Am i right?

From your second point, how can i measure and found out the capacitive / leakage current that is formed between stator and winding of a motor or shorting between them?

From your example, the total leakage capacitive current is 1 amp or higher. This current reading is higher that ELCB protection setting, how can we solve the problem? Change new motor? I believe 1mA leakage current generated by motors are actual fact, what can we do to solve this problem in order to let the 1000 motors run?

Thank you very much

With regards,

Vince

Hi, Guest!

Surprise! (It's always a surprise the first time you see it.) It's perfectly normal to find current in neutral and earthed lines. They cause no damage, since they are, except for the instance of feedback, completely ineffectual and change nothing in terms of operational parameters.

Turn off (lock out) the hot current common to any fixtures/appliances/machinery that share those neutrals/grounds, and don't ground yourself when you're working with them, and nothing will happen when you touch them, either.

Mark

It would be wise if you are worried to measure the current in the earth connection at each machine, if this picks up a large earth current at a particular machine it should be inspected for possible faults. If it turns out to be that your individual earth currents appear to be a small part of the total you should check the continuity of your neutral wiring.

The purpose of the ELCB is, or was, to protect humans downstream in the event of a fault developing. Removal of the ELCB removes the protection.

Fault currents of 3-7A indicate a number of errors in the neutral and earth connections downstream of it. Eliminating the faults and reinstating the ELCB is a good way of assuring personal safety. To do otherwise, knowingly, increases one's risk of liability in the event of a fault developing and someone getting hurt/killed.