10 important (generally neglected) points to ensure electrical safety in LV installations

Electrical Safety and Fire due to Short Circuit


Electrocution and fire due to short circuit are common in our electrical installation in residential, Commercial, and Industrial premise. Annually about 1000 people and property worth 1000’s of crores of rupees is being lost due to these accidents.


The webinar explains 10 most important electrical safety methods to be adopted in a low voltage electrical installation in order to avoid accidents from the wiring and usage of electricity, including SOLAR PV and Electric Vehicles.


The webinar was participated by >200 engineers, including Shri V Suresh, Vice chairman of National Building Code, Shri Bhavani Prasad, Director General (Retd.) of CPWD and many more important personalities.


Video of the webinar Introduction


Video of the webinar main presentation


Video of the webinar Q&A



Question

Answer

Faults and failure in Electric Safety and related fire safety - is it due to : 1. use of substandard electrical materials and appliances; 2.unsafe poor quality installation practices 3. lack of skilled trained certified work force or electricians or 4. lack of in depth supervision?

All the four contribute in a general scenario. How ever in an industrial and commercial building, the use of substandard products are less, where as wrong installation practices are more. (in fact installation and safety standards are not followed)

Do you feel there is lack of full in depth awareness of all regulations under CEA by practitioners?

YES

​would it be desirable to license the practitioners for compliance capabilities and capacities?

Yes. The state governments are yet to implement Chartered Electrical Safety Engineers, which is included in the regulation in 2015.

Is there laxity in electrical inspection and enforcement from electrical inspectorate? Is is capacity constraints in EI team ?

Electrical Inspectorates can not make the tests as per IS732. Inspectorates shall regularise chartered electrical safety engineer to handle this massive job.

Do you have annual/periodic inspections and audit in existing buildings with full occupancy and electrical load

Yes We do it as per IS732 (IEC 60364-6) and National Electrical Code of India

The exposed live electrical wires in the buildings and ducts pose danger??

Yes, if they are accessible.

lightning protection is an important element in tall Buildings and Towers-- How are provisions in NBC and NEC and IER to deal with this? are these compliant with latest IEC /global norms? Is this being monitored or audited by electrical practitioners/ enforced by Electrical Inspectorate?

LPS as per NBC is confirming to the latest global standard IEC 62305. Regulations recommend to carryout LPS as per code of practices of BIS. How ever non standard LPS (such as ESE/DAS) are more installed due tot he lack of awareness in the subject.

what is electric insulation coating.

coating (of insulating paint or resin) in floor in order to avoid shock (increase floor resistance)

What is RCD test

Testing of the disconnection time and disconnection current of an RCD with a RCD test meter.

How to take care of electrical meter fire. In our building transformer outlet comes to a bus bar & an Isolator having fuses. Meter & upstream belongs to Maharashtra Electricity and downstream belongs to society. Meter was changed & working fine showing no problem on downstream side.

Probably due to insulation failure in meter. If the meter is installed before the incoming fuse, it is a problem. If the meter is after fuse, then the fuse is supposed to disconnect before the meter catches fire. Ask the utility company to verify.

Still we have to go for plate earthing for neutral earth or is there any advanced earthing now.


You have to implement a TN-S system in your factory, where plate or rod is not important.

Can we use copper rod earthing for neutral.

The question is about the concept two for neutral (copper), two for body (GI). This concept itself do not exist and is wrong

33kv cable punctured?? lv side load was only 300amps. then what can be the reason for cable puncture on the HT side? is it due to earthing issues?

​Insulation failures are due to reasons related to voltage. (if there is no mechanical reason) In an unearthed system over voltages will be higher as a result higher insulation is necessary.

Kindly forward technical slides regarding fault current calculation

Sorry, we don't share any slides. You have to refer video of the program

We are eager to understand earthing / bounding requirement for Solar PV system, request to put some light on this, if possible.

Sorry due to time constraint, we could not cover it today. we will do it in the next webinar.

After 12 years is there a necessity to revamp earth pits...like replacing chemical earthing and plate earthing.

​Please carry out a test and decide

Do the Electrical Inspectors have the Power to Overcome or Byepass the Indian standards and take any decision to alter the installation for the purpose of ensuring safety??

NO. They are supposed to follow CEA safety regulation. They can not violate regulation and standards.

briefly explain about fault loop impedancee.

​The impedance of the earth fault current loop (phase to earth loop)

starting and ending at the point of earth fault. This impedance is denoted by the symbol Z. The earth fault loop comprises the following, starting at the point of fault:

a) the circuit protective conductor;

b) the consumer’s earthing terminal and earthing conductor, and for TN systems, the metallic return path;

c) for TT and IT systems, the earth return path;

d) the path through the earth neutral point of the transformer;

e) the transformer winding; and

f) the line conductor from the transformer to the point of fault.

Why TNS is suitable for Data Centre Buildings. Since there are multiple Trafo and DG in data center Buildings, a Lot of neutral pits (2 per neutral) by code and dedicated Network Earthing will be there. this will increase the number of pits to 200 pits.

Multiple Transformer and DG in a small area is the reason for implementing TN-S system. You can not implement TT in such applications and is illegal according to the regulation and standards in India.

What should be the earth resistance of an earth pit, is it different for different applications

For TT system earth electrode is mandatory. The IS code says if you use 30 mA RCD, the earth electrode resistance can be up to 1666 ohms

How do identify class2 and class 5 wires? what in the case of ALAR cables of higher size...is there any standard that only certain class cables to be used.

Pl check the documents of the manufacturer.

Which standard applies to the limitations on Neutral current due to triplent order? Limiting the neutral current at the feeder level, rather than installing a K-rated transformer, will considerably prevent fire accidents, in my opinion. A dangerous situation is when the neutral is disconnected due to a high current.

There are two points in the question. In order to achieve safety once when the neutral is over loaded, it shall be sensed and line conductor shall be disconnected. Never disconnect Neutral first.

Are the annual electrical inspections conducted by CEIG - a sample inspection or expected to be exhaustive inspection of all common electrical installations especially in hi rise buildings/ apartment complexes

CEIG will only make an over all inspection. The tests in the standards shall be carried out by the owner with the help of chartered electrical safety engineer.

How to withstand RCCB in existing hospital installation having UPS & inverters & load on UPS & inverters is supplied with common Electricity board neutral. instead of separate neutral for UPS load.

Sharing common neutral is illegal and against safety rules. please refer IS732, clause 4.5

Is there any difference between earthing and grounding?

NO. Both are same. Grounding is used in USA. Earthing shall be used in India

It is reported that in Mumbai, almost 70% fires are related to improper wiring and short circuits and 39% of the installed fire systems are dysfunctional.

So we have a double whammy.


The MFB CFO, has suggested that Joint audit by the fire auditor and electrical safety inspector is important.

Given the acute paucity of competent electrical safety inspectors ,what is the solution.

Conduct electrical safety audits as per IS 732. Cape have trained engineers to carryout this.

in our building we have 40 yrs old of electrical wiring .can you explain is this necessary to rework of each and every elecrtical lines??

Conduct electrical safety audits as per IS 732, based on the result you can decide. Cape have trained engineers to carryout this.

If distribution box have 16 Amp MCB and overcurrent occurred almost 40 Amp. But why are the cause for MCB does not trip? although MCB is good condition.

Check the type of MCB and find out the disconnection current and time. If its not disconnecting, replace it.

fault loop impedance can be done for source LT panels to determine ACB protection.

Preferably do it for the final circuits, but test can be carried out anywhere in a circuit

which equipment is advised to protect against TOV?

Proper implementation of system earthing such as TN-S, TT etc and decide how HT earthing is carried out.

As per NEC 2011 , for good earthing, the earthing value is should be less than 5 Ohms for low voltage systems. But, here in Amravati Maharashtra the electrical inspectorate is asking for earthing value lesser than 2 Ohms. Can you tell us what value is considered sufficient for 433 V systems?

for 433 volt system, earth electrode resistance of both 5 or 2 ohms is not necessary. Try to implement protective equipotential bonding in your building, if it do not exist.

In the market the chemical earthing is considered as maintenance free method of earthing. But, our measurements suggest that, the value changes substantially as the time passes. Can you tell us what type of earthing is necessary for low voltage systems?

TN-S earthing is recommended. Earth electrode and chemicals are immaterial.

For temporary unit set up at such as construction work, DG 125KVA using for getting power, How can we prepare earthing to get in <1 ohm, Soil is Dry land such as sandy area (desert), we always getting 3 ohms only. Any solution for this??

Neither 3 ohm nor 1 ohm is going to help you. Install an RCD of 30 mA in the main switch board. earth electrode value can be even as high as 25 ohms.


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