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Charanjeet
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Join Date: Mar 2010
Posts: 7

Earthing for a Residence

01/08/2012 3:59 AM

Dear All

Happy New Year & Seasons Greetings to all at CR4

We are constructing residential Building for own use, It has six floors and common Lift and Generator 62.5 KVA to be placed on roof top.

Kindly help me to know details about earthing

Details are as under

1) There is one 3 Ph supply with neutral incomer from pole of electric company in front of the building and is distributed through a common distribution panel located at ground floor to six floors

2) There are six separate energy meters for each floor and also a sub meter for some portion of building on each floor and other protection devices fitted in distribution panel.

3) Separate seventh energy meter Common for Lift is also fitted in common panel

4) Combined load is 80 KW

5) Load on each floor is different and it varies from 10 to 20 KW

6) Generator is common for entire building and capacity is 62.5 KVA

7) Soil Resistivity is in range of 14-20 Ohms

Details required are as below

a) Do we need separate earthing electrode for each floor or we can have single earthing electrode for lighting load.

b) Do we need separate earthing for Lift and numbers of electrodes

c) Do we need install separate earthing for Generator and numbers of electrodes

d) What should be the fault carrying capacity of electrode for each application

e) What should be the resistance value of electrode for each application.

f) What are permissible levels of electrode resistance for Residence, Lift & Generator

Thanks
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SolarEagle
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#1

Re: Earthing for a Residence

01/08/2012 8:02 AM

These should be determined by local code guidelines....imo, every meter should be independently grounded, as well as lift and common panel....The building should have separate grounding for lightning protection...

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lyn
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#2

Re: Earthing for a Residence

01/08/2012 9:04 AM

Hire a competent LOCAL electrical contractor. Asking for long distance advice from strangers about something that has the potential to kill people or burn the building to the ground is irresponsible, if not criminal.

You probably aren't worried about liability, so maybe it doesn't matter.
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abasins
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Location: Pakistan
Posts: 126
#3

Re: Earthing for a Residence

01/08/2012 12:01 PM

I am just kind of wasting time posting to this forum but just to reply to your many queries would be hard and the two...

1) You would need earthing system for the main panel on ground floor, main supply.

2) You would need separate earthing system for your emergency power genset. Genset on ground floor (not on top floor -roof)

3) Earthing could be dropped to each floor from the main panel on first floor.

I would not like to solve the entire thing for you, cuz it would be time consuming....

For body earthing you would need star connection of pits if more than one (all I can say) ....

Hope that helps....:)

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lyn
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#4

Re: Earthing for a Residence

01/08/2012 12:18 PM

This concerns me greatly. Why don't you have an engineer on staff for these design issues?

If you get it wrong, people may die.
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wareagle
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#5

Re: Earthing for a Residence

01/08/2012 4:59 PM

Details are as under

1) There is one 3 Ph supply with neutral incomer from pole of electric company in front of the building and is distributed through a common distribution panel located at ground floor to six floors

At this location there should be a main disconnect. A grounding electrode should be install here. Type requirements will depend on your local code. Suggest at lease 2 ground rods along with bonding the water pipes and building steel

2) There are six separate energy meters for each floor and also a sub meter for some portion of building on each floor and other protection devices fitted in distribution panel.

A bonding conductor of the proper size should be installed along with the feeder circuit from the main switch to each meter location

3) Separate seventh energy meter Common for Lift is also fitted in common panel

Same as #2

4) Combined load is 80 KW

5) Load on each floor is different and it varies from 10 to 20 KW

6) Generator is common for entire building and capacity is 62.5 KVA

Depending on whether you switch the neutral or not determines the proper

Grounding technique for the generator. Local code dictates.

7) Soil Resistively is in range of 14-20 Ohms

Details required are as below

a) Do we need separate earthing electrode for each floor or we can have single earthing electrode for lighting load.

You only need one grounding electrode for the whole building. If you should choose to

Install more, they should all be bonded together with proper conductor size determine by The local code.

b) Do we need separate earthing for Lift and numbers of electrodes

All you need to do is bond the lift to the one and only grounding electrode with proper

Conductor size per local code.

c) Do we need install separate earthing for Generator and numbers of electrodes

Depends on if you choose to switch the neutral. I would not switch the neutral so you

Need to remove the generator neutral to frame bonding conductor. Use the building equipment bonding conductor from the main switch to ground the generator frame

.

d) What should be the fault carrying capacity of electrode for each application

You need to determine the fault current first. What will it be?

e) What should be the resistance value of electrode for each application.

There is only going to be one electrode at the main switch. What's with is wanting to drive electrodes all over the property.

f) What are permissible levels of electrode resistance for Residence, Lift & Generator

If you decide to install a grounding electrode here,(I would not) it must be bonded to the

Grounding electrode at the main switch. You have an equipment grounding conductors to each of these sites. Why do you need an electrode?
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abasins
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#11
In reply to #5

Re: Earthing for a Residence

01/09/2012 10:20 AM

He would be needing a neutral earth system, as I have mentioned earlier, for the generator set. For body earthing of the genset could be connected to the body earth system designed for the main panel. What else? Earth conductor size for each installation would need calculation of the entire design? The local code require all the pits (if more than one or two with grounding electrode downed) for body earthing (bldg.earthing) should be connected in star connection. As far as my limited knowledge, the lift's electrical supply by means of Isolator (switch) can be earthed from the main earthing system (Panel) via SMBD _Essentials or whatever name. -SMDB, sub main distribution board on each floor. DB -distribution board for each premise on floor (may be 2 or 3 or 4 flats etc...)

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ianeil18
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#12
In reply to #5

Re: Earthing for a Residence

01/09/2012 10:15 PM

I'm so curious, that neutral coming from the pole, is that from primary or secondary side of the transformer? Or atleast, in your area in the world, what does your code says? Thanks.
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abasins
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#13
In reply to #12

Re: Earthing for a Residence

01/10/2012 11:38 AM

OK, earth fault current flows/directs to ground through earthing system. Whether neutral or body. The transformer neutral is connected on secondary side. [Note: Generator neutral be separate. And all installation from top to bottom of building, ranging from sockets (receptacle in America), lighting points etc. be run/connected into the main earthing system and eventually ground (earth)].

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ormondotvos
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#6

Re: Earthing for a Residence

01/08/2012 10:56 PM

Questions like these serve to remind me of the vast gulf between the USA, with its electrical codes, inspectors and licenses, and the majority of the world, where this sort of guessing game goes on.

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Phil D.
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#7

Re: Earthing for a Residence

01/09/2012 1:43 AM

Is the generator isolated and mounted to be vibration proof ?

I have thoughts of the vibrations going throughout the building, along with the engine noise !

Easier servicing from the ground floor - fuel, coolant, equipment monitoring etc.
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electricalexpert65
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#9

Re: Earthing for a Residence

01/09/2012 7:11 AM

Immedately get a copy of each of the following & sincerely go thro the same:

i) The Indian Electricity Rules, 1956 (latest amendment)

ii) IS 3043-1987 (latest amedment)

iii) IS 732-1989 (latest amendment)

iv) The Indian National Electrical Code 2011

Until and unless you follow whatever has been said in the above documents, pertaining to your instllation, NEVER permit anybody to occupy any of the dwellings.
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Wal
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#10

Re: Earthing for a Residence

01/09/2012 10:18 AM

OP is obviously not a practitioner of the electrical arts.

Asking for help is a good thing. If you have to DIY then more knowledge is better but be aware that a little bit of knowledge may be dangerous and ultimately expensive.

Other respondents have provided sound advice.

The genset location and capacity are a worry to me. 80Kw loading and only 65kVA genset. Hmmm, doesn't quite add up. Will all loading be via an ATS/AMFswitch or will you load shed when running on genset?

Is your street or building curtilage big enough to accommodate a mobile crane to lift the genset onto the roof? If so will it be possible to get a crane in again when it is time to replace the genset in the future?

You could dismantle the genset for removal (done that) but this is not such a good idea for reliable installation. Then there is fuel delivery/storage to contend with. Place the genset at street level if you can. Access matters.

Your soil resistivity would be 14-20 ohm meters, not ohms. This is quite low and you could expect to achieve resistance to earth of 4 ohms or even less quite easily but it should still be implemented correctly especially with such low soil resistivity which may test "good" even if physically inadequate. It's easy to hide shabby grounding practices with your locale's soil condition. The survey was correctly performed right?

6 floors? An elevator? A genset? Quite an investment!! Hire an electrical engineering consultant to prepare some specs, design the reticulation and subsequently sign off on the work. This is the wrong place to save money.

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abasins
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#14
In reply to #10

Re: Earthing for a Residence

01/19/2012 2:09 PM

BS 7430:1998 - 10.2

R = (ρ/2∏L)[Loge(8L/d) - 1] ------(1) Where: L = Length of the rod in m, d = Diameter of rod in metc.Note : As per the local regulation in UAE, the earth resistance value of less than 10Ω is required for a customer earth system. Also steel-cored copper rod of diameter 19mm (19 X 10¯³m) drive to a minimum depth of 3m housed inside in an inspection earth pit of 300mmX300mmX300mm as per local regulations. But the manufacturer has 1.2m rod length available. Therefore coupling to 3 meters needed. The given ρ, by the original poster, in his country area = 14Ω-m,Using the above equation (1). R = 4.3Ω
That is it. One pit with 3m rod could have less than 10Ω earth resistance.However, if go for the ideal case of less than 1Ω,then using all the above two equation on top, including equation 1, and the rest info of soil R, length 3m, diameter 19mm; S = 6m (twice the length of the rod). etc; Then R(6) = 0.9Ω which less than 1Ω That would need six pits connected in star connection. If we increase the length of the rod in the above equations, we could reduce the number of rods in parallel (and pits too)....
Now coming to the total load = 80KW. That would require an LV cable 4CX70 mm²XLPE/SWA/PVC/CU. This should run from the PMT's HDCutout or DPanel to the customer's electrical room on ground floor.For earthing 1CX35 mm² PVC/CU/ECC. MCCB size = 160A.
For generator set KVA = 62.5; KW = 50; MCCB = 100A; Cable = 4CX35 mm² (RYB and N); ECC = 1CX25 mm²
For Lightning Protection System, separate electrode and pits needed. That is a separate calculation. As a rule of a thumb minimum one pit at each corner of the building......Read all my posts above and below to have a clear understanding. Hope that helps....:)

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PWSlack
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#15

Re: Earthing for a Residence

07/01/2024 7:58 AM

It sounds as though the <...We...> needs to consult a local Electrical Designer, as there isn't one on the payroll.

Google search?

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