Previous in Forum: DC Step Down   Next in Forum: Electrical Formula
Close
Close
Close
16 comments
Rate Comments: Nested
Anonymous Poster

Voltage Drop and Cable Size

05/12/2010 8:33 AM

Hi

I want to connect the 10hp submersible water pump in the lake.

For this I have to take electrical supply 415volt from 300 meter away electrical panel board and connection is star delta so 3core 2cable will go up to 300meter by under ground up to 2feet down

My question is for this pump how much -----mm2 cable do I have to use?

Thanks

Sawant Vilas
India

Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

"Almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, vote them!
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 32175
Good Answers: 839
#1

Re: voltage drop and cabel size

05/12/2010 8:38 AM

→ British Standard 7671.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 32175
Good Answers: 839
#2

Re: Voltage Drop and Cable Size

05/12/2010 9:11 AM

3-core cable is not suitable for 3Ø star/delta.

Six individual phase conductors are needed in addition to the protective earthing conductor.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Reply
Guru
United Kingdom - Member - Not a New Member Hobbies - Musician - New Member Hobbies - Fishing - New Member

Join Date: May 2006
Location: Reading, Berkshire, UK. Going under cover.
Posts: 9684
Good Answers: 468
#3
In reply to #2

Re: Voltage Drop and Cable Size

05/12/2010 9:48 AM

Think they meant 2off 3-core cables.

__________________
"Love justice, you who rule the world" - Dante Alighieri
Reply Off Topic (Score 5)
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 32175
Good Answers: 839
#4
In reply to #3

Re: Voltage Drop and Cable Size

05/12/2010 9:58 AM

It does seem that way - provided the cable gland entries to the motor terminal box will accept it, of course.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Reply Off Topic (Score 5)
Guru
United Kingdom - Member - Not a New Member Hobbies - Musician - New Member Hobbies - Fishing - New Member

Join Date: May 2006
Location: Reading, Berkshire, UK. Going under cover.
Posts: 9684
Good Answers: 468
#5
In reply to #4

Re: Voltage Drop and Cable Size

05/12/2010 10:11 AM

10001 posts! Oh, my!

__________________
"Love justice, you who rule the world" - Dante Alighieri
Reply Off Topic (Score 5)
Guru

Join Date: Feb 2010
Posts: 1013
Good Answers: 36
#10
In reply to #2

Re: Voltage Drop and Cable Size

05/13/2010 6:24 AM

he said 2 cables of 3 cores each...

Reply
Power-User

Join Date: May 2010
Posts: 146
Good Answers: 2
#6

Re: Voltage Drop and Cable Size

05/12/2010 1:50 PM

Dear Sawant, I want to answer you. But, before that please answer me for the below questions.

1. Are you contractor or electrician for this job?

2. Are you the client and want to do your self?

3. I understood from your question that you are not even a ITI electrician. How did you get informations such as 415 V, star delta, 300 meter,mm2, 2 feet below,voltage drop,cable size etc?

4. Learning new things are good always. Do you think electrical engg is also can learn by this Q&A and you can work?...

5. If you are not qualified to do this job, why dont you give a chance to qualified , experienced people?

I need answer for these question , because my reply will be based on that.

Reply Score 1 for Good Answer
Guru
India - Member - New Member

Join Date: Sep 2009
Location: Temporarily at Ashburn, VA
Posts: 2744
Good Answers: 164
#7

Re: Voltage Drop and Cable Size

05/12/2010 10:58 PM

There is an effect of voltage drop due to the long cable length, which may make the starter malfunction. This is well known. However, there is a capacitance effect which may prevent the starter dropping off even when a stop command is given. There are lots of papers on this subject, one of which is here ...

moeller

__________________
Nothing worthwhile can ever be taught, it can only be learnt.
Reply
Guru

Join Date: Oct 2009
Location: sometimes Wales,UK.. was Libya, now Oman!
Posts: 1715
Good Answers: 117
#9
In reply to #7

Re: Voltage Drop and Cable Size

05/13/2010 1:27 AM

that paper would be for "LONG CONTROL CABLES"

Not really applicable in the use of suppling POWER to submersible pumps where LONG POWER CABLES are used

__________________
The square root of nothing is what you make it!
Reply
Guru
India - Member - New Member

Join Date: Sep 2009
Location: Temporarily at Ashburn, VA
Posts: 2744
Good Answers: 164
#11
In reply to #9

Re: Voltage Drop and Cable Size

05/13/2010 7:07 AM

Yes you are right, i misread the question. What i would do in such an application is to run the appropriate 3-core power cable and have a local star-delta starter with controls in the panel 300m away. Then the long control cable is appropriate. One saves on the second 3-core cable cost, doesn't one? However, there may be many things which prohibit local control of that pump.

__________________
Nothing worthwhile can ever be taught, it can only be learnt.
Reply
Guru

Join Date: Oct 2009
Location: sometimes Wales,UK.. was Libya, now Oman!
Posts: 1715
Good Answers: 117
#8

Re: Voltage Drop and Cable Size

05/13/2010 1:23 AM

easy... look at cable table that gives you the voltage drop per foot for a certain csa. The larger the CSA or Cross Sectional Area the less the voltage drop, but there is ALWAYS a voltage drop

Then multiply the volt drop per foot by the length of cable you have/require, the that will give you the voltage losses.

So its basically this,

Required Motor Nameplate Voltage + voltage drop of cable length = voltage required at surface.

You might need a step up transformer to provide the correct "Surface voltage" to supply your motor. You will not require a step up transformer if the calculated voltage drop is less than 10% of motor nameplate voltage, and your motor is only 80% loaded. If the voltage drop is 20volts this will not affect the running or performance of the motor, in fact it will improve it as changing the voltage alters the motor performance curves.

Start with 25mm cable and work up!

and throw away that star/delta motor, use a star motor, that way you will not have to mess about with way to much cable... and as a point in delta the motor will stall if the pump becomes blocked.

__________________
The square root of nothing is what you make it!
Reply
Anonymous Poster
#12

Re: Voltage Drop and Cable Size

05/14/2010 7:45 PM

Voltage drop cannnot be determined by length alone.You must know the CURRENT, or amps of the load.

E-IxR.( Current times Resistance)

You can get resistance-per-foot from table, but voltage drop will vary according to load applied.

As previosly stated ,if you are not qualified, do not try this at home.

HTRN

Reply
Guru

Join Date: Oct 2009
Location: sometimes Wales,UK.. was Libya, now Oman!
Posts: 1715
Good Answers: 117
#13
In reply to #12

Re: Voltage Drop and Cable Size

05/15/2010 12:04 AM

not forgetting the temperature.....

__________________
The square root of nothing is what you make it!
Reply
Guru
India - Member - New Member

Join Date: Sep 2009
Location: Temporarily at Ashburn, VA
Posts: 2744
Good Answers: 164
#14

Re: Voltage Drop and Cable Size

05/15/2010 1:00 AM

Let me make these assumptions:

10hp motor @ 415V 3φ so I ≈ 16A ... OK ?

Which part of India ? Temperature can be 50 deg C at the worst?

My calculations tell me that 4 Sq mm cable is just adequate, to be safe you can use 6 sqmm...copper of course.

__________________
Nothing worthwhile can ever be taught, it can only be learnt.
Reply
Guru

Join Date: Oct 2009
Location: sometimes Wales,UK.. was Libya, now Oman!
Posts: 1715
Good Answers: 117
#15
In reply to #14

Re: Voltage Drop and Cable Size

05/15/2010 1:19 AM

you can't make any assumptions, as any results from those assumption will be wrong, however much you would like to help and advise. I would refer you to my first answer, ref motor load and name plate voltage. The best answer was if the OP is not qualified that don't try this at home.

__________________
The square root of nothing is what you make it!
Reply
Guru
India - Member - New Member

Join Date: Sep 2009
Location: Temporarily at Ashburn, VA
Posts: 2744
Good Answers: 164
#16
In reply to #15

Re: Voltage Drop and Cable Size

05/15/2010 5:05 AM

This is India. We do not have such strict rules as you have in the West. Moreover, the self-styled certified electricians here are not like you have over there. You can't leave things to them and relax here. You need to know a little bit yourself.

Don't get me wrong, i am all for safe working with electricity. i have a healthy respect for it. However, i would question if someone says that a large cable is required etc. Especially since the originator is going to run TWO 3-core cables..which will see the internal delta current, which will be 16A/ √3 .. less than 9A. A 2.5 sqmm is more than ample actually.

i have also checked up on the soil temperatures at the hottest spots in India, at the height of summer........

The originator is unlikely to be such a novice that he will hurt himself and others, maybe damage property etc, since he/she is furnishing relevant data alright. So .. assumptions are not that badly out of sight.

In summary, i would like the originator to see if he has a competent electrician he can trust. Take his recommendation by all means. Be safe first.

__________________
Nothing worthwhile can ever be taught, it can only be learnt.
Reply
Reply to Forum Thread 16 comments

"Almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, vote them!
Copy to Clipboard

Users who posted comments:

Alanvaderi (1); Anonymous Poster (1); brich (4); JohnDG (2); kvsridhar (4); LAA_Lucke (1); PWSlack (3)

Previous in Forum: DC Step Down   Next in Forum: Electrical Formula
You might be interested in: Cable Laying Services, Cable Assemblies

Advertisement