Voltage Drop and Cable Size

→ British Standard 7671.

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

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

he said 2 cables of 3 cores each...

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.

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

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

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.

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.

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

not forgetting the temperature.....

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.

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.

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.