Earthing

I'd think a real "electrical design engineer" would have studied this and be capable of performing the work, without having to go to total strangers and ask them to do his job for him.

How can you take money from someone without knowing how to provide the service? Does your customer know you can't do the work? Would he approve of you soliciting free help from strangers while he is paying you to do the work?

I doubt it.

Have a nice day.

I got told off in the mechanical section for saying I'd want my money back if I'd employed a incompetent design engineer.

But, you were still right.

I know I'm "very direct" when calling these people out, but how can you call yourself an "electrical design engineer" and "consultant" if you can't do the work?

Cheers.

if u r "very very direct" then give the answer of this questions. whatever i asked the questions If u better know then give the ans. I want to know how u can give the ans perfectly and smartly.

Nobody is obliged to give you an answer.
Your attitude is not helping at all! Asked in a decent manner most people will go out of their way to help. But I think you're a lost cause.

I know I'm "very direct" when calling these people out, but how can you call yourself an "electrical design engineer" and "consultant" if you can't do the work?

<ahem> <ahem> From my experience a 'consultant' is a general (engineer, etc) who charges you to learn how to advise you on a question or design while taking some of the design risk.

Many times I end up teaching the electrical consultant how to do aspects of the work they are charging us on <cringe>.

<Sigh> Just the way it is I guess.

Consider that in the event of Earth fault the Protection device will open the circuit within say one second, that means you will design the conductor for 1 second duty, you have to consider allowable final temperature rise for copper.

FORMULA: Cross-section area of conductor (mm sq.) = (Fault current) * (Sqrt. of time) / (Temperature range constant).

For a final temperature of 300 deg C the value of temperature range constant is 190.

As a thumb rule consider current density of 200 A/mm square for a final temperature of just over 300 deg C at an ambient temperature of 30 deg. C.

Earthing design is a complex issue which cannot be adequately covered in a discussion form, I suggest you essentially read some books on the subject a keep relevant standards handy.

I assume that the sizes quoted by you are from some "ready-reckoner" tables published by some engineers'/contrcators' associations. Strictky speaking, one must undertake a fault current study, even for the smallest motor and then decide the erath conductor size based on the formula S = I * Sq. Root "t"/K, where, I is the fault current in amperes, 't' the fault duration and "K" a constant depending upon the fault duration, the material of the earthing conductor and the method of installation of the earth conductor. IS 3043 Table 6 details these constants.

But, as the number of motors in an industry would be too large, it is a laborious process to "theoratically" calculate and size the earth conductor for each equipment in the industry. So, people have given some ready-reckoners, considering nominal conductor sizes and lengths. Most of the time the sizes so recommended could be adequate.