Assignment question

[Superm4n]

Hi a very quick question i've had in a recent assignment?

can somone explain to me in fairly good detail the following question please?

explain why the product of an r.c.d rated operating current and earth loop impedence should not exceed 25v for this installation?

ok i know this much i think

the installation is 415v agricultural and also a TT system

the origin of supply is 500mA supply to unit is 100mA and distribution is protected by 30mA (im not really sure this is important)

i know the limit is 25v because its agricultural i also have the formula but i dont understand the question and dont really know what there looking for in my answer

can anyone help if the answer is already in this thread somewhere then forgive my but im obviously been quite thick eh?

anyhow thanks for any help you can offer

 

[plugwash]

the product of the current down an earth rod and the resistance of the rod to earth (which can be conservatively approximated by the EFLI measured with the rod and a leccy board provided supply) gives the voltage difference between your rod and the general mass of the earth.

If this voltage gets above a certain level it can become dangerous both in terms of contact of people/animals with both earthed metalwork and the general mass of the earth and in terms of voltage gradiant in the ground. There isn't much that can be done about this voltage rising initially in a fault but the RCD should be sized so that when a dangerous voltage does occour it isn't allowed to remain.

 

[Superm4n]

thankyou very much, this might be just what i was looking for,

wish id found this site a few months ago i also have a problem with a motor question should i start a new thread for this?

thanks again

 

[Taylortwocities]

Whaddya mean?
Questions about motors always cause confusion!

 

[Symptoms]

Superm4n - I'm going to tell your teacher that you're getting the guys on here to do your homework.

 

[Superm4n]

lol its quite hard some of these questions you know!