min csa of live conductors

[paulthemagpie]

hello peeps,

I could do with some help. And i will greatly be appricated to egt the help.

What is the min CSA of live conductors suitable for CCC and voltage drop for the following:

a. 3kw, 230v water heater
b. 11kw, 400v MIG welder
c. 12kw, 400v three phase machine
d. 5kw, 400v three phase machine

thanks you in advance for your help

 

[paulthemagpie]

how do you do these calculations?

 

[telectrix]

you can't calculate volt drop till you have calculated the current. and you also need to know the length of the cable run.

 

[Amp David]

how do you do these calculations?

Not by someone advising on here in a short thread. This is and can only be taught in a theory class at college surely.

What happens when you get let out in the real world and you need to work it out but haven't got the forum to hand.

Its barmy! The forum is OK for the odd little pointer when it comes to learning, but asking stuff like this, no way boss!!!

Sounds to me though that its not a proper college course anyway, these places should be closed down under the health and safety regs

 

[paulthemagpie]

a. has a cable run of 15meters

 

[telectrix]

ok, so work out current ( I ) from ohms law. then size your cable according to BS7671, allowing for derating, then calculate the volt drop. if VD > 5%, then rethink to a larger csa cable.

 

[paulthemagpie]

were in the bs7671 do i find the cable sizing?

 

[paulthemagpie]

found it now.

so when we doing the calc for voltage drop do we use the amp of the load or the amp of the mcb we using.

for example in the above a. the I comes to 13a so we we use this figure or the 15a mcb we will be using?

thanks

 

[telectrix]

you use the 13A as that is the actual current.

 

[Rockingit]

Just as an aside - watch your terminology here: You wouldn't be using a 15A MCB........ it would either be a what or a what?

Like blankety blank, this.

 

[paulthemagpie]

right so i can work a. out which comes to a VD of 3.51v

were do i apply this to see if the vd is less than the 5%?

my study books are the worst! it gives me an example but just plucks figures from now were to compare it to without explaining why

 

[paulthemagpie]

Just as an aside - watch your terminology here: You wouldn't be using a 15A MCB........ it would either be a what or a what?

Like blankety blank, this.

should it be a 16a mcb

 

[Rockingit]

should it be a 16a mcb

cheque book and pen shall be yours.....

 

[paulthemagpie]

so ive came to the conclusion that for a a 2.5mm would be suitable! ive now worked out vd which is 3.51v but not sure how to work out if its within the limits

 

[paulthemagpie]

cheque book and pen shall be yours.....

i dont get what you mean!