What size cable do I need?

[electricshock]

No No Design current equals 1000 x kva divide it by square root 3 x line to neutral voltage.

So that's 75000 divide by 1.72 x 400

75000 / 688 = 109 amps

Grouping factor is 0.79 as there will be 3x 3phase circuits grouped together touching each other.

There is no ambient temperature factor as temperature will be aboutn room temperature and no insulation factor as it will be clipped direct to wall.

It will be protected by bs88 fuses, 1.25 fuse factor


Design current / factors
109amp/0.79x1.25= 110.37 amps

Volt drop can be only 5% of supply voltage for all except lighting which is 3%. So for 400v max volt drop 20volts.

Looking at table 4e4a I will need 25mm cable.


Volt drop for 25mm 3/4 core swa is 0.14 mv/a/m

I estimated about 30metres length so 30x110.37x0.14 = 463.55

463.55/ 1000 = 0.463 volts.

So that's well within the permitted volt drop.

I can't work out shock protection as I don't have ze value.

This guy is a menace! He needs physically stopping! He's going to kill someone one day!

electricshock, you are contravening BS 7671 by carrying on what you are doing without being competent to do so. You are also breaking the law as you are contravening The Electricity at Work Regulations 1989; regulation 16.

Stop what you are doing before you hurt someone and get a competent electrician to do the work, as you are not!

I for one cannot believe how so many people on here have helped this fella on his merry way, let alone been civil! I'm all for helping people to a certain extent, but this guy needs an education!!!

Calm down. I've connected dozens of machines without any problems.

 

[D Skelton]

Is it possible if someone can check if my calculations are right. Anything I missed. Let's just pretend I'm in class.

Seriously matey, jog on.

Anyone willing to help you go out and potentially kill someone is a fool!

Calm down. I've connected dozens of machines without any problems.

I have seen the result of sparks who snip cpcs at class 1 accessories without any problems! I have seen plenty of builders have a go at electrical work themselves without any problems! I have seen the result of 5WWs playing around with three phase gear that they don't understand without any problems!

You see where I'm going fella?!

One day there will be a problem, and it'll be you hauled up in front of a jury to defend yourself on a corporate manslaughter charge!

 

[electricshock]

Please explain how I will potentially kill someone. According to my calcs what is wrong. At the moment I'm just working on 75kva total power. I'm gonna get full details soon.

 

[D Skelton]

Please explain how I will potentially kill someone. According to my calcs what is wrong. At the moment I'm just working on 75kva total power. I'm gonna get full details soon.

Because you don't know what you are doing! The very fact that you came on here asking what to do in the first place was proof enough!

You are breaking the law if you carry out this work unsupervised, end of!

 

[Geordie Spark]

Is it possible if someone can check if my calculations are right. Anything I missed. Let's just pretend I'm in class.

Yep ... you're in a class allright .... one all of your own!


http://www.youtube.com/watch?v=P5y6C-v5-j0

 

[electricshock]

Because you don't know what you are doing! The very fact that you came on here asking what to do in the first place was proof enough!

You are breaking the law if you carry out this work unsupervised, end of!

Can someone explain where I've gone wrong in my calc

 

[D Skelton]

Can someone explain where I've gone wrong in my calc

YOUR CALC AINT THE PROBLEM!!! THE FACT THAT YOU DON'T KNOW HOW TO DO IT IS!!!

YOU SHOULD NOT BE WORKING IN ANYTHING OTHER THAN A DOMESTIC SETTING!!!

Can you get that into your head?!

 

[electricshock]

YOUR CALC AINT THE PROBLEM!!! THE FACT THAT YOU DON'T KNOW HOW TO DO IT IS!!!

YOU SHOULD NOT BE WORKING IN ANYTHING OTHER THAN A DOMESTIC SETTING!!!

Can you get that into your head?!

If my calc ain't the problem. Then what don't I know how to do?

 

[Darkwood]

Is the machine new or old?
Is the motor DOL, Star/delta, VSD, soft started ?
Is their a long run up time?.... been a drill its doubtful?
Have you calculated supply demand before this machine is fitted (is the existing supply to premises able to cope)?
What is the operational duty of the machine (starting , stopping inching if it has one?)

Seriously i could go on and on and whats the point of spoon feeding you questions if when given the answers you still wouldn't know what they may mean or entail, any one of these questions could have an effect on the cable sizing ....if indeed the 22kw is the main motor where is the rest of the power going approx 60amp per phase .... you have a machine spec' but it probably gives you little info except the supply required... You need to talk to the manufacturers and ask them the correct questions... caution note if you sound like you haven't a clue what your doing i can guarantee they will just say to your customer what can of muppet you got wiring our machine in!...

The machine specs you have supplied don't exactly tally and need confirming why you have 2 values (75Kva and 22kw)... i can teach a monkey to do cable calcs in a day -trust me ive had to do it often enough but it would take yrs in an Industrial environment before i believe someone is ready to spec' machine supplies?

 

[electricshock]

I went there this morning and told them that job is too big for me and won't be able to do it.

 

[D Skelton]

Good man, you did the right thing!

 

[KAS1]

Why didn't you employ an electrical design engineer and add his costs to the job?

 

[telectrix]

might have been a better idea to try and find a spark experienced in this type of work and split the job. you both earn and you learn. customer gets his machine going. everyone's a winner.

 

[electricshock]

I'll just carry on with this school I'm wiring up.

 

[ian.settle1]

I went there this morning and told them that job is too big for me and won't be able to do it.

:clap::clap::clap::clap::clap::clap::clap:

First thing you've done right