What Cable Size And Breaker?

[sparkitrician]

i have a 10 kva generator and am running the supply into a 3-phase DB, which im then using to power 3 smaller DB's. what size cable should i use to run from the generator to the DB? and also what size breaker should i use?

thanks guys

 

[Andy™]

Ask the electrician your working with. unless he has asked you to figure it out and you now want us to do your homework

 

[binky]

take a stab at the question, post it on here, and we will point out whats right and wrong i n your answer. What the forum members won't do is spoon feed you homework answers, cos that way you'll never learn to be a proper sparky...

 

[sparkitrician]

my thoughts were to used a 10mm cable and 63A breaker? also the 3 smaller DB's are single phase, so would i use a 32 amp breaker for each DB because i was told that the 3 combined was 44 amps, or is 32 too big? cheers

 

[ProDave]

63A breaker would supply 14KVA per phase.  you said it's a 3 phase generator.

Try again to pick a more appropriate sized breaker for a 10KVA generator.

What current do the tables in BS7671 say a 10mm cable can carry?

How long is the cable so you can work out the voltage drop?

 

[sparkitrician]

so i want to go down the way?

the run of cable wont even be 10 meters, its just from the generator outside to the DB on the inside of the cabin.

BS 7671 says that a cable of 10mm and in free space can carry up to 60.

sorry if im being a pest haha, ive searched all over the internet trying to find something to help me make sense of it but i cant find anything that explains what i need to know!

would i go down to a 32A breaker?

 

[Sidewinder]

sparktrician,

Welcome to the forum.

If you look in the On-Site guide this will cover all of your questions and give you the methods to calculate the required values.

I would hope that you would have a copy of this that you can refer to?

I would not rely on information found on miscellaneous internet sites for definitive values for such a calculation.

You can obtain current carrying capacities & volt drop values from cable manufacturers web sites, and the calculations for volt drop are actually just Ohms law.

You are lucky on here in that you have a lot of practising electricians and some practising engineers who will not lead you up the garden path, nor will they lie to you, or misinform you.

However, we will not hand you the answer on a plate, keep coming back with your ideas and we will assist you by guiding you to your own answer.

That way, you will be happy that the values you obtain are correct, and you will have a greater understanding of the process for the future.

 

[ProDave]

Look at the generators rating plate or instruction manual. Or even the circuit breakers or fuses built into it. that will give you some idea of the current per phase on a 3 phase 10KVA generator.

I'm not convinced you are actually competent to do this job.

And we haven't discussed earthing yet.