cable sizes

[james king]

ok u used a 70mm 5 core cable? that must be huge. so my answer of 16mm is way to small

 

[james king]

so ypu came out the distribution boards in to a lv switch panel to 125a isolator have you got a diagram i am very interested in massive cables and industrial

 

[pushrod]

Is the 50 kW figure total power or power for each phase? Have they said if there is a power factor involved and whether it is connected in star or delta?

 

[james king]

50kw power intotal: No power factor as i know of. No i do not know if its delta or star! If in delta you would not need to carry a nuetrul to the isolator would you?

 

[pushrod]

50kw power intotal: No power factor as i know of. No i do not know if its delta or star! If in delta you would not need to carry a nuetrul to the isolator would you?

correct,no neutral if in delta.

power=√3 x Vl x Il

so rearrange to get Il which will be your design current Ib

 

[james king]

does that mean even though the DB has a N you still do not need to bring a N to the machine??

and say you have 1x 3 phase (100A per phase) CU with say umm 12 ways and you want to run this 50kw load from this supply..

how does switch panel work and does it run of the DB eg

DB - switch panel - from SP to the mccb then from there to the isolator?

 

[pushrod]

No practical expert by any means but if it is a motor connected in delta there will be no neutral - it will be a balanced load with no resultant neutral current.

Forgot to say before that your power per phase willbe a 1/3 of the total power, still use the √3 though.

reckon your line current in each phase is 24A if ihave used this rubbish windows calculator properly.

edit Il (line current) will be 72A as does not need dividing by 3 - reason you are dealing withtotal power, line currents and line voltages, not Ip and Vp and power per phase

 

[james king]

so if each phase is carrying 24A then a 70mm cable will not be needed. i have taped in a cable calculot on the net and it come up with 16mm. im very confused about what to put and how i got 16mm and some one came up with 70mm??

so what cable will i need?

 

[pushrod]

you also need to take account of grouping and ambient temp -you got an OSG with you?

 

[james king]

yes i do mate

 

[bugsy]

With a design current of 50kw how do you get 24a?

 

[pushrod]

Have a look at page 123 temp at 30C has no affect so can be disregard it in this case (table 6A) the other circuit derates it though-look at top line of table 6C (p126) . You will need to divide your current by 0.8

tricky question this one

 

[james king]

some1 help bugsy how did you work it out and what amps per phase do u get? im confused about the incoming tails say they are in 25mm per phase in to the board would u then come from the DB to the switch panel if so what cable size would u use then? can u some how find a diagram of it please mate

 

[bugsy]

could you please demonstrate the calculation

 

[james king]

lol some one demonstate the bloody calc thats all i ever wanted lol

 

[pushrod]

With a design current of 50kw how do you get 24a?

50 kW is a total power according to OP - so 16.67kW per phase then calc Il with formula given in post 25.

 

[pushrod]

16700W/( √3 x 400v) =24.1A

 

[pushrod]

You still hanging in there?

forgot to say √3 is 1.732

 

[james king]

im still watching lol i will top of the class if i get this with all your help lol

 

[james king]

so pushrod what is your cable size chioce?