Equipment Motors & Other Design Questions

[Guest]

Hello everyone

I need your expertise

I have 20 machines that take at maximum load 5 amps they are all single phases. I will fit it all in the same area but there is not distribution board.The nearest one is 50 meter far away.

so I want to install a three phase sub board in this area where I will wire it with own circuit (Radial) the only thing is I have to calculate the Cable size of SWA that will come out from the D.B and will end to the subboard My calculation is 5x20=100amps. these machines will take 100Amps with one phase.so because I wire the subboard with a three phase the next formula is 100/1.732=57.73Amps the SWA will be run as method C (Clip direct) now I can select a cable size from the regs and it is 16mm2 this cable can take maximum load of 77 Amps.the earthing system will be connect to the earth (steal) of Swa and size will be 16mm2 copper conductor as per regs.

the main cable that it came out from the intake is protect by 3 fuses (three phase) 100 amp each and will terminate to distribution board the main switch of the distribution board is a 4 pole 125amp rated. My question is would you please advise if my calculation is right also the distribution is 12 way and there is space for a three phase MCB the only thing is that L1 has 90 amp rating mcbs (final circuits) L2 is 160 (final circuits) amp rating and L3 is 140 amp rating (final circuits).Also would it be possible that distribution board will overloaded? what are the consequences? this is won`t be a job I just make it for my personal clarification thank you. 

 

[ProDave]

If the 20 machines take 5A each, and you are going to split them between 3 phases, that will be 7 on two of the phases and 6 on the third phase.

So that will be a load of 35A per phase.

Your concern won't be the current carrying capacity of your chosen cable, but the voltage drop over the 50 metre run.

Size your cable to keep volt drop acceptable and I'm pretty damn sure you won't have an issue with CCC.

 

[Guest]

If the 20 machines take 5A each, and you are going to split them between 3 phases, that will be 7 on two of the phases and 6 on the third phase.

So that will be a load of 35A per phase.

Your concern won't be the current carrying capacity of your chosen cable, but the voltage drop over the 50 metre run.

Size your cable to keep volt drop acceptable and I'm pretty damn sure you won't have an issue with CCC.

Thank you ProDave

I did the calculation and 6mm2 is not good and 10mm2 is just ok. Would you please show me your calculation and see if I did right would you calculate as three phase or as single phase?

 

[ProDave]

So what volt drop do you think you will get with 50M of 10mm @ 35A and do you think it will be okay?

Would you size a submain so it is only just adequate for the loads you intend, or do you think it might be better to size it a bit bigger so you can add more loads later on?

 

[Guest]

Thank you ProDave

I did the calculation and 6mm2 is not good and 10mm2 is just ok. Would you please show me your calculation and see if I did right would you calculate as three phase or as single phase?

Ambient temperature 40 degree will be clip direct above the false ceiling 50 metre run

 

[Doc Hudson]

 what are the consequences? this is won`t be a job I just make it for my personal clarification thank you. 

Welcome to the forum, Is this a homework question by any chance. Should I move it to the Student area? 

Doc H.

 

[Guest]

So what volt drop do you think you will get with 50M of 10mm @ 35A and do you think it will be okay?

Would you size a submain so it is only just adequate for the loads you intend, or do you think it might be better to size it a bit bigger so you can add more loads later on?

I make it just for my clarification so if this is was a job I would increase the size just in case to put more load but because it just come as my doubt we can say just we go for the load I described thank you I appreciate your expertise

Welcome to the forum, Is this a homework question by any chance. Should I move it to the Student area? 

Doc H.

this is not an home work it is just for my clarification for the future if you think you feel offended please you don`t have to answer thank you

So what volt drop do you think you will get with 50M of 10mm @ 35A and do you think it will be okay?

Would you size a submain so it is only just adequate for the loads you intend, or do you think it might be better to size it a bit bigger so you can add more loads later on?

So what volt drop do you think you will get with 50M of 10mm @ 35A and do you think it will be okay?

Would you size a submain so it is only just adequate for the loads you intend, or do you think it might be better to size it a bit bigger so you can add more loads later on?

we say that a main distribution boards is a three phase 100 Amp 25 mm2 swa and the subboard will be a 10mm2 swa with voltage drop of 11,2V

 

[Guest]

So what volt drop do you think you will get with 50M of 10mm @ 35A and do you think it will be okay?

Would you size a submain so it is only just adequate for the loads you intend, or do you think it might be better to size it a bit bigger so you can add more loads later on?

the volt drop in each phase is 11,2V I think as it is not a job and accordingly with the regs it just acceptable

 

[Marvo]

Hello everyone

I need your expertise

I have 20 machines..........

Not enough info. What type of machines? Do they have motors or anything else with a high inrush current on start up? What is their PF? Will they start running together or are they independant? If they do have motors and their single phase have you made a generous allowance for long start currents?

 

[Guest]

Not enough info. What type of machines? Do they have motors or anything else with a high inrush current on start up? What is their PF? Will they start running together or are they independant? If they do have motors and their single phase have you made a generous allowance for long start currents?

they are single phases motors there is not an inrush current as they are with an inverter and they are independents please correct me if I am wrong PF is acceptable (0.80 to 1.00) any way even if they have an inrush current when motors starts it should be ok as every radial circuit is protected by an 16mcb type C and the incoming cable is SWA 10mm2 protect by a 50amp clip direct  an earthing conductor 10mm2 as per regs.

 

[ProDave]

 this is won`t be a job I just make it for my personal clarification thank you. 

they are single phases motors there is not an inrush current as they are with an inverter and they are independents please correct me if I am wrong PF is acceptable (0.80 to 1.00) any way even if they have an inrush current when motors starts it should be ok as every radial circuit is protected by an 16mcb type C and the incoming cable is SWA 10mm2 protect by a 50amp clip direct  an earthing conductor 10mm2 as per regs.

For a personal theoretical exercise you are starting to get very detailed.

If each machine only consumes 5A, and is inverter driven with soft start, the choice of type C 16A mcb's could be questionable.

If you have protected the 10mm SWA with a 50A mcb, then to my mind you have designed a 50A submain, so your voltage drop should be calculated at 50A and I think you will find it's too high.

 

[Guest]

For a personal theoretical exercise you are starting to get very detailed.

If each machine only consumes 5A, and is inverter driven with soft start, the choice of type C 16A mcb's could be questionable.

If you have protected the 10mm SWA with a 50A mcb, then to my mind you have designed a 50A submain, so your voltage drop should be calculated at 50A and I think you will find it's too high.

Sorry I made a bit of confusion it is not 50 amp the current rating but is 40 amp

20 machines with not inrush current at 5 amp each at 40 degree ambient temperature. 20 machines divide 3 phase will be Ib= 35 amp designed current. rated current of the device In=40 amp Mcb type c 16 Amp. for radials circuits the incoming cable is SWA clip direct. The current rating is It= 45.97 the cable size is 10mm2 . the formula will be mva 3.8xIb=35 amp x lenght 50/1000= 6.65 volts drop  maximum drop voltage is 11,5 V (5%) the 10mm2 is ok to power up these equipment. Is it this right?

 

[Guest]

Hi

I have 1 motor with inrush current the motor is three phase  and it is 20kw   there is already a distribution board but is 20 meter far.now needs to calculate the cable size and volt drop how would you design the electrical installation?

my design will be I would build a steal conduit 25mm connected to the isolator. the formula will be 20000/400/1,732/0,90 and it is 32.075 Amps three phase designed the rated MCB will be 40 Amp the ambient temperature will be 25 degrees the cable size will be 10mm2 and the volts drop is 2.43 is that correct?

 

[Andy™]

is this going to be wired to your new DB 50mtr away?

 

[Guest]

is this going to be wired to your new DB 50mtr away?

No sir,This time is 20 meters

Accordingly with the regs how would you design your installation thank you.

All this needswill be a good refresh in case one of this job come up.

 

[Lurch]

This is not college work. You are getting members of this forum to design systems for you as you are in over your head somewhere and should not be designing electrical systems.

 

[steptoe]

For a personal theoretical exercise you are starting to get very detailed.

my thoughts exactly

thats why Im not even getting into designing it for him,

if he cant design a simple motor radial then he really shouldnt be allowed in the same building as 3phase, 

just my tuppence.

 

[Doc Hudson]

Two threads merged. Same member very similar content, probably best kept as one thread.

Doc H.

 

[Guest]

Two threads merged. Same member very similar content, probably best kept as one thread. Doc H.

Hello Sir is there something wrong to ask few questions and hear other opinions? Would you think when we say electrician do we mean that knows all the complex fields that this job is involved? I just repeat: my 2 questions were just to confirm if my calculations are right. If I am wrong and I shouldn't ask please let me know Thank you

 

[Andy™]

there is a difference between an apprentice asking a few questions and someone who appears to be a spark way out of their depth and needing help to design a job