Clients requirments

[Graham Coughlan]

The client has specifically requested three phase fan units to be fitted, each appliance draws a current of 8.67A from a 400v, 50hz ac supply.
One appliance is wired using 21m of multi core 90°C themo-setting insulated non shealthed cable.
The circuit is protected by a triple pole bsen 60898 mcb type c. The cable is to be incorporates into pvc rigid conduit fixed surface mounted in an area where ambient temp is 40c.
The conduit will also partlynbe used for 6 x 2.5mm2 standrd single pvc cables...

Ive gotta find...

1 the rating of the protective decive

2 the relevant correction factors

3 min cable size required

4 max size of cable

5 max permmited volt drop

6 actual volt drop

 

[Knobhead]

Try doing your own homework, you learn more.

 

[Graham Coughlan]

not asking you to do it for me asking for help on it...

 

[Plonker 3]

Well show us your workings out and answers then maybe we can help you.

 

[Amp David]

Is this for college or an actual job?

 

[Graham Coughlan]

lege asignment - its worth 14 marks so pretty important

for the first question i got 100A

 

[gaz2212]

100a protective device.... Legend!

 

[Graham Coughlan]

Right so far ive got

a) 10A
b) C[SUB]a[/SUB] = 0.91
c) Minumin cable size = 1.5mm[SUP]2[/SUP]
d) Maximum permitted voltage drop = 5% of 400v = 20v.
e) Vc = (Mv/A/m) x Ib x L / 1000 = 4.55v

Im not sure what other correction factors i need to consider other than the ambient temp

 

[telectrix]

i would say you need to calculate the volt drop per phase , using 230V. so max. permitted per phase is 11.5v.

 

[Brightspark2]

Im not sure what other correction factors i need to consider other than the ambient temp

Grouping?...

 

[IQ Electrical]

i would say you need to calculate the volt drop per phase , using 230V. so max. permitted per phase is 11.5v.

He's right with the 400 Volt calculation-it's based on line-line voltage so you use (assuming a balanced system) per phase VD X 0.866

 

[telectrix]

agreed. 20v line/line or 11.5v line/N. ( 11.5 x sq.rt.3 = 20 )

 

[Graham Coughlan]

Is Cg the conduit factors? if so i think i worked it out to be 474?

 

[Graham Coughlan]

agreed. 20v line/line or 11.5v line/N. ( 11.5 x sq.rt.3 = 20 )

wooah let me catch up... 5% x 230v = 11.5... Right got that...

I dont understand the rest of that

 

[telectrix]

3 phase, mate, 400v is rt.3 x 230

 

[IQ Electrical]

wooah let me catch up... 5% x 230v = 11.5... Right got that...

I dont understand the rest of that

It's using the single phase maximum volt drop figure multiplied by 1.732 (root 3) to get the 3-phase value.

Or to keep it simple, 5% of 400 Volts = 20 Volts