Volt Drop

[huntos33]

Pricing up a job in a factory and have to wire in a 3 phase supply, just going to double check my cable sizing i calculate i need to use a 10m cable

Swa cable clipped direct on its own , 35m run feeding a unit needing a 3 phase 20amp supply am i right ? just seems a little on the heavy side ?

 

[Amp David]

I'd re check your calcs.

Whats the unit to be fed?

And do you mean 10mm or 10m?

 

[huntos33]

Yeah 10mm thinking ive miss caculated the allowed volt drop percentage im right in thinking im allowed a 5 % drop ?

 

[Amp David]

Yes 5% percent of the supply voltage

See here for a handy template

http://www.electriciansforums.net/e...al-regulations/47059-cable-calc-template.html

 

[telectrix]

top of my head 2.5mm is on the limit of VD. 4mm or 6mm is adequate.

 

[huntos33]

Thanks David , coming in at a more sensible size now knew that looked far to heavy

- - - Updated - - -

4mm is the baby was some how working on the wrong volt drop allowence

 

[Thomas123]

Cable type: 70 deg.C Multi (armoured)
Fixing method: Clipped direct

Protection device: CB typeC
Protection rating: 20 A

Cable size: 2.5 mm
CPC size: 2.5 mm
Current carrying capacity of cable in this instance: 25 A

Final circuit: Yes
Ambient temperature: 30 deg.C
Number of cables grouped: 1
The cables are spaced


Voltdrop: 2.62 %
Allowable voltdrop: 5.00 %

Length: 35.0 m
Calculated R1+R2: 0.519 ohms
Calculated Zs: 0.87 ohms
Maximum Permitted Zs: 0.92 ohms

Type of system: TN
Supply: Three phase at 400 v
Ze: 0.350 ohms
Fault current: 0.26 kA

Applied correction factors:
Ca: 1
Cg: 1
Ci: 1
Cc: 1


Using a app I have it says 2.5mm2 is fine, although I would personally use 4mm2

 

[telectrix]

with 2.5mm i get vd of (18 x 20 x 35)1000 = 12.6V , just over 5% then you have to allow a bit for the outgoing cable/s on the load side.

sorry, wrong column. 15mV not 18. so VD = 10.5V so acceptable.