What is the cause of voltage drop within an electric installation?

[paulthemagpie]

hi guys,

what is the cause of voltage drop within an electricinstallation?

 

[telectrix]

cable resistance ohm's law. VD= IR.

say for ex. you have a cable resistance R1+Rn = 0.5 ohms, carrying 20 A.

VD = 20 x 0.5 = 10V. sssimples.

 

[Silly Sausage]

Think about the resistance of a length of cable, the current flowing through it and Ohm's Law.
What does that give you?

 

[Rockingit]

the mice eat some of it along the way.

 

[paulthemagpie]

Im just struggling to find it hard to understand

ohm's law. V= IR.

so if the current is constant, it it basically the longer the circuits the more cabling and components they are that offer more resistance therefore as the current is coming across more resistance the voltage must drop as per ohms law!

is that right

 

[JulianC]

It's mainly due to gravity. Where a cable runs downwards, the voltage tends to drop and collect towards the bottom. Old fashioned rubber insulated cables allowed some bounce so the drop could be counteracted somewhat. However, with modern PVC insulated cables, it is more of a problem. An easy test: measure voltage in your upstairs sockets and compare it to those downstairs - the downstairs voltage will be higher. Ways to counteract volt drop mainly involve fitting undersized cables - the voltage has trouble squeezing along these so tends to stay high. Volt drop is not generally a problem in bungalows.

Next question?

 

[telectrix]

yes. the longer the cable, the higher the resistance, so the greater the VD. if the calculated VD is too high > 5% ( or 3% for lights) then you choose a larger cable to reduce the resistance, thereby reducing the VD.

 

[Rockingit]

Bingo! yes, that's right.