Why Does Voltage Drop Along a Circuit?

[@tedlahm5740]

Exceptional clear explanation. As usual for your learners.

[@TimAppiah-Gates]

I'm a former grammar school physics teacher. The content of this video reminds me of a GCSE and A level physics practical where we would calculate the resistivity of a wire. The resistivity equation being :- p = RA/L Where:- p (Rho) = resistivity {Ohm- metres} R = resistance {Ohms} A = cross sectional area {metres^2} L = length {metres} The formula can be rearranged to calculate the resistance of a given length and width of a particular conductor. (R = pL/A) I was recently asked to calculate the resistance along a 75 metre length of 4mm copper SWA cable. Resistivity of copper (p/Rho) = 1.77 x 10^-7 Ohm-metres Length = 2 x 75 metres = 150 metres XS area = Pi x R^2 = 3.142. x (4 x 10^-3^2) = 0.00005 metres^2 So resistance along 150 metres of 4mm copper SWA is:- R = p x L / A R = 1.77 x 10^-7 (Ohm-metres) x 150 (metres) / 0.00005 (metres^2) R = 0.0531 Ohms

[@G6EJD]

You could have usefully shown an example of a power source supplying a load, for example the losses in the Line and Neutral effectively double the losses, so losses on the line and neutral means the load voltage is less than you said. Also PF should have been mentioned or assumed to be 1.

[@G6EJD]

Electrons that form a current flow collide with the ions in the cable, the collision gives up energy as heat. The result is a drop in voltage.

[@okaro6595]

So the table at 5:05 takes into consideration also the voltage drop in the neutral?

[@retrozmachine1189]

Nice tutorial as usual. It looks like you have similar vagueness, in determining where the voltage at the load will actually end up, to the standard here. There's talk about max percentage drop across the installation, minimum permissible voltage at the load, the minimum voltage required by the load etc but no talk about the state of the supply itself when determining cable required to make it all work. A supply with no load will present higher voltage at the origin than one under maximum rated load and that impacts what happens at the newly attached load in turn affecting the selection of cabling. My own humble 63A supply (about 30m of 25mm2 aluminium from the pole to the PoA) will droop about 6V under full rated load.

[@tedlahm5740]

long time no see.

[@abc123evoturbobonker]

Would this make strip light style led fixtures flash on/off by any chance? - I actually had a spark shout at me 'Thats not how electricity works' when I suggested the light that's been replaced 3 times and still flashes.. on the end of the run.. might not be getting enough voltage.. not a bright spark I guess?

[@G6EJD]

@@abc123evoturbobonker that’s almost certainly what’s happening, voltage too low

[@abc123evoturbobonker]

@ thanks!! 🙏

[@BoomerUKEngland]

This is why audiophiles use seemingly ridiculous size power cables together with heavy wired mains blocks. It's not the current capacity but reducing resistance (impedance) that would effect sound. It's also why some run dedicated lines back to the consumer unit (so nothing else is shared on that line), and also sometimes use clamping devices to clamp micro spikes that can occur on the mains.

[@retrozmachine1189]

No, they use ridiculous size power cables because they have no understanding of what they are doing. There isn't an amp on the market that doesn't have regulated DC within. Even if we do 1kW with a class A amp, so we are throwing away wads of power has heat, a bog standard line cord will result in a supply impedance quite able to deliver sufficient voltage under full load to the amp for a linear power supply to maintain regulation. The only way the line cord is going to make a difference is if the cord being used is pure 100% Chinesium.

[@raymondhoiles]

why is the identical volt drop in the neutral wire ignored ? A 3 volt drop on the 230v supply means 227v at the load L terminal but the load N terminal is not zero it is 3v

[@MalinDixon]

The figures in the table are for the total voltage drop in both the live and the neutral conductors, so if a 3 V drop is calculated, that's about 1.5 V in the live and 1.5 V in the neutral.

[@ardenuf7586]

With micro-generation the voltage can be higher than grid on that circuit.

[@TheEulerID]

It is incorrect to state that the voltage that the DNOs aim to deliver to properties is 230V. It isn't. When the UK adopted the harmonised EU standard for 230V, it involved no changes in the generating or distribution network. What happened is that the tolerance range was widened such that countries which traditionally used 220V, 230V and 240V were all encompassed. The specification was more for manufacturers of electrical appliances in the EU rather than to make countries move to actually delivering 230V. I know in my house and several others that the normal voltage delivered to the property is generally over 240V, often reaching 245V or even a little more. It is no coincidence that your own reading is showing 243.5 actual incoming. Mine is reading 244.2V this very moment. Apparently the average is 242V in practice. Changing it would have considerable cost implications for the network. Of course it should not be relied upon - there will be properties that will get less than this, but nothing actually changed in the real network in 2003. Here's a quote from a company (Leads Direct) about what the actual situation was following the adoption in 2003. ************************************************************************************* "What is the difference between UK voltage and European voltage The voltage used throughout Europe (including the UK) has been harmonised since January 2003 at a nominal 230v 50 Hz (formerly 240V in UK, 220V in the rest of Europe) but this does not mean there has been a real change in the supply. Instead, the new “harmonised voltage limits” in most of Europe (the former 220V nominal countries) are now: 230V -10% +6% (i.e. 207.0 V-243.8 V) In the UK (former 240V nominal) they are: 230V -6% +10% (i.e. 216.2 V - 253.0 V) This effectively means there is no real change of supply voltage, only a change in the “label”, with no incentive for electricity supply companies to actually change the supply voltage. To cope with both sets of limits all modern equipment will therefore be able to accept 230V +/-10% i.e. 207-253V."

[@davideyres955]

My house regularly has 250v according to my Shelly EM, but I am a couple of doors down from the transformer.

[@protectiongeek]

No, the nominal voltage quoted by any DNO for a single-phase LV supply **is** 230V, within the minus 6% / plus 10% envelope. You are correct that there was no widescale alterations required to the LV network when the 230V nominal value was adopted. It was intended at that time that the statutory voltage envelope would subsequently be extended to plus/minus 10%, but that change has yet to be enacted. Secondary distribution transformers supplying the LV networks in the UK usually have a nominal voltage ratio of 11000:433V, which corresponds to a no-load phase voltage of 250V at the LV busbars. This is a deliberate design feature that anticipates voltage drop across the LV network. The transformers are supplied with manual, off-line tapchangers to allow voltage to be adjusted by up to +/- 5% in five steps (-5%, -2.5%, nominal tap, +2.5% and +5%). A small number of distribution transformers have primaries rated at 6.6kV (old urban networks, most of which have been uprated to 11kV) and 33kV (rural distribution in remote areas in Scotland). A small 'island' of network in the Scottish Borders still operates at 22kV.

[@TheEulerID]

@protectiongeek I did not say the nominal voltage is not 230V, I explicitly stated that it is not what DNOs seek to deliver, which is essentially no different to what it was before harmonisation. Nominal literally means in name only. What you will find in the great majority of UK homes is what the DNOs and National Grid aim to deliver, which is around 240V. They do not aim to deliver 230V in normal circumstances to the great majority of domestic properties.

[@protectiongeek]

@@TheEulerID if you apply for a single-phase LV supply, you will be quoted for a nominal voltage of 230V - what the DNO 'seek to deliver', in your terms. DNOs don't 'aim to deliver' 240V. They 'aim to deliver' 230V within the statutory voltage envelope of -6%/+10% and achieve that most of the time.

[@TheEulerID]

@@protectiongeek The do indeed. A nominal voltage is not an engineering target, and the DNOs don;t aime to deliver 230V, they aim to deliver in the range 230V +10%, -6%. That is 216.2 to 253V. That is the engineering target, not 230V. The latter is nominal, and is not what anywhere near what the great majority of UK properties will see, which will be a bit over 240V. The DNOs and National Grid have to use a de-facto target of around 242V for most properties or they won't be able to guarantee voltages within the defined range. That's fine, but 230V as an absolute value is not the target, it's a nominal figure and should not be used as the definition of what people might expect to see. I find this sort of sloppy use of language annoying and misleading. Nothing significant infrastructure-wise really changed when the UK adopted, with others, the EU harmonised 230V standard. We did not move from a position where 240V was the normal voltage to where 230V was. Everything remained essentially the same. If it didn't, and the aim was to deliver 230V as the norm, rather than a bot over 240V then they would have had to reduce the grid voltage by about 5% which is not what happened.

[@seprishere]

I think the 2 ohms resistance is roughly that of the really rubbish cables John Ward reviews when attached to adaptors from "other countries" who apparently care less than we do about electrical safety or efficiency (I don't want random 2 ohm heaters at home, after all!).

[@davidfalconer8913]

Modern LED lamps need very little current to light up ..... With ( some , older ? ) lamps , the capacitance coupling of the switch drop wires ( with the switch OFF ! ) , is sufficient to make the lamp glow , dimly ( very useful as a night light 😝 ) ... but some folk find this annoying ... ( tried - n - tested ) ................. DAVE™🛑

[@tedlahm5740]

Interesting that you always say “ Volt Drop” when everything is written and spoken as “ Voltage Drop.”

[@busman2000]

Do we no longer have to divide by the value of copper ( held by the louvre museum). That was what I was taught. Showing my age. Gordon probably knows what I mean ?! Ummm

[@tedlahm5740]

standards standards standards. m

[@HerbieBancock]

Impedance. There, I just saved you eleven boring minutes.

[@gdelacerda]

@@HerbieBancock not boring.

[@Dr.Stacker]

If were talking reality you won't get near the calculated voltage drop, measure it and you'll see. The voltage drop forumla and tabulated figures are overdesigned, intended for a quick calculation, not real world. Its based on a conductor operating temp of 70c which is unrealistic under normal load and also doesn't take into account "evenly distributed" circuits such as lights where the Ib can be taken as half... Further your example shows a radial, for a ring voltage drop is even less of a concern