Voltage Drop in Electrical Circuits

A demonstration and explanation of voltage drop in electrical installations.
The excessive volt drop shown in this video was caused by a fault with the supply, which was fixed shortly after this video was made.

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[josharnold]

Really starting to like this guy with his straight forwardness and bluntness.

[benhurley]

Got to be the best online tutor in this field, every video is clear and made to be understood by even for the most novice amongst us. Cheers JW 👍🏻

[NorthernMonkeeUK]

Great video as usual John. I had an issue similar to that house you demonstrated on, apart from voltage here dropped to ~100v. It took WPD so long to do anything about the fault in the street that the cable under the footpath actually blew up one evening, taking out one of the phases and therefore a third of the street for over a day whilst they temporarily re-connected people to a different phase whilst they made the repair (which typically involved them destroying my front lawn, again).

[harveysmith]

Thank you John, I am more accomplished in mechanical engineering than anything else, however I am fully aware of how useful knowledge electronics is. I am slowly getting my head around it.
You are clearly very experienced in your subject but unlike many others, you can communicate the subject in a very chapter one way. Many thanks again.

[ndear]

I'm glad you clarified the reason for the low voltage shown during your demonstration. I was very surprised because the UK power grid is generally pretty well-regulated and I was surprised to see the voltage drop below 216.

[driftmanjirc]

Hi john I have my 17th edition exam on 15th of feb and I must say your videos have helped massively in understanding certain things that I was unsure of to start with. thanks pal :)

[proctorbook]

JW should have been a school teacher, I might have gone to school then, love the vids JW

[chumaninxazonke]

Your explanations are so simple to understand. Thank you, John!

[theirisheditor]

That reminds me of a similar issue we had up until about 15 years ago, but in our case it as a 6 volt drop for a 2kW load (e.g. Kettle) as our mains supply ran for something like 500 metres to the transformer. It wasn't a major issue until my my brother (who lived with us back then) got a 35A welder! When I reported the voltage dropping issue to ESB Networks, in just 2 weeks they extended their high voltage lines right up to near our house, fitted a new transformer and now the voltage drops by about 2V in the socket next to the kettle when switched on.

[VivekGangwar]

youre a good teacher, I wish you teach millions of students.

[matthewjones]

Your delivery and content are sublime. Thank you for uploading.

[mrpropergander]

That opening line *"...Hello I'm JW..."* is becoming legendary. 😁

[Dog-whisperer]

Robin electronics, they were located in Watford and made the Robin range of test instruments in the late 90s they stopped trading and re located to Chesham and rebranded as kewtech industry’s and continued to make the Robin meters but changed the colour from yellow to grey and rearranged the model numbers, ie Robin KTS 1620 became kewtech kt 62. Since then the Robin brand has been used by a number of different manufacturers including fluck and amprobe . Great video John very well explained

[johnburns]

In my place mid afternoon. 250v on the 32A ring with nothing on. Measured voltage in a double socket in kitchen - 250v. 800w Toaster plugged into same double socket - turned on drops to 249v. Two rings on induction hob on (separate 40A circuit), drops to 248v. Put 3kW oven on, drops to 247v. Quite pleased.
Maybe very different at peak times.

[astplatinum]

I do hope once the kettle boiled the home owner made you tea!

Again, great video JW.

[johnschlesinger]

I did wonder why the voltage was so low, as whenever I have measured mine, it has been above 245V: the supply industry likes keeping higher voltages than the EU standard of 230V, as we end up using more power! You gave the reason at the end. I have always preferred to err on the side of larger conductor sizes: in my electrical days, I always used 1.5 sq mm for lighting.

[artvandelay]

Hi JW really enjoy your videos and this great explanation of voltage drop. One thing I did note was that there is no mention of the utilisation voltage. I believe in the UK as with Australia the service provider is permitted a +10%, -6% variation in supply at the consumer point of attachment. Further to this BS 7671 and AS 3000 permit a maximum VD of 5% within the premise. Therefore the maximum & minimum voltage (or utilisation voltage) experienced at the consumers outlet could be 230VAC +10%, -11% or 253VAC to 205VAC. A voltage as low as 205VAC is permissible.

[TheEulerID]

I'm glad to read this was due to a fault as a near 10v drop at 10A is ridiculously high. That 1 ohm resistance is the equivalent of 135m of 2.5mm^2 copper cable (so almost 70m of length on a radial). It would require a massive ring circuit to get that sort of drop.

[tedlahm]

Very well presented. In our general math we are told that Parallel loads the voltage is the same at each load. The resistances are added together RESULTING in LOWER resistance and INCREASED amperage.
In your example the resistances are in series. Thank you. Comment please.

[npal]

Fantastic, concise explanation. Where were teachers like this when I was at school?