Chewing The Fat..... "Volt-Drop"...

[SPECIAL LOCATION]

As a sole trader its great being able to manage jobs and plan your diary to suit your own personal work and family commitments with no external pressure from your boss.. [side note: Me- Self-employed since Feb 1999]

But as a sole trader you also don’t have any work colleagues to debate, discuss, chew-the-fat, over any work-related bits that you may want a second opinion on!

So just a bit of “Chewing The Fat” on a Friday night.. theme: “Volt Drop”

I have no problems ensuring that all circuits I design and install comply with BS7671 volt drop requirements…

But sometimes trying to explain to a customer why you need to use a larger CSA cable for a shed 50m down the garden, than the cable that their mate down the pub, who knows electrics, said they needed..

It can sometimes be a tad difficult telling the customer that their mate is an idjut!!

And/Or, I also never really understood why did the permitted volt drop become more critical for lighting circuits, but less critical for other circuits in 2008?? (It’s obviously nothing to do with nominal voltage as that changed in 1995).

So are there any other fat-chewers out there with much greater wisdom and/or easy explanations that can be passed on to myself and/or other lurkers on the forum who may be sh1t-scared to ask, for fear of being called an idjut!!!


Side Notes:- A bit of historic context for any of the younger members;

Nominal Voltage
pre 1995 nominal voltage 240volts -6% (225.6 volt), +6% (254.4 volt)
Since 1 Jan 1995 nominal voltage 230volts -6% (216.2 volt), +10% (253.0 volt)

Permitted Volt Drop
Pre 2008 permitted volt-drop on all circuits was 4% (9.2volts), ref 525-01-02.
Since 2008 to current time, permitted volt drop on lights is 5% (11.5volts), other circuits 3% (6.9volts)
ref 525.202 & 643.11 & Appendix 4 (previously Appendix 12).


I will now open another Friday night beer and await some constructive debate and discussion!!!

 

[binky]

You forgot one, solar 1%, volt drop.

I never understood why lights should be different to power, but I would assume all this is about energy efficiency reducing demand for power generation or prevention of cables overheating. I did once calculate the cable heating effect in a long sub main to a stable block the customer wanted solar panels on. To replace the cable with something larger would have involved digging a 100m trench and £3k in cable to meet the 1%. Customer wasn't happy about that, so I calculated that the energy loss would be around 80watts max. In other words quite neglible.

 

[kerching]

The Copper Development Association used to have an online calculator for cable losses. I used it a few times to calculate supply cable sizes for data centres. Not only did it calculate sizes it also illustrated pay back time due to reduced loses if a larger size was used