Cost-effectiveness of RCDs,SPDs, AFDDs etc., in perspective

[reds42]

I do sometimes check our mains voltage, when my Fluke is to hand and for decades it has always shown 240v +/- 1v. I have even had a min/max logging Fluke on it for 24 hours, with show the same variation. Unusually, I checked it yesterday it read 244v.

I have an energy monitor hooked up that has a voltage sense transformer connected which provides a record of my supply voltage. Mine seems to vary to quite a large degree. I've compared the readings I get from it to two different multimeters and and a multifunction tester and they always match so I have no reason not to believe the accuracy of the results.

Voltage

• reds42
• 24 Jan 2022

 

[Harry Bloomfield]

I have an energy monitor hooked up that has a voltage sense transformer connected which provides a record of my supply voltage. Mine seems to vary to quite a large degree. I've compared the readings I get from it to two different multimeters and and a multifunction tester and they always match so I have no reason not to believe the accuracy of the results.

That appears to be quite a wide variation - are you at the end of a long supply perhaps? I am exactly 100yards from the substation and the Fluke is a True RMS meter.

 

[reds42]

That appears to be quite a wide variation - are you at the end of a long supply perhaps? I am exactly 100yards from the substation and the Fluke is a True RMS meter.

I'm only maybe 100-200 meters away from the substation that feeds the housing estates I live on depending on how the cable is run underground, and I'm not out on the edge of the estates. There's no heavy industry nearby, my supply is no longer looped through to next door, and looking at my power draw compared to line voltage it doesn't look like its caused by voltage drop from the impedance of my supply cable. I was quite surprised at how much it varied, even at night when local solar installs won't be playing their part.

The meters I was using for comparison are all true RMS ones, and as I say for them all to agree with each other I have no reason to think them inaccurate.

EDIT:

This is the last hour, empty house with only load items on standby, and fridge freezer running. 10 second interval on readings.

Voltage_2

• reds42
• 24 Jan 2022

 

[Harry Bloomfield]

I used to have a recording voltmeter, limited range - it could be set to just record within limits, on paper tape, which for mains recording it would be around 200 to 260v, in a beautiful leather carry case, but I binned it years ago. All I have now are the instant reading Fluke and another Fluke which stores min/max and show instantaneous. I got the later to check for potential problems when big pump motors were started.

 

[reds42]

I don't think I could ever bring myself to throw away any tool, even when its well past is useable lifespan. I'm too much of a tool hoarder, much to the annoyance of my other half at times!

One thing I do have now though thanks to my energy monitor is the sometimes debated Christmas dinner cooking scenario in fairly high detail, Watts for vertical scale.

Christmas_dinner_power

• reds42
• 24 Jan 2022

2Kw hot tub on warm up just after 13:00 for couple of hours, two fan ovens running (veggie and meat options for table of 6 diners), induction hob on the go, kettle and microwave occasionally run, plus average house standby loads etc. For all that the highest spikes are no where near as high as one may imagine.

 

[Harry Bloomfield]

Gas is our big bill, which I cannot do much more about - it's mostly heating with a bit of cooking - presently running at just short of £50 pw. Electric is around the £20 pw mark.

I feed the readings for those and water consumption into a fancy spreadsheet each week and onto the suppliers website. I have in mind to modify the spreadsheet, to auto interrogate my suppliers website regularly, for the current standing charges and Kwh charges, to feed into the spreadsheet each week - when I get a roundtuit.

 

[JohnW2]

At least wikipedia claims they come from "IEC 61140" which is titled "Protection against electric shock - Common aspects for installation and equipment" .... Kind of expensive though.

Indeed. Over the years of my asking the question, I have made many attempts to find some (first-hand) 'authoritative' definitions (other than the BS7671 ones) which did not involve £££, but without any real success.

My hope has always been that there would be somewhere out there who has access to relevant Standards/regs who could enlighten me, but such has not happened to date!

Kind Regards, John

 

[flameport]

(first-hand) 'authoritative' definitions

Class I https://www.electropedia.org/iev/iev.nsf/display?openform&ievref=195-06-35
Class II https://www.electropedia.org/iev/iev.nsf/display?openform&ievref=195-06-36
Class III https://www.electropedia.org/iev/iev.nsf/display?openform&ievref=195-06-37

They are the definitions used by almost every other standard, and are identical to those found in IEC 60050.

 

[JohnW2]

Class I https://www.electropedia.org/iev/iev.nsf/display?openform&ievref=195-06-35
Class II https://www.electropedia.org/iev/iev.nsf/display?openform&ievref=195-06-36
Class III https://www.electropedia.org/iev/iev.nsf/display?openform&ievref=195-06-37
They are the definitions used by almost every other standard, and are identical to those found in IEC 60050.

Many thanks. I'll look, and then comment if necessary!

Kind Regards, John

 

[JohnW2]

I have an energy monitor hooked up that has a voltage sense transformer connected which provides a record of my supply voltage.

Interesting. As Harry has said, that seems to be a lot of variability in comparison with what he and I have observed from casual instantaneous measurements (and, at least in my case, I've undertaken such measurements under conditions of very low and pretty high demand from my own installation, and a times of day which should correspond to low and high total demand on the local network).

Particularly noticeable in your data are the very marked, rapid and brief reductions of 10-15V which seem to have occurred at roughly the same time on most days (probably early evening, if the labels on the x-axis relate to the start of the day in question) - which certainly exceeds any variation that I have personally observed in my installation. Would it perhaps be possible for you to show us graph(s) with expanded x-axes showing us the period (maybe just a few minutes) around the time of those dips?

Kind Regards, John

 

[reds42]

Would it perhaps be possible for you to show us graph(s) with expanded x-axes showing us the period (maybe just a few minutes) around the time of those dips

Yeah no problem, here is the January 21st dip in closer detail.

If I put both my ovens on full from cold which is a brief draw of 5.8kw I can create a drop of around a 2V to my incoming supply (but its hard to be too accurate on this given the external variation), but there is certainly no load in my house that could cause such large variations as I'm recording.

Voltage_dip_jan21

• reds42
• 24 Jan 2022

I have wondered whether any substation transformers could dynamically alter their tapping's to cope with variations in demand, possibly causing noticeable step changes in the voltage?

 

[Harry Bloomfield]

I have wondered whether any substation transformers could dynamically alter their tapping's to cope with variations in demand, possibly causing noticeable step changes in the voltage?

If that was a technical question - yes I understand some of them can, they can also auto-reset themselves if they have tripped, or be remotely tripped/reset. Older one had to be manually tap changed and manually reset if they trip.

 

[JohnW2]

Yeah no problem, here is the January 21st dip in closer detail.

Thanks. The individual falls/rises look a lot less dramatic over those short time-scales, but there are nevertheless some almost 'instantaneous' changes of around 6V or so.

If I put both my ovens on full from cold which is a brief draw of 5.8kw I can create a drop of around a 2V to my incoming supply (but its hard to be too accurate on this given the external variation), but there is certainly no load in my house that could cause such large variations as I'm recording. ... I have wondered whether any substation transformers could dynamically alter their tapping's to cope with variations in demand, possibly causing noticeable step changes in the voltage?

I don't know what is possible in terms of their tap-changing (and I've never understood how they seem to be able to do it 'unnoticeably') but I would have thought that it would be a fairly bizarre system that changed taps such as to produce the sort of falls in voltage that you are illustrating.

Having said that, I remain a bit confused, and hence am probably 'missing something', since what you are observing seems to make more sense in comparison with my observations.

The L-N loop resistance on each of the phases of my installations is around 0.3Ω [I was going to check what it is today but, as per another thread, when I switched on my MFT earlier today it appeared to be 'dead'!]. On my most-used phase, the instantons demand can easily vary from 1A to 30A+. Even if one ignores other loads on the local network (which could well show similar patterns of change over time to mine), the change in demand from my installation alone ought to result in a variation in voltage of 9V or more - but, as I have said, in terms of casual instantaneous measurements I've never seen anything approaching that degree of variation.

KInd Regards, John