Residential 3 Phase Supply to Single / 3 Phase

[SUNRAY]

So what. The actual voltage is usually over 415v. Over 415v is more dangerous than 400v.

Well on Sunday I measured my own 1ph supply at 232.1V using an uncalibrated meter (but I've never had any doubts about its accuracy and always agrees well enough with my other meters), calculating up that should equate to 402V or as you say is over 415V.

Today I've been asked to 'baby sit' a DNO/supplier as an isolator is fitted in advance of fusebox changeover. Currently the voltages are:399,398,401,229,232,230. So just to make winston feel good; I'll agree the UK supply is over 415V

Even though my last couple of installations readings are bang on nominal

 

[JohnW2]

... Today I've been asked to 'baby sit' a DNO/supplier as an isolator is fitted in advance of fusebox changeover. Currently the voltages are:399,398,401,229,232,230. So just to make winston feel good; I'll agree the UK supply is over 415V Even though my last couple of installations readings are bang on nominal

I'm not sure that it should make him feel all that good - the voltages you're seeing (as you say, very close to nominal) are way above what they could have been (and probably are, in some installations).

I must say that I'm surprised that they seem to manage to keep domestic supply voltages as relatively constant as they are, whilst ensuring that that both the closest and furthest consumer from the tranny 'always' have voltages within the permitted range (216.2V - 252V).

Kind Regards, John

 

[SUNRAY]

Well on Sunday I measured my own 1ph supply at 232.1V using an uncalibrated meter (but I've never had any doubts about its accuracy and always agrees well enough with my other meters), calculating up that should equate to 402V or as you say is over 415V.

Today I've been asked to 'baby sit' a DNO/supplier as an isolator is fitted in advance of fusebox changeover. Currently the voltages are:399,398,401,229,232,230. So just to make winston feel good; I'll agree the UK supply is over 415V

Even though my last couple of installations readings are bang on nominal

Well that was a PITA, the appointment was 'between 10:00 and 13:00' to 'provide isolator'.
1) He turned up at 14:22 (not really a problem).
2) He didn't have an isolator.
3) He didn't have any cable for tails, I'd have cut existing tails and let isolator in but he said location would not be suitable.
I had enough bits of cable with me to do the temporary customer side work so went to wholesaler less than ¼mile away for an isolator.
4) When I got back at 14:52 he had left (I suspect he wanted to cancel the job as he was running late). Phone call to service rearranged for between '08:00 and 11:00'
5) A different guy arrived at 08:43 today.
6) He took one look at the job, cut the tails, saying he would not be permitted to install mine he let his isolator in.
7) I took advantage of power off to remove tails for 2 redundant fuse boxes from the Henley blocks.
8) He tested, sealed cutout and both sides of isolator and left at 09:32.

After he'd gone I measured the voltages: 232, 234, 231.
I then removed the 2 fuse boxes, cleaned up the debris and measured again: 231, 232, 231.

 

[SUNRAY]

Today I've been asked to 'baby sit' a DNO/supplier as an isolator is fitted in advance of fusebox changeover. Currently the voltages are:399,398,401,229,232,230. So just to make winston feel good; I'll agree the UK supply is over 415V

Even though my last couple of installations readings are bang on nominal

I'm not sure that it should make him feel all that good -

A was of course being a little... shall we say... sarc flippant.

the voltages you're seeing (as you say, very close to nominal) are way above what they could have been (and probably are, in some installations).

I must say that I'm surprised that they seem to manage to keep domestic supply voltages as relatively constant as they are, whilst ensuring that that both the closest and furthest consumer from the tranny 'always' have voltages within the permitted range (216.2V - 252V).

Kind Regards, John

Consistancy doesn't seem to be the problem it used to be. My first house (1983) was the second on a feed covering the whole street, of at least 100 properties. While renovating before I moved in I was getting through bulbs like they were going out of fashion and the display was worthy of a 70's mobile disco show. I measured a minumum of 250V and much more. a complaint to SEEBoard found them installing a pen recorder, I took the paper roll to work to photocopy the 'off the scale' spikes. A phone call following their removal and analysis revealed the scale was 200-300V. There was nothing below 250V and not much below 260V.

Their temporary solution was to provide a box of rough service bulbs. Eventually they installed another cable to the other end to make it a ring. It improved but still very noisy.

I had high volts when I moved to my current home in 1994 and a complaint found them blaming loose screws in my CU but the funny thing was seeing the voltage drop when they checked everything was OK at the sub.

 

[JohnW2]

A was of course being a little... shall we say... sarc flippant.

Yes, I obviously realised that - and was merely adding my own bit of flippancy

Consistancy doesn't seem to be the problem it used to be. My first house (1983) was the second on a feed covering the whole street, of at least 100 properties. While renovating before I moved in I was getting through bulbs like they were going out of fashion and the display was worthy of a 70's mobile disco show. I measured a minumum of 250V and much more. a complaint to SEEBoard found them installing a pen recorder, I took the paper roll to work to photocopy the 'off the scale' spikes. A phone call following their removal and analysis revealed the scale was 200-300V. There was nothing below 250V and not much below 260V.

I don't know what size conductors they use for their 'main' cables supplying a whole pile of properties, but if one does the sums, one needs a pretty low impedance to be fairly sure that (on one phase) the 'farthest' property does not get less that 216.2V, whilst the first does not exceed 253V, in the situation of a transient very high demand from 'downstream' properties.

Even more odd, my property is close to being the farthest from the tranny, yet my supply is usually between 240V and 245V, virtually never below 240V, so I have to wonder what voltage those closest to the tranny are getting!

[I'll leave EFLI to 'correct' me, if necessary, as regards furthest/farthest - no matter how many times I look it up, I never remember the answer!!]

Kind Regards, John

 

[EFLImpudence]

Farther away; further updates.

 

[AdrianUK]

From the ISKRA M750 measurement centre on our meter tails at home....

In the approx. 8 years this has been connected, its not unusual to see these kinds of variations.

 

[AdrianUK]

Yes, I obviously realised that - and was merely adding my own bit of flippancy
I don't know what size conductors they use for their 'main' cables supplying a whole pile of properties, but if one does the sums, one needs a pretty low impedance to be fairly sure that (on one phase) the 'farthest' property does not get less that 216.2V, whilst the first does not exceed 253V, in the situation of a transient very high demand from 'downstream' properties.

Even more odd, my property is close to being the farthest from the tranny, yet my supply is usually between 240V and 245V, virtually never below 240V, so I have to wonder what voltage those closest to the tranny are getting!

[I'll leave EFLI to 'correct' me, if necessary, as regards furthest/farthest - no matter how many times I look it up, I never remember the answer!!]

Kind Regards, John

Its not unusual to set a distribution transformer on the 433V tap (ie. -7.5% on the primary side)

 

[SUNRAY]

From the ISKRA M750 measurement centre on our meter tails at home....

View attachment 244912

In the approx. 8 years this has been connected, its not unusual to see these kinds of variations.

That looks rather lovely at 230 to 255V top level virtually within regs, (might just be with a differeny meter)

 

[JohnW2]

From the ISKRA M750 measurement centre on our meter tails at home....

A little clarification would be helpful ...

Do I take it that 'actual' means 'average' (since last reset)?

It seems regard nominal as 250V. The line across the voltage bar in the chart is presumably the 'actual', and looks about right (given that 239.47V is about 95.8% of250V). However the minimum recorded (229.91V) would be just over 80% of (250V) nominal. That makes me wonder what the length of the bars in the chart represent, since they are clearly not the total range (since the bottom of the voltage bar is about 92% on the chart. Does the bar perhaps represent an inter-quartile range or something like that?

In the approx. 8 years this has been connected, its not unusual to see these kinds of variations.

It's a long time since I last did any continuous monitoring here but, as I said, when I have done I have very rarely seen much less that 240V for any significant period of time (see below), and never anything like as low as, let alone below, the nominal of 230V.

I say 'for any significant period of time' since just looking at extreme summary statistics (like minimum and maximum) can be very misleading. One really needs to look at the pattern of variation over time (e.g. a graph of voltage vs. time), rather than just at extreme values - can your system provide that (and, if so, what does it show)?

Do you know what its criteria are for determining the 'minimum'? For example, if the voltage had fallen to, say 229V for a few seconds (or even just a few cycles) at some point since it was last reset (1st September), would it ('literally') report the 'minimum' as 229V, even if the voltage had been, say, above 240V for all but that few seconds of the month? If so, that would underline the need to look at the pattern of variation.

Kind Regards, John

 

[JohnW2]

Its not unusual to set a distribution transformer on the 433V tap (ie. -7.5% on the primary side)

That what I would have presumed was the norm, since that corresponds to a single-phase voltage of about 250V, hence 'within limits' even for a consumer very close to the tranny at a time of low demand. However, the voltage at the tranny obviously could not go appreciably above that without risking an 'above limits' voltage for the closest installations, at least 'at times'.

Kind Regards, John

 

[AdrianUK]

That what I would have presumed was the norm, since that corresponds to a single-phase voltage of about 250V, hence 'within limits' even for a consumer very close to the tranny at a time of low demand. However, the voltage at the tranny obviously could not go appreciably above that without risking an 'above limits' voltage for the closest installations, at least 'at times'.

Kind Regards, John

Bear in mind that the 433V will be the nominal voltage at full-load. When TX is lightly loaded & assuming, say, 5% regulation, its going to be heading towards 260V at the TX terminals. For this reason its rather difficult to maintain the voltage at the consumer terminals using distribution transformer taps alone (remember that DTx taps are almost always manual off load tap changers on the primary side)

 

[JohnW2]

Farther away; further updates.

Yes, I know, even though I usually forget (or, at least, lose confidence it my memory. It's one of those situations in which, although I suppose I actually 'know' which is correct, I nearly always question/doubt myself when I use one or other of those words!

What should be an easier way of remembering is that "far..." fairly clearly relates to distance (whilst 'further' tends to imply 'additional').

However, given that its nearly Friday, I wonder how you would feel about "a further distance apart", "further miles apart" or "further travel"?

Kind Regards, John

 

[JohnW2]

Bear in mind that the 433V will be the nominal voltage at full-load. When TX is lightly loaded & assuming, say, 5% regulation, its going to be heading towards 260V at the TX terminals.

Well, if you're talking about the full-load voltage, then that's the very problem I'm referring to - since if it provides 250V on full load, consumers very close to the tranny are presumably at high risk of getting >253V when the load is light.

For this reason its rather difficult to maintain the voltage at the consumer terminals using distribution transformer taps alone (remember that DTx taps are almost always manual off load tap changers on the primary side).

Indeed - the ideal would obviously be some sort of automated process, but that would presumably be very expensive to implement for every transformer. However, they presumably must try to keep the voltage supplied to consumers below the 'permitted maximum' (even those close to the tranny, at times of low demand) - presumably increasingly so since, as I understand it, 'over-voltage' will switch off PV systems.

Kind Regards, John

 

[BS3036]

Yes, I know, even though I usually forget (or, at least, lose confidence it my memory. It's one of those situations in which, although I suppose I actually 'know' which is correct, I nearly always question/doubt myself when I use one or other of those words!

What should be an easier way of remembering is that "far..." fairly clearly relates to distance (whilst 'further' tends to imply 'additional').

However, given that its nearly Friday, I wonder how you would feel about "a further distance apart", "further miles apart" or "further travel"?

Kind Regards, John

This interpretation sounds like something Winston would come up with. Neither the Oxford, nor the Cambridge English dictionaries support this interpretation, though they do point out that taking farther to mean distance is mostly an American usage. I guess EFLI encountered someone with a bee in his bonnet who convinced him it was right and has never been prepared to reconsider. I once knew a handyman who insisted that we had to call plugs plug-tops. Doesn't make it right.