Are Over Voltage Problems widespread

[matthunt]

Are any of you seeing High voltage problems in houses with Solar/PV installed in same street?

I attended a call out a few weeks ago due to the fuse board apparently smoking. When i arrived it transpired it was the shower circuit, the voltage measured was 246v and the current 36 amps meaning a 7.5kw shower drawing 8.8kw through a cartridge type Wylex db. The fuse was rated at 30amps and you just could not touch it due to the heat. We all know of the inherant problems with this type of fuse whilst continuing to operate on steady over current. Has anyone else seen this type of problem? as i am aware that multiple PV installs in a street on the same phase will obviously boost the voltage due to the nature of the invertors.

 

[matthunt]

all equipment sold in the UK should be rated for that full voltage range.

Similarly all installations including cables, MCBs etc should be sized to be capable of carrying the maximum current that unit can produce at all voltages. If it's not then that's not the fault of solar PV installations, it's the fault of whoever under-specified the cable / MCB in the first place.

If the local grid is going outside the allowable voltage limits due to solar installations, then it probably means those systems inverters haven't been set up properly to G83 protection settings, and the DNO would have the power to require those systems to be disconnected.

btw - the allowable instantaneous voltage limit is 264V, 253 is the maximum 10 minute average voltage.

fwiw, Northern PowerGrid have recently dropped the voltage across their networks by 6V to allow for greater solar PV input / reduce over voltage issues - many of which were actually down to the grid delivering power above the 253 limit prior to the PV being installed anyway.

There will be more and more issues around this, but if installed to current standards the issues should more be around voltage swings around the 253V mark as inverters cut in and out. We're hopefully going to be trialling a system with Northern PowerGrid to resolve this issue by setting the inverters to reduce their output as it approaches the voltage limit instead of just cutting in and out.

Hi Gavin, i think you are missing the point, the higher the voltage level the more power you use, as current is relative to voltage

 

[matthunt]

Where prey did you get that gem of misinformation. You (well I do) pay for electricity by volume. I.E. KWHr

Hi Tony, would that meter register a higher KWHr readingat 240v or 220v??

 

[Gavin A]

Hi Gavin, i think you are missing the point, the higher the voltage level the more power you use, as current is relative to voltage

no I'm not missing that point, I'm pointing out that circuits and CPDs should be designed to cope with the maximum possible power draw from the fixed device connected to that circuit at the maximum allowable voltage level.

In the case of a nominally 7.5kW rated shower (presuming it's rated at 230V), ohms law would give a maximum actual possible consumption level of 35.8A or 9kW at 253V, so the cable and protective device ought to be specified to be able to cope with that level of continuous load from that device. (actually the one I just checked was rated at 240V, which would be a lot less problematic - it also gives 35A as the rating needed for a cartridge fuse fwiw).

The problem in your situation in the OP wasn't solar pushing the grid voltage up, it was that whoever installed the circuit / shower unit had underspecified the fuse, so it was overheating while the grid voltage was well within the acceptable limits.

You're probably right to raise it as an issue though, as I reckon there's probably a fair few systems installed along similar lines out there, but the issue you described was more at the bathroom fitter end of the situation than the solar installer IMO.

 

[JD6400]

Hi Gavin, i think you are missing the point, the higher the voltage level the more power you use, as current is relative to voltage

Hi Mike , i think what Gavin has written does answer your op quite well ?

 

[matthunt]

Hi Mike , i think what Gavin has written does answer your op quite well ?

Hi Dip, thanks for your input

 

[JD6400]

Hi Dip, thanks for your input

You got it then !:hurray:

 

[GLENNSPARK]

no I'm not missing that point, I'm pointing out that circuits and CPDs should be designed to cope with the maximum possible power draw from the fixed device connected to that circuit at the maximum allowable voltage level.

In the case of a nominally 7.5kW rated shower (presuming it's rated at 230V), ohms law would give a maximum actual possible consumption level of 35.8A or 9kW at 253V, so the cable and protective device ought to be specified to be able to cope with that level of continuous load from that device. (actually the one I just checked was rated at 240V, which would be a lot less problematic - it also gives 35A as the rating needed for a cartridge fuse fwiw).

The problem in your situation in the OP wasn't solar pushing the grid voltage up, it was that whoever installed the circuit / shower unit had underspecified the fuse, so it was overheating while the grid voltage was well within the acceptable limits.

You're probably right to raise it as an issue though, as I reckon there's probably a fair few systems installed along similar lines out there, but the issue you described was more at the bathroom fitter end of the situation than the solar installer IMO.

its what i was gettin at n all.....poor choice of OPD..
possibly cable and install methods n all...

 

[matthunt]

no I'm not missing that point, I'm pointing out that circuits and CPDs should be designed to cope with the maximum possible power draw from the fixed device connected to that circuit at the maximum allowable voltage level.

In the case of a nominally 7.5kW rated shower (presuming it's rated at 230V), ohms law would give a maximum actual possible consumption level of 35.8A or 9kW at 253V, so the cable and protective device ought to be specified to be able to cope with that level of continuous load from that device. (actually the one I just checked was rated at 240V, which would be a lot less problematic - it also gives 35A as the rating needed for a cartridge fuse fwiw).

The problem in your situation in the OP wasn't solar pushing the grid voltage up, it was that whoever installed the circuit / shower unit had underspecified the fuse, so it was overheating while the grid voltage was well within the acceptable limits.

You're probably right to raise it as an issue though, as I reckon there's probably a fair few systems installed along similar lines out there, but the issue you described was more at the bathroom fitter end of the situation than the solar installer IMO.

Thanks Gavin, i am not trying to point the finger at anyone on the install or indeed if the solar install effected the voltage, the point is that higher voltage means excess current and unlimately will cause overheating prolems and sometimes fire.

 

[matthunt]

You got it then !:hurray:

Ok Dip, what am i meant to of got? go on humour me

 

[Gavin A]

Thanks Gavin, i am not trying to point the finger at anyone on the install or indeed if the solar install effected the voltage, the point is that higher voltage means excess current and unlimately will cause overheating prolems and sometimes fire.

not on a properly designed system it won't, at least not as long as the grid voltage stays within the allowable limits.

poorly designed systems may cause fires at higher grid voltages, so if you're not going to point the finger then I will - it's the fault of whoever designs and installs an under specified system, though in this case I'd hope the fuse would blow before it actually caught fire.

I suspect from the figures in the OP that in this case the installer may have been caught out by the shower itself being specced at 230V (possibly even 220V) rather than the 240V that a quick check shows seems to be more standard in electric showers for some reason, which pushes a 30amp fuse from borderline to significantly underspecced.

 

[JD6400]

Ok Dip, what am i meant to of got? go on humour me

Come now Matt by the very use of dip instead of DP i would say you got it and are now just playing .

 

[BillyTheSparks]

I've read this through and in not sure if I'm missing the point or whether I just don't get it as its been a long day.
But the shower is rated at 7500w max load (if I'm not mistaken) and the supply voltage is 253v this makes the current drawn at maximum use 29.64amps.
And at 210v 35.71amps,
then at the nominal 230v a current draw of 32.60amps.
So how or where can the shower be drawing 8.8kw of power?

I'm I on the wrong line here?

 

[matthunt]

not on a properly designed system it won't, at least not as long as the grid voltage stays within the allowable limits.

poorly designed systems may cause fires at higher grid voltages, so if you're not going to point the finger then I will - it's the fault of whoever designs and installs an under specified system, though in this case I'd hope the fuse would blow before it actually caught fire.

I suspect from the figures in the OP that in this case the installer may have been caught out by the shower itself being specced at 230V (possibly even 220V) rather than the 240V that a quick check shows seems to be more standard in electric showers for some reason, which pushes a 30amp fuse from borderline to significantly underspecced.

So if the 17th Edition Regs are based on 230v (of which the calculations are) and we design the cable calcs disconnection times around this,whose fault is it if the incomming supply is 240-250v (of which it is) and the circuit cannot take this voltage/current and subsequent load.

 

[Gavin A]

I've read this through and in not sure if I'm missing the point or whether I just don't get it as its been a long day.
But the shower is rated at 7500w max load (if I'm not mistaken) and the supply voltage is 253v this makes the current drawn at maximum use 29.64amps.
And at 210v 35.71amps,
then at the nominal 230v a current draw of 32.60amps.
So how or where can the shower be drawing 8.8kw of power?

I'm I on the wrong line here?

yes, you've forgotten about applying ohms law as the load is a resistive load, so the rated output only applies at a specific voltage. At higher voltages the ampage and wattage drawn also increases.

 

[matthunt]

Come now Matt by the very use of dip instead of DP i would say you got it and are now just playing .

Sorry DP, my friends call me Isacc :vanish: