Cable Size

[newman]

We ALL now know the inverter is correctly parametered to G83/1; so he can stuff THAT idea where the sun won`t illuminate it!My point was, as Prodave put in a better way, that 7671 is not the only set of rules to be followed here - but it DOES need to be looked at, in conjunction with other relevant publications.

Any installer who "tacks on" a PV install, as part of an existing, undersized final circuit, isn`t worth much. Sadly, there are lots of non-compliant installs around, `cos some companies wanted to maximise their instant revenue, by employing inexperienced persons to do their PV electricals - people whom most of us wouldn`t trust to make a cuppa on site safely, without supervision.

I know that doesn`t help you with this specific issue - maybe you need to speak to REAL assurance, or even MCS regarding this?

I have had a word with the installer to day about the G59/G83 settings and why he still thinks the inverter is set to G59, this is what he says

G83 has a wider voltage tolerance band than G59. SMAs default position is to set their inverters at this country

 

[newman]

The DNO came today and fitted the meter, he also did a few measurments for me

He measured between phase and neutral .4ohm

Phase and earth .1ohm both at the incoming source at the property

Also measured between phase and neutral .97ohm

Phase and earth 1.27ohm both of these at the inverter connection point

Does this help in any way ?

 

[NozSpark]

The DNO came today and fitted the meter, he also did a few measurments for me He measured between phase and neutral .4ohm

Phase and earth .1ohm both at the incoming source at the property

Also measured between phase and neutral .97ohm

Phase and earth 1.27ohm both of these at the inverter connection point

Does this help in any way ?

 

[Andy™]

+1

 

[newman]

[quote name='Andy

 

[ProDave]

Those readings don't quite make sense.

BUT the important ones (if they can be trusted) are phase to neutral at the supply point, 0.4 ohm, and phase to neutral at the inverter 0.97 ohm.

So from that we can deduce the cable resistance from incoming supply to the inverter is 0.57 ohms

So when your inverter is working flat out, producing 16A output, the voltage at the inverter will rise by 15.52 volts, and the voltage at the incomer will rise by 6.4 volts. If your nominal supply voltage is 240V, then it's not surprising that the inverter trips out at 253V.

So only 9.2V of that voltage rise is within your control.

9.2V represents a volt drop (rise) of 3.8%, so it complies with the general volt drop limit of 5%, it does not comply with the 3% volt drop for lighting (assuming the sumbain also feeds some lights) and it most certainly does not comply with the recommended volt drop of 1% for solar PV

Did he measure what the supply voltage was when he visited? or does the meter have a display on it that you can read off the voltage (picture of the monitor would be interesting)

There are 4 solutions:

1) the DNO can "improve" the supply. highly unlikely they will do that.

2) the DNO could reduce the nominal voltage. highly unlikely they will do that.

3) the DNO could authorise the installer to change the inverter parameter. At best a bodge.

4) the installer should come back and do something to lower the impedance of the cable (probably by fitting a larger cable) to reduce the volt drop within your installation.

So after lots of talk and debate, it looks like you now have some evidence to give to your installer to get him to actually come and do something about the excessive volt drop in the cable.

Incidentally, I found an almost identical problem being discussed on another forum, and the "solution" was the DNO authorised a change of inverter grid parameter. A cop out if you ask me.

---------- Post Auto-Merged at 22:08 ---------- Previous post was made at 22:00 ----------

What do you mean ?

the readings are a bit suspicious:

"He measured between phase and neutral .4ohm

Phase and earth .1ohm both at the incoming source at the property"

You would normally expect phase to neutral to be lower than phase to earth.

 

[NozSpark]

Those readings don't quite make sense.BUT the important ones (if they can be trusted) are phase to neutral at the supply point, 0.4 ohm, and phase to neutral at the inverter 0.97 ohm.

So from that we can deduce the cable resistance from incoming supply to the inverter is 0.57 ohms

So when your inverter is working flat out, producing 16A output, the voltage at the inverter will rise by 15.52 volts, and the voltage at the incomer will rise by 6.4 volts. If your nominal supply voltage is 240V, then it's not surprising that the inverter trips out at 253V.

So only 9.2V of that voltage rise is within your control.

9.2V represents a volt drop (rise) of 3.8%, so it complies with the general volt drop limit of 5%, it does not comply with the 3% volt drop for lighting (assuming the sumbain also feeds some lights) and it most certainly does not comply with the recommended volt drop of 1% for solar PV

Did he measure what the supply voltage was when he visited? or does the meter have a display on it that you can read off the voltage (picture of the monitor would be interesting)

There are 4 solutions:

1) the DNO can "improve" the supply. highly unlikely they will do that.

2) the DNO could reduce the nominal voltage. highly unlikely they will do that.

3) the DNO could authorise the installer to change the inverter parameter. At best a bodge.

4) the installer should come back and do something to lower the impedance of the cable (probably by fitting a larger cable) to reduce the volt drop within your installation.

So after lots of talk and debate, it looks like you now have some evidence to give to your installer to get him to actually come and do something about the excessive volt drop in the cable.

Incidentally, I found an almost identical problem being discussed on another forum, and the "solution" was the DNO authorised a change of inverter grid parameter. A cop out if you ask me.

---------- Post Auto-Merged at 22:08 ---------- Previous post was made at 22:00 ----------

the readings are a bit suspicious:

"He measured between phase and neutral .4ohm

Phase and earth .1ohm both at the incoming source at the property"

You would normally expect phase to neutral to be lower than phase to earth.

Exactly,,

So either the guy measured them wrongly, you misunderstood what he said or you have a serious problem with your supply

 

[newman]

Those readings don't quite make sense.BUT the important ones (if they can be trusted) are phase to neutral at the supply point, 0.4 ohm, and phase to neutral at the inverter 0.97 ohm.

So from that we can deduce the cable resistance from incoming supply to the inverter is 0.57 ohms

So when your inverter is working flat out, producing 16A output, the voltage at the inverter will rise by 15.52 volts, and the voltage at the incomer will rise by 6.4 volts. If your nominal supply voltage is 240V, then it's not surprising that the inverter trips out at 253V.

So only 9.2V of that voltage rise is within your control.

9.2V represents a volt drop (rise) of 3.8%, so it complies with the general volt drop limit of 5%, it does not comply with the 3% volt drop for lighting (assuming the sumbain also feeds some lights) and it most certainly does not comply with the recommended volt drop of 1% for solar PV

Did he measure what the supply voltage was when he visited? or does the meter have a display on it that you can read off the voltage (picture of the monitor would be interesting)

There are 4 solutions:

1) the DNO can "improve" the supply. highly unlikely they will do that.

2) the DNO could reduce the nominal voltage. highly unlikely they will do that.

3) the DNO could authorise the installer to change the inverter parameter. At best a bodge.

4) the installer should come back and do something to lower the impedance of the cable (probably by fitting a larger cable) to reduce the volt drop within your installation.

So after lots of talk and debate, it looks like you now have some evidence to give to your installer to get him to actually come and do something about the excessive volt drop in the cable.

Incidentally, I found an almost identical problem being discussed on another forum, and the "solution" was the DNO authorised a change of inverter grid parameter. A cop out if you ask me.

---------- Post Auto-Merged at 22:08 ---------- Previous post was made at 22:00 ----------

the readings are a bit suspicious:

"He measured between phase and neutral .4ohm

Phase and earth .1ohm both at the incoming source at the property"

You would normally expect phase to neutral to be lower than phase to earth.

Thanks for that ,he is back next week so I will get the readings checked,

The voltage at theincoming source was 246v-247v, at the inverter was about 249v

The phase to neutral readings ,I am pretty sure are correct.

 

[ProDave]

Thanks for that ,he is back next week so I will get the readings checked,The voltage at theincoming source was 246v-247v, at the inverter was about 249v

The phase to neutral readings ,I am pretty sure are correct.

So if you have a supply of 247V and the inverter trips out at 263V then you only have a margin of 17V to play with.

 

[steptoe]

I think you have a bad neutral,

I cant remember that far back, but what is the supply type, TNS?

on reading up on another PV topic these past few days, the reasoning behind the 1% volt drop, esp on long runs, is due to the fact the inverter is 'only' pushing out a relatively small current so the voltage will be required to rise somewhat excessively at the inverter end in order to match your incoming voltage by the time it reaches your consumer unit,

this is why your inverter is tripping on overvoltage so much, the DNO supply is probably pretty much irrelevant now I am privvy to this further info i have absorbed,

I will have another scan read and get you the documentation this came from.

 

[newman]

I think you have a bad neutral,I cant remember that far back, but what is the supply type, TNS?

on reading up on another PV topic these past few days, the reasoning behind the 1% volt drop, esp on long runs, is due to the fact the inverter is 'only' pushing out a relatively small current so the voltage will be required to rise somewhat excessively at the inverter end in order to match your incoming voltage by the time it reaches your consumer unit,

this is why your inverter is tripping on overvoltage so much, the DNO supply is probably pretty much irrelevant now I am privvy to this further info i have absorbed,

I will have another scan read and get you the documentation this came from.

Yes the supply is TNS

 

[steptoe]

OK, why VD must be minimised,

according to 'PHOTOVOLTAICS in BUILDINGS' 2nd edition, DTI/Pub URN 06/1972

section 2.3.1

The a.c. cable connecting the inverter/s to the consumer unit should be oversized to minimise voltage drop. A 1% drop or less is recommended. ,,,,,

Note 1

When generating, the voltage at the inverter terminals is higher than at the consumer unit. This voltage drop must be kept to a minimum in order to prevent the inverter nuisance tripping on over voltage.

 

[professional]

Just a thought but ....

If the inverter/SWA feeds sockets/lights DOWNSTREAM of any rcd protection then how can the installation meet the requirement for supplementary protection for socket outlets. The allowed clearance time for inverters ( I believe) is 500ms, well in excess of the 40ms that the installation may have been designed for?

 

[kme]

Just a thought but ....If the inverter/SWA feeds sockets/lights DOWNSTREAM of any rcd protection then how can the installation meet the requirement for supplementary protection for socket outlets. The allowed clearance time for inverters ( I believe) is 500ms, well in excess of the 40ms that the installation may have been designed for?

Close mate. If the inverter is capable of re-connecting to the grid "180 degrees out of phase", ( which every one I have ever dealt with is), that disconnection time rises to 5 seconds maximum.

This is the reason for the other big, ongoing issue with PV systems being installed onto "spare ways" of 16th- and 17th- ed. boards.

The inverter circuit is a distribution circuit. According to the BGB, it should not be fitted on the load side of ANY protective device feeding other final circuits.

And an RCD is a protective device..............

 

[newman]

Close mate. If the inverter is capable of re-connecting to the grid "180 degrees out of phase", ( which every one I have ever dealt with is), that disconnection time rises to 5 seconds maximum.This is the reason for the other big, ongoing issue with PV systems being installed onto "spare ways" of 16th- and 17th- ed. boards.

The inverter circuit is a distribution circuit. According to the BGB, it should not be fitted on the load side of ANY protective device feeding other final circuits.

And an RCD is a protective device..............

Sorry.............Whats the BGB

 

[wozz]

I though all phase neutral loops had to be below 0.35 to comply with supply regs to prevent voltage dips?

 

[professional]

Close mate. If the inverter is capable of re-connecting to the grid "180 degrees out of phase", ( which every one I have ever dealt with is), that disconnection time rises to 5 seconds maximum.This is the reason for the other big, ongoing issue with PV systems being installed onto "spare ways" of 16th- and 17th- ed. boards.

The inverter circuit is a distribution circuit. According to the BGB, it should not be fitted on the load side of ANY protective device feeding other final circuits.

And an RCD is a protective device..............

So, the installation of the PV system (and connection to the grid) is notifiable under Part P - presumeably the notification states that the install meets the building regs, but they don`t as they fail to meet BS7671 AND the building regs .... what standard ARE these installations adhering to with regards electrical safety?

What has actually been done about this longstanding "issue"?

 

[Jono Pashley]

MIS3002 4.2 (Pg 8)

Solar PV Microgeneration systems shall be designed and installed in accordance with the DTI

guide; "Photovoltaics in Buildings

 

[kme]

So, the installation of the PV system (and connection to the grid) is notifiable under Part P - presumeably the notification states that the install meets the building regs, but they don`t as they fail to meet BS7671 AND the building regs .... what standard ARE these installations adhering to with regards electrical safety?What has actually been done about this longstanding "issue"?

Very little, unfortunately.

The quote from the BGB is only from the amended 17th.

You are correct in that the PV installs are notifiable - yet, as Jono quotes so eloquently, MCS STILL post a "spare way in the fuseboard"; even though that won`t necessarily be compliant.

But, it DOES highlight the problem with "tacking the install" onto a pre-existing sub-main - it simply does not comply with anything.

The biggest problem is that many of the installation teams were "run" by the roofer - who employed a "part p spark" ( :slap `scuse me), who`d never had dealings with MCS, PV, DC or have the slightest idea that volt drop or disconnection times could have any implication in the real world - the bit about monkeys and peanuts comes back to mind.

They didn`t want fully qualified sparx; because they charge for for their time. The whole industry was poorly controlled and regulated; this is the beginning of the visible resultant fallout.

It didn`t help matters with the rush to get jobs installed before the deadline(s) - there weren`t enough qualified / competent guys out there to fulfil the demand - so anybody who knew which end of a screwdriver to hold had a guaranteed "job".

It is a 5h1te state of affairs mate. NIC AEs can`t decide between `em what is or isn`t compliant; IET haven`t replied to my emails yet (yawn).

what is "being done", you ask?

F` all - is the simple answer.

 

[steptoe]

KME.

what is the reg that you refer to here

According to the BGB, it should not be fitted on the load side of ANY protective device feeding other final circuits.