This discussion is locked.

You cannot post a reply to this discussion. If you have a question start a new discussion

Tingles from lead flashing on house with solar array - anyone else seen this?

A long phone call today with a good friend who is a Niciec Contractor, who is now facing a rather odd problem with a domestic solar array installed by others. The DC string cables from the panels on the roof to the inverter run along some distance under lead flashing, and now workers on the roof are reporting tingles from the metal flashing when standing on their scaffolding.

As part of the testing , the cables have been checked and are isolated from the metal and not damaged in any way. There is a rather variable AC voltage on the lead, relative to the scaffolding, which is at more or less the same as local earth potential. The measured voltage is considerably more when the inverter is on though does not fall completely to zero when it is not.

Now I have not seen the set up, as it is many miles away, but as the voltage is so variable depending on conditions, I am minded to suggest it is capacitive coupling between the DC string cables and the adjacent metal.

I'm also going to suggest earthing the flashing in any case.

However, has anyone else with more experience of modern domestic solar installation ever seen this sort of thing?

And am I even right in assuming the inverter action means DC strings are commutating at 50Hz relative to the mains, as would be needed to explain this effect?

Or am I going up the wrong tree altogether ?

The inverter suppliers are not much help, being more of a kit supplier than technical experts on what they stock, and this is not in their FAQ.

Parents

0 Jam over 5 years ago

First of all a clarification/correction: MIS 3002 v3.5 is still apparently current according to Gemserv and this makes no mention of the IET Code of Practice, so strictly speaking installers working to that can still use the 2013 "MCS Guide v2" as 'tis known and controm to contractual obligations. MIS3002 is a pre-requisite for the FIT, and it's possible that a local installer didn't get the memo about the about turn that means (£69) best practice contradicts their go-to main (free) standard. I don't often get involved in domestics these days though so there may have been an advisory, although with MIS 3002 most recently being updated in 2019 and the IET COP coming out in 2016 (with the same lead authors - plus others - as the MCS Guide) I'd expect to see it written into the standard by now if it were going to be.

A summary of the decision tree in the IET COP is visible on p15 of this BRE presentation.

In the document is the following statement

CHANGE FROM PREVIOUS APPROACHES IN THE UK

This Code of Practice requires that the PV array frame is connected to earth in all circumstances. This differs from the approach taken in some previous UK guidance documents.

The arguments for and against earthing an array frame are relatively complex and cannot be described in detail within this Code of Practice. However, the approach whereby PV array frames are earthed in all circumstances has the advantages of:

(a) allowing the d.c. isolation fault detection systems that are now provided within inverters to operate correctly (i.e. earth insulation resistance, residual current monitoring);

(b) removing the shock risk due to leakage currents on systems with transformer- less inverters; and

(c) bringing the UK in line with the approach taken in most other countries around the world (and IEC standards/documents).

In some circumstances an installer may need to work on or inspect a system installed to a previous standard that did not require array frame earthing:

(a) where an old inverter is being replaced by a modern device that includes d.c. isolation fault measures, it is recommended that, where practical, the installation of an array frame earth be included as part of the replacement works;

(b) where an installer is performing an inspection test on an older system, it is recommended that the lack of an array frame earth be noted on the condition report

(For those interested in such things, the original decision to not bond the array goes back to the first edition of the "DTI Guide" as twere known in 2002. DTI published an interesting and open commentary, "Background Information to the Installers Guide for Small Scale Mains Connected PV", DTI S/P2/00355/REP/2.... they appear to have been aware of the hazard but took the other path)

So the latest advice, from the IET of all people, would be that the array should be bonded, but both options appear to be current.

As an aside on larger commerical installations the accumulated leakage current can be into the dangerous region, but the scope of the MCS guide is only up to 50kWp so hopefully above that everyone is referring to the IET COP by now.
Cancel
Vote Up 0 Vote Down

Cancel

Reply

0 Jam over 5 years ago

First of all a clarification/correction: MIS 3002 v3.5 is still apparently current according to Gemserv and this makes no mention of the IET Code of Practice, so strictly speaking installers working to that can still use the 2013 "MCS Guide v2" as 'tis known and controm to contractual obligations. MIS3002 is a pre-requisite for the FIT, and it's possible that a local installer didn't get the memo about the about turn that means (£69) best practice contradicts their go-to main (free) standard. I don't often get involved in domestics these days though so there may have been an advisory, although with MIS 3002 most recently being updated in 2019 and the IET COP coming out in 2016 (with the same lead authors - plus others - as the MCS Guide) I'd expect to see it written into the standard by now if it were going to be.

A summary of the decision tree in the IET COP is visible on p15 of this BRE presentation.

In the document is the following statement

CHANGE FROM PREVIOUS APPROACHES IN THE UK

This Code of Practice requires that the PV array frame is connected to earth in all circumstances. This differs from the approach taken in some previous UK guidance documents.

The arguments for and against earthing an array frame are relatively complex and cannot be described in detail within this Code of Practice. However, the approach whereby PV array frames are earthed in all circumstances has the advantages of:

(a) allowing the d.c. isolation fault detection systems that are now provided within inverters to operate correctly (i.e. earth insulation resistance, residual current monitoring);

(b) removing the shock risk due to leakage currents on systems with transformer- less inverters; and

(c) bringing the UK in line with the approach taken in most other countries around the world (and IEC standards/documents).

In some circumstances an installer may need to work on or inspect a system installed to a previous standard that did not require array frame earthing:

(a) where an old inverter is being replaced by a modern device that includes d.c. isolation fault measures, it is recommended that, where practical, the installation of an array frame earth be included as part of the replacement works;

(b) where an installer is performing an inspection test on an older system, it is recommended that the lack of an array frame earth be noted on the condition report

(For those interested in such things, the original decision to not bond the array goes back to the first edition of the "DTI Guide" as twere known in 2002. DTI published an interesting and open commentary, "Background Information to the Installers Guide for Small Scale Mains Connected PV", DTI S/P2/00355/REP/2.... they appear to have been aware of the hazard but took the other path)

So the latest advice, from the IET of all people, would be that the array should be bonded, but both options appear to be current.

As an aside on larger commerical installations the accumulated leakage current can be into the dangerous region, but the scope of the MCS guide is only up to 50kWp so hopefully above that everyone is referring to the IET COP by now.
Cancel
Vote Up 0 Vote Down

Cancel

Children

No Data

Tingles from lead flashing on house with solar array - anyone else seen this?

Join us to get the best from IET EngX.

Community Rules & Guidelines