Array bonding needed?

[malcolmsanford]

What amazes me here is the complete lack of electrical knowledge in this

When I did my PV course and this came up, and the tutor said yes you bond back to the MET unless it is PM-E, which it wouldn't be, but I let it pass it is TNC-S in the installation, when it is TNC-S you stake it .................what!!!!

Why ........because the DTI say so....ahhhhhh so if you had a stainless steel boiler flue that could be touched while also touching the frame, that flue is obviously connected to the boiler, pipework is connected back to the MET via main equipotential bonding, and you then bond your frame to an earth stake ................how safe is that when you have 2 potentials within touching distance on the roof ...................blank stares we shall move on

I have yet been given an answer to this, though I know what will happen, if you had a fault within the installation and you were in contact with both potentials..................

Again this is another of these belt and braces decisions by someone, who believes that because it is a TNC-S system, there is a danger of a lost neutral, so it is do it this way and there is less risk, rather than doing what is right and having the competent electrician design and install what is the correct installation.

I have no problem if the DTi want us to bond to a stake if there is a TNC-S system, providing that TNC-S is not on a roof already .................but I would rather them say regarding bonding that the qualified, competent designer should assess each installation as he sees it, and with the information given by the manufacturer, design, install and test an installation suitable for conditions, but then I'm assuming to much perhaps.

 

[rich.250]

I couldn't agree more malc. There doesn't seem to be knowledge behind these statements. Just 'cos it says so' lol.
There a lot of things that bug me with a lot of pv installs at the minute.....
Another is disconnection times.
Feeding into a Rcd way on a cu and then completely destroy the disconnection times for the property or a number of ccts with our even knowing what they are doing is wrong.........

 

[SolarCity]

I couldn't agree more malc. There doesn't seem to be knowledge behind these statements. Just 'cos it says so' lol.

Well I do 'know' that is 'says so', so I suppose there is some knowledge behind it. As soon as you're writing the guidelines that I'm expected to adhere to then I suppose I'll be doing it your way.

There a lot of things that bug me with a lot of pv installs at the minute.....
Another is disconnection times.
Feeding into a Rcd way on a cu and then completely destroy the disconnection times for the property or a number of ccts with our even knowing what they are doing is wrong.........

A pretty general statement. Most of the installers on this forum know that that is bad practice so to I don't really see your point.

 

[rich.250]

Well I do 'know' that is 'says so', so I suppose there is some knowledge behind it. As soon as you're writing the guidelines that I'm expected to adhere to then I suppose I'll be doing it your way.



A pretty general statement. Most of the installers on this forum know that that is bad practice so to I don't really see your point.

I wasn't having a go at anyone in particular.
Yes a lot of people know, just saying that shouldn't it be an important part of the course??
It's not just bad practice. It's dangerous. Say you have a TT with Rcd upfront in the cu. then you had a pv cct in the spare way at the end. Now instead of a 0.2 sec disconnection time. It's probably 5secs depending on equipment used.
You may aswell throw the Rcd in the bin and fit a main switch LOL.
Like I said not pointing fingers just see a lot of it....

 

[rich.250]

Also it is all in bs7671. So follow those guidelines

 

[SolarCity]

I wasn't having a go at anyone in particular.

Nope, just the industry in general

Yes a lot of people know, just saying that shouldn't it be an important part of the course??

Of course, as should plenty of other stuff. So should a lot of stuff on the 6 week sparky courses.

Say you have a TT with Rcd upfront in the cu. then you had a pv cct in the spare way at the end. Now instead of a 0.2 sec disconnection time. It's probably 5secs depending on equipment used.

Like I say, most of us know this already. So I ask again, what is your point? It doesn't seem at all relevant to the current discussion.

You may aswell throw the Rcd in the bin and fit a main switch LOL.

That truly is a rib tickler.

 

[malcolmsanford]

Solar I think what Rich and I mean is that unfortunately the electrical industry as a whole as gone through this "belt and braces" approach to things, and if i'm honest I think PV is perhaps on line with the much maligned Electrical Trainee.

I did my course in May 2010 and to be honest it was pitiful and frightening the guys on it, that were roofers and plumbers, and were passed to be competent in all aspects of PV installation, and some of the basic lack of electrical knowledge on the forum as a whole is terrible.

Now the course may have improved, but in all honesty you just read this thread and some her can't determine whether it is earthing or bonding, and the sad thing is those who don't know what it is, don't think it matters, after all it does the same thing and goes to the same place .....................

The electrical industry as a whole and domestic and PV particularly does suffer it's fair share of poorly trained incompetent installers.

This is my worry, when an organisation feels it needs to compensate for this poor training, by adopting a belts and braces approach to an industry, it is going down the road to creating more problems. They are covering over cracks in an industry that unfortunately is in it's death throes.

The lads in our industry have won a significant battle over BESNA, but we are going to create an industry so fragmented in regards to trained and competent sparks in commercial/industrial and A N Others in domestic. There will be incidents happening IMO with this belt and braces approach, you can not compensate for poor training with a one size fits all appraoch, not in our industry.

 

[SolarCity]

I think in general I'm largely in agreement with you, Malc.

Unfortunately, with regards to this issue PV installers must go by the decision tree - whether they like it or not.

As for bonding and earthing, I know what you mean. The Dti guide itself refers to it as both bonding and earthing in different instances which confuses people even further. Bonding IS, for reasons that escape me, badly misunderstood.

 

[rich.250]

Yes malc. That was my point. Thanks for explaining.
If some installers don't know about disconnection times and earthing and bonding. They shouldn't be doing it!!
Like I said solar, I'm not having a go at you or the industry (cos I'm in it too)
Just as you said the Electrical Trainee. Or 5dw in some cases lol.
I know this probably isn't relevant to 90% of forum members.

 

[SolarCity]

If you read most of my posts, I have often moaned about the lack of electrical expertise in this industry.

A lot of the installs appear to be installed as kits with the electrician having no input whatsoever. They are handed an inverter, some isolators and told what to do.

The survey and design stage appears to be no more than 'will it fit?', 'where can I buy a kit' and 'how much shall I charge'.

 

[rich.250]

That sounds like the surveying they done on a rental property of mine some 5years ago. LOL

 

[malcolmsanford]

I think in general I'm largely in agreement with you, Malc.

Unfortunately, with regards to this issue PV installers must go by the decision tree - whether they like it or not.

As for bonding and earthing, I know what you mean. The Dti guide itself refers to it as both bonding and earthing in different instances which confuses people even further. Bonding IS, for reasons that escape me, badly misunderstood.

Well mate that just about sums it all up .................. we have a guide written by the looks of things by civil servants and not a technical input in sight.

Bonding in misunderstood because the training these guys receives is pitiful. We are no longer training guys to teach them an industry, but to pass exams and assessments so that they can stumble along in the industry and hopefully not kill or injure someone.

I sometimes wished we had more incidents in our industry, a few more deaths or a few more properties burnt down, may just may convince the bureaucrats that what they are doing to it is criminal. Yes domestic is not rocket science a few cable pulled in here and a few bits and bobs and there you go, bit like a nurse or a doctor taking your blood pressure, whack on a cuff, read a screen and there you go .....high blood pressure, but isn't it wonderful that that doctor will know why it's high, and what he can do to decrease it, that is called training, we just have guys that know yes wire A goes into equipment B not not a clue why

 

[Earthstore]

I could not agree more with Malcolm, I am not a sparky, but my background is more mechanical, if you get an electrical problem on a car, it is far more complex, 108 tiny wires to an ECU and you have to find the fault, so you have to understand how it works, to then work out why it does not.
It is sad that I appear to have a better understanding of PV systems than some sparky's (only some), and they are installing it.
The bureaucrats do seem to believe that if you can fill in reams of paper work, then the customer will get a quality install, I am waiting for the sad day when someone does get hurt.

 

[rich.250]

I don't think the people you talk of earthstore are actually electricians.... Else they could work out what is right and what is wrong.
Ok yes, training they receive is a big factor, but as a professional should it not be on your shoulders to ensure the job you do is correct and up to current standards??

 

[rich.250]

Malc, the doctor nurse description perfectly sums it up.

 

[Earthstore]

Thank you, Professional, I like that,
I do not install, I will help if need but only as an assistant, when I have sold a job, I kind of project manage it from beginning to end, I check that all work is to a high standard, from mounting of the panels through to the wiring, I work with the installers to make sure everything is right for the customer, so that I am proud of the work that I have sold.
I have learnt so much from this forum, as there are many experts here, so I am aware of how it should be done.
The PV industry has now got so complex, but I try my hardest to keep up with it all.
Pride is a word that appears to be lost in modern society, but some of us still have it.

 

[moggy1968]

strange how when managing projects it's the time served apprenrice trained electricians who have tried to insist everything has to go on an RCD under 17ed, and that it's fine for the PV to go on a shared RCD, and aren't prepared to listen to anyone telling them different. At least the short course guys tend to be willing to listen and learn, unlike the arrogance of some time served sparks.

Now, shall we stop making sweeping generalisations and chucking insults at people and get back to the topic.

 

[Earthstore]

Sorry...
So should an array be bonded and earthed???

 

[Gavin A]

What amazes me here is the complete lack of electrical knowledge in this

When I did my PV course and this came up, and the tutor said yes you bond back to the MET unless it is PM-E, which it wouldn't be, but I let it pass it is TNC-S in the installation, when it is TNC-S you stake it .................what!!!!

Why ........because the DTI say so....ahhhhhh so if you had a stainless steel boiler flue that could be touched while also touching the frame, that flue is obviously connected to the boiler, pipework is connected back to the MET via main equipotential bonding, and you then bond your frame to an earth stake ................how safe is that when you have 2 potentials within touching distance on the roof ...................blank stares we shall move on

tbf to the dti guide, this was a problem with your tutor, not the guide.

The guide says bond to MET if it's in the equipotential zone to avoid this issue.

 

[saint]

Earthed no never. Bonded no but for some reason we are told we must. This will change soon surely.

 

[rich.250]

strange how when managing projects it's the time served apprenrice trained electricians who have tried to insist everything has to go on an RCD under 17ed, and that it's fine for the PV to go on a shared RCD, and aren't prepared to listen to anyone telling them different. At least the short course guys tend to be willing to listen and learn, unlike the arrogance of some time served sparks.

Well you always get some. Tend to be the ones who hate updates and testing there own work as they know it's good LOL

 

[moggy1968]

yep, I'm afraid it's not how you trained that matters, it's how good you are at your job

 

[moggy1968]

TBH the whole issue of having to go to a spike if it's TNCS makes no sense to me, it's totally inconsistent to my mind. If we say an attached garaged is in the equipotential zone then why is a structure attached to the roof not? It's even acceptable to bond back to the MET on a detached garage according to ELECSA as long as it's not too far away (this was the scenario on my first assessment, they declined to say what 'not too far way' actually meant).
I can't really fathom why there is such an inconsitencey.

 

[rich.250]

You can extend a equip zone anywhere in theory. Aslong as you bond any services or parallel paths in that part back to the MET at the origin with a unbroken cable. I.e normal bonding rules. The only thing is you need to calculate the size of conductor required to stay under your 0.05 ohms.

As for bonding the array. I don't see that it should be introduced into the zone. As it is not in contact with the ground. So no parallel path. At all.

This reminds me of an example. Would you bond your knife and fork, there metal. And you can touch them and a bonded pipe..... LOL

 

[rich.250]

Theres a sticky on here to look at on exporting tncs

 

[moggy1968]

I don't see why it should be either, but if it has to be I don't really see why it needs a spike on a TNCS when other things don't.

This reminds me of an example. Would you bond your knife and fork, there metal. And you can touch them and a bonded pipe..... LOL

I've seen door handles and bannister rails supplementary bonded!

 

[rich.250]

The stake on a tncs is an absolute no no. I'd never even contemplate it.
All you will do is cause a potential difference.

I seen this on a farm, well reversed.
Retarded spark put new cct on tncs. And the difference in potential between the farm (TT by requirement)
And the new cct. Killed cattle.

 

[malcolmsanford]

tbf to the dti guide, this was a problem with your tutor, not the guide.

The guide says bond to MET if it's in the equipotential zone to avoid this issue.

Are you a PV installer, becasue even though i'm not I still know that the current DTi guide tells you that if you have a TNC-S system that needs bonding it must be spiked ....................or am I wrong

 

[malcolmsanford]

yep, I'm afraid it's not how you trained that matters, it's how good you are at your job

Is that a serious remark .................... your telling me that it is irrelvant how you are trained

 

[Gavin A]

All you will do is cause a potential difference.

potential difference to what though?

under the DTI guide 2006 decision tree the frame should only be bonded to a seperate earth spike in situations where there is nothing else for there to be a potential difference to. If there is anything within reach of the frame that was bonded to the MET then the frame would have to also be bonded to the MET.

That's the argument in favour of this as far as it goes, along with not unnecessarily bringing the equipotential zone out on to the roof (via bonding to the MET), as anyone then accessing the roof / frame via a metal ladder, or scaffolding and touching the frame would then introduce the danger of a potential to earth via the ladder / scaf that was different enough to that via the MET bonding to cause problems if both were touched at once (pretty likely).

Personally though we've not been installing earth spikes, or earthing the frame at all unless we actually measure a potential to earth from the frame since last Autumn when I realised that the new draft guidance matched our real world experience and measurements that show bonding the frame to not be necessary unless there already was a potential to earth.

Comparing the risks from the few micro-amps worth of leakage current the panels / frames may end up carrying with a TL inverter vs the risk from either earthing or bonding the frame resulting in a potential to earth that didn't exist before, and IMO the safest option is not to bond or earth the frame.

If there is potential to earth via the frame already, then that changes things.

The risk of a slight tingle from the frame in damp conditions can be entirely removed by switching the DC isolator off anyway before accessing the roof, which is the instruction we give to our customers.

 

[Gavin A]

Are you a PV installer, becasue even though i'm not I still know that the current DTi guide tells you that if you have a TNC-S system that needs bonding it must be spiked ....................or am I wrong

you're wrong.

In the equipotential Zone? >> Yes >> bond to MET*


if it's not in the equipotential zone, then you would bond to an earth spike if you were following the 2006 DTI guide.






*actually it calls it the consumer earthing terminal, but I take it you'd accept that this is what it means.

 

[malcolmsanford]

Are you still not following the 2006 guide, as the new guide is still under consultation I believe ..............or have you started working to it?

How is something on a roof in the equipotential zone, unless you extend the zone out to it which the 2006 guide tells you can't ?

 

[rich.250]

Yes that makes sense. I can see that bonding it to the met in a TN system could introduce a potential to a metal ladder. Which as you said. Is exactly why it should not be bonded. At all unless you do somehow measure continuity from the frame to the met.
I think more people need to just stop for a second and think before just following these guides like yourself. It will make perfect sense to them if they think about it. And after all they are just guides.

 

[Gavin A]

Are you still not following the 2006 guide, as the new guide is still under consultation I believe ..............or have you started working to it?

mostly we are, but in this case no we're not because we believe it to be unsafe, and the draft guidance gave me sufficient support for what I was already thinking to take the decision to stop doing something that was unnecessary and potentially dangerous just because some 6 year old guidance written when TL inverters had only just hit the market said we should.

I'd be surprised if the authors of the 2006 DTI guide had installed anywhere near as many TL systems as we have, and our real world experience indicates that the issue they were trying to guard against is simply not a problem in reality.

How is something on a roof in the equipotential zone, unless you extend the zone out to it which the 2006 guide tells you can't ?

it's in the equipotential zone if some other bonded metal system is already bringing the equipotential zone on to the roof within reach of the frame (eg gas flue), or it's below a velux and within touching distance of a radiator etc. (or by some interpretations of it, just being within touching distance of a velux itself).

 

[rich.250]

The velux??
That doesn't need bonding either.... Lol.
I can see your point about people hanging out the window and holding the rad for support. But like you said if the array isn't bonded then there's no chance of them coming to harm as it is on the roof with no path to earth.

 

[moggy1968]

Is that a serious remark .................... your telling me that it is irrelvant how you are trained

yes it is, yes I am. To a point. As before, lets stay on topic. Start a seperate thread if you want to discuss this.

 

[wstevew]

So would I be right in saying that most think bonding isn't required but some are doing it because the current DTI decision tree says so?

Im not sure why SMA suggested getting the installer to make sure the array is bonded when I asked about the 601 error (unless they think a difference in potential somewhere would be detected as DC current by the inverter). I believe the arrays are not bonded.

Anyway the 601 events which happen approx twice a week up until now were before and after feed in. I now think this may be a coincidence as I was up and out earlier this week as I have been working away and there was a 601 error around the time I was getting ready (i left at 6am, a while before feed in).

The only things electrical I would have used would have been lighting. My suspects at the moment are.

Led lighting 6 x 3w mr11 running off 3 12v 1a DC psu (2 lamps on each psu)
Led lighting 5 x 6w mr16 GU10 240v

Illuminated Bathroom mirror 140w halogen with wound transformer (has a pull cord I need to replace as one set of contacts are going bad, pull cord is on the 12v ac side).

 

[grandfortune]

DOnt just think of people hanging out of houses and such, there are other considerations to think of, Its an important subject that needs some clarity, Nice little report here, long winded but pictures alone look good, remember shock date results are based on 60Hz.


http://www.mikeholt.com/files/PDF/firefighterSafetyPV.pdf

 

[Vegelen]

SMA recommend that solar panel rails are earthed when using SMA inverters without a transformer. i.e TL's.

Quote from an email received from Mark Ryder at SMA:

"SMA do suggest that you earth the solar panel rails when using inverters without a transformer.


Kind regards, Mark Ryder, SMA UK"


The Importance Of Earthing Solar Panels:

Earthing solar panel frames - Energy Matters

The reason to earth solar array frames installed with transformerless electronic

inverters, may be for functional operational reasons, not just for safety concerns.

I have seen evidence of a solar system with SMA 3000TL perform differently relative

to another local system, after it was earthed 10 days after installation.

Earthing the array frame changed its performance relative to another local system.

 

[JulianC]

I had/have a DTI document which provides guidance and explanations to the content of v2 of the DTI PV guide. Unfortunately I can't find it at the moment (and may not have liberated it from my previous employer). It did go into the reasons why they required an array frame to be bonded if using a transformerless inverter. Bear with me on this as my memory is sketchy, but it was something to do with the simultaneous occurance of a fault on the inverter sending AC to the array and a fault with the array or DC wiring presenting AC to the array frame work, coupled with the likelihood of some chap up an aluminium ladder that is connected to earth touching said array frame. Don't quote me 100% on that but it was something equally as convoluted and unlikely.