To Bond Or Not To Bond? - That Is The Question

[stevie gill]

Hi All,

I know this topic has been covered to death, but can't really find a definitive answer for my particular query in previous posts; therefore I'm after a little advice;

We are about to commence work on a 24kWp (2 separate arrays) system, fixed to a metal sheet roof. We are using 2 SMA Tripowers - a 12000TL and a 10000TL.

The TL inverters need bonding as per smaller domestic versions.

There is access onto the roof for maintenance purposes so you could state that it still forms part of the equipotential zone and therefore needs bonding.

My query is, the building is having a lightning protection system and both arrays will be connected to this, so do I still need to bond the arrays using traditional methods???

Any help you guys can provide would be greatly appreciated.


Regards,

 

[SibertSolar]

Steve, by bonding do you mean earthing? If you are electrically connecting the array framework to an existing LPS then that pretty much gives you the electrical earth connection I think you are referring to. Bonding between metalwork of the array may be required but I would imagine that you would need to run some continuity/resistance tests to ascertain this?

Bear in mind that if a PV array framework is electrically connected to an LPS then you may need to consider Type1 combined lightning/surge protection for the DC inputs to the inverters. If you need any assistance with that then feel free to contact me to discuss further,

Andy

Edited to add - see here for an overview of different types of lightning/surge protection and associated scenarios

 

[stevie gill]

Thanks Andy. Just sent you an email with details of our setup.

Steve

 

[Worcester]

The TL inverters need bonding as per smaller domestic versions.

DO THEY ????? Are you talking there about the array or the inverters themselves?


The "3rd edition" of the pV guide makes it all a lot simpler and clearer..... Now an MCS publication (see page 38 on) At least that section makes good sense now. (Even if others don't)

What most people also forget when 'Bonding' (as opposed to earthing) is that it is perfactly acceptable to use the building framework as bonding conductors.

Technically there is a big difference between bonding, and connecting to LPS.

 

[stevie gill]

Wasn't very clear with my wording. When taking about inverters needing to be bonded, I actually meant the array frame itself.

First time we've come across working alongside an LPS hence why I'm querying it, but thanks for taking the time to respond.

 

[Worcester]

In which case in either a commercial or a domestic situation you'll find that there is rarely any need to either bond or earth the array. (LPS Aside) - Please read the guide - it's has been officially out since February.

 

[stevie gill]

Officially out since February but only in force since May 7th. As a rule of thumb, we always bond arrays when using TL inverters (with no galvonic isolation) as we deem it is still part of the equipotential zone, but others will argue until they're blue in the face about whether it is needed or not.

Andy is providing me with his thoughts RE LPS systems and the requirement for SPDs etc which I look forward to reading a little later on.

 

[Gavin A]

Officially out since February but only in force since May 7th. As a rule of thumb, we always bond arrays when using TL inverters (with no galvonic isolation) as we deem it is still part of the equipotential zone, but others will argue until they're blue in the face about whether it is needed or not.

Andy is providing me with his thoughts RE LPS systems and the requirement for SPDs etc which I look forward to reading a little later on.

no argument, it just isn't unless it's an extraneous conductive part.

IME metal roofs are either fixed to wooden supports and not conductive to earth, or they're fixed to multiple massive steels embeded in the ground and are so conductive to earth that they don't need bonding.... but easily enough worked out via a test of the frame continuity to earth / Zs reading.

Personally I'm really reluctant to take the equiptential zone out on to the roof unless it's absolutely necessary as the most likely scenario for danger is that some future installer get's a belt off the panels while stood on a metal ladder purely because of an earth fault elsewhere in the building that's fed back down your bonding and formed an earth loop via the installer, metal ladder to earth..... and belts like that while stood on ladders are likely to result in a fall from the ladder that's far worse than the belt itself.

 

[moggy1968]

no argument, it just isn't unless it's an extraneous conductive part.

IME metal roofs are either fixed to wooden supports and not conductive to earth, or they're fixed to multiple massive steels embeded in the ground and are so conductive to earth that they don't need bonding.... but easily enough worked out via a test of the frame continuity to earth / Zs reading.

Personally I'm really reluctant to take the equiptential zone out on to the roof unless it's absolutely necessary as the most likely scenario for danger is that some future installer get's a belt off the panels while stood on a metal ladder purely because of an earth fault elsewhere in the building that's fed back down your bonding and formed an earth loop via the installer, metal ladder to earth..... and belts like that while stood on ladders are likely to result in a fall from the ladder that's far worse than the belt itself.

I had a call out to a tenanted house where this happened through the taps. Main earth was loose, so making a bad connection. A kitchen socket without a grommet had worn through the cable, which shorted out on the back box to earth, via the taps as the main earth was missing. had there been a solar array that could easily have become live if bonded, exactly as you say.Is there really a risk of the array frame becoming live with DC currents under fault conditions, I can't see it myself. There is no AC anywhere near it, but if you bond it to the MET, then there is a possibility.