Flexible steel conduit as mechanical protection

Hello I’m new to the forum (posting on it anyway). I could do with some advice...

Over the last 2 years I have been subcontracted (labour only) to commission solar PV systems. Often these are newbuild properties and when I get there the panels are already on and the DC cabling done.

About half the time the inverter is downstairs next to the CU and so the DC cabling is routed in the plasterboard stud walls in flexible steel conduit and clipped every 40 cm. In some places this cable run is within 50 mm of the surface of the finished wall.

The main contractor who is responsible for selecting and specifying this conduit was under the impression that it was sufficient mechanical protection as per reg 522.6.204 (iv) but I think this is wrong.

I have mocked up the situation and done my own rudimentary test. The conduit deflects away from a nail or screw in between clips, but if it happens where the clip is, or where the conduit is otherwise held, then on the nail or screw will easily pass through.

So, in order to asses the risks, my questions are -

What are the risks from the DC cabling?
What would happen if someone did put a screw or nail etc into one of the string cables?
What would happen if they hit both?

Thanks

Hello I’m new to the forum (posting on it anyway). I could do with some advice...
Over the last 2 years I have been subcontracted (labour only) to commission solar PV systems. Often these are newbuild properties and when I get there the panels are already on and the DC cabling done.

There is a potential issue with the DC cabling ( I.e. that it is not properly mechanically protected and is sometimes within 50mm of the finished wall surface - see my other thread for details - Flexible steel conduit as mechanical protection - 



I have tried repeatedly to get the main contractor responsible for the cabling to notify their certification body to get an answer as to whether the installations need to be fixed as this is a safety issue – but no joy. They say they have spoken to their MCS inspector who says they have no problem with it. I have no written proof of this and they won’t even tell me who it is.

So does anyone have any suggestions on the best way to go forward with this? Who are the correct body to inform?
I feel it would be wrong to drop it at this stage as there is a potential danger to the householders...

Flexy conduit is not adequate protection from screws nails etc.

Sidewinder said:

Flexy conduit is not adequate protection from screws nails etc.

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How do we get away with plastic capping then?

Plastic capping is not suitable for protection against penetration by screws nails etc also.

binky said:

How do we get away with plastic capping then?

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its sole purpose is to protect the cables while being plastered. thats it. if offers no mechanical protection to nails / screws

Andy™ said:

its sole purpose is to protect the cables while being plastered. thats it. if offers no mechanical protection to nails / screws

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I had noticed that . Can't stand the stuff. But it's clearly considered mechanical protection against a plasterer's trowel. So how is mechanical protection defined / what guidelines are there for that? I don't recall ever seeing any.

enough mechanical protection to stop the mud slingers trowel cutting the cable. someone hammering a nail into a wall to hang a picture? no chance. its also not required anyway

and 522.6.204(iv) is the one you want... which specifically states to protect from penertation of the cable by nails, screws and the like. exactly what is adequte is debateable, but since for capping (inc steel), you can easily hammer a nail throguh it, so definately not adequate

borneo said:

Hello I’m new to the forum (posting on it anyway). I could do with some advice...
Over the last 2 years I have been subcontracted (labour only) to commission solar PV systems. Often these are newbuild properties and when I get there the panels are already on and the DC cabling done.

There is a potential issue with the DC cabling ( I.e. that it is not properly mechanically protected and is sometimes within 50mm of the finished wall surface - see my other thread for details - Flexible steel conduit as mechanical protection - 



I have tried repeatedly to get the main contractor responsible for the cabling to notify their certification body to get an answer as to whether the installations need to be fixed as this is a safety issue – but no joy. They say they have spoken to their MCS inspector who says they have no problem with it. I have no written proof of this and they won’t even tell me who it is.

So does anyone have any suggestions on the best way to go forward with this? Who are the correct body to inform?
I feel it would be wrong to drop it at this stage as there is a potential danger to the householders...

Click to expand...

I have merged your two threads together as they are both relating to the same topic. 

Doc H.

Andy™ said:

and 522.6.204(iv) is the one you want... which specifically states to protect from penertation of the cable by nails, screws and the like. exactly what is adequte is debateable, but since for capping (inc steel), you can easily hammer a nail throguh it, so definately not adequate

Click to expand...

You could bang a nail through swa cable or drill a hole through steel conduit. So where do you draw a line.

binky said:

You could bang a nail through swa cable or drill a hole through steel conduit. So where do you draw a line.

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you could, however SWA is designed to protect the cable by shorting whatever you hit to earth and tripping the MCB./ fuse. its not required to stop a cable going through, unlike a steel plate etc. its all in 522.6.204

Having given those regs a read, if the steel flex conduit is earthed, it would suggest it would comply. But, as the DC cabling has no fuse protection as such, it wouldn't do a lot. Inverters do have DC monitoring built in, but that would not stop the solar panels pumping energy to the fault location. I once had a plumber core drill through the DC cabling, it eventually stopped shorting out about 6 inches above the short, when the ends of the cable had burnt out in a way that prevented it from arcing out anymore.

the steel in the flex conduit isnt designed to handle a fault current enough to operate an OCPD so still cant be used

Andy™ said:

the steel in the flex conduit isnt designed to handle a fault current enough to operate an OCPD so still cant be used

Click to expand...

fair enough.