Swa on top of fibre glass roof

[Rockomuir]

Hello all, was supposed to be running a bit of 6 mm swa along outside of building for a shed. My plan was just to clip it along wall above ground floor extension. Customer now wants me to just lay swa on top of fibre glass roof. They are saying they don’t want to see cable clipped to wall from back of garden. This does not seem right to me. I cannot find anything in regs to say no. Just wondered what people’s thoughts are?

 

[Mikegh]

Is there any regulation on 'securely fixing cables' ?

Is the swa creating a hazard being on the roof ?

Can't think of much else, I'm not familiar with bs7671

 

[buzzlightyear]

Customer now wants me to just lay swa on top of fibre glass roof.

tell your customer that by doing that the cable is not secured. reg 522.8..4.. 05.

 

[Rockingit]

tell your customer that by doing that the cable is not secured. reg 522.8..4.. 05.

I think that's a misinterpretation of the regulations. The point of horizontal/vertical support is to avoid undue stresses to the mechanical properties of the conductors. A cable which is laid on something, end to end, is by nature actually supported along its entire length - it's no different to having that SWA buried in a trench or cables in conduit.

HOWEVER - what does come into play here is temperature. That cable is going to get roasting hot on a roof in the summer, and with fibreglass it's not going to have any radial dispersion at all. So the ambient temperature needs to be readjusted in the design calcs which might well mean that a larger conductor size is required or using xlpe @90+ ℃.

OP - have a read of App 4, 7.1

Goes without saying...... rough as dogs, even if it's 'legit'.

 

[Marvo]

............HOWEVER - what does come into play here is temperature. That cable is going to get roasting hot on a roof in the summer, and with fibreglass it's not going to have any radial dispersion at all. So the ambient temperature needs to be readjusted in the design calcs which might well mean that a larger conductor size is required or using xlpe @90+ ℃.............

Maybe you could just tell them to reduce the load by a few Amps for the few days of summer..?

 

[IAmSparkytus!]

Whats the shed being used for? Can't imagine a shed pulling 50-60amps

 

[buzzlightyear]

Whats the shed being used for? Can't imagine a shed pulling 50-60amps

It depends on his loading, might be a big shed or out house.

 

[westward10]

Is it suitably supported to prevent premature collapse in the event of a fire.

 

[GBDamo]

Is it suitably supported to prevent premature collapse in the event of a fire.

I think the water faeries would be more concerned being entangled in a few tons of collapsing roof that the few kilos of SWA on top of it.

Or is it a bit like the Covid cause of death? If there's unsupported cables within 28m of a dead water faerie then the cause of death is entanglement?

 

[LewisM]

Say you'll do it but you'll have to attach cable tray to the roof with adhesives. See what they say then

 

[littlespark]

I was on a similar job years ago. Flat roof. We laid 2x2 slabs on the roof, then screwed the regular tray brackets to them.

Can’t remember now if it was swa or pyro we ran on the tray???

The roof in the OP may not be flat

 

[IAmSparkytus!]

Aren't fibreglass roofs fire retardant making the premature collapse thing a non-starter anyways??

 

[westward10]

Aren't fibreglass roofs fire retardant making the premature collapse thing a non-starter anyways??

Fibre glass is resilient to fire but it will melt.

 

[buzzlightyear]

Me I tell the customer if it not fasen down the cable on top of the roof might start moving in high winds.

 

[IAmSparkytus!]

End of the day, if you aren't happy with the way they want it done and they won't be swayed, give the job a miss ?