Wiring PIV Unit in Loft

peter212693 · 22 Oct 2017

Hi all,

Im looking at installing a PIV unit in the loft and this comes with a 3amp unswitched fused spur. House was rewired during a renovation in 2014 so all up to standard.

Can I add a junction box to one of the lighting circuit wires then run the same 1.5mm2 cable to the fused spur then from the spur to the unit? Ive not been in the loft for a while so cant remember if there is already a junction box up there but if there is I presume I can just tap of this as a spur? Draw on the unit is between 1 watt and 15 watt.

The unit

Jadele · 22 Oct 2017

no reason why not other than the obvious testing that wont happen following the alteration.

peter212693 · 22 Oct 2017

I presume this needs "sign off" with a minor works certificate for it to comply with regs?

Jadele · 22 Oct 2017

well thats a loaded question right there. The answer is yes. its up to you what you do.

Iggifer · 22 Oct 2017

peter212693 said:
I presume this needs "sign off" with a minor works certificate for it to comply with regs?

Doesn’t need signing off as such. If you were paying someone to do it, you would get a minor works.

Technically all DIY electrical work should have a minor works carried out by the person that carries out the work, but, in the real world, it doesn’t.

What you propose to do is fine

peter212693 · 22 Oct 2017

Thanks for you help guys, I will check for an existing junction later in the week. If there isn't one will I need a 5A junction box ?

flameport · 22 Oct 2017

20A will be far easier to wire, or just connect into an existing ceiling rose, or if there is enough slack on a cable use the FCU itself as the junction.

peter212693 · 22 Oct 2017

Thanks flameport, The closest rose isn't that far actually, so simply run a cable from this rose into the FCU then onto the unit?

Failing that, cut an existing cable and join it again using the FCU and then run from this to the unit?

Jadele · 22 Oct 2017

peter212693 said:
Thanks flameport, The closest rose isn't that far actually, so simply run a cable from this rose into the FCU then onto the unit?

Failing that, cut an existing cable and join it again using the FCU and then run from this to the unit?

Yeah cut cable has both ends in the supply side of the fcu and the feed is taken from the load side probably best done in flex and using the flex grip on the fcu if thats how you plan to wire the piv.

peter212693 · 22 Oct 2017

Thanks again, yea length of flex comes with the piv.

aptsys · 23 Oct 2017

Alternatively, depending on the amount of slack, you can disconnect from the nearest rose and run a new length of cable from the FCU back to that ceiling rose to avoid the need for any junction boxes. Depends on the logistics really.

peter212693 · 23 Oct 2017

Thanks for all your help. One final question, im looking at potentially using the "heat" model, which has a 400w heat element which kicks in if the temp of the air from the loft is below a set threshold. This model still comes with a 3a FCU so presume its still ok to install on the lighting circuit? Just 400w seems a lot but I suppose not much different to a high powered security light?

aptsys · 23 Oct 2017

I'd assess the rest of the items on the lighting circuit. So long as you don't have a whole bunch of GU10 downlights you'll probably be ok, but check the overall demand is unlikely to exceed around 1.2kW

JohnW2 · 23 Oct 2017

peter212693 said:
Thanks for all your help. One final question, im looking at potentially using the "heat" model, which has a 400w heat element which kicks in if the temp of the air from the loft is below a set threshold. This model still comes with a 3a FCU so presume its still ok to install on the lighting circuit? Just 400w seems a lot but I suppose not much different to a high powered security light?

400W is about 1.7A. Assuming that you have mainly 'modern' ('energy saving'/CFL or LED) lights, which use minimal electricity, I would personally see no problem in having such a load on a (presumably) 6A lighting circuit.

Kind Regards, John

peter212693 · 23 Oct 2017

Cheers,

Yea I have around 10 downlights in 2 of the bedrooms and energy bulbs on the upstairs lighting circuit.

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Wiring PIV Unit in Loft

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