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Cables in heating voids

Martyn
Hi Folks,


'intresting' day today...


So at the moment I am replacing a 150kW gas warm air unit, a huge thing in a commercial building.


Today I finished ripping out the old unit (146kW) the system draws in fresh air from outside and distributes the warm air via a network of underground ducts, really they are just concrete tunnels large enough to crawl through.


So being inquisitive and not being able to resist this unknown hole to somewhere in the floor of the plant room I stuck my ladders down there and went for a wander (pig in sh*it comes to mind ?) as soon as I get in there are 4 25mm galve conduits (building lighting 10x 10A) and a 25 2c SWA (feeding a kitchen sub 100A) with a 10mm earth attached snaking through there, I wander further 25m ish still the armoured and conduits but also a few fire alarm cables have entered the scene.


Swa -90's

Conduits - either 73 or 90's


Clearly a very convienient route for cables and none of them are showing any outward signs of distress (cant see in the galv conduits ofcourse)


Thoughts? Just canvasing opinion...
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    AJJewsbury:

    It's common practice is some parts of the world to run cables in ventilation ducts - the Americans have specifically "plenum" rated cables for the purpose.  Obviously ambient temperature needs to be taken into account - but if it's not cooking people near the outlets it's presumably more "warm" than "hot". So perhaps a bit of a de-rating factor, but I wouldn't be having kittens about it.

       - Andy.




    Hi Andy,


    Cheers for the reply.


    The Δ t for the unit heater is 39.6 ᵒC, on high fire, most of winter to be fair, that said the losses to the concrete will ce significalt, The SWA is never really loaded to much above 40A, though it is on a 100A fus.


    I am not unduely worried as noting visible is dispalaying any signs of thermal damage, that said 50-60 ᵒC  in there would'nt be unusual.


    Cheers


    Martyn

Reply
  • 0

    AJJewsbury:

    It's common practice is some parts of the world to run cables in ventilation ducts - the Americans have specifically "plenum" rated cables for the purpose.  Obviously ambient temperature needs to be taken into account - but if it's not cooking people near the outlets it's presumably more "warm" than "hot". So perhaps a bit of a de-rating factor, but I wouldn't be having kittens about it.

       - Andy.




    Hi Andy,


    Cheers for the reply.


    The Δ t for the unit heater is 39.6 ᵒC, on high fire, most of winter to be fair, that said the losses to the concrete will ce significalt, The SWA is never really loaded to much above 40A, though it is on a 100A fus.


    I am not unduely worried as noting visible is dispalaying any signs of thermal damage, that said 50-60 ᵒC  in there would'nt be unusual.


    Cheers


    Martyn

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