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Thread: Anybody ever worry about fire when mounting a powersupply in a plastic box?

  1. #1
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    Default Anybody ever worry about fire when mounting a powersupply in a plastic box?

    I am working on wiring for my house outline. I am a little concerned about putting a power supply in a plastic box in my attic (blown in insulation) or under the house eves. Everything will be fused dc side, ac side gfci.
    Am considering using metal boxes, but wonder if I am overthinking this. Anyone ever have one of the typical cheap power supplies fail in a possible fire hazard sort of way?

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    Default Re: Anybody ever worry about fire when mounting a powersupply in a plastic box?

    Never had a PSU go up in flames. I have had a few buck converters melt the surface of an enclosure before the fuses popped. Not to say it cannot happen, but I suspect many of us have the PSUs in a variety of plastic enclosures (mine are CG1500 cases) and have not had significant issues with them.


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    Default Re: Anybody ever worry about fire when mounting a powersupply in a plastic box?

    Quote Originally Posted by aknflyer View Post
    I am working on wiring for my house outline. I am a little concerned about putting a power supply in a plastic box in my attic (blown in insulation) or under the house eves. Everything will be fused dc side, ac side gfci.
    Am considering using metal boxes, but wonder if I am overthinking this. Anyone ever have one of the typical cheap power supplies fail in a possible fire hazard sort of way?
    My first thought was not to mount in the attic....too hot. Some electronic equipment may not be rated for temperatures the attic can generate.
    For your plastic box vs metal box: If you feel you need a metal box, then you should also use metal encased wire to that box. A failure of the power supply should open the fuse and shutdown before any damage, if not, then the incoming wire has become the fuse and is overheating against bare wood.
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    Default Re: Anybody ever worry about fire when mounting a powersupply in a plastic box?

    Suggest you forget about the attic anyway. Aside from possible fire issues, Controllers do need a little TLC once in a while, and you want them to be easily accessible........

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    Default Re: Anybody ever worry about fire when mounting a powersupply in a plastic box?

    I too echo the advise that you do not put these in an attic unless you put them in a UL approved metal AC junction box.

    Anything can go up in flames. Especially something that is attached to the AC power.

  6. #6
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    Default Re: Anybody ever worry about fire when mounting a powersupply in a plastic box?

    Hi, I’m UK and an ex-electrician; I do have two power supplies in my loft space.

    • My loft space is ‘cold’ i.e. the insulation is in the loft floor not the roof.
    • The average temperature of my loft during the show period is -10 to +10 Deg C.
    • Both power supplies are only run at about 50% and are in large galvanised metal boxes, mounted to a none flammable surface.
    • All cables that enter or leave the enclosure pass through glands and there are no ventilation holes.
    • The cable that feeds the supply is fused at its source which is outside the loft.
    • All the fuses that protect the cables from the supply are contained within the steel box.

    I like you may have over thought this but it suited me to have supplies in the loft space so I looked at the risks mainly fire.

    • The cable that feeds the supply – fused at source.
    • The power supply – contained in a fire proof enclosure (metal box).
    • The outgoing cables – fused at the power supply.
    • Fuses blowing and discarding molten parts – outgoing are contained within the metal box, incoming are not in the loft space.
    • Power supply failure or fuse blowing resulting in fire or hot parts being discarded – both contained within a metal box and all entry and exits being through glands.

    I agree with the posts above that in an ideal world you wouldn’t have a power supply and cabling in a loft space or come to that your house. But if you are going too, remember that fuses stop cables catching fire.

    30A power supply -> 3 x 10A fuses feeding 3x 10A rated cables -> 6 x 5A fuses feeding 6 props each with 5A rated cables.

    Unless contained within an enclosure (metal or plastic) I would not use automotive type fuse inside a home because of the risk of hot discarded elements, however correctly selected glass fuses will contain hot material in the event of a fault.

    Too finally answer your question – no I haven’t had issues with any power supply, but given my build any fail should only be an inconvenience not a life threat.
    Last edited by Barnabybear; 07-11-2018 at 08:51 PM.

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    Default Re: Anybody ever worry about fire when mounting a powersupply in a plastic box?

    Thank you all for the replies. My home design requires the supplies mounted under the eves or in the attic, as it is a very large home. I was leaning to UL approved metal boxes with fusing. Heat is not really a big issue as I am in Alaska and only would run lights in the winter, average temp -20 to +20F, so I do not think heat will be an issue. My Megatree box never exceeded 30 degrees with a server supply running 1500 pixels.
    I am a 30+ year telecom tech and understand fusing.
    Thank you Barnabybear, I had not considered that automotive fuses were less safe than the glass fuse type. Also fusing the input remotely is a great idea. The attic is much safer to access in the winter than a 20ft extension ladder in the winter.
    Family safety is much more important to me than a few extra $ to do it right.
    I have seen pics of some people's displays that look downright dangerous.

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    Default Re: Anybody ever worry about fire when mounting a powersupply in a plastic box?

    Simple answer is to use power supplies rated for the are you put them in, that way no plastic boxes needed..

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