Discuss Is Running Power at 12v 0.3A/300ma Outside A Potential Fire Hazard? in the Security Alarms, Door Entry and CCTV (Public) area at ElectriciansForums.net
I'm about to install a burglar alarm siren box outside on my house's exterior wall powered by an ordinary power supply running at 12V 300ma/0.3A. (the power supply is indoors)
As i bought this cheap(ish) on Ebay i have no guarantee that the siren is weatherproof like it is advertised.
Are there any safety considerations related to fire i should be aware of please?
The worst case scenario - rain water manages to get into the siren unit and shorts it out.
I assume this low current wouldn't cause the siren box to catch fire but could the power supply that is powering it heat up to dangerous levels in these circumstances?
Do these cheap chinese power supply always have fuses? Would the household fuses protect me or could the power supply catch fire?
1) you're quite right - assume nothing about chinese imports other than they got made at gunpoint.
2) 12v supplied from a SELV transformer is normally safe hence why it's used in bathrooms.
3) transformers do burn out but normally from too high loadings rather than water shorts - there's not enough voltage to allow enough current to flow (short of a dead short)
4) If it did, then yes in theory your overcurrent protective device (BS3036 rewireable fuse or BS60898 MCB) should trip when the device shorts when it catches fire, but might not. This is why RCD's are used for fire protection on circuits.
Hi Rockingit, thanks for your reply. Do you think a cheapish plug-in RCD will fully protect me? I assume i can get one in argos for about ÂŁ10?
@ telectrix, thanks for your reply too but i can't establish if this siren is outdoor or not. There's plenty on ebay with no definite info on whether it is weatherproof. Only the guy that sold me the alarm system says it is!
Something just looks wrong, like it's too glossy and fragile looking to be used outside!
As an inexperienced DIY'er in general, i'm worried when i fit it to the brick wall outside i'll leave a small gap between the siren and the wall and the rainwater might trickle inside that way!
Hi Tek, yes - if you're not sure of your electrical setup and whether or not your house has 'inbuilt' RCD protection, and you want to be completely belt and braces, then you could plug the alarm panel into a socket and use a plugtop RCD.
Just be aware though that it will need to be reset everytime the power trips.
Tek - I'm not daft enough to offer you an official qualified opinion over a chat forum, but I have a suspicion that were I to see it and the rest of the install in real life I'd probably be saying you've nothing to worry about!
Rockingit - thanks for the advice, i'll get a plug-in RCD on the cheap. Any decent brands for the ÂŁ10 - 15 mark? I've seen a Masterplug one on Argos for a tenner.
Any special features i'd need? Are there different types? (sorry you probably guessed i know nothing about RCDs)
Tek - this really IS belt and braces approach!! Any of the high street ones will all be sold to the relevant BS and CE marked, so grab the cheapest you can find.
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