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Topic Title: Is Santa going to be safe?
Topic Summary: Protection for 12V d.c. systems on a Rotary-club sleigh.
Created On: 01 November 2011 08:51 PM
Status: Read Only
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 01 November 2011 08:51 PM
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Avatar for davidlindsley.
davidlindsley

Posts: 17
Joined: 18 January 2003

Our sleigh carries two heavy-duty 12V batteries to power the PA and lighting systems. Can anybody advise on the nature of the protective devices that should be fitted to guard against fire in the event of an accident?

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David Lindsley
 02 November 2011 08:36 AM
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gkenyon

Posts: 4486
Joined: 06 May 2002

Relevant standards are BS7671 and BS7909.

HBC fusing (or alternatively a circuit breaker which is specifically made to operate with extra-low voltage at the voltage level you are using - see below) as near as possible to the battery terminals is highly recommended, due to the very high prospective short-circuit current at the battery terminals.

Sub-fusing should be provided with the same type of fuse, or alternatively using something like "blade" fuses for 30A and lower circuits.

All fuses, switches, circuit breakers, etc., should be rated for the voltage you are using (12 or 24 V d.c. I'd assume from your post ?). If ordinary mains devices are used, you may find "welded contacts", or, in the event of a short-circuit, melted parts. Equipment suitable for Automotive/Caravan, or alternatively Automation Systems, would be ideal.

If you're running supplies from an Inverter, at "low voltage", then you would be advised to check against the relevant parts of BS7909 and BS7671. Protection depends on your "means of earthing" of the inverter (or whether it's generally going to be IT, i.e. effectively insulated from the general mass of earth).

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Eur Ing Graham Kenyon CEng MIET TechIOSH
 02 November 2011 09:44 AM
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davidlindsley

Posts: 17
Joined: 18 January 2003

Thank you, Graham and Alan. As I shall be sitting on top of the contraption for part of the time I am naturally concerned, but the prospect of having so many kids' Christmas ruined by the incineration of Santa was my greatest concern. I shall now see that all is made safe.

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David Lindsley
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