Burglar Alarm

[John Whitworth]

Rather a generic question here. I haven't bought one yet, but is there any reason why an installed burglar alarm wouldn't be wired into the normal ring mains? Or would it normally have it's own circuit?

JW

[Martin]

I'm no expert on this, but I can't think of one. Ours is spurred off the ring and, of course, battery back-up takes care of the obvious concern.

[Narrer]

It is normal practise to fit a burglar alarm with it's own dedicated supply i.e. appropriately sized cable and mcb/ fuse and connected directly to the consumer unit - for obvious reasons.

[John Whitworth]

Can you expand a little please, as I can think of only one obvious reason that is slightly applicable - and that is minimising the risk of the circuit being tripped by something else? But even then, as previously stated, battery back up will surely help there?

I cannot see that it needs a dedicated supply due to it's load, as that will surely be very low.

Not trying to answer my own question here, it's just that the obvious doesn't seem that obvious to me.

Thanks

JW

[ARWadsworth]

No it is not.

Adam

[Cash]

Narrer,

My alarm was professionally fitted some years ago, and the supply is spurred off the nearest socket to the control unit and has its own fuses - and battery back-up.

Cash

[cj]

Hi Speaking from experience an intruder alarm must be supplied with a "permanent " mains supply .Current BS and EU regulations make no stipulation of where this supply is fed from only that it complies with local & regional HSE and Electrical safety standards. If however Smoke detectors are part of the system a dedicated supply is specified but this is subject to layout and usage. Where the confusion arises is that most Industrial systems have a dedicated supply for maintenance/simplicity and also this supply feeds the of-site monitoring systems. Add to this the fact that due to split board mains units being more common ,electrical contractors are wiring a dedicated 6A circuit for intruder alarms. On a personal note I have been called to systems that were just plugged into a 13A socket (some even had 13A fuses in the plug top) these had been fitted by a so called approved alarm company. The industry is governed by the old NACOS and the more recent EU body SSAIB Both of which recommend an unfused spur within 2m of the panel fused to suit the panel but that is all .No specification of where this supply is fed from. This is amended for industrial usage dependant on site requirements.Also some businesses specify a stand alone supply and even a UPS as well as the panel battery.

So the list goes on....... In a nutshell for domestic use think of it as any other appliance .As long as it is safely connected to the supply it's fine.

"John Whitworth" wrote in message news:4b4f2b41$0$2486$ [e-mail]...

[John Whitworth]

Great - thanks.

John

[Java Jive]

*unfused*

*fused*

[cj]

TYPO should read unswitched. sorry.

[Andrew Gabriel]

I tend to connect to lighting circuit because (prior to 17th Ed regs) it tends not to be RCD protected, so it's less likely to trip off, and being a lighting circuit, you very quickly notice if it has failed. (If your lighting circuit trips off every time a bulb blows, then it's probably not such a good idea.)

[John Whitworth]

That's that theory out for me then! ;-) Every time one of the candle bulbs in the fancy light-el-abra thing she wanted in the living room goes, the whole lighting circuit trips out.

JW

[Doctor D]

I cured this problem for my mother in law by changing the MCB for a 6 amp type C which allows a longer short term overcurrent to be drawn as the lamp fails. A home I cured it by never using the centre light fitting, only table lamps with CFLs fitted!

[John Whitworth]

That's not a bad idea...may see if I can get one. I presume it will still be safe with the Type C?

JW

[ARWadsworth]

On a properly designed/installed lighting circuit then swapping a B type MCB for a C type MCB is normally fine.

However for lights using a 6A MCB there is one exception to that rule:

If you have a TN-S supply and are using 1.5 T&E cable on a non-RCD protected circuit. In this case there is a very small chance that a C type breaker cannot be used as it is possible that the earth loop of the lighting circuit is too high for a C type MCB to protect the circuit in the event of a LE fault.

Adam

[John Whitworth]

Hmmm...OK - thanks Adam. That all sounds very much like it could apply here. I'll leave as is I think! Can't find the Part-P stuff now, which described the supply, but TN-S sounds familiar.

JW

[ARWadsworth]

FWIW in my experience type C MCBs trip just as often as a type B MCB when a lamp fails. So you probably would gain nothing by changing the MCB.

It is still only a small chance that the circuit is not able to to take a C type MCB. Without measuring the earth loop readings I would recommend that no-one should swap MCB types.

Adam

[Andrew Gabriel]

It's going to depend on the supply impedance if a switch to type C fixes it, or makes no difference. Changing to a BS1361 5A cartridge fuse is probably more likely to fix it, as is swapping out mains filament lamps for something else.