Spuring from a spur...

[Lectrician]

I was waiting for your view on this one   the point about the alarm being spurred off a socket circuit that is RCD fed < Im sure most have done this at some time or another including me - apart from nuiscence tripping, does it violate code or regs??

53564[/snapback]

Putting the alarm on an RCD protected circuit is certainly not against our regs, I was unsure if it was against any of yours?? Possibly unavoidable if a TT system, or if a spark with no knowledge of earthing systems has installed a new CU with a 30mA RCD as the main incommer (why do sooooo many sparks do that!)

[Guest]

Putting the alarm on an RCD protected circuit is certainly not against our regs, I was unsure if it was against any of yours??  Possibly unavoidable if a TT system, or if a spark with no knowledge of earthing systems has installed a new CU with a 30mA RCD as the main incommer (why do sooooo many sparks do that!)

53627[/snapback]

prob because the offer cu's you get have the mcbs of your choice on a split load bus with 30mA rcd as part of the package - they dont think to change it.

[mcelec]

guys as i said in my previous message its all a matter of design, bs7671 is there as a guidance for design principles not a must do document, just because its not a method described in bs7671 does not mean its wrong, which is why it is a requirement for the person responsible for designing the installation to sign the initial verification certificate to accept liability for his work, and also to note any deviations from bs7671 but like i said before if you have no technical experience in the design of electrical installations then just follow the guidance of bs7671 to the letter.

for those who are a bit uncertain about final ring cct's i have attached a excert from a guide to bs7671 printed by the eca and nic eic, i hope this is of some help to some of you.

"i would of added the ring guide if the site would let me upload file, i will try again tommorrow"

[Guest IM_Alarms]

NICEIC technical manual, BS7671 and On SIte Guide all say,'' A non-fused spur feeds only ONE single or ONE twin socket outlet or ONE permanently connected equipment. Such a spur is connected to a circuit at the terminals of a socket-outlet or junction box or at the origin of the circuit in the distribution board''.

None of these mention any room for design alterations for low-load or otherwise.......... Unless they are all missing a page

[Guest johnburger]

The mains supply to my alarm panel is a spur taken from the ring main (fed via a 32 A MCB) using 2.5 T&E through an FCU containing a 3 amp fuse. The total length of cable from the junction box to the FCU is about 3.5 meters. I want to add a 1 amp Elmdene power supply to my system. Is it OK to take another spur from the FCU supplying my alarm panel? I know your not supposed to spur off a spur, but with such a neglegible load on the spur at present, is it OK? I will be adding another FCU for the PSU, but if I can help it, I'd rather not go to the trouble of extending the ring up into my attic.

Thanks!

The first spur must be fed with 2.5 t&e and fitted with an appropriate fuse protecting all wiring after it. You should have a DP isolator for each piece of equipment so you could simply use DP 20 Amp switches. Alternatively use 1 spur switch as the main and then on its load side use several 1 for each appliance with smaller fuses than the main one. It will all need testing though.

[Guest johnburger]

So I'm alright if I connect the power supply to the load side of the FCU that's already there? That makes things easier. I think I'll stick another FCU on for the PSU anyway, just cos I'm like that

If you do it that way the second fcu must be connected to the load side of the first one therefore limiting the load to a max of 13 amps not 26.

[Pierre]

If you do it that way the second fcu must be connected to the load side of the first one therefore limiting the load to a max of 13 amps not 26.

According to 7671 (in a domestic installation) you can have as many sockets and fused connection units as you like on a ring main as long as the floor area covered is no greater than 100 sq. mtrs. You can also spur off the ring with as many sockets or FCU's as you like, as long as the number of these points do not exceed the number of points on the ring.

Still with me? How can you tell which sockets are on the ring and which are already spurred? This requires a complicated 'figure of eight' test which is done with the power off. However back in the real world I would suggest that there is no problem connecting 2 FCU's to an existing point if they are to be used for a control panel and a PSU, as the current they draw is negligible. All work however should be tested and approprite certification issued...'minor works' if an existing circuit is added to or an 'installation certificate' if a new circuit is installed.

If anyone is still awake at the back, a 13amp socket outlet is so called because this is the maximum rating of any equipment plugged into each outlet. In reality an assessment of the maximum demand of a circuit involves adding up all the equipment likely to be connected (which may include a table light at less than half an amp) and then allowing for diversity which assumes that it is unlikely that every bit of equipment will be in use at all times. A bit like a 30 Amp cooker circuit which probably only runs at 30 Amps on Christmas day, with all elements and heaters flat out.

[Pierre]

I forgot to mention, in the above diatribe, that prior to extending or altering an existing installation (even if it is only adding a spur) an inspection and test should be carried out to ascertain if it is safe to do so.

My advice to anyone, without the required knowledge and equipment, would be to get an electrician in to install the spurs and make sure you receive the appropriate certification on completion.

[jb-eye]

You can also spur off the ring with as many sockets or FCU's as you like, as long as the number of these points do not exceed the number of points on the ring.

I think you should clarify the above as it

[Pierre]

I think you should clarify the above as it