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In a ring circuit can the length of spurs be additional to the 50m maximum for the ring, or do all the spur lengths have to be counted as part of the 50m maximum? In a ring circuit, in order to determine the safe length for any one spur cable does the voltage drop have to be calculated...

Got it. Thanks Damocles.

Thanks, ban-, plugwash.

ban-all-sheds wrote: "The worst case voltage drop in a ring is equivalent to the drop of a run of 2.5mm2 cable ¼ the total length of the ring." Is the voltage drop in the cable length of a ring circuit not calculated in the same way as in the single cable length of a radial circuit? When I...

Is the voltage drop in the cable length of a ring circuit not calculated in the same way as in the single cable length of a radial circuit? When I add the total length of a cable in a ring it either turns out to be too long in my calculations, or the circuit will only support around 10amps, and...

Thanks indeed, ban

Thanks, ban. Could I just add the voltage drop for 15metres of 2.5mm cable, onto the complete 1.5mm length when working out the calculation? I assume you mean the voltage-drop factor, not the actual drop in voltage in the ring?

Thanks for the useful link, ban (the attic in my 1908 town-house forms a third storey, and is below the loft space). securespark: yes, the switched FCU is to go in a 2.5mm ring, not in a lighting circuit, with a 10 amp fuse eg. this means that there will be two sets of 2.5mm core connected...

I want to power three or four outside security lights off a ring main in the attic. I intend to spur one 1.5mm cable from a switched FCU. I shall have to insert some junction boxes also in this spurred radial circuit to branch off to each light. What are the limits for the (total) lengths of...

dingbat replied thanks dingbat

Those metal plates that you can get for fixing over cablesthat lie in notched floor joists, so are not below 50mm from the top, provide mechanical protection so don't need earthing.[How to earth conduit, quote: shaggy] Are these plates an available product please? Does anyone know any brand...

I wondered if there any general quidelines regulating the placing of PIR type floodlights (switched by movement), or the sensor type (switched by onset of darkness) to the front of a house which faces the street and almost directly over the pavement. I am interested in a product by Micromark...

My thanks to Lectrician, AdamW and fubar. (I now know there are 'acceptable zones' as well as 'Zones'). But, if a cable runs directly horizontally or vertically from a socket (therefore in an acceptable zone) can this cable be unprotected even if it is less than 5cm from the surface, and...

Many thanks, Lectrician. Please how can I determine 'zones' in my attic area? I have a copy of 'The Electrician's Guide' by John Whitfield in which book zone dimensions are only described in bathrooms areas etc (p135). And please, why would the cable need to be protected if outside of a zone...

My attic has internal walls of 3" deep x 2" wide timbers supporting lath and plaster. I have had to route some 2.5mm sq cable, though keeping it always horizontal or vertical, outside or offset of a direct alignment with one socket. Wherever the cable passes through a stud (it is less than 2"...

In the case of copper or steel water (filled) pipes though, wouldn't the water itself act as a good earth source – as long as the water is not drained out or air-locked.

Thanks ban-all-sheds, I trust in the rigour of your replies. biblio

Can anyone recommend an IEE guide covering most of the basics for house wiring. A version of OSG is offered by Amazon at about £14, then there is another guide at £76. Does this price difference reflect breadth of content eg. Thanks

In my house now there are really too many ceiling and wall lights on one 5amp lighting circuit. Pendants number 14 and wall lights number 8. The average wattage is around 50 (there are roughly as many 60s as 40s) as we don't need to switch them all on together fortunately, we never test the...

Instead of inserting a junction box, is it okay to hard wire a switched FCU directly into a ring circuit (2.5mm cable, 30amps cartridge fuse in CU). I want to spur, via a frost stat, to a double socket (with a 13amp fuse). I have two heaters in the roof protecting all my water pipes etc. I am...