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by russell fields
Sat Nov 12, 2011 1:22 am
Forum: Electrics Forum
Topic: Stud or ring main ? What's best ?
Replies: 4
Views: 3344

Re: Stud or ring main ? What's best ?

Spurs from ring mains are not protected by the fuse in the plug. if a short circuit occurs on a spur the fuse in the plug will never blow. only the protective device for the circuit will operate. the ring circuit is the only permitted circuit where the CCC of the cable is LESS than that of the prote...
by russell fields
Sat Nov 12, 2011 12:49 am
Forum: Electrics Forum
Topic: RCD trip when circuit off
Replies: 4
Views: 6070

Re: RCD trip when circuit off

if your supply is TN-CS neutral and earth are connected together within your distributors cut-out normally less than 3m from your CU 3m of 25mm cable has a resistance of approx 0.0022 ohms to obtain a voltage drop of 50volts from CU to cut-out neutral current must be: i=v/r i=50/0.0022 i=22925A (not...
by russell fields
Sat Nov 12, 2011 12:32 am
Forum: Electrics Forum
Topic: MCB, RCD & RCBO`s
Replies: 3
Views: 4518

Re: MCB, RCD & RCBO`s

how can voltAGE drop stop an RCBO operating?
also RCBOs that take up one space can be double pole.
by russell fields
Sat Nov 12, 2011 12:19 am
Forum: Electrics Forum
Topic: could spar of a spar to run a light
Replies: 3
Views: 3325

Re: could spar of a spar to run a light

a spur is wiring that tees of from either a ring or a radial circuit. (see BS7671 part 2 definitions) App 15 of BS7671 explains it all. an unprotected spur from a 2.5mm ring must be 2.5mm and only feed one outlet, no mention of length. if a spur is is protected by a 13A fuse in a fused connection un...
by russell fields
Sat Nov 12, 2011 12:06 am
Forum: Electrics Forum
Topic: RCBO
Replies: 3
Views: 3908

Re: RCBO

neutral and earth are both at zero volts potential, therefore a neutral to earth fault is of no danger. in TN systems the neutral is physically connected to earth, in TN-CS systems this connection is in the distributors cut-out there is no requirement to test an RCD or RCBO under neutral to earth fa...
by russell fields
Fri Nov 11, 2011 11:58 pm
Forum: Electrics Forum
Topic: Chocbox or Junction box
Replies: 2
Views: 3930

Re: Chocbox or Junction box

remember all conections must be accesible
by russell fields
Fri Nov 11, 2011 11:56 pm
Forum: Electrics Forum
Topic: Complete rewire Help!
Replies: 4
Views: 3307

Re: Complete rewire Help!

for re-wires new heights may be the same as old heights, but all socket outlets must be mounted at least 100mm from floors or worktops
by russell fields
Fri Nov 11, 2011 11:36 pm
Forum: Electrics Forum
Topic: RCD wont trip on Neutral to earth
Replies: 5
Views: 3331

Re: RCD wont trip on Neutral to earth

just to clarify RCD test tested at half times the RCD rating should not trip when tested for 2 seconds (both half cycles) tested at 1 times the RCD rating should trip within 200mS if it is an old bs RCD or 300mS for a newer bs-en RCD(both half cycles) if the RCD is used as additional protection then...
by russell fields
Fri Nov 11, 2011 10:12 pm
Forum: Electrics Forum
Topic: 17th Edition 2382 MOCK exam from past papers
Replies: 2
Views: 4743

Re: 17th Edition 2382 MOCK exam from past papers

First of all the prospective short circuit current (pscc) and the loop impedance are 2 completely different things. pscc and pefc are measured where ever protective devices are installed, in an installation with 1 consumer unit they are measured at the incoming supply. they are measured as near to t...
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