How to trace the wiring of a mains circuit.


==Options==
There are several possible ways to do it.


===See what's live===
Option A is to switch all circuits off bar the one you want to trace,
and test which lighting points or sockets are still live. If you're
only looking for lighting points and sockets, this can be done by
plugging light bulbs or portable lights in.

If you're also looking for junction boxes or loose cable ends, you'd
need to access the live wires and use a multimeter. This means live
working, which is not recommended, and doubly not recommended if you
need to read this article.


===Multimeter===
Option B is a [[Multimeter]] and a long [[Flex|wire]]. Power must be
off on /all/ circuits to use this, then you can trace where the live
[[Cable|wire]] goes using the low resistance range on any
[[multimeter]]. Check the resistance from L to N on the circuit first,
it needs to be not low. You may need to remove or switch off loads on
the circuit to get this.

You need to trace the live wire, not neutral or earth wires, as the
latter are normally connectoed to those on other circuits even when
the [[MCB]]s in the [[CU]] are off or the [[fusebox]] [[fuse]]s
removed.

Note that turning the main CU switch off doesn't electrically separate
the circuits, all MCBs still need to be off, or all fuses pulled.


===Flasher===
Option C is a flasher and either light bulbs or a mains live wire
detector. The flasher (with a [[fuse]] built in) is fitted in place of
the fuse at the [[fusebox]]. It turns the mains power on the circuit
on and off frequently, making the circuit easy to trace.

Flashers are no longer popular since they aren't easy to plug in to a
modern CU using [[[MCB]]]s.


===Signal generator===
Option D is a signal generator and a sniffer. Feed an hf signal down
the live wire, then use the sniffer to locate where it runs. The
[[MCB]] of the circuit being tested must be off before connecting the
signal generator.


===Neon screwdrivers===
These are not recommended. They produce both false positives and false
negatives, making them a safety liability. See [[Neon screwdriver]]


==Which is best==
If you need to read this article to find out how to do it:
* option A with no live working
* option B if you also need to trace junction boxes or loose cable
ends.


==Safety==
Live working should be avoided.

Flashers, if used in place of a CU [[fuse]], need suitable fusing to
maintain safety. [[Fuse|20mm fuses]] are entirely unsuitable for this.

If you're working on an unfamiliar property and wish to use a method
requiring that all power be off, check that everything is dead before
proceeding, in case there's a 2nd CU somewhere else still supplying
power.


==See also==
* [[Fuse]]
* [[MCB]]
* [[CU]]


[[Category:Electrical]]
[[Category:Basics]]