Circuit detector

[DrPhill]

Hi all,

New house new problems..... there are some 'creative' wiring solutions here, and identifying circuits can be tricky.

Can anyone recomend an effective (and cheap?) live-circuit detector? Something that I can hold at or near a wire and detect if it is live. Preferably able to detect 'liveness' without a current flowing. I have never used such before so am not sure which might be good value for money.

(At present my most certain way is to cut the wire and see which breaker trips (hammer) . Now where is that 'bodgit' smiley when I need it?))

Thanks in advance for any help.

Phill

 

[finneyb]

No idea on live circuit testers.
But don't take any chances - electricity can and does kill; esp when you don't know if it was a muppet who installed it.

 

[Hivenhoe]

Try one of these but needs voltage prescent http://www.fluke.com/fluke/usen/com...categories/electrical/voltagedetectoruses.htm

 

[lanemaux]

As posted above , do not trust that it is off til you are sure. Test , check , re-check and then be paranoid. When I was young and foolish I moved into a condominium style unit and needed to replace a plug for the dryer unit in the laundry room. Went to the fuse panel and found it very neatly labeled for each circuit ... bonus thinks me! The plug to be replaced was right next to the panel , so off goes Michael to fetch his drivers and the new plug unit...easy! In Canada only the heavy main power equipment uses 20 or 30 ampere breakers so when the slot marked dryer was matched to a 30 amp , I felt secure switching it off and setting to work. My next recollection was wondering how I had gotten so far from what I was doing...8 or 10 feet straight back with a quivering screwdriver in my hand. Apparently I had inadvertently formed a ground for my power to flow through... through my dazed mind floated my wifes voice." Mike , the oven won't work , what did you do to it?" Needless to say , the oven was the OTHER 30 amp breaker in the box!

 

[Lons]

What Mike and Finneyb said.

I was refitting a bathroom on an old barn conversion and needed to change the light fitting. Not taking any chances, I turned of all the electricity at the main consumer unit and unfortunately was distracted by the owner so didn't test it. Got a fair old kick which knocked me off the stepladder and never did find out how the supply bypassed the main switch as I refused to do it and told her to get an electrician in at the end of the job.

Maybe she was hooked into the street lights :?

Bob

 

[DrPhill]

I hear what you all say - but I was born paranoid, and I have done a fair amount of lecky work. It looks as if a proper sparks did a rewire job (and put in the consumer unit), and a subsequent 'DIYer' changed things around a little.

I have ordered one of those Fluke 1AC pens (Thanks Hivanhoe). I can test the wire concerned, then switch off circuits until there is no voltage. Then I can be reasonably sure that I have isolated the wire. If I cannot get an initial voltage detection and a subsequent failure to detect voltage then I will call in a proper sparks.

Thanks

Phill

 

[Eric The Viking]

Phill,

Such a pen is no substitute for using a test meter properly. The "detectors" work capacitatively, and will often give readings when there's no current flowing but the neutral is connected. For proper safety, check live-to earth AND neutral-to-earth voltage of sockets on the cable in question, until you're sure it's off.

You really can only go through the sockets and breakers methodically to identify what's connected to where. Regarding unidentified wiring, a detector will help, but check by using the breaker on a known circuit to see if you get false positives. Bear in mind, if it's NOT working properly, it will show a cable as safe when it isn't (they're not failsafe devices). I've got some horrendous bodges in this house (not done by me!), including three rooms where one single socket has been wired through the wall from the ring next door. Only one of these meets the regs. The others are getting sorted as we come to refurbish the rooms involved.

I've also seen quite a few live-neutral reversals in my time. You used to be able to get mains testing plug tops with three neons in them that would indicate a live socket and fault states too. When I was a BBC sound engineer, we used them on site surveys (for Radio outside broadcasts), to make sure that what we wanted to plug into was safe. I once found a 32A (blue) connector at a site wrongly wired! To be fair, it's easily done, but it should have been TESTED!

E.

PS: I've seen enough old cable left in situ 'accidentally' live, not to trust anything I haven't proven.

PPS: Assuming the mains wiring is off and isolated, you can use a CAT5 tester with croc clips to prove circuits. Assuming the mains is off and isolated... did I mention off and isolated - it must be!

 

[DrPhill]

Yes, I hear you. And I am a coward when it comes to electricity. But we have a modern consumer unit as the only 'client' of the meter so that affords some protection. Also, I am used to assessing levels-of-proof (considering false positives and false negatives). And if in doubt will get a professional.

What I have is the following:

A room with a horrid suspended ceiling thing (translucent plastic tiles on an aluminium frame) that we have removed. Above the suspended ceiling the original light has been replaced by two flourescent striplights (more light needed to penetrate the tiles?). From the hole where the original ceiling rose was come two pieces of flex (flat grey lighting grade?). These were hidden above the suspended ceiling (but now exposed) and disappear into the wall.

The position of these cables is perfect to run through the wall and then under the plaster to an added (and completely superfluous) wall light and switch in the hall. My working assumption (to be tested) is that these wires are an extension to the lighting circuit. If I can demonstrate this to be the case, then I can remove said wall light and the 'flying' cable - I even have a junction box ready to place where the old ceiling rose was - neat simple, safe.

So I have a length of flex but do not know where the ends are. No good testing sockets and the like since I do not know for certain which sockets are attached to this flex. If I cut the flex (after turning off all power) and I am wrong, then a repair will make an even uglier solution until a proper sparks can fix it. I am hoping that the detector will confirm that the wires are part of the lighting circuit.

If I cannot demonstrate to my satisfaction that these wires feed the hall light then a real sparks is needed to tidy up the electrickery anyway.

(PS: I have one of those three pin plug circuit testers - must get it out and give this old house a check).

Edit: I have shown that the wall light is on the lighting circuit.

 

[Eric The Viking]

You might get lucky; you might not.

What you're after is a 'permanent live' on the lighting circuit. It might have been done in various ways, depending on what else is on that circuit. For example, there could be an incoming live+neutral, and that live is extended to the switch. Ordinary ceiling rose boxes are intended to accommodate that arrangement, and there will be THREE pairs of wire altogether: (1) incoming live, neutral (and earth), (2) switched live to and from the switch plate (and earth carried through), and (3) the pair of wires going out to the light fitting itself. If the light fitting is Bakelite, the last pair may not have earth extended

Occasionally, the permanent live doesn't go to the rose at all, but is brought down to the switch from elsewhere. If there's only two pairs of wires altogether, something coming in and something going to the actual light fitting, that's probably the arrangement.

A good clue will also be if any blue or black wiring in the ceiling rose is marked: it's often not done, but neutral wires used as switched live should have a piece of red (or now brown) tape or sleeving on them to confirm that's what they are being used for. Theoretically they should be marked that way at both ends - in the ceiling rose and in the wall switch, but as the usage is a bit obvious behind a single switchplate, it's often omitted, at least there. The assumption of the regs is that anything plain red or plain brown is always live (i.e. what you want in this case).

The easiest thing, by far, is to use a digital multimeter, on voltage range, with probes, undo the ceiling rose box and test for the presence of 240V (to neutral or to earth) on the various blocks inside.

Start with the light ON, so you can identify (and avoid) any blue or black wires used as switched live, but not properly marked as such.

Test blue/black first, against earth. Ignore anything at 240V - that's a switched live (that's switched on).

When you find the black or blue wire block that is at roughly the same potential as earth, that's the neutral. Remember it for later...

Then switch the light OFF at the wall, and check again for any blocks in the box that are still at 240V (red/brown). That *should* be the permanent live of the lighting circuit, which you can use to give you the spur into the hall.
Confirm it by checking it's not switched by other light switches in other rooms, just in case). Yes, even professional sparkies produce the most horrid mistakes occasionally.

Once you know which are permanent live and neutral, confirm it by using the breaker at the box. If the circuit doesn't go dead when you trip the breaker, it's not the right breaker! This isn't madness necessarily: historically, hall and landing lights were wired onto the opposite lighting circuit. That way, if the downstairs lights fused, the hall light would still work, and vice versa. You have to be VERY careful working on hall/landing lights in old properties for that reason: pulling the hall floor fuse won't necessarily isolate all the switches in the hall!

If you find what you want, don't forget the green/yellow sleeving for the earth wires - added in junction boxes and anywhere else earth wires are terminated.

Hope that helps,

E.

PS: If in any doubt, run the cables (1mm twin+earth for domestic lighting), and get a sparks to do the final wiring-in and commissioning.

 

[DrPhill]

Ah, yes, perfectly sensible, and I thank you for taking the time to set it out clearly.

One slight problem (I did allude to it, but not clearly enough) is that there is no ceiling rose at present. Just two wires coming out of the ceiling! So neither end of the 'flying wires' has anything that I can tap into to check voltages (without cutting). A sparks would have the same problem.

I understand the common switching circuits, and assume that the two wires are an extension to the lighting ring with the switching wires run from the back of the light fitting. I can examine the superfluous switch and light to determine the circuit, but the buried wires mean that I cannot be 100% certain that the 'flying wires' are connected to the superfluous light/switch.

My plan is to detect leccy in them when the lighting circuit is on, and detect none when the lighting circuit is off. That will show that they are part of the lighting circuit (and therefore safe to cut). If the detector thing detects wires-in-use then I can turn off all lights but the superfluous one and be reasonably certain of demonstrating that the wires go to this (or demonstrating the reverse).

If the former, then it is worth proceeding.
- Switch off power and examine the superflous light.
- Check that it is wired as an extension to the lighting ring, that I can identify the two flyng wires (from above) and the switch leads (from below) and that like-colours are joined.
- Anything indicating that my suppositions are in error would require a professional. Otherwise:
- Cut the flying leads
- Join in a junction box
- Switch on again.

 

[Lons]

Hi Phill

There would originally have been a rose or light fitting in the ceiling with one of the arrangements thjat Eric mentioned. The usual practice is to extend the original incoming neutral and the switched live to the new fittiings (flourescents in your case) and use a junction box or connectors to join the ring circuit though the original rose is often left in as it is the easiest solution ablove a suspended ceiling.

I'm not saying the above is the correct way to do it but it is the most commonly used in my opinion and I have encountered such an arrangement in many cases. Be aware that there will be an extra wire if the circuit is 2 way switched.

Have I read it right or got the wrong end of the stick?

Bob

 

[DrPhill]

This is all I see.......

 

[RogerS]

.....

PPS: Assuming the mains wiring is off and isolated, you can use a CAT5 tester with croc clips to prove circuits. Assuming the mains is off and isolated... did I mention off and isolated - it must be!

And even then you can get a belt! I was replacing a consumer unit (pre-Part P) in a flat. Wiring single core cables inside metal conduit. I removed the main board fuse that fed the flat from the fusebox out in the hall of the common parts. In my flat, I labelled up the wires and removed the old consumer unit. While rewiring the new CU in, my knuckle grazed one of the to-be-connected neutrals and I got a belt. Turns out some of the neutrals in my flat belonged to the flat next door. And vice versa. So removing the neutrals still meant that power was being fed via whatever equipment was 'on' in next door's flat. The neutral wire then floated up to mains voltage as I'd disconnected it.

 

[Eric The Viking]

.....

PPS: Assuming the mains wiring is off and isolated, you can use a CAT5 tester with croc clips to prove circuits. Assuming the mains is off and isolated... did I mention off and isolated - it must be!

And even then you can get a belt! I was replacing a consumer unit (pre-Part P) in a flat. Wiring single core cables inside metal conduit. I removed the main board fuse that fed the flat from the fusebox out in the hall of the common parts. In my flat, I labelled up the wires and removed the old consumer unit. While rewiring the new CU in, my knuckle grazed one of the to-be-connected neutrals and I got a belt. Turns out some of the neutrals in my flat belonged to the flat next door. And vice versa. So removing the neutrals still meant that power was being fed via whatever equipment was 'on' in next door's flat. The neutral wire then floated up to mains voltage as I'd disconnected it.

Yup: always assume the previous sparks was a certifiable idiot and go on from there.

I nearly got into trouble replacing skirtings a while back: Old ceramic switch surface mounted, the sort with a two-pin socket on the side. Rubber covered cable behind, covered in layers of paint and the crud of decades. Turns out it had been helpfully wired back into the ring by whoever re-wired the flat five years earlier. The rubber was so perished it fell off when I levered the skirting off the wall. Something prompted me to put the cutters down and test it first. I so nearly just went for it.

E.

 

[Phil Pascoe]

All the switches were off at the fuse box, so I went ahead. I got up the ladder against the stud wall I was removing, and hacked at the piece of lead clad 6mm that supplied the cooker from the dining room light. Bang! I hit the floor. I ring up S.W.E.B. (as was) and the guy comes out. "It was supposed to be dead - and it was all switched off" says I. "Didn't think to put a meter on it, then?" says he, tutting loudly and shaking his head. "You shouldn't presume anything" he says. " Oh, I thought it'd be ok to presume there was no power there" says I. "why on earth did you think that?" he says - at which point I show him the card from S.W.E.B. telling me the phone no. I had to ring to apply for the house to be reconnected. "Jeeeeeesus Chriiist....................."says he.

 

[Eric The Viking]

Impressive!