Extractor not staying on (on lighting circuit)

[gravelld]

Looks like I'm in over my head again...

 

I purchased one of these: https://www.greenwood.co.uk/product/153/unity-cv2gip to replace an existing extractor fan. I wanted this new unit as apparently it can run in trickle mode then boost when humidity gets too high. The old extractor just worked when the light was on, then had a variable overrun.

 

According to this: https://www.amazon.co.uk/ask/questions/Tx25QNH37J3GAUG/ref=ask_ql_ql_al_hza the new fan should run when the lights are off.

 

I simply rewired from the old extractor to the new one.

 

First time, red into L, black into L1, unsheathed earth into N.

 

 

I turned the power back on at the fusebox, with the light switch off... The fan turned on as I would expect, but the LEDs either side (coming off the same junction box) also 'glowed' on and off (other LEDs in the room were unaffected). If I turned the light switch on the fan turned off, and the LEDs turned on fully.

 

So - oh dear - not really understanding what I was doing I rewired so black into L, red into L1, unsheathed earth into N. Now, with the light switch off, everything was off. With the light switch on, all lights turn on properly and the fan starts up.

 

However, the fan stops when the light switch is turned off. Which is no good, as per the above requirements. It extracts at the trickle rate when the light is on.

 

Before I check with the manufacturer I wanted to check I wasn't doing something silly with the wiring... or is the junction box setup somehow an issue? The LEDs use transformers to make them low voltage.

CV2_Installation_Instructions.pdf

Edited May 25, 2019 by gravelld

[Jeremy Harris]

The wiring's wrong, as the earth should never, ever be connected to a live terminal (neutral is classed as being a live terminal).

 

The earth conductor should be parked in the terminal marked "C" on the right hand diagram.  I say parked, as I believe that it's not used, as this fan is probably double insulated (most are).

 

The wiring needs two line connections and a single neutral connection.  The two line connections are a permanently on line (via an appropriate isolator switch) and a switched line from the lighting circuit.  The neutral needs to be common to both the switched line and the permanently on line, so the permanently on line needs to come from the lighting circuit, but before the switch.

 

With this type of fan it's normal to install an isolating switch that can isolate both line connections and the neutral, for safety reasons.  This is the normal type of fan isolator: https://www.screwfix.com/p/mk-logic-plus-1-gang-10a-3-pole-fan-isolator-switch-white/12319 or this one: https://www.screwfix.com/p/british-general-1-gang-10a-3-pole-fan-isolator-switch-white/69862

 

Your wiring looks to be the old colour codes, so red is line, black is neutral and the bare wire (which must be sleeved) is earth.

 

The permanently on line goes to L, the switched line from the lighting switch goes to L1 and the neutral goes to N.

[ProDave]

+1 to the above, if you only have a 2 core and earth cable then you first need to change that for a 3 core & earth cable back to either the light fitting or light switch, wherever you can pick up a neutral, permanent live and switched live.  Where you connect to depends how your lights are wired.

[gravelld]

Thanks, looks like I've got a lot more studying to do.

 

Quote

Your wiring looks to be the old colour codes, so red is line,

 

Do you mean a switched line, i.e. are you saying only a switched live is present, with no permanent?

 

How can I tell if the junction box has a permanent live? And if there's no such cable, I work back towards the switch? Bearing in mind this is old fashioned colour codes...

Edited May 25, 2019 by gravelld

[Jeremy Harris]

43 minutes ago, gravelld said:

Thanks, looks like I've got a lot more studying to do.

 

 

Do you mean a switched line, i.e. are you saying only a switched live is present, with no permanent?

 

How can I tell if the junction box has a permanent live? And if there's no such cable, I work back towards the switch? Bearing in mind this is old fashioned colour codes...

 

 

The wiring to the fan should be:

 

L = permanently on line from lighting circuit, connected via new three pole fan isolator switch.

 

L1 = switched line from lighting circuit, connected through the isolator switch (makes isolating the fan much safer).

 

N =  Neutral from lighting circuit, also connected through the isolator switch.

 

The only sure fire way to trace back the wiring is to check it with a meter to find the permanently on line and the switched line.  If your lighting has been wired so that it's loop in switch, then all three connections needed should be in the switch.  A photo of what's behind the switch should allow one of us to tell if it's loop in switch or not.

 

Given the age of the installation I rather suspect it's loop in fitting, which means that the neutral won't be available at the switch, only the permanently on line and the switched line.  Again a photo of what's behind the switch should help one of us tell if that's the case.  If it is, then it means a bit more digging around to find the best place to connect to.

[gravelld]

Thanks, I'll be back in the loft asap!

 

Out of interest and to further my understanding, how dangerous was the initial wiring?

[Jeremy Harris]

4 minutes ago, gravelld said:

Thanks, I'll be back in the loft asap!

 

Out of interest and to further my understanding, how dangerous was the initial wiring?

 

Connecting the earth conductor to neutral was the lucky choice when getting things a bit awry, as usually the two will be at about the same potential.  I'm guessing that you don't have an RCD, though, as I'd have thought that the imbalance when trying to run power via the earth conductor would have been more than enough to make it trip. 

 

Photos of the wiring you find might help one of us suggest the best way to connect things.

[ProDave]

It is not at all  uncommon to find people who have changed an ordinary bathroom fan for a timer version and then had to be "inventive" to make it work with a 2 core & earth cable.  Usually using the CPC as a neutral.  I have even encountered a bit of 3 core flex used with the green / yellow used as the switched line.  You meet all sorts of horrors.

[Jeremy Harris]

I'll admit to getting inventive when wiring a timer fan to the last house, as the way the cables ran in the loft made it much easier to run two lengths of 1mm² T&E to the fan, with only one of them carrying the neutral, rather than run a single length of 3 core + E.

 

I was also a bit naughty in that I fitted a DP isolator in the loft, by the hatch, that isolated the whole bathroom lighting and fan circuit.

[ProDave]

I personally am not a fan of fitting fan isolators.  I removed them all from our rental properties to stop tenants turning the fan off because it was noisy, and then complaining about the damp and mould.

 

I am still waiting for someone to give me chapter and verse on WHY we fit them.  Maintenance is a poor excuse, any sparky that cannot isolate at the CU is not trying. It is no different to changing a light fitting that is looped at the light, so has a permanent L connection. We don't fit a 3 pole isolator next to each of those do we?

 

I am convinced that we fit one because some directive says you must have a local isolator at a "fan"  Now I can see that so when the HV engineer has the cover off and is changinf the belt on a 3HP fan motor there can be no possibility of it starting unexpected and taking his arm off.  But to apply that to a poxy bathroom fan that would do no more than give you a bit of a nip if you put your finger in the rotating blade is a bit silly.

 

So I have no problem with one in the loft, or even not fitted.

 

But I always fit them on jobs because it is the "done thing" though nobody has shown me the actual wording of WHY we fit them.

 

[Jeremy Harris]

1 minute ago, ProDave said:

I personally am not a fan of fitting fan isolators.  I removed them all from our rental properties to stop tenants turning the fan off because it was noisy, and then complaining about the damp and mould.

 

I am still waiting for someone to give me chapter and verse on WHY we fit them.  Maintenance is a poor excuse, any sparky that cannot isolate at the CU is not trying. It is no different to changing a light fitting that is looped at the light, so has a permanent L connection. We don't fit a 3 pole isolator next to each of those do we?

 

I am convinced that we fit one because some directive says you must have a local isolator at a "fan"  Now I can see that so when the HV engineer has the cover off and is changinf the belt on a 3HP fan motor there can be no possibility of it starting unexpected and taking his arm off.  But to apply that to a poxy bathroom fan that would do no more than give you a bit of a nip if you put your finger in the rotating blade is a bit silly.

 

So I have no problem with one in the loft, or even not fitted.

 

But I always fit them on jobs because it is the "done thing" though nobody has shown me the actual wording of WHY we fit them.

 

 

I agree, and suspect like a lot of stuff in BS7671 it's just people at the IET that have nothing better to do than dream up ever more convoluted regs, in the desire to reduce risks which are already acceptably low.  Take a read of the new Section 722 if you want a laugh, that stipulates stuff that's close to being unobtanium, and so is being very largely ignored by all the big national installers.

[Ed Davies]

Does BS7671 actually require isolators for this application? I.e., is @ProDave's (rhetorical?) question “why does BS7671 require isolators?” or is it “where in BS7671 or elsewhere is there a requirement for isolators?”?

 

Also, how many question marks can I fit into one sentence?

[Onoff]

4 hours ago, ProDave said:

I have even encountered a bit of 3 core flex used with the green / yellow used as the switched line.

 

The old favourite for two way switching! 

[Jeremy Harris]

11 hours ago, Ed Davies said:

Does BS7671 actually require isolators for this application? I.e., is @ProDave's (rhetorical?) question “why does BS7671 require isolators?” or is it “where in BS7671 or elsewhere is there a requirement for isolators?”?

 

Also, how many question marks can I fit into one sentence?

 

There's no requirement in the regs to fit 3 pole isolators to bathroom fans for TN-C-S or TN-S installations, it's only a requirement for TT installations, and even then it's questionable, IMHO.  There is a requirement (462.2 and 464) to fit isolating switches, and there seems to be an assumption that the fuse or MCB in the board is not OK as the only means of isolation for a bathroom/WC fan.  As some 3 pole fan isolators are designed to be able to be locked off, I suspect that the requirement in 464 may be driving the apparent need for these things.

 

All the marked fan isolator switches available seem to be 3 pole, presumably to deal with TT installations where this is a requirement, but a 2 pole switch (switching the L and L1 conductors) would technically be OK in any installation that's either TN-C-S or TN-S. 

 

 

 

 

[gravelld]

Ok, just got the chance to trace the wiring.

 

The fan runs into the following junction box:

 

The cable (I'm calling it that because it's stiff, maybe it should be correctly called flex) is the bottom-left cable.

 

The lighter coloured cable to the fore at the bottom right then runs toward the light switch and into this junction box:

 

  

The cable running into this box from the previous junction box is the one at the bottom.

 

The cable to the right is the one that runs to the light switch. But before I show you that, there's another cable with a different colour code, coming from the ceiling in the general area of the light switch (but not actually visible in the light switch):

 

 

The cable I'm talking about is the snipped one with blue, red and white coloured insulation. You can see it disappearing into the ceiling. Not shown on the other side of the junction box is a cable with the same colour codes.

 

You can also see the cable from the junction box disappearing into the ceiling to the light switch.

 

To clarify, the junction box you see above is the same one as the previous photo.

 

Finally, the light switch:

 

 

Are there any obvious strategies from here, do I need to do some more digging?

[Jeremy Harris]

Going from the bottom photo up, the light switch shows clearly that the lighting is wired as loop in fitting ( https://www.practicaldiy.com/electrics/lighting-wiring/light-wiring-loop.php ).  The two conductors in the switch cable are the line (red) and switched line (black with red sleeve).

 

This means decoding the cables going into the junction boxes, which gets a bit less certain to work out by remote control.  Dealing with the top photo, with the cable to the fan.  First a few observations and questions.  Is the flex with the new harmonised colours the drop down to a light fitting?  It really needs tidying up so that there are no single insulated conductors exposed, with the outer sheath inside the junction box (or better still made off to a separate junction that includes a cable clamp).

 

I'm guessing here, as it looks like the switched live red sleeve has been left off from the switch cable, and I'm assuming that the switch cable is the one that is coming in at the lower right, with the black conductor (which should be red sleeved) being the switched line, leading to the terminal at the top.

 

Referring just to the top photo, I think that the terminals in that junction box are:

 

Top - Switched line to light (and should go to the fan L1 terminal)

 

Left - Earth

 

Right - Neutral to light (and should go to the fan N terminal)

 

Bottom  - Permanently on line to switch (and should go to the fan L terminal)

 

It's good practice to run the feed to the fan (the L, L1 and N) through a 3 pole isolator switch, so the fan can be isolated without needing to isolate the lighting circuit.

 

If you have a meter, then it would be a good idea to test the terminals in the junction box in the top photo to be sure that the connections are as I think they may be.  Testing between the bottom terminal and the right hand terminal should show as being live when the power is on.  Testing between the right hand terminal and the top terminal should only be live when the light switch is on (with the power on).

 

 

[gravelld]

22 minutes ago, JSHarris said:

This means decoding the cables going into the junction boxes, which gets a bit less certain to work out by remote control.  Dealing with the top photo, with the cable to the fan.  [...]  Is the flex with the new harmonised colours the drop down to a light fitting?  It really needs tidying up so that there are no single insulated conductors exposed, with the outer sheath inside the junction box (or better still made off to a separate junction that includes a cable clamp).

 

Yes - good point. It's going to a light fitting.

 

22 minutes ago, JSHarris said:

I'm guessing here, as it looks like the switched live red sleeve has been left off from the switch cable, and I'm assuming that the switch cable is the one that is coming in at the lower right, with the black conductor (which should be red sleeved) being the switched line, leading to the terminal at the top.

 

Yeah, the cable from the switch junction box (this is what I will call the "switch cable")  is the one at the lower right. There are two cables coming in here - the switch cable and... another one which I haven't traced.

 

However the black conductor does not lead to the terminal at the top, it leads to the terminal on the right. The red conductor leads to the bottom terminal.

 

22 minutes ago, JSHarris said:

 

If you have a meter, then it would be a good idea to test the terminals in the junction box in the top photo to be sure that the connections are as I think they may be.  Testing between the bottom terminal and the right hand terminal should show as being live when the power is on.  Testing between the right hand terminal and the top terminal should only be live when the light switch is on (with the power on).

 

I'm not that comfortable using a multimeter on a live circuit but I happened to have a voltage detector easily to hand so I tested for a current with that - it shows all cables into the bottom left and right of the junction box (so those from the switch and from the extractor fan are carrying current (with the light switched off).

 

Let me know if I need more info.

[Jeremy Harris]

First off, I'd not be that confident about trusting the results from a voltage detector pen/screwdriver thing, as they are notoriously unreliable.  Perhaps gain some confidence from trying out the test meter on an easy to access circuit, making sure that the meter is set to measure AC voltage and the test leads are plugged into the voltage sockets on the meter (if there is a choice).  If you keep your hands clear of any live terminals the worst that can happen is that you will blow a fuse in the meter if you get something wrong.  With luck you should gain a bit of confidence and feel OK with carefully testing the terminals in the junction box.

 

I've been trying to label the various cables into that junction box with where I think they go/come from:

 

 

Some connections are certain.  The earth on the left, the neutral on the right and the switched line at the top (this has to be right as it goes to a light drop).  The area of uncertainty is the lower terminal, as it's not clear that the switch cable has a line (red) connection to it, as it's hidden under what I think is the incoming power cable.

 

If you don't want to use the test meter, then I would suggest that you remove the cable running to the fan, with its dodgy earth conductor being used as a switched line, and run a length of 3 core + E so that the earth connects to the earth terminal (with green/yellow sleeving), the brown wire goes to the line terminal at the bottom, the black wire (sleeved with brown) goes to the switched line terminal at the top and the grey wire (with a blue sleeve) goes to the neutral terminal at the right.  I know this colour coding seems at odds with what you've got, but under the harmonised rules black can be a phase colour like brown, so shouldn't be used for neutral.

 

[ProDave]

 Your second picture shows a junction box were none of the cables have a CPC.  These are old cables before it was normal practice to fit an earth to lighting circuits.

 

You might want to consider getting the lighting circuit rewired or at least a thorough EICR so you know what state it is in.

 

With so much of the lighting circuit having no CPC I would not trust that any earth conductors you do find really are properly connected anywhere, and I would want to be damned certain you have a proper earth connection if you have any class 1 light switches or light fittings.

[Mr Punter]

@ProDave what is a CPC and EICR? Could not find it in the glossary but maybe they are more specialist acronyms.

 

[ProDave]

CPC Circuit Protective Conductor.  Earth wire to most people

 

EICR Electrical Instalation Condition Report

[Jeremy Harris]

CPC = Circuit Protective Conductor, the physical wire that is connected to PE, the Protective Earth (commonly just called earth)

 

EICR =  Electrical Installation Condition Report, the report produced following the inspection and test of an electrical installation.

[gravelld]

4 hours ago, JSHarris said:

First off, I'd not be that confident about trusting the results from a voltage detector pen/screwdriver thing, as they are notoriously unreliable.  Perhaps gain some confidence from trying out the test meter on an easy to access circuit, making sure that the meter is set to measure AC voltage and the test leads are plugged into the voltage sockets on the meter (if there is a choice).  If you keep your hands clear of any live terminals the worst that can happen is that you will blow a fuse in the meter if you get something wrong.  With luck you should gain a bit of confidence and feel OK with carefully testing the terminals in the junction box.

 

Ok, another step forward, I girded my loins and ran these tests.

 

The bottom and right terminals give 240v.

The top and right terminals, with the switch off, give 15v (! not sure if this was the multimeter)

The top and right terminals, with the switch on, give 240v

 

4 hours ago, JSHarris said:

 

Thanks so much for taking the time to label those.

 

It turns out you are one step ahead even on the identification of the cable. The cable you have labelled "power in?" was, I thought, the switch cable. It turns out it was a switch cable, connected as in my previous photos, but to a different switch in the original part of the house (maybe this explains the older wiring). The cable you labelled "To switch" is indeed to the switch I pictured above, in the same room as the fan.

 

4 hours ago, JSHarris said:

Some connections are certain.  The earth on the left, the neutral on the right and the switched line at the top (this has to be right as it goes to a light drop).  The area of uncertainty is the lower terminal, as it's not clear that the switch cable has a line (red) connection to it, as it's hidden under what I think is the incoming power cable.

 

Do the test results above confirm the lower terminal?

[gravelld]

3 hours ago, ProDave said:

With so much of the lighting circuit having no CPC I would not trust that any earth conductors you do find really are properly connected anywhere, and I would want to be damned certain you have a proper earth connection if you have any class 1 light switches or light fittings.

 

All the lights in this room are low voltage fed from an appropriate transformer, but what about the light switch? Thanks for the heads up.

[Jeremy Harris]

9 minutes ago, gravelld said:

 

Ok, another step forward, I girded my loins and ran these tests.

 

The bottom and right terminals give 240v.

The top and right terminals, with the switch off, give 15v (! not sure if this was the multimeter)

The top and right terminals, with the switch on, give 240v

 

 

Thanks so much for taking the time to label those.

 

It turns out you are one step ahead even on the identification of the cable. The cable you have labelled "power in?" was, I thought, the switch cable. It turns out it was a switch cable, connected as in my previous photos, but to a different switch in the original part of the house (maybe this explains the older wiring). The cable you labelled "To switch" is indeed to the switch I pictured above, in the same room as the fan.

 

 

Do the test results above confirm the lower terminal?

 

Well done!  The test results do indeed seem to confirm that the top terminal is the switched line (L1) and the bottom terminal is the permanently on line (L), with the right hand terminal being the neutral.

 

If you connect a 3 core + E cable as suggested earlier then the fan should work as intended.

 

The 15V you measured when the switch was off will just be induction, and is normal.  These induced voltages in cables are one reason that the volt pen type detectors are pretty useless, as they will often light up from an induced voltage.  A meter discriminates between a low induced voltage and the supply voltage, so is usually more reliable.