Contactor not energising with voltage present.

Lost neutral would be my guess if you have voltage on the coil

This sounds more like an interlock system - though of course we cannot see it. It is probably worth checking that there is not some other things in the chain with the contactor coil - this may be the equivalent of the emergency stop error, where there is no fault except someone has done something that locks it off.

Also when you say you get the voltage to the contactor is that a two probe meter reading with one side of the meter on each side of the coil or just verify that live gets to one end of it ? there may be a chain of microswitches in the loop that require the ventilation to be on, or doors open or shut or similar conditions, or a thermal fuse somewhere  and even perhaps a stop button to be released. Do we know what was done to it  since it last worked - such as cleaning or moving or a small fire  ? This may give a clue where to look.

Mike.

Is this in a commercial kitchen? If so it's common to have an interlock system between the ventilation system and the cooking appliances - usually it just operates a gas valve, but I wouldn't have thought it entirely beyond the realms of possibility for someone to think that shutting off electrically powered appliances might be a good idea as well. If that is the case then check the fans and pressure sensors in addition to Mike's suggestions. This kind of thing: www.banicocontrols.com/.../instruction_579720.pdf

   -  Andy.

Thanks for all the information people, really appreciate it. It’s in a student accommodation communal kitchen. I had 240V at the top of contractor in terminal 1&3. I’m quite sure there’s nothing between the db and the contactor. 

There’s another identical set up next to this contactor for another oven in the kitchen, it works fine. I must be missing a JB or some kind of interlocking component as you’ve suggested. Thanks again. 

Have you got a photo of the bottom of the contactor?

it looks like the mcb is for the control circuit and is fed from the live side of the contactor so you would need to follow the wire out of the bottom of the mcb which I would expect to go to whatever triggers the contactor and then make its way back to terminal A2.

Thanks for your reply. The wire from the bottom of mcb goes in to the right hand flex and goes to a JB in the cooker hood where it’s connected to a fire suppression device.

In the JB I did notice that a neutral from one cable was connected to an earth from the other cable. I checked the other hood for the oven that’s working fine and the wiring is exactly the same. 

The fire suppression flex goes into what looks like a pump or canister. As I’m writing this I remember it being taped up where the cable enters and a bit of a kink in it. I didn’t know much about the device so I didn’t play with it. 

Thanks again. 

Thanks for posting the photo, that seems to confirm suspicions. It looks like they’ve used the brown and blue cores in the flex as the live and neutral supply to the remote device and the “earth” as the switched live back to trigger the contactor. 
It seems that whatever the fire suppression device is that’s where the issue lies.  Without any more info on that it’s not possible to know what the problem might be and I suspect you may have to involve someone else who knows more about these unfortunately. 
If you want to confirm that the contactor is working you could turn off the mcb, remove the live to the flex from the mcb and the earth from the flex from A2, and put a link wire from the mcb to A2. When you turn the mcb on the contactor should trigger. This could only be for a quick check though as it obviously removes the safety interlock so would need to be put back how it was.

Thanks Mark, really useful information. I’ll prove the contactor next time I’m there and will also find out who put the fire suppression in and either get them down there or get technical support over the phone. Thanks again for the quick response

Hmm that  does look like a bit of fast and loose playing with the colour schemes. I think, probably, that the black in the armour is earth, and I agree with SparkyMark above, that if that is the green and yellow going to the lower 'A' terminal for the actuating coil, then that is not an earth at all but a switched signal at whatever the interlock on the flex comes out at. As you have a working one next door, it may be worth comparing voltages are the same.

Here is my best guess - take with a large pinch of salt.

Heavy black wire assumed earth linked from supply to oven but no sleeving and needs to be confirmed

Heavy  brown and blue to top of contactor probably Incoming live and neutral - live splits to MCB to give a 'fused live' to the flex.  Expect power here all the time

Flex brown, should be fused live,
Flex blue should be un-switched  neutral
Flex Green and yellow NOT EARTH, but a signal live to pull on contactor - probably live when fire is not detected but check on the good one. 

The two central  'A'  (Actuate) terminals on the contactor need to have 230V between them for the contactor to pull in (assuming a 230V coil - most likely but I suppose the fire alarm could be 24V or something.)

One should be neutral and the other should be switched live, probably but check the other kitchen - it is possible to be live all the time and then to have the neutral side switched I suppose.

Contactor lower terminals outbound  switched L and N to cooker, via second  heavy cable.

Good luck and please let us know how you get on.

Mike.

I think what often happens is.

Someone does a temporary lash up to get things started with whatever is to hand and honestly intends to sort it properly later.

then weeks months later amends it a bit more and again intends to tweak it to become a proper set up.

then a year or three later alter/amend/fix an aspect of it after looking and trying to remind themselves what they first did and thinks "Oh I really must amend colours etc and leave a chart/manual to let me and others know what`s going on".

years later they leave for some reason then somebody else gets the job of trying to guess what was done in the first place, then what was changed and why? 

Does that person then make charts and manuals etc ? Despite best intentions not always.

And that`s if yer lucky