contactor problems

i have a square d ccn240 contactor. it is supposed to be used between a wall situated thermostat and underfloor heating mats.

i know that the contactor is supposed to be normally open so that when the switch line from the thermostat tells the contactor to go on, the contactor should close and the power should go to the mats.

however, this is not happening, and the contactor seems to be closed all the time. although once, after turning the power on at the fuse board, it made a noise and didnt call for power initially. then, when the thermostat sent the signal via the switch line, it made a noise and closed and the mats received power. when the thermostat later tried to tell the contactor to open again (ie so the mats would switch off), the contactor made a funny noise and then seemed to close again, as if maybe it was broken inside, is this possible?

or have i purchased a normally closed contactor? there is no such info on the internet or with the product.

ps.

a. the contactor is 40 amp rated but i probably only need 13a or 16a, so if i am buying a new contactor, which one should i buy?

b. does it matter that the thermostat is powered by the same fuse as the contactor/matting? i appreciate that the thermostat should be supplied from a lower rated fuse on the fuse board but at the moment there is no other way to power it. therefore i just want to check that having them both powered off the same fuse/cable isn't causing these problems.


thanks

It is common to put a fuse or mcb adjacent the contactor in the same enclosure for the control circuit.

Has the contactor been energised (contacts closing) onto a fault? This can cause the contacts on cheap contactors to weld together, and even cause internal parts to be completely dislodged.

Contactors do not come in normally closed (relays do), but you can purchase add on blocks for them. I would be 99% sure yours is normally open as expected.

Can you press the contacts in - usually a small square or toggle you can move to force the contacts manually.

A photo of the actuall one would help.

Can you draw a wiring diagram so we can double check there is no issues with that?

i dont know how to upload image/photo/diagram. i could email them to you?

what do the toggles/squares look like? are they like little loops under neath the squares where the cables are inserted?

i have just noticed there is a little hole in the front like a window. the window is blank.

i have another contactor (merlin gerin multi 9 ct) which i tried to wire up but that one seems not to pull any power at all. the plastic square window on that one is red.

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The contactor opens when you kill the control power to it? Sounding more like a control wiring problem to me. N/C contactors are not commonplace and in your case, not needed. It is sounding like you have just wired it? The power source will not be causing the problem but you should ensure the cables are all adequately protected by the single protective device. Can you post a photo of the contactor and associated wiring? Remember to turn off the electric before removing the cover!!

ok. i worked out how to close the contacts manually, so that the red shows in the window.

i also checked inside and its not welded together - it is open.

therefore maybe it is the wiring.

fuse board has live going to the stat and to no 1 on the contactor.
neutral from fuse board goes into stat, into a2 and also to the mat.
stat has 3 cables (live and neutral to fuse board as above), the switch line goes to a1 on the contactor.

the contactor has four cables (switch live and neutral as above) and from no2 there is the brown cable to liven up the mats.

i have tried with two thermostats, same result, so presumed it was the contactor. is it actually the wiring? this is how square d told me the contactor should be wired.

i still think that somehow its the contactor. but any thoughts are welcome. thanks

i think the contactor is fine. i think the problem must be the signal being sent down the switch line from the thermostat to the contactor. when i take the switch line out of a1, and turn it on at the fuse, the contactor does not close.

have i wired the thermostat up wrong somehow? or is the contactor being closed by a very small signal from the switch line when its turned on at the fuse? or is it something to do with the electronics on the thermostat that is causing the switch line to be on even when its not supposed to be?

its driving me insane now; i have tried two thermostats.

Is it a 3 core to the stat?

I assume brown to the live supply, grey to neutral and black the switched live to the contactor?

If so, try joining the brown and black at the stat in a terminal block and the leave the neutral on its own. Turn on the supply and see if the contactor pulls in. Then try the same with the brown and black seperated. The contactor should not pull in.

What type of stats have you tried, and what terminals are you using?

i am pretty sure it is the stats. they are from floorheatech and they were meant to be 16amp rated, but when i did this, they blew. their electronics panels are slightly different.

i had a nightmare with floorheatech, they are not good supppliers.

anyway, the two i tried first where the contactor went on immediately, they were the same as each other.

i then used another old one i had which used to work without a contactor, but after it was painted over it no longer worked. anyway, this one when wired up didnt cause the contactor to go on immediately.

i will try another company's stats tommorow!

It may be the thermo stat in the OFF condition has enough leakage to hold the contactor in the energised state.

When the thermostat is OFF and you then press the contactors mechanical button to fully close the contactor does the contactor come open when you release the button /If not then there is a leakage in the thermostat

If it does release afte that then the back EMF from the contactor coil ( the voltage spike when the thermostat turns off ) may be false triggering the thermostat output back to ON. Would need a Transorb or similar spark suppressor across A1 A2

could your tell us what numbers are connected to what cables on the contactor and if there was any preconnected cables?
it sounds like once the stat energises it the contactor the holding contacts take over to keep it in, some contactors are pre wired .

sarahproperty said:

i dont know how to upload image/photo/diagram. i could email them to you?[/img]

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Sarah to upload a photo follow this link