What contactor size for a 9kw electric boiler

Brendo · Jun 1, 2018

Hi all.
Don't have much experience on this topic.

Called to a job with an electric boiler. It has a dedicated 10mm supply from a 50A MCB. I narrowed down the fault the the contactor which was only feedig 1 of tge 3 elements and had scorching marks around the other 2 terminals. And is currently a 20A. The boiler has 3 x 3kw elements.
My query is surely the 20A is insufficient for the 9kw load from the elements and shouldn't I fit a 40A contactor in it's place.

Thanks

Brendo · Jun 1, 2018

darkwood said:
Looks like the plumbers done that, either explain you will have to upgrade it or walk, that is an appalling installation.

I agree. It's a joke that people still complete works like this and leave and even get paid for it.

elsparko · Jun 1, 2018

Brendo said:
I agree. It's a joke that people still complete works like this and leave and even get paid for it.

best thing to do now is go and show the customer the state of the electrical installation

a contactor may not be heavy in your hand, but on the end of a cable vibrations can cause movement, which causes arcing , everytime that contactor comes on its going to move the connections, loosening them slightly

i think you will find once you clean up this mess and install properly there will be no more "faults" with the system

Darkwood · Jun 1, 2018

I take it elsparko you don't fit many contactors, I would never choose that brand to run a heating load or anything tbh, they are cheap for many reasons, I have come across loads of them failing and been the cause of problems.
7.5Kw budget chint contactor about £10
7.5Kw recognised quality brands £40 - £90

You get what you pay for and the elements may have gone due to age but if there is overheating at the terminals of this contactor then I wouldn't overlook it is the contactor as the cause here of the cables getting hot.

elsparko · Jun 1, 2018

darkwood said:
I take it elsparko you don't fit many contactors, I would never choose that brand to run a heating load or anything tbh, they are cheap for many reasons, I have come across loads of them failing and been the cause of problems.
7.5Kw budget chint contactor about £10
7.5Kw recognised quality brands £40 - £90

You get what you pay for and the elements may have gone due to age but if there is overheating at the terminals of this contactor then I wouldn't overlook it is the contactor as the cause here of the cables getting hot.

i may not do many of them but i know that chint is a brand only seen to be used by diyers , ive always believed in buy cheap buy twice

i still think the install is questionable lol

Darkwood · Jun 1, 2018

elsparko said:
i may not do many of them but i know that chint is a brand only seen to be used by diyers , ive always believed in buy cheap buy twice

i still think the install is questionable lol

Hence I said upgrade it, if the OP repairs it then he becomes responsible for it and that includes the mess it is in, best to strip it out dinrail mount a quality contactor with dinrail connectors and linking clips for them, I would even provide a derated fuse size for the elements unless he can show the Zs is good at the elements.

elsparko · Jun 1, 2018

my contactor experience mainly comes from lighting controls, but the theory remains the same

a contactor just held in place by the cables it supplies which are not themselves secured could lead to loose connections, but like you say chint is a pile of crap so could just as easily be the contactor itself, i wouldnt fit a new contactor without sorting out the mess though

Octopus · Jun 1, 2018

Chint ............ Not a make I would fit

elsparko · Jun 1, 2018

Murdoch said:
Chint ............ Not a make I would fit

dont know any wholesalers who even stock this, that speaks for itself.

Darkwood · Jun 1, 2018

I wasn't arguing your theory elsparko and it is quite possible for the reasons you raise, I was just saying that the install (viewable in the upload) should be scrapped and started again but of course the customer will be given the option he does this or walks... I meant the whole mess too in the picture not just the contactor which I explained earlier.

Brendo · Jun 1, 2018

I've contacted the agent in the meantime and spelled out the issues. I agree rather chop it all out and start again with the components designed for the system I.e a new main control board and capillary thermostat to start with.

Brendo · Jun 1, 2018

The action of the contactor in this instance is retrofitted together with the timer and crude wiring.
Best do it properly.

Thanks all for you advice

Pete999 · Jun 1, 2018

Brendo said:
I've attached a photo of the contactor which is a Chint NC1-0910

View attachment 42565

Kin ell is that the finished article? Better get an Electrician in to do the job properly

Wilko · Jun 1, 2018

Looked up that contactor - advertised as 9A rated - so not tooo good for 3kW loads

[ElectriciansForums.net] What contactor size for a 9kw electric boiler

Pete999 · Jun 1, 2018

Brendo said:
Hi all.
Don't have much experience on this topic.

Called to a job with an electric boiler. It has a dedicated 10mm supply from a 50A MCB. I narrowed down the fault the the contactor which was only feedig 1 of tge 3 elements and had scorching marks around the other 2 terminals. And is currently a 20A. The boiler has 3 x 3kw elements.
My query is surely the 20A is insufficient for the 9kw load from the elements and shouldn't I fit a 40A contactor in it's place.

Thanks

Wilko · Jun 1, 2018

Oops - just read the rest of the advert, that's the AC3 rating that's 9A. The AC1 is quoted as 20A, but they don't say how many operations it's good for