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Brendo

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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
 
Firstly is this 1ph or 3ph and if the latter is this 9Kw per phase or 3Kw a phase would be my first few questions, have you clamped the load to see what 1 element pulls if you are in doubt?
I guess 1ph but that would rely on the fact the installer got it right and we should never assume in this game.
 
Firstly is this 1ph or 3ph and if the latter is this 9Kw per phase or 3Kw a phase would be my first few questions, have you clamped the load to see what 1 element pulls if you are in doubt?
It's a single phase supply. I've clamped the 1 load which is working at 13.68A.
 
Your contactor is 20amp per pole so it is sufficient for a resistive load a 3kw element per pole, the problem is likely to be poor termination, this is a high current load, have the cable ends been suitable dressed with rated crimps or lugs?
What is the brand of contactor - is it a recognised reliable brand or cheap import.
 
Firstly is this 1ph or 3ph and if the latter is this 9Kw per phase or 3Kw a phase would be my first few questions, have you clamped the load to see what 1 element pulls if you are in doubt?
I guess 1ph but that would rely on the fact the installer got it right and we should never assume in this game.
There is usually an electronic control board which is installed with his system but it's blew in the past and someone has hard wired it up with this 20A contactor and a 16A timer
 
Your contactor is 20amp per pole so it is sufficient for a resistive load a 3kw element per pole, the problem is likely to be poor termination, this is a high current load, have the cable ends been suitable dressed with rated crimps or lugs?
What is the brand of contactor - is it a recognised reliable brand or cheap import.
I've attached a photo of the contactor which is a Chint NC1-0910

What contactor size for a 9kw electric boiler 20180601_113134 - EletriciansForums.net
 
chint...and where is the housing etc? that looks a right mess lol, i know you didnt install it
No I would never install this.
The black box/housing above the contactor usually would contain the main pc control board with digital display. Someone just removed that and fitted.this instead
 
Looks like the plumbers done that, either explain you will have to upgrade it or walk, that is an appalling installation.
The cheap contactor brand says a lot about the installer too.
 
No I would never install this.
The black box/housing above the contactor usually would contain the main pc control board with digital display. Someone just removed that and fitted.this instead
if i was you i wouldnt try and improve upon this install without starting from fresh

id say the "fault" is down to poor installation than the boiler or contactors themselves
 
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
 
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 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
 
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.
 

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