Amptec 12kw boiler melted incoming cables

[jason1958]

Well from the terminal photos...

1) Looks like booster cables from the PCB terminals

Cable could be XLPE or silicone, to permit high operating temp.
The concern would be the cable-to-PCB-to-connector track size,
if that is not sized sufficiently it will be a source of heating.


2) Terminals themselves are interesting

Measure the gap between the PCB pins on the grey connector...
- 55A terminals are on a 10mm PCB pitch
- 85A terminals are on a 16mm PCB pitch

Whilst a 55A terminal will handle 16mm solid, 10mm stranded, there is a current rating to beware of - ie, 63A MCB is quite a lot higher than 55A.

If the terminals are designed to run cool...
- H07RNF is ok - 60oC to 85oC max temp (for warm not hot conditions)
If the terminals are designed to run hot...
- Butyl or silicone is better - >100oC max temperature

The terminals must be designed to run cool...
- Polyamide type block is typically limited to 100oC
- Going much beyond that is going to invite PCB track problems

If there is any heating beyond 60oC the cause is...
1) Terminals not tightened sufficiently (heating)
2) PCB tracks are undersized re size/thickness (heating)
3) Heater is itself defective and pulling too much current


Cable choice...
- Looking at the terminals, I would ask Amptec if a flex were better.

Annealed copper...
- Annealing makes copper soft, it work hardens with flexing/compression
- This can make terminal tightening a 2-step process on large cables

When an oblong cage clamp terminal is tightened onto 7-strand cable it will first take a lot of force to distort the strands into an oblong shape. Over time the copper will tend to flow sufficiently for the clamping force to reduce - sufficient to cause a high resistance contact. A second tightening is required - typically some time later, 15mins and even again the next day.

Using flex does NOT eliminate the problem.
However it might provide a higher surface area & lower heating.


I assume someone has actually verified the impedance of the heater?
Vis., that the element is not actually defective and drawing 70-72A?

That you found insulation bubbling says...
1) Terminals not tight enough
2) Defective element
3) Bad design re cable-to-terminal heating or terminal-to-PCB heating (PCB track area is too small & track too thin for the current)

That they have used "booster" cables from the PCB terminal tracks does not necessarily indicate they believe the tracks are too thin, but it might.
Such "booster" cables are more usually run to the PCB pin of the terminal itself - if they are needed it is because of PCB track heating, and in which case running them to a point short of the PCB pin is a bit illogical

 

[mrrigidtool]

Hi thanks for your reply got a link for the terminal
http://www.weidmuller.co.uk/43534/P...o-25-mm-cross-section/LUP-Series/products.asp

the original cable in was 16mm armoured however i could see that it was pulling at the board were it was so stiff, in order to keeop warm i ripped out what the sparky did and wired in the 60a mcb as per instructions included a 100a dp MK isolator i have run 40cm of the ho7 to the switch then 30cm of ho7 to the heater and i disconected the two lives from the circuit board which are stranded cable and screwed them into a hemly block then connected to my live i connected the nuatral as normal as that connector was fine and the ran a separate 2a supply up stream of the pcb which controls the stat ect. since changing to the ho7 it has not overheated however i have tuned the max temp down to half way. The new board has now arrived so i need to swap it over. you mention that the terminals are rated for 50a and Aptec recommend a 63a mcb so i'm already on a loser. What would you reccomend for the ends of the cable when connecting them as h07 has lots of fine strands would you flaten,twist or tin them..

Thanks for input also the engineer could not test impedance as he never had board to fire it up, as i understand its tested in series however not sure would like to run 60a through my little prongs any over way to test it.

 

[jason1958]

> you mention that the terminals are rated for 50a

No - there were various sized of terminals.

If that is the your terminal, it is rated to 76A = fine.


> the original cable in was 16mm armoured however i could
> see that it was pulling at the board were it was so stiff

SWA must be glanded off into a metal adaptable box.
You NEED a proper electrician to connect this thing in.

Most likely install method...
- Meter - Isolator - Henley Block - House-CU & Boiler-CU
- Boiler-CU contains 100A RCD as isolator & 60A MCB
- Cable to Boiler, if SWA gland off to adaptable box
- Adaptable box with suitable terminals to 10-16mm H07RNF

Why are you using SWA?
- Any cable run which is not in a cable to 522-06-06 needs an RCD
- SWA would negate the need for an RCD
- SWA however does not negate the need for proper termination & cleating

You MUST follow the manufacturers instructions.

Cable size...
- I recall the manufacturer said 10mm
- If they say the terminals are 10mm capacity, you USE 10mm only

Terminal block re 16mm SWA to 10mm H07RNF...
- This MUST be capable of handling 60A+
- Yes there is 60A terminal strip made, in a suitable big adaptable box
- However an electrician would probably source a proper box
- I would use a 2-way Pratley Box with CW gland for the SWA and stuffing gland for the H07RNF with Pratley's own cable connectors & covers.

That is sized sufficiently, with suitably sized connectors designed for sustained high current (I suspect this lot goes inside a cupboard re aesthetics).

You really can not connect this yourself. Any mistake and you will not only have a fire, someone could be dead or you could lose your eyesight.
_____________________________________
You need to get an Industrial Electrician in.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Just reading further - did you bypass the PCB *which controls the thermostat*?!

 

[jason1958]

Oh, and NEVER tin the strands of any flex.

- Solder is very soft
- Any heating causes the material to soften further and FLOW
- Thus your terminal will loosen, heat more, loosen, heat more, BURN

__________________________________________________________
You need an industrial electrician to connect this up & check switchgear.
Then to perform the dead electrical tests before it goes live.

 

[mrrigidtool]

i did not use swa the sparky did, i'll explain full set up now. supply fuse, henley block to home cu and 100a isolator box, 10meter run with swa 16mm to a metal cu with a 80a rcd and 60 mcb. This is then run into a small 100a isolator box with a switch next to the boiler using the h07 then h07 into the boiler both with stuffing glands. Origanly the sparky did not read properly and rated the heater at 50a and used a 50a mcb with 10mm twin & earth, it would keep tripping and the cable would get hot. then he used the cable out of the swa instead and foolishly he bypassed the mcb. Since seeking advice from amptec up dated mcb to 60a replaced swa from cu to boiler with 10mm ho7. Only i have had to bypass the pcb connector until the new one arrived yesterday, the bypass was ok the two main wires going into the melted terminal was sniped then put into a connector, upstream were there dry solder join was i soldered onto it and ran a separate supply from a 2a fused plug. The board is functioning fully however had to leave lid off due to the compact size of the unit. Did not want to do this however there was a 3 week lead time on a board. We slept at a hotel for 1 week before attempting to fix it. now i have a new board and the electrics have been follwed to manufactures instruction, i did not want to wire this in the first palce hence using a sparky, it's hard to find someone that knowledable like yourself i have spoken to another that's on our site he looked at amptecs diagram and said whats there now is fine, he did not have much knowledge of connecting up to high amperage heaters. So its a case of swapping boards now the old one has been functioning well for two weeks has n't overheated or tripped mcb, i'm drawing the conclusion that the cable was pulling on the terminal and with the heat it damaged the board as the edge of the board was bent were the terminal was in the direction of the cable.

 

[jason1958]

Ok, so it appears the overheating problem has been resolved.
Likely the original SWA was not tightened sufficiently - result obvious.

Now you must ensure two things.
- All covers must be in place with everything live (!)
- You need electrical tests performing re Continuity, R1+R2, IR, EFLI

Those tests should have been done before connection (!)

Originally - I assume it was a competent scheme registered spark?
Now - it is DIY so subject to LABC Part P & BCO/3rd party inspection

If you choose to ignore the Part P BCO Completion Certificate...
- I would suggest you at least get a spark to do a PIR of the boiler f.c.
- So electrical tests are done
- So design can at least be eyeballed for anything erroneous
- So installation materials & workmanship can be checked

Basically so he can pick up on anything that may not be a problem now, but may become one later on. You've already had a terminal fry-up, you do not want something to bite you later - peace of mind.

District Surveyors Association GUIDANCE is that a PIR is one way to achieve Regularisation. So the spark may offer to do a PIR on that f.c.
It would be useful if you have any future boiler trouble, because you then have something to kick Amptec with should the need arise.

 

[Spark123]

What is protecting the 10m of 16mm² feeding the second CU?
What type of CU is this, is it rated to accept a 60A (or 63A?) MCB?

 

[mrrigidtool]

the 10m of 16mm is armoured and the cu 's are both MK metal types.

 

[ban-all-sheds]

What is protecting the 10m of 16mm² feeding the second CU?

was what is protecting the cable against overload or fault currents - MCB? Fuse? What rating?

And "MK metal types" doesn't answer the question about whether they are rated to accept 60/63A MCBs....

 

[mrrigidtool]

the same thing that protects my tails on the houshold cu, the main incoming fuse, there is a 100a dp switch in the first box supply the secound box which has a 80a rcd and a 60amcb

 

[Spark123]

What size is the main fuse and have the DNO given you permission to use this for the protection of your cable?
Still non-the-wiser regarding wether or not your 2nd CU is suitable.