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
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