I had never heard of boilermate, so first think was I looked at the installation guide, and what I realised is it uses pulse width modulated controllers which run on quite a high frequency, I could not find a reference to RCD's but am wondering if it needs a type F.
There are three things with RCD's testing wise, one is the RCD its self, two is the insulation resistance, and three is back ground leakage. Simple ohms law one would think if the insulation resistance is high then there would be little leakage, however we test insulation resistance using DC, where the supply is AC, so with AC we have capacitive and inductive leaks which the DC meter will not pick up. So the clamp on ammeter shows us the actual leakage.
This can be between 100Hz – 5000 Hz (1000Hz nominal)
(Lab tested figure of 562Hz recorded in steady state conditions).
rings alarm bells for me, it may be that this is not superimposed on the mains supply, and a type A RCD is good enough, however it refers to IEE not IET as it is now, so the manual must be old, maybe before everything was RCD protected.
In the early days I could not test for DC or read 1 mA leakage on the clamp on, 10 mA was lowest reading, and I have had RCD's tripping when the RCD tester showed A1 and the insulation tester also showed as OK, but swapping the RCD got rid of the problem, at that point we had the type that tripped in 40 ms and the delayed type S. There were no other marking on RCD's, today we have 5 types. As well as S delayed we have
the first type AC is no longer used, but old RCD's may be type AC the next type A will allow 6 mA DC without freezing, the next type B is for DC and the last type F is for frequency over 50 Hz.
this explains further there is a link in that article to even more.
If we read it then it says how
Type F RCDs are used for frequency controlled appliances and equipment.
Examples of equipment include:
- air conditioning controllers with variable speed drives
- some Class I power tools
- washing machines
- dishwashers, and
- tumble driers which contain synchronous motors.
Some times I think they need to get real, I have seen type A and AC RCBO's as single modular width, even with double pole switching, but not type F or B, so to change from type AC to F is likely not an easy job, however I would start with simple tests insulation résistance, RCD test and leakage with a clamp on, and if these show clear would try swapping the RCD anyway.
It's the pump which can cause the problem, so again swapping the PWM controller for the pump may also help.
Good luck, and please tell us the outcome.
). Is that how it's normally done?
