RCD types. I'm getting more confused the more I read into it.

Ok, so we changed from Type AC to Type A, as backfed DC current from appliances could saturate the RCD coil, and stop it operating in fault conditions. Right, I can see that.

It's now been brought to our attention that some RCDs are not bi-directional, so need to be changed to bi-directional if current is likely to flow back through the RCD. Ok I can understand that more than the Type A vs AC.

Now, I'm going to fit a Heat Pump. Until recently, these were fitted on Type A RCDs, and still are by the bulk of Installers. (Manufacturers instructions are useless, one I have here in front of me says nothing about overcurrent protection, it just says a public supply of >16 and <75 amps).

Reading the Hager definitions,(linked below) it appears I need a Type A, or B, or possibly a Type F, as most HPs now use variable speed inverters. So how do I narrow it down as to what I require?

Do I go for the Type A, which Hager have listed as for  "Single phase in­vert­ers,"

The Type B, which says "In­vert­ers for speed con­trol, ups, EV char­ging where DC fault cur­rent is >6mA, PV "

Now note, they recommend the Type B for PV, so that is another I will have to change.

Or, do I go for the Type F, which says " some air con­di­tion­ing con­trol­lers us­ing vari­able fre­quency speed drives "

Clearly, there is a dilemma here. Without Manufacturers direction, I need to ensure compliance with this Countrys requirements - 7671 et al.  So the Type A could be fine, the Type B, probably, but I may need the Type F.

And, after reading the Hager explanation, I now also need a Type B bi-directional for any PV supplies.

So, how do we choose what to go for?  And If I go for a 'B', what does the Type F do differently?

And, on a similar subject, if the backfed DC current can affect the RCD on that circuit, can it also affect the other RCDs in the DB? They are all connected to a common neutral and earth, so could the backfed DC make its way through the neutral/earth to stop adjacent RCDs tripping under fault conditions if they are Type AC, or another type that can be affected in another way, say a F and A?

And, one I hinted at a few weeks ago, what happens when you fit a new DB, and find out one of the largest DB suppliers does not do a Type B or F?

Personally, I think this is getting to be a real mess, that's why people are still putting in Type A's, when, if reading into it, a B or F is required, but, actually finding out what is required is so difficult.

Hager link: hager.com/.../selection-of-rcd-types