Level of risk to tenants for heat pump on a shared type A rcd

If you know (or suspect) that there's a defect which may give rise to danger, and then someone gets hurt, what will be the excuse?

The point of an EICR is to check whether there are any issues that haven't been identified and in so doing provide an expert's opinion on whether the installation remains servicable, not to provide a reason to delay maintenance.

How many heat pumps, and shared with what?

Are there a couple of heat pumps on their own RCD, or do they share the RCD with other types of circuit?

What is your concern please?

The thing is I don't fully know the risk (if any) BS7671 does not mention heat pumps neither does best practice guide 4. The latter suggest that wrong rcd type on an evse could be a C3.

Im hoping they will gain a new entry in special locations in the future.

This will affect many properties,the developer states they were installed as per the regs at the time.

The regs are not retrospective and it states something installed to an earlier edition could still be safe.

Our contractor initially gave a C2 but niceic advised them to change to a C3 during a recent inspection.

If it was my design I would specify a type B HP, I have been informed these were not available at the time and I'm not sure these even have a standard?

One heat pump per property on a dual rcd board, I don't have details with me but from memory sockets and lights are on the shared type A rcd 

I would specify a type B HP

From what I can gather, the "B HP" types differ from more conventional types in that they're less sensitive to high frequency components of the residual current (e.g. min threshold of 150 mA for frequencies over 1 kHz, even for what's nominally a 30mA device) - so as I see it specifying a "B HP" type is in part to reduce nuisance tripping, rather than improve safety from a shock perspective. So if it's already installed and working satisfactorily, you're probably OK on that score.

Next question is whether you'd need a B type rather than a A type - that's harder to answer - d.c. currents (e.g. over 6mA) can certainly blind an RCD - but I suspect a HP is less risky than say an EV on that score - there being no big battery that could be connected to the a.c. supply by a fault in the electronics and no deliberate d.c. run along c.p.c.s as a pilot signal.

    - Andy. 

I don't see the problem.

Unless heat pumps are particularly prone to nuisance tripping, sharing that half of the DB with other circuits simply means that if any of them trips the RCD, half of the board trips. I do not see any risk over and above any other dual-RCD board.

If the manufacturers require a type B RCD, I would be surprised. After all, there is nothing new about heat pumps: air-con has been around for decades. They contain a motor and some control circuitry, neither of which seems very risky.

OK, they are contained in a steel box which is outdoors, but a type A RCD should deal with any risk of the casing becoming live, which should trip ADS in any event.

They contain a motor and some control circuitry

I suspect the problem comes from the fairly hefty inverter drive in the more modern HPs - so there is a sizeable d.c. bus in there (probably with some substantial smoothing capacitors) ... but how likely that is to feed back into the a.c. side of things (e.g. via the c.p.c.) is less clear. Hopefully far less of  risk than an EV or transformerless PV inverter, but whether it's quite negligible not not we can only rely on the manufacturer's instructions to tell (if they do). If the original instruction suggested an A type would be OK, you should be in the clear.

they are contained in a steel box which is outdoors, but a type A RCD should deal with any risk of the casing becoming live

I would hope, on a TN system, the MCB would be more than adequate for ADS. Which brings me back to asking whether the RCD is needed at all - it's not in a bathroom or on a socket circuit or domestic lighting, so unless they've concealed soft sheathed cables in walls (perhaps unlikely for a retrofit?) I don't think there's any general BS 7671 requirement for one at all.

   - Andy. 

I was in a quandry similar to this a few years ago. I asked the heat pump company (Nibe) what type of rcd was required but they couldn't answer. I then sent them a link to an online article by Dpoeke which described the 'blinded RCD' phenomena and they promptly said they requried a Type B.

Basically, the designers/manufacturers/installers didtn know until prompted. My guess is a type B was recommned more out of panic than reasoned thinking and they had never heard of a Type B RCD before I sent them the item.