Faulty consumer unit

Not really. It's potential sparks and overheating that emanaates from the CU is why it has to be metal. You should get that when all there is are connectors.

Mine were installed in 2017. I see that they've no longer been permitted since 2023. What was the reason for disallowing them, do you know? Does it apply to all three types (A, B & C), which I understand merely describes the current they trip at? I don't have an RCD as such. I shan't be changing mine any time soon!

They aren't banned as such, just the suitable applications are quite limited.

"Regulation 531.3.3 of BS 7671:2018+A2:2022 tells us that Type AC RCDs shall only be used on circuits where the load current contains no DC components. How can we know that? Essentially this means circuits with purely resistive loads. In the old days, 100w lamps, rings on the electric cooker, 9 kW shower, etc., they were all resistive loads which Type AC RCDs were happy with.

Now, though, literally everything has electronic control circuits with, i.e. fridges, ovens, EV chargers, everything. These loads with electronic circuits can impose a small amount of DC onto the circuit. The DC ‘blinds’ AC RCDs by saturating the ferrite core of the RCD and, hence, the RCD locks up and fails to operate when required."

That's the 'curve' of the MCB, not the 'type' of the RCD. A typical RCBO might be a Type-A RCD combined with a B-curve MCB. Many suppliers are loose with their descriptions and call them a B-type/C-type/etc RCBO, when they are actually contain a Type AC RCD.

If you have Type AC RCBOs then you aren't as protected from DC earth leakage faults as you would be. But still better protected than you would have been with whatever you had before.

If that was a concern, you could always upgrade the RCBOs on those circuits which see potential SMPSU loads - eg sockets - while leaving the cooker, immersion and electric shower which are fine on Type AC.

Theo

Thanks Theo; good explanation.

Many thanks for all the advice given here.

After professional inspection and evaluation, it seems that the problem is a relatively simple one of the PIV equation.

Shower: 8.5 Kw Breaker: 32A Current drawn: approx 37A (assuming 240v supply)

A couple of options are being explored.

I am grateful for the help.

All fixed. New breaker installed within the consumer unit and the electric shower now working better than it has in years (and without going off halfway through a drenching).

And all for a very reasonable price.

Now I need a tree surgeon and someone who can fix fences.

Onward and upward.

The "would sometimes trip the consumer unit off completely" does not suggest an over current cause though.

The devil is in the detail[1], although it is common that they will recommend "rule of thumb" solutions since it saves doing detailed calcs, and will allow more future options. Also worth remembering that the difference in cost of cable is not large if paying for professional installation.

You would need to pay careful attention to the installation method, in particular its thermal environment. Also on longer cable runs, its total voltage drop.

Some of what they showed looked more like PBJ than standard VIR. You could see fabric encapsulated in the insulation.

I could not agree less :-)

Hmmm, and?

There is a "push" - just an implicit one - new work gets done to current standards. Some of that will drive updates to the old stuff. There will come a point where a rewire is required, and then it will all be to current standards.

Peanut butter and jam? I could see why that would be coded C1.

Theo

It's a big step-up in safety, for not a lot of cost. Util recently, only my garage, workshop and outdoor outlets, were covered by a single RCD. I was desperately short of ways in my 1980's consumer unit, so as a cheap upgrade, I swapped that for one with many more ways, but protected by two RCD sections, and one with optional no RCD protection. I decided to make use of the unprotected side, to run a special circuit, just for fridges and freezers.

A single, or dual RCD board, is only an inconvenience, when a fault develops. In my case, I could quickly determine the circuit, and isolate it.

Don't you think it would be even more stupid, if every time the regulations changed, you had to fork out to upgrade your electrical installation? Imagine every few years, having to fork out several thousand pounds for a rewire, and all the disruption which goes with it. An installation does not suddenly become dangerous, simply because the IEE Regs are updated.

What seems more likely, is that an MCB tripped, rather than an RCD. MCB's react much more quickly, than a simple fuse-wire. A fuse-wire will survive a lamp failing, with internal arcing, an MCB will react.

We have to keep the standards boys in work.

They still had the original rewireable fuses. A Whole house RCD was added before the fuses.

As time progresses, new devices become available, then the regs can be updated to include them. As the writers of regulation become aware of issues, they can retrospectively revise them.

It's a complete nonsense, to expect every installation to be upgraded/revised, every time the regulations are revised. An installation is no less safe (usually) than the day it was installed and the set of regulations it was installed to.

They didn't scrap every car, the instant the seat belt laws were passed, it was a gradual process of vehicle replacement, as they wore out.

Having said that, it is always worthwhile, with an older installation, adding a whole house RCD, even if one is not mandated.

The problem has now been cured by the replacement of the 32A breaker by a 40A unit. Hot showers now the norm again.

:-)