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Surge Protection Devices

trebor12345 · 2026-02-20T16:26:11Z

This Topic has been changed by the Moderators in order to address only the fitting of Surge Protection Devices (SPDs) to consumer units. The Original Post, which follows here, concerned the type of protection device which supplied a heat pump.That portion of the discussion has been deleted as it gave incorrect information on the subject of electrical safety devices. I am having my existing heat pump changed to a Vaillant (another story). The question of fuse type has come up in conversations. According to the Vaillant spec I need this: The current fuse I have is this: Is this the right one?

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Air Source Heat Pumps (ASHPs)

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JamesPa

(@jamespa)

Illustrious Member Moderator

Joined: 3 years ago

Posts: 5002

11/06/2026 6:20 pm

@batpred of course you could just leave out the RCD altogether which is what my electrician did.

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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Batpred

(@batpred)

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Joined: 1 year ago

Posts: 993

11/06/2026 7:08 pm

@jamespa

I suggested to have a Contactum RCBO and the installer´s anxiety was very clear! Obviously the Hager CU is worth it, to avoid the emergency electricians that he had in the past. And not knowing for sure if the DC leakage is solved, I definitely want to make sure it is in place - we are resigned to add yet another CU to our collection. We kept some old CUs, but clearly this large RCCB comes with a matching Hager CU.

The other topic that we became aware of is that the Arotherm Pro heatpump is still not in the ENA list. I have no idea if the special RCBO that is needed for the current Plus is listed nor whether the Pro will also have it. It reminded me that the DNO step is an application, not a notification. 🤨

8kW Solis S6-EH1P8K-L-PLUS hybrid inverter; G99: 8kw export; 16kWh Seplos Fogstar battery; Ohme Home Pro EV charger; 100Amp head, HA lab on mini PC

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Transparent

(@transparent)

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Joined: 4 years ago

Posts: 3249

11/06/2026 8:11 pm

Posted by: @batpred

↑

And not knowing for sure if the DC leakage is solved,

The issue isn't DC leakage.

Type-B RCDs and RCBOs will trip correctly despite the waveform having a DC component present.

You need the contacts to open when there is a genuine difference of 30mA or more between the AC current being supplied via the Live and returning in the Neutral. A Type-B will do so; ie the DC element is ignored.

The presence of a DC component is usually regarded as an undesirable effect imposed by EV Chargers.

The presence of harmonics is generally associated with heat-pumps.

It seems odd to me that Vaillant have introduced an AC to DC power supply into their ASHPs which is imposing both errors onto the mains incomer to sufficient extent that the company has teamed up with Hager to recommend a particular protection trip. The message it gives to me is "our power supply design isn't good, and we haven't fitted HF filters either!"

Consumers shouldn't be asked to spend £600 having an expensive RCD fitted just because the heat-pump power supply has design deficiencies.

I've created the above timeline from spreadsheet date sent to me by a DNO.

It shows the absolute deviation of voltage imbalances which are being passed through local substations and on to the higher voltages of the Distribution Grid (11kV and above).

Whilst losses due to phase imbalances are substantially occurring only at the local substation level, harmonics pass right through every transformer on the grid. This is what causes the audible hum when you're in the vicinity of larger transformers. That's energy being lost.

Save energy... recycle electrons!

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