Short answer
A charge point must be protected against DC faults. That can be done with a type B RCD, or with a type A combined with 6 mA DC detection in the charger itself. What you need depends on what is built into the charger; that is in the manual and on the rating plate.
Who this article is for For anyone having an EV charger fitted, or who already has one and wants to know whether the protection is right. Measuring and swapping is work for an electrician.
Why an ordinary RCD is not enough
An RCD measures whether current is leaking away. The common type A sees AC and pulsating DC. But an electric car contains an inverter, and if it develops a fault it can produce a smooth DC fault. Such a fault saturates the core of a type A, after which it can no longer reliably do its normal job either.
That is not just theory for the standard: it means the protection of the whole circuit can suffer.
Two ways to do it properly
1. Type B RCD. Also sees smooth DC. More expensive, wider in the consumer unit, but always right.
2. Type A plus 6 mA detection in the charger. Many modern wallboxes have DC detection built in. Then a type A may be used in front of it, provided the manufacturer specifies this. This is now the most common solution.
What applies to your charger is in the manual under the installation heading. If it says nothing about DC detection, assume type B.
How to see what you have
The RCD has a symbol on it. Type A has a half sine wave, type B also has a small block or the letter B. If in doubt, take a photo of the consumer unit and send it; that saves a visit.
The RCD has a symbol with the letter; if in doubt a photo of the consumer unit is enough.
Exactly what the differences are is covered in detail in RCD type A, B or F.
The RCD trips when charging
If that happens at the same moment every time, there is usually something wrong with the car or the cable, not the installation. If it happens at random, it can also be down to another circuit on the same RCD. A charge point should have its own RCD, not shared with the washing machine.
What you can check yourself is in RCD keeps tripping.
Testing is part of it
An RCD is a mechanical device that can seize up if it never moves. Press the test button twice a year, including the one for the charging circuit. How to do that and what to do if it does not come back on is in testing an RCD.
From my own work
During an inspection in Sittard I found an EV charger connected to an ordinary type A RCD, without the charger itself having DC detection. The installer was a handyman firm that had "just done it on the side". With a fault in the car that RCD would not reliably switch off. A type B went in, and the customer could charge with peace of mind again.
When to call an electrician
- You do not know whether your charger has built-in DC detection
- The charger was connected by someone without an installation certificate
- Your RCD trips as soon as the car starts charging
I check it and test the installation. See also RCD type A, B or F and the fault service if it is going wrong now.
Frequently asked questions
How do I know whether my EV charger has DC detection?
It is in the manual under installation, usually as 6 mA DC detection. If it says nothing about it, assume a type B RCD in the meter cupboard.
May my EV charger be on the same RCD as the washing machine?
No, a charge point should have its own RCD. Otherwise a leakage current in the car also stops your fridge, and the other way round.
Roughly what does a type B RCD cost?
The component itself costs several times as much as an ordinary type A and takes up more space in the consumer unit. I put exact amounts in the quote, because they vary a lot by brand and version.
Further reading
EV charger at home: single-phase or three-phase, and which protection
The choice depends as much on your car as on your connection. With the costs, the RCD debate and why load balancing is not an optional extra.
Which cable to the EV charger, and what the distance does
The further the charger is from the meter cupboard, the thicker the cable has to be. That is usually the item that decides the price.
Load balancing: why your main fuse can cope after all
Without load balancing the car keeps charging at full power while the oven and the tumble dryer are on too. With load balancing the car automatically charges more slowly.
Questions and comments
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