Electric Vehicle Charging Equipment Installation – RCD requirements?

Guidance for Installers

The basic requirements for RCD^[1]  protection can be found in the IET’s “Code of Practice for Electric Vehicle Charging Equipment (EVCE) Installation”, with references to BS7671. This code of practice does not cover in detail the issues associated with the selection and use of RCDs (see Table below), leaving the Installer to verify the selection of the “Type” of RCD required. Consequently from a safety and legal perspective the “competent person”/ installer should take careful note of the information detailed in clause 5.5.3

 

EVCE RCD Specification Issues

The Code of Practice states under section 9.1 “During and on completion of the installation, and before being put into service, the installation shall be inspected and tested to verify that the installation complies with BS 7671 and the charging equipment manufacturer’s instructions”.

Refer to clause 5.5.3: quote “Type A RCDs are preferred, as they will provide some protection if the vehicle develops a d.c. fault to earth”  this clause goes on to explains that Type A are only suitable for use where the following  applies: “tripping is ensured for residual sinusoidal alternating currents, for residual pulsating direct currents, for residual pulsating direct currents superimposed by a smooth direct current of 0.006 A, with or without phase-angle control, independent of the polarity”.  See fig 1 for definition of the wave form contained within the standards referred to in 5.5.3.

Type A RCDs can only be used where the leakage current does not contain any high frequency AC content. If the charging equipment is likely to generate leakage currents with characteristics that exceed the above limits, it would not be safe to use Type A RCDs as the RCD tripping characteristics cannot be guaranteed – reference clause 133.1.3 page 20 of BS7671.

Battery chargers used on Plug–in EVs can produce high levels of harmonic distortion, due to the technology employed and the nonlinear loading of the supply during charging. Type AC & A RCDs are only designed for use on supplies with standard 50Hz waveforms. High frequency AC flowing through these RCDs can cause overheating of the trip circuit components, leading to failure of the RCD due to incorrect application. The other issue associated with the rectifier circuits incorporated in battery charging technology, is the transfer of DC earth leakage components into the AC supply under fault conditions. DC flowing through standard RCDs produces magnetic saturation in the RCD’s AC iron core – it will not be able to detect the imbalance created by AC leakage currents. In this situation someone using the equipment, coming into contact with a current carrying conductor or conductive surface (live due to internal fault) and earth would potentially be at high risk of electrocution.

 

Checking the Type of RCD Required as part of the Installation Assessment

The Code of Practice defines a list of basic checks that must be performed, documented and agreed with the client prior to commencing any installation work – reference Annex C to E. Including the RCD selection criteria and Type of RCD proposed in the initial assessment, should help avoid any arguments or issues at a later stage.

For example section 8 details requirements for Commercial and Industrial locations; section 8.5 covers RCDs, in which it states Type A RCDs are preferred (8.5.3) – this is a minimum requirement but does not mean that it is suitable for the application.

Table 2: Summary of Charging modes and possible residual currents based on the charging technology.

 

Table 2	Voltage supply UK	RCD Minimum requirements*	RCD Protection mounted in the charging point	Comments
Mode 2	Single phase	Type A	RCD built into EV charging cable	Car manufacture responsible for the in-cable RCD. The Installer is responsible for any RCD installed in the circuit existing or new, that could be affected by the load connected to the charge point.
Mode 3	Single phase Three phase	Type A   Type B	30mA  2 pole RCCB   30mA  4 pole RCCB	Leakage current as defined in EN61008 & 9  (see IET C of P page 27  clause 5.5.3)     Type B  if leakage currents exceed parameters defined for  Type A RCD
Mode 4	Three phase	Type B	30mA  4 pole RCCB	AC/DC bridge and EMC filters Risk of smooth DC and HF AC currents
*Type A RCCB:  Tripping for residual sinusoidal alternating and pulsating direct currents at 50Hz / Smooth DC<6mA *Type B RCCB:  As type A with the addition of smooth DC and non mains frequency AC currents For additional information on Type B RCCBs / down load free technical guide visit www.doepke.co.uk

 

Refer to the Car Manufacturers recommendations with regard to the type of charging technology and any specific charging circuit supply and protection requirements for EVCE.  For sites where the AC charging facilities are designed for multiple vehicles (Mode3 – to deliver the power requirements), different car manufacturers will have varying requirements due to the individual charging characteristics of the vehicle concerned – the assessment must consider the worst case scenario. Some International car manufactures already specify Type B RCCBs, due to the load characteristics of the car charging technology for Mode 2 & 3. With Mode 4 you must use Type B RCCBs to meet existing safety standards. 

When selecting “Type B”, check the upper frequency limit detailed in the RCD manufactures technical data. Three phase EMC filters normally produce leakage currents in the kHz range which is above the 1 kHz reference in the existing code of practice. 

Test Certificates – Signing off

RCDs are classed as a 2nd line of defence and if selected, installed and maintained correctly, can reduce the risk of death or serious injury.  Following the basic selection process that is required to ensure that the correct device is installed, checked and signed off by the person responsible for the installation, will help to reduce the risk of the Customer receiving a fatal shock.

 

Please see below for a list of some of the independent guidance available relating to EVCE selection and installation. For specification, applications or questions relating to the application of RCDs, specialist manufactures such as Doepke offer full technical help and support in the UK.

Chaz Andrews – Technical Manager, Doepke UK Ltd

sales@doepke.co.uk or www.doepke.co.uk

Reference documents:

Provision and use of Work Equipment Regulations 1998

Electricity at Work Regulations 1989

IEE Wiring Regulations / BS 7671 (2011)

IET Code of Practice for Electric Vehicle Charging Equipment Installation

OLEV Government ecar technical specification

BEAMA Electric Vehicle Infrastructure Project