04-11-20

Knowledge blog: Residual Current Devices

KennisblogOur engineering manager John Meijer shares his knowledge. Every month, he discusses a different topic in the field of electrical safety. This time his blog is about: residual current devices.

In this blog we will zoom in on the RCD (residual current device). Why are RCDs used and when do we use them? Voltages greater than 50 VAC or 120 VDC are not touch-safe and therefore automatic shutdown of the power supply within the specified time, is required. Nowadays, the NEN1010 and NEN60204-1 indicate that it is mandatory to have an earth leakage protection of 30mA with every socket for general use.

Where does that 30mA come from?

A good working 30mA earth leakage circuit breaker should trip between 15 and 30mA. Above 15mA it is often no longer possible for a person to let go, because the muscles will cramp. In order to prevent respiratory problems or a fibrillating heart, this touch protection must therefore automatically switch off the power. You should never just use another RCD of 100 or 300mA arbitrarily.

Effects on the human body

Below, the effects of a certain amperage intensity on the human body are given. The effects of different amperages have been recorded in tables by various scientists. These are various amperages at 50Hz and a through the body from hand to hand.

0,5 mA – 1 mA at 50 Hz    Pain threshold
1 mA – 5 mA at 50 Hz    Muscle twitching
5 mA – 10 mA at 50 Hz    Pain, release limit
10 mA – 15 mA at 50 Hz   Cannot release
< 100 mA   at 50 Hz    Breathing difficulties
> 100 mA   at 50 Hz    Fibrillating heart

Rules in accordance with NEN 1010:2015

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Since 1 July 2016, it is no longer permitted to sell and install 3-phase group cabinets where circuit breakers (groups) are connected to a 4-pole earth leakage circuit breaker. A 4-pole residual current device is a 3-phase residual current device. This is no longer permitted after the NEN 1010: 2015 has taken effect. The 4-pole earth leakage circuit breaker will not disappear, but will only be used for a different application. According to NEN 1010: 2015, 230V circuit breakers may only be connected to a 2-pole earth leakage switch. The rule still remains that a maximum of four circuit breakers may be connected to one earth leakage circuit breaker. The difference between the use of the earth leakage circuit breaker in NEN 1010: 2007 and NEN 1010: 2015 is based, on the distribution of the leakage currents of groups in a 3-phase connection, among other things.

Circuit breakers in PV installations (solar panels)

With transformerless inverters it can happen that a DC leakage current starts to flow in the AC part. For that reason, a type B must be used. This type has an extra measuring circuit to measure DC currents. This is further explained in the NEN1010 and NPR 5310.

Do you have any questions about RCDs in response to this blog? Please do not hesitate to contact us.