What mains connected equipment needs a >6mA DC leakage current detector? (and why?)

[cupoftea]

Hi,
I am trying to find out what type of mains connected electrical equipment need a 6mA DC leakage current detector?...and why they need it?
I have searched www widely but find no reasoning behind the need for it.

EV chargers need it, and according to the following, this is because of the “DC powered battery”.

Article explaining the need for >6mA DC Leakage current detector:
https://www.electropages.com/2021/03/new-leakage-current-sensor-electric-vehicle-charging-stations

So are we saying that any mains connected equipment that comprises a DC voltage needs a >6mA DC leakage current detector? -That would mean that virtually all offline SMPS would need it, because all offline SMPS contain a DC Bus, on both the primary, and secondary sides.

Please may this thread be kept separate from the thread on fluxgate current sensors, as it is essentially different?

 

[FvM]

6 mA DC sensitive RCD are specifically required for EV charging by German standard VDE 0100-722:2019. May be there are other similar national standards.

I'm not aware of general applicable regulations requiring RCD for home installation, neither standard nor DC sensitive type.

 

[cupoftea]

I'm not aware of general applicable regulations requiring RCD for home installation, neither standard nor DC sensitive type.

Thanks, do you know if a Tesla power-wall would need a 6mA DC leakage current detector?

--- Updated Sep 25, 2021 ---

Also, the following video, turns the world of RCD protection upside down!...because from 13:48 to 14:22, it says that the following domestic items could all result in >6mA of DC leakage current...

Video discussing DC leakage and its effect on Type A/AC RCDs....

1...faulty VSD in domestic washing machine
2....faulty phone charger
3....faulty USB socket
4.....PV panel leak of DC directly into the mains
5.....Faulty EV charger
6.......something to do with "inverter"? (couldnt tell what was meant?)

So basically, what we are saying is that "normal" Type AC RCDs are no longer allowable, and everyone, everywhere must now use at least Type B RCDs ?

 

[D.A.(Tony)Stewart]

Thanks, do you know if a Tesla power-wall would need a 6mA DC leakage current detector?

--- Updated Sep 25, 2021 ---

Also, the following video, turns the world of RCD protection upside down!...because from 13:48 to 14:22, it says that the following domestic items could all result in >6mA of DC leakage current...

Video discussing DC leakage and its effect on Type A/AC RCDs....

1...faulty VSD in domestic washing machine
2....faulty phone charger
3....faulty USB socket
4.....PV panel leak of DC directly into the mains
5.....Faulty EV charger
6.......something to do with "inverter"? (couldnt tell what was meant?)

So basically, what we are saying is that "normal" Type AC RCDs are no longer allowable, and everyone, everywhere must now use at least Type B RCDs ?

That's a 2nd order fault. A faulty equipment left running that causes an unbalanced AC current (DC) while also creating a ground fault. USB? I don't think so

 

[FvM]

Thanks, do you know if a Tesla power-wall would need a 6mA DC leakage current detector?

I presume it has an metal cabinet connected to protective earth. Why should it need a RCD?

6 mA RCD has been introduced for EV charging and is required in this field (at least in some countries) by safety standards. Do you know safety standards in other application ranges requiring it?

 

[D.A.(Tony)Stewart]

It may be possible to balance in open loop by over-driving a very square BH loop with low coercivity. I believe it is called perming. Integration would still occur but gating out the perming pulses to balance the flux at a higher rate than the signal bandwidth.

 

[BradtheRad]

I've been thinking how everyday ground fault interrupters are related to the topic of sensing leakage in mains-connected appliances. I'm not sure whether a GFI particularly senses AC or DC.

Anyway their assumption is that any imbalance between live wire compared to neutral (return) wire, means that a human touching the device is carrying current. Since just 100uA can be fatal (let alone 6mA), the GFI must trigger at the slightest imbalance and shut off the wall outlet. (We must press a reset button to turn it back on.)

The fault might be in a live section, or neutral wire, or metal enclosure.
The metal enclosure may or may not be grounded.
The human may or may not be grounded.
The fault can be due to a broken connection, or a bare wire making a connection, or a human touching a wire (or metal enclosure) accidentally or intentionally.

Bathroom and kitchen installations in the US routinely have GFI's in the wall outlets. I imagine Europe is equally up to standards.

 

[cupoftea]

I've been thinking how everyday ground fault interrupters are related to the topic of sensing leakage in mains-connected appliances. I'm not sure whether a GFI particularly senses AC or DC.

Thanks good question....some RCDs detect DC and some dont. Some detect pulsating DC at various frequencies. Its impossiblE to find a table to show all the types of RCD and what exact frequency range of DC and AC imbalance they can detect fault currents (including magnitudes).......and the standards dont seem to define exactly what frequency range of AC imbalance or DC fault that each RCD must detect.......so it makes you wonder how you could design your own, eg , Type B RCD.

 

[crutschow]

Why the question about DC current imbalance when we are talking about AC?

A standard GFCI (at least here in the U.S) senses any AC current imbalance between hot and neutral using a magnetic coil.
Over 10mA through the body is considered to be potentially lethal ( which may correspond to 100µA directly through the heart).
Here a GFCI outlet is required wherever handheld appliances are used and there is a good chance that the person would be grounded, such as the kitchen, bathroom, garage, or outdoors.

 

[cupoftea]

Why the question about DC current imbalance when we are talking about AC?

We are talking DC leakage current, since small levels of DC in the mains, can blind type A RCDs.

the detection of DC leakaage current in the mains requiress current sensors which are vastly more expensive than simple AC or A type RCDs

I presume it has an metal cabinet connected to protective earth. Why should it need a RCD?

Because there are associated solar panels, which are outdoor DC equipmet, and could leak DC into the mains.......i dont see how this could easily happen, but the authorities have declared it.

--- Updated Sep 26, 2021 ---

***********************************************************************
On the subject of DC Leakage current detection.....

The DC leakage can be pure DC, or it can have a pulsing frequency of zero to 200kHz. And at each frequency, the magnitude of the average current can be 6mA to 300mA.

....As you can see, this presents an absolutely vast verification operation, so that you can be sure that eg, your equipment can detect eg 149khz DC leakage by way of pulses, where the avereage value of this DC is , say 158mA.

*****************************************************************************
The mains equipment to test if any EVSE equipment meets the standards, is to buy the metrel MI3152 tester with the metrel A3512 EVSE adaptor...

But the datasheets of these testers dont tell you want magnitude of DC they test at, and at what frequency, so i cant see how you can use them to assure that you have passed the standards

Metrel MI3152 Electrical tester:
https://www.metrel.si/en/shop/EIS/multifunctional-testers/mi-3152h.html

Metrel tester being used to test EVSE...but how do they know they have fully and properly tested out the DC leakage detection.....?....

 

[cupoftea]

Hi,
What RCD type is needed by a solar/battery system connected into the household 220-240VAC mains in UK/EU/USA?
The battery has an inverter/charger and the solar hooks in to the grid via an inverter.
The whole thing (apart from panels obviously) is in one box (enclosure).

The inverter/battery is in the garage.

 

[D.A.(Tony)Stewart]

DC-RCD's exist but are expensive until the closed loop fluxgate variety is avail. It appears that an open loop version works at threshold too with more exotic magnetics.

The DC causes saturation of inductance and weakens the pull on the relay, which they call "blinding" the RCD. In the old days DC current probes from Tek were crazy expensive and had to be degaussed before use for best accuracy.

If I recall GFCI's in North America support the UL std of 2.5mA max for leakage and RCD's in EU support the std of 16 mA (?) which may have changed

TL;DR https://www.mddionline.com/components/leakage-current-standards-simplified

 

[Hellohanx]

There are answers published on the internet, but it was posted after your searching.

1) What can cause DC residual current at EV charging application? Actually it was not brought by the batteries. It was mostly resulted by OBC insulation fault.

Why is 6 mA DC RCM used in AC EV charging pile?

6 mA DC RCM- officially named as RDC-MD in IEC 62955:2018 - is widely integrated in AC EV charging piles, so as to detect DC residual current that can cause the malfunction of Type A 30 mA RCD. It is interesting to know why DC RCM is used for AC charging

www.bituo-technik.com

2) DC 6mA detection is used only at EV charging so far. It is defined by IEC 62955:2018 as specification of RDC-DD. A introduction about RDC-DD are as following

What is a RDC-DD, RDC-MD and RDC-PD？

RDC-DDs are used at mode-3 EV charging system to ensure that the proper functionality of RCDs type A or type F is not impaired by DC residual currents above 6 mA. RDC-DDs are classified as the two classes of RDC-MD and RDC-PD.

www.bituo-technik.com

3) Many power electronic applications might generate smooth DC fault current, if they are not well designed or experiencing aging issues, such as PV inverters and frequency converter. In order to protect people from electric shock, type-B RCD against smooth DC fault current can be used. A Type B 30mA RCDs trips btw. 15- 60mA smooth DC current covering all applications, while RDC-DD trips btw. 3~6mA focusing on EV charging applications.

 

[D.A.(Tony)Stewart]

) What can cause DC residual current at EV charging application? Actually it was not brought by the batteries. It was mostly resulted by OBC insulation fault.

I highly doubt insulation is the fault of DC leakage currents of 30 mA even with 1kVdc which represents an insulation of R= 33kohm.

The asymmetry of OCB or charger conduction bipolar resistance and thus net RMS DC current difference should be the main cause. If this saturates inductance in sub-optimal AC RCD's then they do not perform as expected.