What household items need a 6mA DC leakage current detector?

[treezleef]

Hi,
Electric car charge points need a 6mA DC leakage current detector.
This is supposedly needed since the EV contains a high voltage DC battery....and the insulation between the high voltage battery and the mains line and neutral may fail.

Document showing Why 6mA DC leakage detectors are needed......

New leakage current sensor for electric vehicle charging stations

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...however, all Power factor corrected Switch mode power supplies have a ~400VDC bus, and they dont need a 6mA DC leakage current detector.......Why dont they need it?

 

[Mikegh]

Probably makes sense to incorporate the DC tripping into the charger

Detection and testing with DC fault currents is a bit of a bodge atm.

Mains supplies and boards and testers were designed to work on AC up to now

 

[telectrix]

with ev chargers, all you need to do is install a d.c. only earth rod. these are available from Tesco. any a.c. leakage is divereted into the E10 fuel pumps to reduce our carbon emissions. the d.c.leakage goes straight into the ground topower ground source heating. ssssimppless.??

 

[Lucien Nunes]

Switch mode power supplies have a ~400VDC bus, and they dont need a 6mA DC leakage current detector.......Why dont they need it?

But they do. The reasoning for introducing type A / F / B RCDs stems from the possibility of non-sinusoidal leakage currents arising from electronic devices that rectify and/or frequency-convert the mains.

In practice the non-isolated DC section of a typical SMPSU is small and localised and unlikely to cause significant leakage. The DC bus of an EV is much more extensive and more at risk of generating sufficient leakage to blind a type AC RCD.

You mention SMPSUs with active PFC; they are not a special case for DC leakage. Most SMPSU's rectify the mains; the active PFC just adds a boost converter into the rectifier output to enable the bus capacitors to charge over a greater part of the AC waveform.

 

[treezleef]

You mention SMPSUs with active PFC; they are not a special case for DC leakage.

Thanks, yes i appreciate that, but as you know, the voltage on Boost PFC output caps is about 400V..and thus it is a candidate for causing the DC leakage problem mentioned.
Do you agree that its the magnitude of the DC voltage present that causes the DC leakage current problem.

In practice the non-isolated DC section of a typical SMPSU is small and localised and unlikely to cause significant leakage. The DC bus of an EV is much more extensive and more at risk of generating sufficient leakage to blind a type AC RCD.

Thanks, so it is the physical extensiveness of the DC bit that causes the DC leakage problem.....?....what if i have an offline , isolated battery charger charging a huge 55v Battery bank....is that at risk of feeding DC leakage current back into the mains?......or, due to the low voltage (55v), would it not be considered a problem?

But they do. The reasoning for introducing type A / F / B RCDs stems from the possibility of non-sinusoidal leakage currents arising from electronic devices that rectify and/or frequency-convert the mains.

Thanks, but i believe you already know, and i also can assure that offline SMPS dont have 6mA DC leakage current detectors in them.

 

[pc1966]

While many electronic items have ~400V DC in them from SMPSU you also have to look at the risks related to a fault, and the probabilities of different fault scenarios.

For example, many low powered items are class II (double-insulated), so you need two faults on the rectified size and someone touching it. Many other larger items are class I so a fault can dump a very high current and so disconnection on the over-current protection is likely (plug fuse in the UK, or the MCB at the CU, etc) so again you need two faults, an open CPC and a fault to chassis. The majority of those are indoors and in dry locations, so again the shock risk is lower than something outdoors like a car.

Things like EV and PV installations have a lot of DC capabilities and they are also outdoor so any simple fault to Earth is going to result in a current that is too low to trip the OCPD and yet might be high enough to blind a type AC or even type A RCD so they are not disconnect at that point. Also they tend to have smoother DC than your typical SMPSU so there is little AC component to allow the likes of a type A RCD to trip.

If you have a TT install (high impedance earth due to local rod instead of the supply CPC) then you have a more difficult situation as you can't generally expect the OCPD to stop a rectified DC to Earth fault (as it will not stop an AC to Earth fault) and you are wholly depended on RCD action somewhere for fault disconnection.

 

[treezleef]

Hi,
What RCD type is needed by a solar/battery system connected into the household 220-240VAC mains in UK/EU/USA/AUS?
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.

 

[pc1966]

Hi,
What RCD type is needed by a solar/battery system connected into the household 220-240VAC mains in UK/EU/USA/AUS?
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.

You should check the manufacturer's instructions.

At the very least it should be type A (as most things should be today), but probably type B given the huge reserve of smooth DC.

 

[EricMark]

My understanding was pulsed DC from a half wave rectified AC was not as much as a problem to continuous DC, so EV batteries and solar panels can give a continuous DC so that why those two items are of more concern.