Author Topic: What equipment needs a >6mA DC leakage current detector? (and why?)  (Read 679 times)

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Offline Faringdon

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

This article says equipment needs it if it's mains connected and  contains a  "DC powered battery"

https://www.electropages.com/2021/03/new-leakage-current-sensor-electric-vehicle-charging-stations
 

Offline Siwastaja

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Re: What equipment needs a >6mA DC leakage current detector? (and why?)
« Reply #1 on: September 25, 2021, 12:35:07 pm »
What: Electric vehicle.

Why: Because there might be a slightly conductive fault inside the HV DC battery pack, think about a coolant leak.


Now, whether 6mA was a good choice is up to debate but it is what it is. You can argue lower current limit is always better for safety, as long as it can be implemented, and as long as it doesn't cause nuisance tripping on non-faulty equipment. 6mA DC leakage detection can be implemented for example using fluxgate sensors, so that's no problem.

In Europe mostly, AC leakage detectors ended up using higher thresholds (such as 30mA) because on AC, capacitive reactance exists and it causes nuisance tripping, for example due to EMI filters. On DC, such element does not exist by definition, so 6mA DC leakage has to be all resistive by definition, and on a 600V battery pack that means 3.6W is dissipated somewhere, which is becoming a fire risk. So using such low threshold is IMHO a good idea for safety. And you can see the required delay for 6mA is very long, don't remember exactly but it's some seconds, clearly suggesting fire safety is the real motivator. For protection against electric shock, the reaction time needs to get faster at some 30mA and beyond.
« Last Edit: September 25, 2021, 12:37:55 pm by Siwastaja »
 
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Offline Faringdon

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Re: What equipment needs a >6mA DC leakage current detector? (and why?)
« Reply #2 on: September 25, 2021, 12:49:54 pm »
Quote
And you can see the required delay for 6mA is very long, don't remember exactly but it's some seconds, clearly suggesting fire safety is the real motivator. For protection against electric shock, the reaction time needs to get faster at some 30mA and beyond.
Thanks so much!....you know i hadnt thought of that...you are right, the reaction time for >6mA of DC leakage is about 10 seconds in the standards.

So its for fire reasons, not electric shock reasons. I missed that one...thanks again! Then again, mightnt it just be for electric  shock reasons?...i mean, the 6mA DC leakage woudl blind an RCD.....maybe its 10 seconds reaction time because it'd be an awful coincidence if someone got an EV electric shock within 10 seconds of a DC leakage current occurring. (does anyone know if 10 seconds is correct?)
« Last Edit: September 25, 2021, 01:35:36 pm by Faringdon »
 

Offline Faringdon

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Re: What equipment needs a >6mA DC leakage current detector? (and why?)
« Reply #3 on: September 25, 2021, 07:00:49 pm »
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 ?
 

Offline Siwastaja

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Re: What equipment needs a >6mA DC leakage current detector? (and why?)
« Reply #4 on: September 26, 2021, 06:19:39 am »
You are missing one type: type A.

Type AC indeed is insufficient.

But you don't need type B. Type A is quite fine. It catches fault currents after rectified mains.
 
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Offline Faringdon

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Re: What equipment needs a >6mA DC leakage current detector? (and why?)
« Reply #5 on: September 26, 2021, 05:45:06 pm »
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.
 


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