Why does a "granny" charger for EV (<10A) not need an RCD?

[treezleef]

Hi,
With a "granny" charge point, you can just have an extension socket going from your indoor house plug mains and charge your vehicle like that.

But if you have a 16A + charger then you need a expensive type B RCD to be installed....which has DC 6mA and 30mA imbalance detection.

Why the difference?.....why no RCD needed with the granny charger?

"granny" charger <10A

UK 3-pin to Type 1 EV / PHEV Charging Cable, Duosida Portable Home Charger, Granny Cable - 10amp 240v - 5 Meters

Brand New - 5 meter Long EV / PHEV Charging Cable with in-line EVSE charging device. 10amps, 240v / 2.4kw per hour IP55 - rainproof For Charging any Electric or Plug in Hybrid vehicle with a type 1 socket - see the list of vehicles below Free carry case & Free UK delivery 3-pin UK plug to Type...

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[Julie.]

Hi,
With a "granny" charge point, you can just have an extension socket going from your indoor house plug mains and charge your vehicle like that.

But if you have a 16A + charger then you need a expensive type B RCD to be installed....which has DC 6mA and 30mA imbalance detection.

Why the difference?.....why no RCD needed with the granny charger?

"granny" charger <10A

UK 3-pin to Type 1 EV / PHEV Charging Cable, Duosida Portable Home Charger, Granny Cable - 10amp 240v - 5 Meters

Brand New - 5 meter Long EV / PHEV Charging Cable with in-line EVSE charging device. 10amps, 240v / 2.4kw per hour IP55 - rainproof For Charging any Electric or Plug in Hybrid vehicle with a type 1 socket - see the list of vehicles below Free carry case & Free UK delivery 3-pin UK plug to Type...

shop.evchargersdirect.co.uk

It does, because all socket outlets require RCD protection in any case.

Also you should dedicate a particular outlet for this purpose, and select a suitable RCD for the type of load.

 

[treezleef]

It does, because all socket outlets require RCD protection in any case.

Thanks, but i think a household RCD cant detect the >6mA of DC?

A >16A EV charger needs to be protected by an RCD which can detect >6mA of DC...(and not be blinded by it)
Why does this apply to 16A chargers, but not to 10A chargers?

 

[westward10]

It does, because all socket outlets require RCD protection in any case.

Also you should dedicate a particular outlet for this purpose, and select a suitable RCD for the type of load.

Not necessarily all socket outlets.

 

[Julie.]

Not necessarily all socket outlets.

Which 13a outlets don't in a home?

The op was talking about 13a outlet to a granny charger

 

[Julie.]

Thanks, but i think a household RCD cant detect the >6mA of DC?

A >16A EV charger needs to be protected by an RCD which can detect >6mA of DC...(and not be blinded by it)
Why does this apply to 16A chargers, but not to 10A chargers?

It doesn't have to, the rcd only detects an unbalance between phase and neutral (or all phases and neutral) by their very design no rcd operates on dc itself.

They need to not be blinded by the dc and the charge point itself needs a device that detects >6mA DC. These are two seperate functions as the rcd operates on unbalance whilst the detection of dc is not necessarily unbalanced

 

[treezleef]

They need to not be blinded by the dc and the charge point itself needs a device that detects >6mA DC.

..Thanks, yes , a 16A charge point needs a device that detects >6mA DC....the thing is, if you use a 10A granny charger, then you dont have any device in the path that detects the >6mA DC...so why do 16A charge points need to detect >6mA DC?

These are two seperate functions as the rcd operates on unbalance whilst the detection of dc is not necessarily unbalanced

Thanks, but the thing is, that the device that detects unbalance, and the device that detects DC, is the same device, its a "fluxhgate based current sensor"....at least, this is the case in a 16A chargepoint.

The mystery is why detection of DC leakage is not necessary in a granny charger?

 

[treezleef]

Thanks, why does the granny charger not need to have detection of DC leakage?
(woops sorry, my above post suddenly re-appeared)

 

[westward10]

Which 13a outlets don't in a home?

The op was talking about 13a outlet to a granny charger

Ah but you quoted all socket outlets.

 

[Julie.]

..Thanks, yes , a 16A charge point needs a device that detects >6mA DC....the thing is, if you use a 10A granny charger, then you dont have any device in the path that detects the >6mA DC...so why do 16A charge points need to detect >6mA DC?

Thanks, but the thing is, that the device that detects unbalance, and the device that detects DC, is the same device, its a "fluxhgate based current sensor"....at least, this is the case in a 16A chargepoint.

The mystery is why detection of DC leakage is not necessary in a granny charger?

Probably because it is both considered a small power, and is a legacy design.

I don't think they should be allowed tbh because they don't have the proper protection range applicable to a genuine charge point.

The design of all charge points is down to the individual manufacturers, sure some may use a combined device, but many, in fact the majority at the moment do not.

 

[Julie.]

Ah but you quoted all socket outlets.

In relation to a post about a specific device which plugs into a 13A socket outlet!!

Re-word it if you want

"All socket outlets, in relation to this question, relating to but not exclusive to the device that may or may not be used within that outlet, in respect of the current range identified within this question, located within or associated with the property or properties associated with this question, must have rcd protection "

If you don't believe it is rather obvious to anyone reading this thread.

 

[treezleef]

Probably because it is both considered a small power, and is a legacy design.

Thanks for confirming that a granny charge point (10A) doesnt need a ">6mA DC detection".

To my mind, this is a little non-sensical, as the voltage is just the same, and the danger to human life is just the same. Would you agree?

It really does make you wonder why the ">6mA" detection has been mandated for 16A chargers?

...or why it hasnt been mandated for the granny chargers?

 

[Zerax]

A 'granny cable' or more correctly a Mode 2 charging cable will incorporate an In-cable Control Box (ICCB) that has RCD functionality.

 

[Julie.]

Thanks for confirming that a granny charge point (10A) doesnt need a ">6mA DC detection".

To my mind, this is a little non-sensical, as the voltage is just the same, and the danger to human life is just the same. Would you agree?

It really does make you wonder why the ">6mA" detection has been mandated for 16A chargers?

...or why it hasnt been mandated for the granny chargers?

No, I wouldn't agree, the backfeed of 6mA is not related to voltage, but to the current being rectified in the vehicle.

As you increase the current there is a potential corresponding increase of dc component being backfed; so say a malfunctioning rectifier circuit introduces 0.04% dc - with a 10A charger this is 4mA this is below the limit for B type rcd, so a suitable Rcd would still operate if there were a fault. However if you have a 16A charger, then .04% would give 6.4mA - this is above the allowed value for the rcd, therefore it may become blocked, it is therefore necessary to either provide an Rcd which will continue to work with dc much greater than this, or provide additional protection that operates if the dc component is larger than that which could be acceptable to the rcd.

Basically you need to ensure a rcd will operate if there is an earth fault, or if you cannot, you must disconnect the circuit in case there is an earth fault as the rcd protection wouldn't be guaranteed.

 

[treezleef]

As you increase the current there is a potential corresponding increase of dc component being backfed

Thanks..
Though According to the following, the cause of DC leakage with EV's is insulation failure, coupled with the fact that there is a large DC battery in the EV...

It says nothing about DC leakage currents being more likely, the higher is the charge current...

New leakage current sensor for electric vehicle charging stations

The latest electronic component news from the world’s leading component distributors and manufacturers.

www.electropages.com

...so from the above, you would again have to ask, why dont granny chargers, that charge at 10A, need a DC leakage detection for >6mA DC leakage?

 

[Julie.]

Thanks..
Though According to the following, the cause of DC leakage with EV's is insulation failure, coupled with the fact that there is a large DC battery in the EV...

It says nothing about DC leakage currents being more likely, the higher is the charge current...

New leakage current sensor for electric vehicle charging stations

The latest electronic component news from the world’s leading component distributors and manufacturers.

www.electropages.com

...so from the above, you would again have to ask, why dont granny chargers, that charge at 10A, need a DC leakage detection for >6mA DC leakage?

Well any electronic conversion of ac to dc will introduce harmonics back into the system due to the nonlinearity of the electronic rectifier - although dc is not strictly an harmonic it will be introduced, and you could do a Fourier analysis to calculate it.

 

[treezleef]

Well any electronic conversion of ac to dc will introduce harmonics back into the system due to the nonlinearity of the electronic rectifier - although dc is not strictly an harmonic it will be introduced, and you could do a Fourier analysis to calculate it.

Thanks, but that isnt the cause of the ">6mA DC leakage " that needs to be detected by the 16A EV chargers.

Also, the harmonics from SMPS's doesnt put any DC into the mains.

The >6mA DC leakage is due to insulation failure, and this is just as likely with a 10A charger as with a 16A charger, so why do 10A chargers not need ">6mA DC leakage detection"?

 

[telectrix]

surely the need for a RCD or not is dependent on granny's last will and testament. no point in electrocuting her if you're not included.

 

[littlespark]

We used to chuck grannies off buses. But we’ve been told not to as she’s our “mammies mammy”

 

[Zerax]

...so from the above, you would again have to ask, why dont granny chargers, that charge at 10A, need a DC leakage detection for >6mA DC leakage?

You need to re-read post #13...