Discuss Why does a "granny" charger for EV (<10A) not need an RCD? in the Electric Vehicles Advice Forum area at ElectriciansForums.net

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:   American Electrical Advice Forum

Reaction score
5
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
 
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


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.
 
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?
 
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
 
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?
 
..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.
 
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.
 
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?
 
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.
 
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...


...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?
 
Last edited:
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...


...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.
 
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"?
 
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.
 

Reply to Why does a "granny" charger for EV (<10A) not need an RCD? in the Electric Vehicles Advice Forum area at ElectriciansForums.net

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc
This website was designed, optimised and is hosted by Untold Media. Operating under the name Untold Media since 2001.
Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock