copy of 1st Amendment of 18th ed

[Gavin John Hyde]

The IET have put the pdf file on the IET website for the final version 1st Amendment of 18th Edition.

Do you recall them saying it will be free? well not quite...

Its free to view and read but apparently we have to pay £5 if we want to print it without the DO NOT PRINT written in the file.
I think they are a bit naive if they believe that! As good boys and girls I know you will only read it and not print it without paying £5...

Annoyingly they will now update the IET best practice guides for EV installs, so if you bought it recently an new one is out for £50+ Imagine other books will get updated in due course to keep the dosh rolling in

 

[Risteard]

Interestingly the 35% member discount does NOT apply to Amendment No. 1, i.e. even members have to pay full price.

 

[Vortigern]

Thanks for that @Gavin John Hyde looking through it (not intensely) I see reference to RDC-DD, what is that referring to? I ask as I know you do EV charge points.

 

[Gavin John Hyde]

Thanks for that @Gavin John Hyde looking through it (not intensely) I see reference to RDC-DD, what is that referring to? I ask as I know you do EV charge points.

@Vortigern
I had this conversation with the technical folks at Andersen a couple weeks back when doing some training on the chargers, as I understand it, it is a residual direct current detection device RDC-DD, it monitors the DC current levels and in event of a fault disconnects the conductors making the systems safe. if used then you must still use a Type A RCD/RCBO either in the charger or upfront to provide protection against possible DC fault currents saturating the coils in common rcds/rcbos such as type ac in the property.
A lot of the chargers incorporate this and have done for some time, but its taken a while for the regs to catch up fully with the technology. I am sure one of the technical minded folks on the forum will be able to give a better explanation of how the RDC-DD works better than me though... @Lucien Nunes - One for you? I just fit them within the chargers

 

[Vortigern]

That is a perfectly adequate explanation @Gavin John Hyde thanks! I think if Lucien explained I might not understand it again Oh yes and I am familiar with the problems of hysteresis of the toroidal coil on AC types.

 

[Julie.]

RDC-DD is Residual Direct Current - Detecting Device.

As neither the type ac or type a rcd can work/trip with continuous DC, in the event the charger feeds back any DC into the electrical system, the wall unit (which we usually call the charge point) must detect this and disconnect or else the DC could flow back through the network blocking all the rcd - not just those 'upstream', the generic name for this detection device is RDC-DD

 

[Vortigern]

As neither the type ac or type a rcd can work/trip with continuous DC

So you are saying the DC current from an EV charger is fully rectified DC i.e. smooth(ed) DC current, as type A are for pulsating DC current. So presumably Type B should be used in this case? It begs the question why @Gavin John Hyde was advised by his trainers to use type A and recommendations in the BEAMA guide regards type A. So in short your statement leaves me somewhat confused, perhaps you could expand on that a little?

 

[snowhead]

Maybe this may help, or just confuse things even more, from Podpoint;

https://d3h256n3bzippp.cloudfront.net/Earth-Technical.pdf

 

[Julie.]

So you are saying the DC current from an EV charger is fully rectified DC i.e. smooth(ed) DC current, as type A are for pulsating DC current. So presumably Type B should be used in this case? It begs the question why @Gavin John Hyde was advised by his trainers to use type A and recommendations in the BEAMA guide regards type A. So in short your statement leaves me somewhat confused, perhaps you could expand on that a little?

These are two different things.

If the car charger fails and injects DC into the network, this would be between line an neutral, so wouldn't warrant the operation of a rcd.

However this DC has to go somewhere, so it flows into any load that it can, the largest will be the supply transformer as this would appear like a direct(ish) short to DC, but it would also go into any other loads, let's say it delivers 5A DC into the network, 90-99% may go into the supply tx, but several mA may flow into a shower, and into the lighting circuits etc.

If these are protected by type a or ac then this DC could block them - so if there is a fault on the shower, it doesn't trip because the rcd is blocked even though it's not in the direct path transformer -> charger.

Therefore you need to have RDC-DD protection to prevent this impact on the wider system.

However RDC-DD does not offer anything in regards to earth fault protection in itself so it is still necessary to provide rcd protection as well.

Under normal operation, the charger may inject pulsating DC therefore type A or above would be required

 

[Vortigern]

@snowhead the link did not work for me.

may flow into a shower, and into the lighting circuits etc.

DC into the network, this would be between line an neutral

If these are protected by type a or ac then this DC could block them

So given the above why would a type A not operate? It seems that EV charging needs much improvement in design. Not that I have studied the matter in any depth. So what, if any effect, would there be on SPD or AFDD just asking as a matter of idle interest.