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Discuss copy of 1st Amendment of 18th ed in the Electrical Forum area at ElectriciansForums.net

Gavin John Hyde

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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
 

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Risteard

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

Gavin John Hyde

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  • Thread Starter Thread Starter
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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

Advent Win
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.

Advent Win
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

Advent Win
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?
 

Julie.

Advent Win
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

Advent Win
@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.
 

Julie.

Advent Win
@snowhead the link did not work for me.



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.
Because a type A would be blocked by DC - it is suitable for AC and pulsating DC.

In addition, the DC throughout the system would block many of the other rcd, which as standard tend to be ac
Post automatically merged:

Sorry, missed the point about spd etc.

Spd shouldn't be an issue, they either work by having a spark gap, (which the DC should be too low to jump) or a voltage dependent resistor (used to be a trade name metrasil) which drops sharply in resistance after the knee point.

As for AFDD - I doubt even the makers would know!

I agree the situation with ev charging is a mess, it appears driven by manufacturers and their wants.

I don't think it should be part of the 18th, it's a separate device, so should be treated as such, the 18th doesn't go into the ins and outs on how other devices work - they have their own specifications.

In my view the 2nd ammendment (I would have hoped the first would) should be very simple, the charge points shall be fully self contained, and not reliant on external protection devices, contain all operational and protective features for the charger, and prevent DC back into the system, detect any earth leakage (which implies an rcd), and detect or prevent an excursion of the local earth in potential (which is achieved by a local TT, or specialist devices)

Not go down a rabbit path on how it's to be done!
 
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Midwest

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See our current government has brought forward proposals to ban petrol/diesel cars by 5 years. So all these things need sorting, sooner rather than later.
 

Vortigern

Advent Win
Because a type A would be blocked by DC
So what type of DC is EV DC and why do you think the installer trainers are recommending Type A? Anyway it all seems to be an accident waiting to happen, complex system, inexperience installers, end users all seems to equal a problem.
Post automatically merged:

@snowhead that link worked. It somewhat irked me that they are sharing their knowledge with NICEIC as opposed to all CPS bodies and interested parties. As if NICEIC are the de facto, go to authority and final arbiter. Seems to me this just gives them advantages that other cps schemes are not benefiting from.
 
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Julie.

Advent Win
So what type of DC is EV DC and why do you think the installer trainers are recommending Type A?.......
Under normal operation an ev charger could produce pulsating DC - so it needs to have type A or above.

Under certain circumstances - a failure of the charger could inject continuous DC - type A and below would be blocked.

Therefore the point needs to protect against continuous DC (the RDC-DD) to prevent this failure mode.

And there needs to be rcd protection for earth fault just like any other circuit, but because of the pulsating DC which may be present it needs to be type A or above.
 

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