What does the term "Compounded RCDs mean?

[electronumpty]

I have recently had an electric EV charge point for our electric car fitted at our house.
I obtained 5 quotes in total and two from the main leading recommended installers. One quote was for £823.80, the other was £299.
I posted the quote results (making sure I did not name either company) on the online EV forum and mentioned that I was going with the cheaper company.

At this point the expensive company posted and asked for pictures of the finished job.

Two weeks later the job was done and the charge point fitted smoothly, neatly and efficiently and the results posted online, at this point the Expensive company posted a comment to say there was a problem with the installation and that I had "Compounded RCD's".

Anyone ever heard of that term?
I've tried a Google Search for that term and come up short other than the EV forum this company posts on and it appears to be the only place I've seen it written.

Any clues?

 

[Adam_151]

Its a new one on me, though I am guessing they could be referring to having more than one RCD of the same rating (or different ratings, but no time delay) in line. This is considered undesirable, but is not a safety issue.

Perhaps you could post pictures of the job here, or link across to the other thread?

That is a big gap in quotes, I am guessing out of the 5 they are top and bottom figures? were the rest somewhat similar to each other and grouped somewhere around the mid point out of interest?

 

[flameport]

2 RCDs in series perhaps?

Picture of the installation & consumer unit(s) would help.

 

[electronumpty]

Hows this?

The other quotes that were offered were for different units, some were rent only, some had conditions that meant you had to pay for servicing or other issues which discounted them. As for cost they ranged £150 - £700. The two I chose were because the units supplied were rated the best.

 

[securespark]

EV charging circuits should have a Type A RCD, which detects DC. Yours is Type AC, which does not.

If there is a Type A RCD incorporated in or adjacent to the charging unit, then this is what they probably meant by compounded RCD's.

Namely that there is a possibility the non Type A RCD could trip instead of the Type A one, thus omitting the DC detection ability.

The symbols denoting types are here:

https://www.tlc-direct.co.uk/Technical/DataSheets/Wylex/WylexRcd.pdf

Is there another RCD in the circuit?

 

[electronumpty]

There is an RCD on the EV Charging unit too.

Is this like a belt and braces then?

 

[securespark]

Either way (EV charging circuit installed using Type AC RCD or EV charging circuit installed using Type AC RCD and Type A RCD downstream) it is not installed in accordance with the regs.

 

[securespark]

What Type is the EV charging unit RCD?

 

[securespark]

Is this like a belt and braces then?

Not really. It does not comply with regs as there are two RCD's in the circuit and the board's RCD trips may trip in preference to the EV unit's RCD. If this happens, that RCD does not have the capability to detect pulsating DC currents.

Assuming, of course, the EV charger's RCD IS Type A....

 

[electronumpty]

This.

 

[DetlefSchmitz]

I looked at your other forum and can see that this has got heated, way beyond any sensible point. Two RCDs in series is not necessary but is hardly a major problem. It is also even not terribly unusual. Against regulations? I'll leave that to the 'angels on the head of a pin' brigade.

Personally I think you should stop posting on the subject. You got a reasonably priced install. What else are you trying to get?

 

[securespark]

That is a Type A 40A DP RCBO.

So as well as having two ELCB's in circuit, you have a 40A RCBO fed from a 32A MCB.

Be interesting to see the test sheets to see how he managed to test both devices.

 

[flameport]

It does not comply with regs as there are two RCD's in the circuit and the board's RCD trips may trip in preference to the EV unit's RCD. If this happens, that RCD does not have the capability to detect pulsating DC currents

If the AC RCD had tripped, the circuit is already disconnected and there would be no current of any kind for the type A to detect.

 

[electronumpty]

Thing is I know nothing on this subject and am just looking for an answer to the statement the other person posted.

I'm happy with the EV Charger and the price so am not really bothered.
The thing that bothered me was the person who kept posting trying to bash the installation without letting the other people reply first and then trying to say I could have got it cheaper with them. When both companies had the same chance and same information to provide a quote.
The expensive company guy just seemed to me to be justifying his costs by disparaging the other company.

I got annoyed that he posted my pictures without even asking, which I did not appreciate, then got even more angry as the moderators were agreeing to the guy posting my pictures. Small point but if I let that slide it's like I'm agreeing with the expensive guy. I'm sure I've come off as a tool in this regard.

All I want to know if I need to do anything about the install if it is proved to be incorrect.

 

[Adam_151]

The RCD in the EV charger in the photograph is type A.

Thought that has just occurred me is that even if you have a type A local to the charger and that will be covering the charger, you could have an issue with the type AC device which is covering the supply to the charger and other circuits... If the charger is pulling current with a distorted waveform and this has the ability to 'lock' an AC RCD by saturating the core (this effect was used in a particular made of loop tester). Then it would be possible if the charger was in use and this locking of the RCD was occurring, for the RCD at the origin to fail to trip on a fault occurring elsewhere in the installation.