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AC/DC RCD's


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Although I have a RCD in my Main DB I decided to put one on the output of my Inverters before it returns to the Main DB (Which is in another room)

Because the boards in my Inverter room takes Din Mount breakers I ask for a RCD to fit and was supplied with an AC/DC brand, Model NL2-40.

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After only 2.5 Hours of use I could hear a high frequency buzzing sound coming from the RCD. In this 2.5 hours of operation the load did not exceed  2kw (8 Amps).  I touched the RCD and found it to be quite hot by any standards, went and fetch the Flir and recorded this. First image is from the front and the second from the side. 

IR_0016.jpg.92a491fc2ebb421d79198c8610661227.jpgIR_0017.jpg.3f33bc18d6813a21dbf8eab656c9f1e3.jpg

Measured load was at 5.6 amps at this stage. A minute or two later while still trying to to figure out what was causing this, the RCD tripped and i decided to rather remove it from the Circuit. A quick check of the temp of the Earth leakage Unit in the main DB showed 27 degree C.  

As you can see from the images, its not a loose connection causing this. 

These are surely not suitable for use with inverters. 

 

 

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Dude, I've read everything I could find about RCDs. Essentially it's a big old current transformer sitting around both conductors so that only the difference in current is detected (according to the right hand rule, if the current is equal in the two opposite-running conductors, the magnetic fields cancel out). These days it seems they use a small toroidal core. Then you have a secondary winding on this that triggers the trip mechanism. Of course this means all the normal rules about transformers apply, ie saturation of the core is bad... DC components are bad... etc. However, DC components should not make it into the core, and saturation should not happen because it trips at really low values. But there might also be high frequency on the line (that dissipates heat, but may not trip the RCD) and all sorts of things.

In all my research I also found that there's a huge range of quality. A Hager RCD for example is rated for 2000 electrical events. An ABB breaker, which usually costs twice as much, might be rated for 10 000 events.

So frankly, I would not touch anything from the AC/DC cheap parts bin when it comes to RCDs. Hager is about the lowest spec I would use, and I really like the look of the ABB breakers (though I have to tell you... good grief they are expensive). Also, nowadays I would use at least a type-A breaker wherever electronic loads are concerned.

Not really an answer, but it's becoming clear to me that garden variety type-AC RCDs are no good for use with inverters (and yet you cannot find anything else in the local shops). Got to go at least type-A.

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Hi Jaco,

I will not buy a AC/DC product. In total we've had five of their  rcds faulty.

I've also had a faulty brand new Hager rcd.

I have a earth leakage tester which I use for determining the ma at which a rcd trips and I have yet to see one that meets its specs.

It would be interesting if you could measure the ma at which this one trips - also if it is a fast or slow tripping one.

When I rebuild my boxes I bought the expensive rcds - the one looking after the high amp side was going for around R1200.

I am having nuisance earth leakage trips now which is indicating a fault on my outside pumps circuit with the current wet weather. This box was done by qualified town sparkies but needs to be redone due to the poor installation quality. But I am laid up because I had a back fusion operation and my wife was shown how to reset it until I can attend to it. 

I rather measure the stray current going to earth than the live load.

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23 minutes ago, plonkster said:

Not really an answer, but it's becoming clear to me that garden variety type-AC RCDs are no good for use with inverters (and yet you cannot find anything else in the local shops).

This was the problem. I need to change everything to Gewiss or something else. 

 

23 minutes ago, Johandup said:

I will not buy a AC/DC product.

After this, I will also not. 

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11 minutes ago, Jaco de Jongh said:

Gewiss

A Gewiss type-AC breaker, at ACDC, costs like R700 or so. A Hager is around R350, half the cost, and I've had no bad luck with them (other than the nuisance tripping at the moment, a problem the ABB also has). If you want to go one better, I'd go ABB. EG here is a well priced ABB RCD. It's only 25A though, but still a very good price compared to a Gewiss.

This is the one I am looking at now. It's a type APR that has 10 times more resistance to nuisance tripping. But look at the price! I'd prefer to know it is going to work before spending the dosh, but it looks like the equipment I'd need to make the call will cost even more. In fact the nice leakage current tester I bought was more than that already.

Edited by plonkster
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  • 2 weeks later...
On 2018/10/14 at 4:53 PM, plonkster said:

Not really an answer, but it's becoming clear to me that garden variety type-AC RCDs are no good for use with inverters (and yet you cannot find anything else in the local shops). Got to go at least type-A.

Do you have any like research or sources in the industry for this?

(Not an accusations, I'm genuinely curious because I cannot think of a single reason there would be ANY difference between sine wave from an inverter and a power station).

EDIT: wow maybe like secondary high frequency harmonics, but that just seems so very unlikely.

I'm using a CBI RCBO (overpriced for what it is frankly but it fit with what I had) and have noticed absolutely no difference.

Edited by Gnome
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7 hours ago, Gnome said:

EDIT: wow maybe like secondary high frequency harmonics, but that just seems so very unlikely.

That's more or less what I'm thinking about. So none of this constitutes official research, but most of what I read suggests that ever since the world fell in love with switching power supplies and the accompanying EMI filters they often have to have, and also surge arrestors, and now (or actually for the last two decades already) a hefty standing loss to earth is part and parcel of every installation. For this reason, first type-A RCDs and then later more advanced types were designed... yet here we are running bare basic 1970s tech.

Then again... there is nothing wrong with old tech. I actually take back what I said and I will replace it with something softer: If you run many modern loads you should CONSIDER using a slightly better RCD, with or without inverter in the mix, but obviously more likely when using an inverter.

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  • 2 months later...
On 2018/10/26 at 3:37 PM, Gnome said:

Do you have any like research or sources in the industry for this?

(Not an accusations, I'm genuinely curious because I cannot think of a single reason there would be ANY difference between sine wave from an inverter and a power station).

EDIT: wow maybe like secondary high frequency harmonics, but that just seems so very unlikely.

I'm using a CBI RCBO (overpriced for what it is frankly but it fit with what I had) and have noticed absolutely no difference.

Power from the powerstations run along kilometers of power lines and go through numerous step ups and downs before it gets to your house. By the time it gets to you all th eharmonics etc has been watered down a bit. Also, most likely at the generation plant it would be kinetic energy converted into electrical energy by way of a moving machine with a generator bolted on one side and heaps of filters and regulators. On your power system at home it is all electronic and only the few small filters inside the inverter helping it.

 

When you use a type AC RCD/RCBO/RCCB, it is possible for the core to get saturated from DCcurrents and then won`t work at all. Especially the lower cost units. When you are uncertain if this is the case, always test it using a RCD tester.

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  • 4 weeks later...
On 2019/01/08 at 12:17 PM, anotherbrownbear said:

Power from the powerstations run along kilometers of power lines and go through numerous step ups and downs before it gets to your house. By the time it gets to you all th eharmonics etc has been watered down a bit. Also, most likely at the generation plant it would be kinetic energy converted into electrical energy by way of a moving machine with a generator bolted on one side and heaps of filters and regulators. On your power system at home it is all electronic and only the few small filters inside the inverter helping it.

 

When you use a type AC RCD/RCBO/RCCB, it is possible for the core to get saturated from DCcurrents and then won`t work at all. Especially the lower cost units. When you are uncertain if this is the case, always test it using a RCD tester.

Things is, the total harmonic distortion for a sine wave inverter is almost always much lower than power from a power station.

The inductive loads on the grid cause a lot of distortion, ie>

pqnfig2.jpg?itok=iuzzvuiO

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17 minutes ago, Gnome said:

Things is, the total harmonic distortion for a sine wave inverter is almost always much lower than power from a power station.

From what I have seen the grid signal is a pretty hard one. The output created by a Multiplus has a very clear step-pattern (obviously created by the PWM action used to shape a sine wave) and quite often you might also notice a little flat spot as it goes through the zero-point. The other interesting data point is sound people... most of them prefer a large generator or grid power when they do sound at an event... cleaner power 🙂

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1 hour ago, Gnome said:

Things is, the total harmonic distortion for a sine wave inverter is almost always much lower than power from a power station.

I would be very surprised if the harmonic distortion is lower when a load is supplied from a sine wave inverter versus grid power.

One reason is that the grid has an extremely low source impedance. So any distortion on the current drawn from the load will cause less of a voltage distortion when compared to an inverter.

Will do some measurements and report back on findings.

1 hour ago, Gnome said:

The inductive loads on the grid cause a lot of distortion

Inductive loads will cause the current to lag the voltage but not create a distorted waveform. 

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