Type A RCBO,s and the regs

[Ralphster]

Hi all,

Firstly I,m a trainee, and hoping you can make sense of my question.

I,m working on a project for college, designing circuits and using RCBO,s on my circuit design. I see 61009,s and Type B,C,D ect in tables in the OSG and regs, but no type A. What is the reason for this or have just missed something?

Thanks in advance

 

[Bob Geldoff1234]

The type B,C and D refer to the overcurrent side of the breaker.Like you'd have a B6 lighting breaker.Or a C16 feeding a motor circuit.
The type A refers to the RCD side of the breaker.Main ones being type A(modern,most RCBO's are type A whereas the older double pole RCD's were usually Type AC.).They don't usually mark Type A or AC on the breakers,preferring to use ac waveform symbols to depict each type just to confuse us!

 

[Pretty Mouth]

The symbols @Bob Geldoff1234 mentions can be found on page 19 of Beama's RCD handbook:

https://www.beama.org.uk/static/fbf52c82-78e8-4b89-8e7cf271aa9dd8bb/BEAMA-GUIDE-TO-THE-SELECTION-AND-APPLICATION-OF-RESIDUAL-CURRENT-DEVICES-4RCDs5.pdf

 

[Ralphster]

The type B,C and D refer to the overcurrent side of the breaker.Like you'd have a B6 lighting breaker.Or a C16 feeding a motor circuit.
The type A refers to the RCD side of the breaker.Main ones being type A(modern,most RCBO's are type A whereas the older double pole RCD's were usually Type AC.).They don't usually mark Type A or AC on the breakers,preferring to use ac waveform symbols to depict each type just to confuse us!

Thanks Bob

 

[James]

ok, there are 3 options here

1. I am being thick

2. there is no such thing as a bi-directional rcd/rcbo for the following reasons.

a. an rcd only compares live and N currents and trips if there is an imbalance, it has no interest in what side is supplying the energy and what side is consuming it.

b. the overcurrent part of an rcbo again has no interest in the direction of energy travel, if it overheats the bi-metal strip, it will trip.

c. the way we transfer energy with an AC waveform means that electrons and therefore current, flow back and forth at 50Hz, the difference between using energy and generating energy basically comes down to which end of the circuit has a higher voltage at that point in the AC wave and is therefore "pushing the electrons"

3. the whole bi-directional thing is just a marketing exercise to promote a device that has been tested in both directions and by definition, all rcd devices would work under both circumstances.

I so wish that lucian was still here as I am sure he would be able to put me straight with a 2 page lecture about how it all works.

 

[Ralphster]

The symbols @Bob Geldoff1234 mentions can be found on page 19 of Beama's RCD handbook:

https://www.beama.org.uk/static/fbf52c82-78e8-4b89-8e7cf271aa9dd8bb/BEAMA-GUIDE-TO-THE-SELECTION-AND-APPLICATION-OF-RESIDUAL-CURRENT-DEVICES-4RCDs5.pdf

Thank you, that's a really useful pdf, will have a good read of it.

 

[Avo Mk8]

ok, there are 3 options here

1. I am being thick

2. there is no such thing as a bi-directional rcd/rcbo for the following reasons.

a. an rcd only compares live and N currents and trips if there is an imbalance, it has no interest in what side is supplying the energy and what side is consuming it.

b. the overcurrent part of an rcbo again has no interest in the direction of energy travel, if it overheats the bi-metal strip, it will trip.

c. the way we transfer energy with an AC waveform means that electrons and therefore current, flow back and forth at 50Hz, the difference between using energy and generating energy basically comes down to which end of the circuit has a higher voltage at that point in the AC wave and is therefore "pushing the electrons"

3. the whole bi-directional thing is just a marketing exercise to promote a device that has been tested in both directions and by definition, all rcd devices would work under both circumstances.

I so wish that lucian was still here as I am sure he would be able to put me straight with a 2 page lecture about how it all works.

Wouldn't Lucian's erudite contributions be helping us all!

A couple of points I've gathered:

1. An RCBO is only uni-directional when it's been designed such that it matters which terminals are feed and which the load. Some brands created designs right from the start that didn't require marking supply and load (which automatically made them bi-directional). To do with the internal electronics design I suspect.

2. An RCBO has to detect both AC and DC leakage currents to meet the standard.

 

[James]

Wouldn't Lucian's erudite contributions be helping us all!

A couple of points I've gathered:

1. An RCBO is only uni-directional when it's been designed such that it matters which terminals are feed and which the load. Some brands created designs right from the start that didn't require marking supply and load (which automatically made them bi-directional). To do with the internal electronics design I suspect.

2. An RCBO has to detect both AC and DC leakage currents to meet the standard.

I still suspect that there is no technical difference, just marketing or testing approvals.

I do concede that there is a significant technical difference between detection of ac and dc leakage. Also preventing dc voltages from saturating ac detection coils.

 

[Pretty Mouth]

Supposedly a uni-directional RCD can be damaged if wired the wrong way round. Here's another BEAMA document that I found informative:

https://www.beama.org.uk/static/c3939aab-9b55-44e0-8b379d55d5fa305b/BEAMA-Technical-Bulletin-Connection-of-Unidirectional-and-Bidirectional-Protective-Devices.pdf

 

[newfutile]

I think the test button can cause problems (if pressed) as it will always be in circuit till the inverter shuts down, the resistors are not rated for this time,bi directional rcbo have an extra contact for the test button or alternative internal wiring