PME Trip Times etc advice

[EFLImpudence]

Is that true of all passive RCDs? I had imagined that at least some, just like active ones, had electronics which triggered a power-operated trip mechanism.

RCBOs do.

Is that why their times are far more similar, both with regard to the different tests and to other RCBOs.

 

[bernardgreen]

algerbraically.

It is the difference between the currents in Line and Neutral i.e. left over. (adding would not be useful)

Algebraic addition takes account of the direction of flow. adding 6 to minus 6 gives zero..

 

[bernardgreen]

Is that true of all passive RCDs? I had imagined that at least some, just like active ones, had electronics which triggered a power-operated trip mechanism.

The RCDs that I have taken apart ( and not re-used ) have had nothing more than the toriodal sensor core feeding a solenoid that operated the trip mechanism.

I can understand the reluctance to use electronics with active semi-conductors ( transistors etc ) in protective devices in premises where there is not a reliable and routine testing system in place. Transients on the supply could easily damage semi-conductor devices rendering the protective device in-effective, a fault which would not be found until the protective device failed to protect when necessary.

 

[EFLImpudence]

Algebraic addition takes account of the direction of flow. adding 6 to minus 6 gives zero..

Ah, fair enough in one respect.

Direction of flow ? Plus and minus ?

How do you know which is plus and which is minus?

Larger I - smaller I = residual I

Or measure the residual current.

 

[bernardgreen]

How do you know which is plus and which is minus?

It doesn't matter as long as one is plus and one is negative,

Larger I - smaller I = residual I

smaller I - Larger I = residual I in the opposite direction.

it changes direction 50 times a second.

 

[JohnW2]

Algebraic addition takes account of the direction of flow. adding 6 to minus 6 gives zero..

Ah, fair enough in one respect. Direction of flow ? Plus and minus ? How do you know which is plus and which is minus?

This is getting a bit over-simplified. It's not actually algebraic addition but, rather, vector addition - since the whole range of phase differences (not just 180° out of phase - a.k.a. 'plus and minus') is possible. In the context we're discussing, this could become a factor if the fault path was not entirely resistive.

Kind Regards, John

 

[JohnW2]

Is that true of all passive RCDs? I had imagined that at least some, just like active ones, had electronics which triggered a power-operated trip mechanism.

The RCDs that I have taken apart ( and not re-used ) have had nothing more than the toriodal sensor core feeding a solenoid that operated the trip mechanism.

Fair enough. It's quite some time since I last dissected an RCD - and I have to say that those I've taken apart in the past are as you describe. However, I thought/suspected that this may have changed - as EFLI says, it's certainly true that RCBOs utilise electronics triggering powered tripping (at least, every one I've looked inside does).

I can understand the reluctance to use electronics with active semi-conductors ( transistors etc ) in protective devices in premises where there is not a reliable and routine testing system in place. Transients on the supply could easily damage semi-conductor devices rendering the protective device in-effective, a fault which would not be found until the protective device failed to protect when necessary.

Yes, that all makes sense - 'KISS' is always nice. However, given that, I wonder why do RCBOs appear to have taken the other route?

Kind Regards, John

 

[Spark123]

I thought active and passive was to do with wether or not the RCD stays on when power fails, regardless if they are electronic? I'm pretty sure you can buy active and passive RCDs with electonics in them.

 

[EFLImpudence]

It is.

 

[ban-all-sheds]

 

[ban-all-sheds]

it changes direction 50 times a second.

100 times, actually....

 

[JohnW2]

I thought active and passive was to do with wether or not the RCD stays on when power fails, regardless if they are electronic?

As has been said, it is.

I'm pretty sure you can buy active and passive RCDs with electonics in them.

As I've said, that's what I thought - but Bernard has now put doubts in my mind. As I wrote yesterday, it's a while since I dissected one, bit I don't recall ever having seen a passive RCD in the past which contains electronics. However, as I also said, I haven't seen an RCBOs (passive) which doesn't contain electronics - indeed, I think that's what started the whole debate about whether the 'functional earth' connection from an RCBO (allegedly to ensure function of the electronics in the case of a neutral supply fault) actually is necessary.

Kind Regards, John

 

[Spark123]

I have seen RCBOs without electronics in them, they were two modules wide.

 

[JohnW2]

I have seen RCBOs without electronics in them, they were two modules wide.

Fair enough. I couldn't comment on that, because I've never taken a 2-module one apart. Is a pattern perhaps emering? is it possible that the ones without electronics need to be two module (like most RCDs) in order to accommodate the non-electronic trip mechanism??

Kind Regards, John

 

[Spark123]

I think so, the ones I had were made by GE. They didn't have the "no megger" statement on them hence I took it they weren't electronic.