RCBOs vs RCDs Pt2

[rodgearing]

OK we are told RCBOs are the way to go.
Agreed.
Because this will do away with using a RCD but, and I guess this has been questioned and possibly answered before, why buy an RCBO that only protects phase side (single pole RCBO) of the cct?
Have I missed something?
Do we put in one RCD!?
Fred

 

[Octopus]

Why would you put in 1 RCD only??

 

[Engineer54]

If you're that worried, use SP+N RCBO's that are becoming increasingly available!!

SP RCBO's are not as bad as some make them out to be, we have been using them for a good number of years now, (without any major safety concerns being reported) and SP MCB's and fuses for a damn sight longer!!

 

[telectrix]

double pole RCBOs or single pole with switched N are the best way, but cost is a factor.

 

[rodgearing]

Why would you put in 1 RCD only??

It was just a statement
Does one put any RCDs in a unit that has all SP RCBOs?

 

[Deleted member 9648]

OK we are told RCBOs are the way to go.
Agreed.
Because this will do away with using a RCD but, and I guess this has been questioned and possibly answered before, why buy an RCBO that only protects phase side (single pole RCBO) of the cct?
Have I missed something?
Do we put in one RCD!?
Fred

It's the phase side that bites,thats why.

 

[telectrix]

It was just a statement
Does one put any RCDs in a unit that has all SP RCBOs?

only if you want a 100mA type S upfront.

 

[richy3333]

Why would you put in 1 RCD only??

Agreed and isn't Amend 3 stopping this?

 

[ipf]

Agreed and isn't Amend 3 stopping this?

Tell you when it arrives on my desk..

 

[Knobhead]

If you're that worried, use SP+N RCBO's that are becoming increasingly available!!

SP RCBO's are not as bad as some make them out to be, we have been using them for a good number of years now, (without any major safety concerns being reported) and SP MCB's and fuses for a damn sight longer!!

You’ve changed your tune.

The trouble is the SP RCBO just don’t match what it says on the tin. For this reason I think many have accepted them as an instant cure all in every situation. This can only be attributed to lack of knowledge on the part of the electrician. (The ones that bite my head off now will be the ones in the know.)

Some manufacturers do point out the short comings of the SP RCBO in handling a N→E fault. To my mind it should be made clear to everyone. As we’ve often discussed it seems to be the doctrine of colleges to preach fitting RCD’s to everything.

 

[Deleted member 9648]

You’ve changed your tune.

The trouble is the SP RCBO just don’t match what it says on the tin. For this reason I think many have accepted them as an instant cure all in every situation. This can only be attributed to lack of knowledge on the part of the electrician. (The ones that bite my head off now will be the ones in the know.)

Some manufacturers do point out the short comings of the SP RCBO in handling a N→E fault. To my mind it should be made clear to everyone. As we’ve often discussed it seems to be the doctrine of colleges to preach fitting RCD’s to everything.

A single pole MCB wont react to a N-E fault. To my mind the RCD element of an RCBO on a TN system is likely to be additional protection only,not fault protection.

 

[davesparks]

A single pole MCB wont react to a N-E fault. To my mind the RCD element of an RCBO on a TN system is likely to be additional protection only,not fault protection.

An mcb is not designed to react to N-E faults so there is no issue there.
It reacts to L-L, L-N or L-E faults by disconnecting the L or Ls

A SP RCBO does react to N-E faults, but the way it reacts is to disconnect the L which has no fault in it.
This is the problem.

 

[Deleted member 9648]

An mcb is not designed to react to N-E faults so there is no issue there.
It reacts to L-L, L-N or L-E faults by disconnecting the L or Ls

A SP RCBO does react to N-E faults, but the way it reacts is to disconnect the L which has no fault in it.
This is the problem.

None of which really matters if the RCBO is simply used as an MCB with additional protection.

 

[davesparks]

None of which really matters if the RCBO is simply used as an MCB with additional protection.

What on earth are you talking about?

If an mcb is needed you use it as an mcb.

If RCD protection is needed in addition you either install an RCCB before or after the mcb or an RCBO to provide both functions in one.

Whatever reason you install an RCBO for then if it is SP it will detect N-E faults and not disconnect them, it will disconnect the L.

 

[Deleted member 26818]

Is disconnecting the L on a N-E fault a problem?

 

[davesparks]

Is disconnecting the L on a N-E fault a problem?

It's completely pointless, you might as well have a device which switches the gas off when the water main bursts!

It could also give a false sense of security as someone might assume that since a protective device has operated whatever fault is present will have been disconnected and so not worry about investigating in a hurry. But a N-E fault will still be connected which could present a massive fire risk through diverted neutral currents

 

[Deleted member 26818]

Wouldn't the N & E already have those diverted neutral currents present if the system is TN-C-S?

 

[davesparks]

Wouldn't the N & E already have those diverted neutral currents present if the system is TN-C-S?

No, the current would only divert through the fault once the fault occurs!

 

[Deleted member 26818]

I think I need you to explain where these diverted neutral currents originate.

 

[davesparks]

I think I need you to explain where these diverted neutral currents originate.

The whole installation!