2 pole (mini) RCBOs

[333rocky333]

AFAIK
Heard rumours DP rcd's will possibly be more widespread very soon, along with new boards to help conform to 17th.
Crabtree I think are one of the first to get the boards out.

Apparently there is concerns that with the extra rcd use in the 17th ,the single pole will not isolate the fault from the system.
Unless there is another DP rcd before it

In event of a neutral earth fault, even though it breaks the phase conductor, And no worse than a single pole mcb it would leave the N-E fault still present.

ApparentlyThis Neutral To earth fault could if left unrectified , also effectively turn an installation into a tnc system.

The problem then would be all the other circuits neutrals would also feed part of there neutral load up that shorted / damaged neutral to earth causing the main supply Rcd if fitted to trip out due to imbalance.

 

[Lectrician]

You wouldn't have RCD's before other RCD's if designed correctly.

 

[plugwash]

you mean the right-hand one in the pic? I think you are right, SPSN not DP.

Of course once you put the RCBO pod on a current in the neutral without a corresponding current in the live will trip the breaker so there doesn't seem to be any need to use a true DP breaker.

 

[ban-all-sheds]

Yup - look here.

Single Pole, SWITCHED neutral.

OK - what is the difference between Single Pole Switched Neutral - the last two words of which would indicate that when it operates it opens the neutral as well as the phase, and Double Pole, which when it operates opens the neutral as well as the phase?

If they are the same, why the two different terms?

If they are different, in what way is the switching of the neutral different in a SPSN device from that in a DP device?

 

[JohnD]

A DP MCB (and i'm sure I've seen them but might be rambling again) would trip if current went overrating on either of the poles.

Since an RCBO incorporates an MCB and an RCD, you could conceivably have a DP RCBO; which would trip on current imbalance between poles (using the RCD function) and also on overcurrent or shortcircuit on either pole (using the MCB function).

The action of the trip of a DP RCBO like that would be to break both poles, in the same way as an SPSN RCBO

I don't know if anyone has ever seen a DP RCBO, i'm sure I haven't (apart from the 100v one in the MEM link)

 

[bongos]

Is there a situation where a DP RCBO would be preferential to a SP one?

I'd always assumed (probably wrongly ) that the MCB aspect would take account of overcurrent faults and the RCD aspect would cover earth leakages etc. What sort of other fault is likely that would be picked up by a DP RCBO as opposed to a SP one?

 

[Spark123]

A DP RCBO will be preferable where there is another RCD upstream i.e. in a TT system where a 30mA device is used to provide supplementary protection against direct contact and a 100mA (Time Delayed) upstream is protecting the supply cables.
In the above scenario, a fault after the 30mA device can also cause the 100mA device to trip when the Neutral isn't disconnected.

 

[Lectrician]

Yup - look here.

Single Pole, SWITCHED neutral.

OK - what is the difference between Single Pole Switched Neutral - the last two words of which would indicate that when it operates it opens the neutral as well as the phase, and Double Pole, which when it operates opens the neutral as well as the phase?

If they are the same, why the two different terms?

If they are different, in what way is the switching of the neutral different in a SPSN device from that in a DP device?

The Double Pole MCB's will operate due to overcurrent in either of the two poles, usefull if you have two phases in an appliance, for example many welders are often rated at 415v and require just two phases. I have also used them to give two live supplies to a 4 pole rotary isolator (so two lives and two neutrals). This then supplying, say, two immersions in a tank - Very common on farms.

It is not very common, and I connot think of any reasonable reason why you would want to use a true Double Pole to monitor the neutral in a single phase situation.

A Single Pole Switched Neutral simple switches the phase at the same time as the live, but only the live pole will operate due to overcurrent.

 

[Spark123]

Which manufacturers make the RCBOs with overcurrent protection in both poles? I have seen items such as the Merlin Gerin add on RCD modules - never had a need to use them.

 

[RF Lighting]

Arn't DP MCBs / RCDs used in caravans to keep an installation with accidental reversed polarity safe?

Not my area of expertise though, so I may be wrong.

 

[Pensdown]

Is there a situation where a DP RCBO would be preferential to a SP one?

I'd always assumed (probably wrongly ) that the MCB aspect would take account of overcurrent faults and the RCD aspect would cover earth leakages etc. What sort of other fault is likely that would be picked up by a DP RCBO as opposed to a SP one?

Is there a situation where a DP RCBO would be preferential to a SP one?

DP RCBO's are used on TT systems when a 100mA type S is used on the incomer/main switch. If SP RCBO's are used the type S will trip on a N-E fault which will not meet 314-01-01 & 314-01-02.

Also, if they are being used for circuit isolation in an installation forming part of a TT system (461-01-01 & 537-02-01) they must also be DP.

Edit...to slow

 

[Pensdown]

Arn't DP MCBs / RCDs used in caravans to keep an installation with accidental reversed polarity safe?

Not my area of expertise though, so I may be wrong.

You're not wrong

608-03-02 & 608-04-01

 

[Spark123]

Are they not normally 2 devices i.e. a Double Pole RCCB and a separate DP MCB? (or a few DP MCBs)

 

[Lectrician]

Arn't DP MCBs / RCDs used in caravans to keep an installation with accidental reversed polarity safe?

Not my area of expertise though, so I may be wrong.

In touring caravans with an appliance inlet, yep.

Must be DOUBLE POLE, not SINGLE POLE, SWITCHED NEUTRAL.




To be honest though, these types of caravans always come kitted out, and the CU already done. It is very rare to have to alter the CU, add circuits, or replace any thing in the life span of the caravan.

 

[JohnD]

benstoneham seemed to want some DP RCBOs, but he hasn't said why.