SP/DP RCBO's for domestic .Do you have a preference ?

[LukeD]

Ive seen a few guys happy to fit both and a couple of others who only fit DP's . Do you have a preference ?

 

[LastManOnline]

Welcome back by the way

DP rcbos don't have an advantage that is not also offered by SPSN RCBO's in the UK.

Iyou don't consider been able to isolate a neutral to earth fault on a final circuit a disadvantage ?
You don't consider been able to carry out an IR test on a final circuit without first having to disconnect a disadvantage ?
SPSN rcbo,s generally contain more electronics than their DOP equivalent.
I suspect that DP (and double module) rcbo,s dissipate heat better.
The single advantage I see SPSN having is the need for less space.Otherwise I see only disadvantages

What is the benefit of DP protection in a system which had a reliably earthed neutral?

See the above

Mainland Europe does not have the same electrical system as the UK.

Mainland Europe shares TNC-S and TT systems which are the two most widely used systems in the UK

I don't like this idea that 'DP is better than SP' without having a good supporting argument.

We are all entitled to personal opinion.But I can assure you that if you carried out more work in the domestic sector you would find DP rcbo,s make your life and the customers life considerably more convenient

Years ago in the UK DP protection was the standard because it was necessary, but we improved our electrical systems so that it is no longer required.

What are these "improvements" specifically?

 

[nicebutdim]

SPSN rcbo,s generally contain more electronics than their DOP equivalent.
I suspect that DP (and double module) rcbo,s dissipate heat better.
The single advantage I see SPSN having is the need for less space.Otherwise I see only disadvantages

Dissipation of heat isn't generally an issue in domestic installations. It shouldn't be an issue at all if breakers are arranged in such a manner that circuits drawing high loads are kept separate from each other - eg. not placing shower and kitchen socket circuits next to each other, but that's good practice regardless of breaker size.

While there may be advantages to having double module breakers, in a domestic environment these are outweighed by constraints on space. In fact I generally see single module RCBOs in commercial and industrial environments, without any issues arising from heat.

I wonder if statistics exist to highlight different rates of failure between single and double module RCBOs., but I honestly wouldn't expect a higher rate of failure from single module units.

Is there any advantage to having double module DP as opposed to single module SPSN or would such a move be the equivalent to 'upgrading' to CRT televisions and 1980s sized cell phones?

 

[happysteve]

I suspect there's some confusion about RCBO terminology going on here.

I suspect some folk regard SPSN = single pole switched neutral.

I suspect some folk regard SPSN = single pole solid neutral.

I suspect some folk couldn't convincingly tell you the difference between single pole switched neutral, and double pole.

I suspect I'm in this category. If I had to hazard a guess, it would be that the RCD side of things doesn't care which is the line, and which is the neutral (as the device is measuring a difference between the two), but that overcurrent is determined by what flows through the line only. Whereas a double pole device could detect overcurrent in either line or neutral. But that's only a guess. Happy to be schooled, though

 

[nicebutdim]

I suspect there's some confusion about RCBO terminology going on here.

I suspect some folk regard SPSN = single pole switched neutral.

I suspect some folk regard SPSN = single pole solid neutral.

I suspect some folk couldn't convincingly tell you the difference between single pole switched neutral, and double pole.

I suspect I'm in this category. If I had to hazard a guess, it would be that the RCD side of things doesn't care which is the line, and which is the neutral (as the device is measuring a difference between the two), but that overcurrent is determined by what flows through the line only. Whereas a double pole device could detect overcurrent in either line or neutral. But that's only a guess. Happy to be schooled, though

As an apprentice I'm ready to be shot down but, as RCDs & the RCD element of RCBOs detect imbalance between line & neutral, it matters not which side current is leaking from. What matters is the detection of imbalance above a predetermined level.

DP isolates both poles, SP isolates line only and SPSN (single pole switched neutral) is a single pole device which also switches neutral - to all intents and purposes the latter isolates both poles, but it is the manner in which this happens that differentiates between DP & SPSN. I've read details on this forum about how the latter works, but can not recall sufficient detal to offer a concise explanation. I suspect @pc1966 might fill in the blanks.

 

[loz2754]

@happysteve is correct.

A single pole switched neutral RCBO does indeed switch both poles when operated (either by residual current detection, or by overcurrent).

The difference between a SPSN RCBO and a DP RCBO is that the SPSN only reacts to an overcurrent that occurs in the line, and not the neutral, whereas a DP RCBO reacts to an overcurrent in either the line or the neutral. The result is the same though, as both poles are isolated when the device operates.

With a single pole RCBO, the neutral is connected straight through, and will possibly cause upstream devices a headache in the event of a neutral to earth fault.

 

[Mike Johnson]

If I remember correctly its only the line that has the solenoid that trips, the neutral is just dragged along with the switch when tripping, obviously in a double pole double module RCBO or MCB the neutral is isolated when tripped, not so when its connected to all the other neutrals on the top rail. Fault finding on a full dual module dual pole board is so much easier and the boards are big enough to work on as well.

 

[LastManOnline]

With a single pole RCBO, the neutral is connected straight through, and will possibly cause upstream devices a headache in the event of a neutral to earth fault.

It's a simple choice really.

For the customer , SPSN rcbo,s means his installation is not protected against N to E faults in certain circuits.

For the electrician ,SPSN rcbo,s complicate what would otherwise be a relatively simple fault finding procedure.

 

[pc1966]

For the electrician ,SPSN rcbo,s complicate what would otherwise be a relatively simple fault finding procedure.

Surely you mean SP RCBOs?

With SPSN it allows the N path to be isolated making it simpler to IR test or stop an up-stream delay RCD tripping on a N-E fault.

 

[LastManOnline]

Surely you mean SP RCBOs?

Correct

 

[happysteve]

Thanks for the clarification.

I'm struggling to think of a circumstance where a fault (or combination of multiple faults) would be detected and cleared by a "true" double pole RCBO (one with overcurrent detection in N as well as L), where it wouldn't with a single pole switched neutral RCBO. Anyone?

 

[LastManOnline]

Thanks for the clarification.

I'm struggling to think of a circumstance where a fault (or combination of multiple faults) would be detected and cleared by a "true" double pole RCBO (one with overcurrent detection in N as well as L), where it wouldn't with a single pole switched neutral RCBO. Anyone?

You are correct.The issue only arises with SP rcbo,s where the neutral is unswitched.These are the only ones I personally have worked with to date.

 

[pc1966]

Thanks for the clarification.

I'm struggling to think of a circumstance where a fault (or combination of multiple faults) would be detected and cleared by a "true" double pole RCBO (one with overcurrent detection in N as well as L), where it wouldn't with a single pole switched neutral RCBO. Anyone?

Historically some of the EU had both live connections off a three-phase supply (220V delta, not the 400V L-L seen now) so basically you needed fault protection on both lines.

In the UK the only likely situation is likes of 110V site transformers where again you have two line as 55V-0V-55V instead of line/neutral and a fault to earth needs over-current protection for both cases.

Yes, the RCD side of a SPSN RCBO should trip due to the imbalance but (a) I am not sure the 'SN' side is rated to break much as it probably assumes L opens first, and (b) the I2t let-though for a RCD is far higher as the trip times are typically several times longer than the 'instant' magnetic trip side of a MCB.

 

[pc1966]

Mainland Europe shares TNC-S and TT systems which are the two most widely used systems in the UK

That aspect is perfectly true, but historically they have not has the "strong polarity" assumption of the UK where we had polarised plugs and often line-only switching & OCPD due to N being very much definitely N by design & test.

 

[brianmoooore]

In the UK the only likely situation is likes of 110V site transformers where again you have two line as 55V-0V-55V instead of line/neutral and a fault to earth needs over-current protection for both cases.

And with the 230 - 0 - 230 volt supplies that are common in my area. I've fitted many DP MCBs over the years.

 

[brianmoooore]

@Mike Johnson or anyone else with knowledge of French electrics. Off topic, but is the polarity of sockets specified in France? Most of my encounters with French electrics are 16A sockets on camp sites, and, while most are wired neutral on the left when earth at the top, as in the UK, it's not at all unusual to encounter one with the live on the left.