Selectivity at Static Caravan

[JoeMagin]

Hi all,

Just a electrical student here, and on holiday at a caravan park so, of course, i go snooping about a bit for the electrics.

I notice the caravan at the hook up is fed off a 30mA RCD and 32A MCB. The board within the caravan contains a 30mA RCD and a 32A ring.

As im just learning I might be being completely green here, but in terms on discr.. ahem... selectivity, wouldnt the RCD and the MCB at the hook up have to be rated higher.

Are caravan sites special cases for tbese sorts of things? Any clearning up would really scratch that itch at the back of my mind.

Cheers!

 

[plugsandsparks]

Hope you having a great holiday ! - No sweat over selectivity. Caravan Hook up providers have to allow for worst case (Caravan with very rudimentary electrics) - You are right though if there is a fault, likely to be Hook up RCD first or both together.

 

[buzzlightyear]

green here, but in terms on discr.. ahem... selectivity, wouldnt the RCD and the MCB at the hook up have to be rated higher. Time

No, because the rcd in the caravan is lower then the hook up, down stream is correct selectively 63amp time delay is I order before it takes out the main cut out. Or other. I would be more bothered the caravan not up to date on testing and the hook up, eye spy.

 

[pc1966]

It is unusual to see 32A for the supply, many hook-up points are fed with 6-16A MCBs (often C-curve for slightly better handling of surges). The issue of selectivity applies more for cases when:

• The upstream device (RCD/MCB/fuse) supplies multiple circuits, or
• The protective device(s) are locked against unauthorised access to reset them

Then any fault on a final load has to potential to cause significantly more and long-lasting outages.

In the caravan situation normally the folks using the caravan can easily reset both RCDs so the impact of one or both tripping is less serious. However, the impact of a failed/stuck RCD and the higher that usual risk from a metal vehicle with cables flexed many times means it is sensible to have two RCDs, both with 30mA "instant" protection against shock, providing no single point of failure as the most safe and sensible approach.

Generally speaking MCBs in series have poor to very-poor selectivity and ought to be avoided from a design point of view, but again there are cases when the risk of greater outage is less than the cost/complexity of a better solution such as an MCCB or fuse upstream of the MCB. That is either very expensive (MCCB) or unsuitable for most electrically-unskilled folks to fix (fuse, especially bolted-in ones).

 

[nicebutdim]

In the caravan situation normally the folks using the caravan can easily reset both RCDs so the impact of one or both tripping is less serious. However, the impact of a failed/stuck RCD and the higher that usual risk from a metal vehicle with cables flexed many times means it is sensible to have two RCDs, both with 30mA "instant" protection against shock, providing no single point of failure as the most safe and sensible approach.

Upstream RCD has 0.1s printed on it and appears to be 30mA time delayed.

 

[mainline]

Upstream RCD has 0.1s printed on it and appears to be 30mA time delayed.

It's not time delayed, the 0.1s is the fault current cut off time.

 

[pc1966]

Upstream RCD has 0.1s printed on it and appears to be 30mA time delayed.

I didn't think they made time-delay 30mA devices, and in any case 0.1s is within the test limits for In for "instant" RCDs.

 

[mainline]

I didn't think they made time-delay 30mA devices, and in any case 0.1s is within the test limits for In for "instant" RCDs.

https://www.electricalcounter.co.uk/products/Circuit+Protection/Cudis+CPN+Circuit+Protection/Devices/Time+Delayed+RCDs/Cudis+CPN+RC263-030T+63A+Double+Pole+Type+AC+30MA+Time+Delayed+RCD/545305925

 

[pc1966]

Interesting, I guess it makes sense if you had some 10mA final circuits downstream (RCD sockets, etc), etc, but odd as usually 30mA have to be fast enough for "additional protection".

 

[mainline]

Interesting, I guess it makes sense if you had some 10mA final circuits, etc, but odd as usually 30mA have to be fast enough for "additional protection".

Probably Chinese non time delayed ones that failed on the production line

 

[JoeMagin]

Wow lads, cheers for the replies. A lot to get my head around but i suppose theres no rush.
Completely forgot about time delayed RCDs, not something ive come across yet. Will the delay usually be printed on the front with the other information?

As for the holiday, We're having to make a hasty escape as my baby boy got a bit sick in the pool and they had to close it for an hour!

 

[westward10]

I suspect if you test that S type 30ma RCD at ×5 it may well disconnect in less than 40ms but that is speculative.

 

[buzzlightyear]

We're having to make a hasty escape as my baby boy got a bit sick in the pool and they had to close it for an hour

what ashame , it could be worst could have been chocolate log floating around ,bloody hell not again every body pointing at the owner .

 

[JoeMagin]

It's not time delayed, the 0.1s is the fault current cut off time.

Just looked up the spec sheet for this rcd (god my life's interesting) and the 0.1 is in fact the time delay. They could have made it a little clearer couldnt they.

 

[mainline]

Just looked up the spec sheet for this rcd (god my life's interesting) and the 0.1 is in fact the time delay. They could have made it a little clearer couldnt they.

Technical Datasheet

B10R
In accordance with IEC 61008-1
Certification CE, SEMKO
Pole composition 2P, 4P
Rated current: 16A, 25A, 32A, 40A, 63A, 80A, 100A, 125A
Residual current characteristics: AC, A
Calibration Temperature: +30°C
Rated frequency: 50/60Hz
Rated voltage: 110VAC/230VAC/400VAC
Rated residual operating current I∆n: 30mA, 100mA, 300mA
Max. Switching Time@ I∆n: 100ms
Residual tripping current range: 0.5 I∆n ~ 1 I∆n
Rated conditional short circuit current: 10kA
Electrical lifetime > 4,000 cycles
Fastening torque: 2.0Nm
Terminal capacity: 35mm2 solid, 25mm2 stranded conductor
Mounting on DIN Rail EN 60715 (EN 50022)
Protection degree: IP20
Operating temp


Where does it say its a time delayed rcd ?


It says max switching time 100ms the typical time for a 100ma Time delayed rcd is around 200ms

 

[JoeMagin]

Technical Datasheet

B10R
In accordance with IEC 61008-1
Certification CE, SEMKO
Pole composition 2P, 4P
Rated current: 16A, 25A, 32A, 40A, 63A, 80A, 100A, 125A
Residual current characteristics: AC, A
Calibration Temperature: +30°C
Rated frequency: 50/60Hz
Rated voltage: 110VAC/230VAC/400VAC
Rated residual operating current I∆n: 30mA, 100mA, 300mA
Max. Switching Time@ I∆n: 100ms
Residual tripping current range: 0.5 I∆n ~ 1 I∆n
Rated conditional short circuit current: 10kA
Electrical lifetime > 4,000 cycles
Fastening torque: 2.0Nm
Terminal capacity: 35mm2 solid, 25mm2 stranded conductor
Mounting on DIN Rail EN 60715 (EN 50022)
Protection degree: IP20
Operating temp


Where does it say its a time delayed rcd ?


It says max switching time 100ms the typical time for a 100ma Time delayed rcd is around 200ms

WOOPS, sorry, just checked it again, you are right. Seems i was a bit trigger happy reading out the specs.

Thanks for pullin me on that. In the codes, i saw Type AC (selective 0.1s). Thatll teach me for rushing!

 

[mainline]

I suppose in reality it could be argued that all rcds, mcbs and fuses are time delayed even if they were at the speed of light

 

[telectrix]

the site owner needs to fit a 30mA RCD. to prorect the hook-up flex and allow for a caravan with no RCD or dodgy install.

caravans come fitted with 30mA RCD as standard. posh ones may have RCBOs. either way, you have no discriminatioon and have to live with maybe going out in the cold and rain in your pyjamas just to watch "millionare" repets in bed.

 

[mainline]

the site owner needs to fit a 30mA RCD. to prorect the hook-up flex and allow for a caravan with no RCD or dodgy install.

caravans come fitted with 30mA RCD as standard. posh ones may have RCBOs. either way, you have no discriminatioon and have to live with maybe going out in the cold and rain in your pyjamas just to watch "millionare" repets in bed.

There is an rcd protecting the hook up or do you mean S type rcd ?