RCBO Ratings

[Red Squirrel]

Hi Folks,

Having issues with outdoor hookups for a caravan park, it’s getting very frustrating!

The park is tripping back at the main breaker without any tripping at the individual pitches which all have 16amp fuses.

Having not much luck with any electrician giving the exact reason for this I am trying to find out any information myself!

From what doing some research I think I might have come across something..I would love someone to give me a heads up if I am talking sense or BS

Each caravan has fuse inside with a sensitivity rating of 30mA and current rating of 16amps, outside each caravan has its own hookup (3 pin plug) with fuse on the same sensitivity rating of 30mA and current rating of 16amps. Now back to the main board there is a 300mA breaker.

My theory is when a certain caravan overloads or draws too much current, the fuse outside is not tripping as it has the same sensitivity rating as the internal fuse?

I know details are lacking but am I going down the right track on this? I can upload photos if required.

I really appreciate any help, pulling my hair out here!

 

[Sharpend]

How many caravans? A simple earth leakage test might give some indication.

 

[Red Squirrel]

How many caravans? A simple earth leakage test might give some indication.

Approx 50pitches. Occupation at around 25%

My theory mean anything?

 

[binky]

Ok that's not a fuse its an RCD, you have 50 pitches at 30 mA so 1500 mA total, protected by a single 300 mA RCD. So the earth leakage from all the pitches could easily overload the main RCD without tripping themselves.

 

[SPECIAL LOCATION]

My theory is when a certain caravan overloads or draws too much current, the fuse outside is not tripping as it has the same sensitivity rating as the internal fuse?

I don't think your theory is correct and..
I think you may not correctly understand how MCB's RCD's and/or RCBO's work..?

First you don't actually have any fuses..
(i.e. cartridge type devices that fit into a holder such as a 3-pin plug, or larger devices in main suppliers intake cut-out.)

You have a device with a switch that when it trip's, is manually reset by operating the switch.. (i.e. No fuse or fuse-wire needs to be replaced)..

Now to complicate issues for you.. your devices that have 16A, 30ma & 300ma ratings are detecting TWO DIFFERENT types of fault..

The 16A rating is the Overload detection bit.. (similar to a 16A fuse rating).
A device called an MCB, (miniature circuit breaker) is a switched equivalent to the traditional fuse..
e.g. if greater than 16A of current flows for a specified duration then the fuse would blow or the MCB would trip.

The 30ma and 300ma ratings are the Earth Leakage detection bit.. (Traditional fuses and MCB's cannot detect earth leakage currents)..
[ earth leakage is where electrical current is flowing back down the earth path.. e.g. if a person is being electrocuted by touching a live part ]
Devices called Earth Leakage Circuit Breakers (ELCB's) or Residual Current Devices (RCD's) compare the current flowing though the Live & Neutral conductors..
If the current differs by the "ma" rating then the ELCB / RCD will disconnect the power..

IF you have separate MCB's & RCD's it is easy to know what type of fault, (overload or leakage), has caused the trip..

BUT.. there are also devices called RCBO's which combine BOTH the MCB and RCD function..
So if an RCBO trips it can be tricky to know exactly what type of fault has caused the trip..

ALSO.. unless an RCD is a time-delayed device..
If the leakage is greater than 300ma it can be pot-luck as to which device trips first.. if you have two devices, (300ma & 30ma) connected in series.

We need to know if your tripping is MCB, RCD or RCBO... (photos could help?)

BUT..
just pondering here..

IF you have a cable fault, after the 300ma device but before the 30ma devices, where neutral & earth are making contact.. (e.g. damp in a damaged joint).. MCB's will NOT be able to detect this but RCD/RCBO would...

So any caravan supplied via the 300ma device drawing a load well below 16A could leak sufficient current to trip the a 300ma RCD/RCBO.

NOTE:
RCD's MUST trip if the rated value is exceeded..
RCD's MUST NOT trip if half the rated value is exceeded..

e.g. a 30ma device must NOT trip at 15ma, but MAY trip between 16ma to 29ma, and MUST trip at greater than 30ma

Any COMPETENT electrician should have no problem with these basic operating concepts..
and as Sharpend suggest a few simple tests should narrow down a few possibilities..

e.g. A clamp meter that can measure earth leakage AND load current..
An insulation resistance tester and continuity tester, that can check the physical condition of the circuit cables.
An RCD tester that can verify that any RCD's RCBO's are operating within specified parameters..

I hope this all makes some sense and has not caused total confusion?
BUT in summary we need to know if we a looking at an OVERLOAD or LEAKAGE fault?

How old is the installation wiring?
Have you had any recent alterations / additions?

 

[Red Squirrel]

@SPECIAL LOCATION wow that’s a wonderful response and very helpful, you are correct in that my knowledge is limited - I take no offence I just like to understand why an issue occurs and resolve/determine the problem!

The overload and leakage issue make sense, and I now understand why it would be difficult to determine which is causing the issue when rcbo’s are involved.

To make things easier I shall upload some images…

Typical hookup outside to which caravan is hooked up to via 3 pin plug



Now the main RCD? at the consumer unit end.



This main RCD controls various different breakers for lights, sockets and different sections of the park. At no point does any over this breakers trip - never - it always 100% trips the main switch.

Coming to think of it when we had a faulty outside light - fed from this box - it would trip the main switch, not it’s own breaker.

I would be more than willing to perform any test you seem fit to narrow the issue.

I thank you for your time in helping me out!

 

[Red Squirrel]

Ok that's not a fuse its an RCD, you have 50 pitches at 30 mA so 1500 mA total, protected by a single 300 mA RCD. So the earth leakage from all the pitches could easily overload the main RCD without tripping themselves.

Thanks. We are never at capacity, normally at around 25% so approximately 10 caravans occupied. Always happens when it’s cold which led us to believe it’s stand alone electric heaters causing the issue.

Is there anyway around this earth leakage issue? Maybe determine which pitch is causing the most leakage perhaps?

 

[binky]

So 10 times 30 mA is 300 mA . Sounds like you have a damp problem with one of the supply cables rather than the individual pitches. It's possible the 300 mA RCD is tripping at say 280mA as no RCD ever trips at its nominated capacity. It's a really difficult sort of fault to find, but, I would look at splitting the be supply over multiple Main RCDs, your current set up is not going to be reliable. It needs a proper assemement based on your earthing arrangements at source and like loading from the pitches.

 

[SPECIAL LOCATION]

View attachment 13091

Second image not loading/visible..??

But just to confirm on the above photo..
The device does actually say RCBO on it..

but even if it didn't the '61009' bit after the IEC confirms this is an RCBO to 61009 specifications..

The 'B16' confirms the 16A overload protection..
and the '0.03A' confirms 30ma leakage protection.

 

[Sparksfly]

Thanks. We are never at capacity, normally at around 25% so approximately 10 caravans occupied. Always happens when it’s cold which led us to believe it’s stand alone electric heaters causing the issue.

Is there anyway around this earth leakage issue? Maybe determine which pitch is causing the most leakage perhaps?

I am with sharpend on this... Take leakage measurements from main RCD Isolate circuits one by one. Also you could be right it could be a light or other another circuit causing an issue along with the cumulative effect of the other pitches, dampness etc.

 

[Red Squirrel]

For reference here is a photo of the setup inside a typical caravan



Then again the typical setup outside to which each caravan is hooked up to



Note the inside setup has the same rating (30mA) as the outside - although it would seem the load rating is 40amps?

 

[Red Squirrel]

Further to this our park is split on different breakers - served by the 300mA. Here I post an image of the setup splitting two parts of the park (on the left x 2), plus a breaker (on the right) for another board located on the park (image below) for other pitches (Approx 10). Below this is the 300mA breaker which is tripping.




Here is an image of the 'Distribution Board B' located else where on the park

 

[binky]

so the earth leakage tripping the 300mA RCD could be the combination of leakage from everything electical across the whole site. It could also just be a fault that occurs when its cold and damp, combined with earth leakage across the whole site.

As said above, you need someone with earth leakage test gear to see if it's one particular cct or a combination.

Personally I think you have rather too much stuff on a single 300mA to offer a reliable system as you are finding out. I'm trying to think of a cost effective way of improving the situation, but it maybe possible to get rid of the 300mA and put RCBOs onto the distribution ccts instead. I need to consult the regs book, I don't get involved with caravan sites, and they have some specitic regs.

It would also appear you have a TT set up, hence the 300mA RCD on the incoming supply, ie you have your own earth rod rather than an earth supplied by the DNO for your area. Sometimes it is possible to get that changed by the DNO, and get rid of the 300mA RCD, but it's dependent on the electrical cabling in your area.

 

[Red Squirrel]

@binky thank you

It would seem we really need to get some earth leakage tests done…I assume there is no way for a person like myself to carry out any tests? My kit comprises of a clamp meter and multimeter!

As for the earthing rods yes we have earth rods at every pitch plus the distribution board. I have attached an image of a typical earthing rod on a pitch. In my opinion it doesn’t look great but perhaps this doesn’t effect earthing.

 

[michael8554]

40A RCD inside the caravan
16A RCD at each caravan hook-up point
100A 300mA at the incomer.

Can you have too many RCB's in series ?

 

[SPECIAL LOCATION]

40A RCD inside the caravan
16A RCD at each caravan hook-up point
100A 300mA at the incomer.

Can you have too many RCB's in series ?

RCD operation ratings are measured in milliamps..

Any AMP ratings are just the maximum current that the electrical contacts can safely break/make..
The trip ratings are certainly not in the Amps range..

So without any time delayed RCD's it can be pot luck which RCD operates first when any leakage fault current is half an amp or more..

 

[SPECIAL LOCATION]

@binky thank you

It would seem we really need to get some earth leakage tests done…I assume there is no way for a person like myself to carry out any tests? My kit comprises of a clamp meter and multimeter!

As for the earthing rods yes we have earth rods at every pitch plus the distribution board. I have attached an image of a typical earthing rod on a pitch. In my opinion it doesn’t look great but perhaps this doesn’t effect earthing.

View attachment 13104

I don't think I would be wiling to admit I had installed that if it were my work..
looks a bit pi55-poor IMHO..

Obviously it would need its electrical integrity properly tested to see if it is actually functional and safe to use..

 

[michael8554]

RCD operation ratings are measured in milliamps..

Any AMP ratings are just the maximum current that the electrical contacts can safely break/make..
The trip ratings are certainly not in the Amps range..

So without any time delayed RCD's it can be pot luck which RCD operates first when any fault current is half an amp or more..

Thanks,

I appreciate that which RCD would trip may be random, but shouldn't there be a strategy for the protection ?

Hence my question "can you have too many RCD's in series ?"

Perhaps a 30mA in the caravan, and the 300mA at the incomer ?

(And why 40A IN the caravan, but only 16A TO the caravan ?

 

[Fleeting]

It is inevitable you will have a 30ma rcd protected socket at the caravan pitch and a 30ma rcd within the caravan. Is the TT system at the source of supply or remote at the pitches.

 

[binky]

It is inevitable you will have a 30ma rcd protected socket at the caravan pitch and a 30ma rcd within the caravan. Is the TT system at the source of supply or remote at the pitches.

I reckon is TT throughout, hence the 300mA RCD at the main board.

To improve the reliability of the system, I would be looking at getting rid of that 300mA RCD - replacing it with a main switch, and RCDing the sub mains. I'm just trying to remember what the requirements are for the meter tails on TT entering a metal enclosure ie the dis board. If I remember correctly, as long as the tails are protected from the metal edges of the board then it is acceptable to do that. I was also thinking of getting rid of the 100mA RCD at the sub board in favour of RCBOs for the individual ccts.