RCCB Trip and Downstream

Have your electrician look at the wiring and report back to you.

We can't quite see it from here.

If both are 100ma, it may be random (or just blind luck) which trips first. For better coordination, it usually helps to place the more sensitive components "closer to" the loads.

Don't know where you're from, but in the UK it is "against code" (BS7671, AKA "the regs") to have more than one rccb on the same feed, whether they're the same trip rating or not.

Because there is a connection between earth and neutral somewhere between the two rccbs that should not exist. The fault current is therefore being shared between the neutral conductor and the earth conductor between these two rccds, causing an imbalance between live and neutral at the upstream rccd sufficient for it to trip as described. The same phenomenon can be caused also by the presence of high current normal loads downstream of the second rccd.

Please don't cause deliberate short circuits, as they can be hazardous to health and also give rise to unpopularity with the premises' fire insurance cover provider.

• Been there, done it, secondhand T-shirt available on eBay (other internet auction sites are available) right now. In this particular case it turned out to be a woodscrew holding the earthed bracket of a wall light to a vertical partition wall timber inadvertently just puncturing the insulation and kissing the neutral conductor of an incoming cable incorrectly located too close to that timber. The symptoms were a whole-house trip when the third ring of an electric cooker was turned on, and the 30mA circuit cooker circuit rccd remaining un-tripped. It took just three days' work to find it and 20 minutes to eliminate it, allowing for swearing time.

_<Ahem>

_{Cannot agree with above statements on rccds in series, because on a domestic TT system, a 100mA rccd is needed on the incoming supply to cater for the prospect of a poor local earth connection; downstream rccds for final circuits need to be 30mA to comply with current UK codes for minimising the risk of electrocution.}

_</Ahem>

If in doubt, consult a qualified local Electrician.

LOL!!

Normal practice would be to have discrimination between cascaded RCCD's. IE 100mA-S (time delayed) feeding the DB and 30mA for the equipment. You'll find all the information in BS7671

As suggested get a qualified electrician to look at the set up. He will be able to carry out ramp tests and issue test certificates.

I do agree with Tornado in this <<For better coordination, it usually helps to place the more sensitive components "closer to" the loads.>>,.. But my question addressed to the questioner: Why do you intend to use the suggested number of RCCBs as depicted in the question? As you know such kinds of CBs are mainly used in wet places of houses (like kitchens, bath rooms)..

Is it possible that your second RCCB is installed downstream of a VFD or other waveshape modifying device?

Standard RCCBs are not very effective on non-sinusoidal waveforms and may not trip as intended.

I'm guessing that you're referring to a short circuit to earth, as an RCCB will not normally trip on a short between live conductors

Our protection system is based on the level of device discrimination that is standard in most countries. What we sometimes fail to see is the minor details in the specifications of each device we installed. In your case, u have installed both RCCB of the same rating (100mA) which makes tripping becomes random on either device when a fault occurs. For a start try looking at the sensitivity rating of the mechanism in each device. This is represented by the (kA) rating. Try getting a lesser kA rating for the device installed at the final circuit and a higher kA rating at the mains side. Normally for mains it is recommended at 25kA and for final circuits, recommended rating is at 15kA or lesser depending on the design of your earthing system.

Hope this helps.

In simple terms, the rcd cannot look backwards to an earth fault. Only forward. So 2 devices on one circuit, one at each end, DB and equipment, the DB side looks towards the equipment and any leakage detected on this circuit, the DB side will trip. If the leakage was in fact at the equipment and ahead of the rcd, then only the equipment rcd would trip.

RCD units are not equal in leakage current detection, so no two rcd will trip on the same leakage current rating. They will trip within a narrow range. They do not calibrate the coils to be the same and the coils vary in sensitivity. If the CB's are functioning correctly they would trip before the rcd trips on a short, on the equipment, preventing sufficient current getting to the coil of the rcd and not causing an imbalance on the circuit to trip the rcd.

Someone is not understanding what an RCD is and does!! Same as I don't know what a DB is! Some sort of breaker maybe? The web gave me this:-

Dbsymbol

1. the chemical element dubnium.

Read here for RCD infos:-

Residual-current device

What you APPEAR to need is a "RCBO, residual-current circuit breaker with overcurrent protection!

Or simply add an over current circuit breaker to what you already have.....

A circuit diagram would also have been a really intelligent idea as well.....(assuming that there is not one "later" in this blog!! There isn't)

Do please never forget "GIGO", it will be easier to find accurately on the web than DB!!!!!!

Distribution Board

Many thanks.

That is here its a "SK"......

Google was no proper help either!!

Sadly, anyone posting here with just Acronyms faces the "luck of the draw" always.....also, not placing a simple diagram here as well "increases the risk!" so to say....

Happy Solstice Day to everyone!!

I thought it would be a happy Equinox day..But perhaps it's different where you dwell

Its the same the world over, on those 2 days a year!!

This particular one in German is "Frühlingstagundnachtgleiche".....

What a mouthful!!!

Generally speaking, translating a document from English into German, increases its size, (not necessarily the word count!), by around 20%, but is VERY variable.....