RCD trips out when CBus loads increase

Can a CBus system be fed via more than one RCD (residual current circuit breaker) e.g. one for each enclosure containing a number of CBus DIN rail units?
If just one CBus network is involved (CBus cable daisy chained between all units in panel then on to next panel etc.) can it cause an imbalance and trip the RCD?
Is it OK to feed the CBus control unit sides of dimmer / relay units in one enclosure via a first RCD, then for a second enclosure feed the CBus control unit sides via a second RCD etc. (with a common single CBus network). For CBus units in a particular enclosure, the control and power sides would probably be downstream of the same RCD.
The existing setup of approx 85 circuits is fed by a single upstream RCD in the consumer unit which trips every week or two. However, when approx 60 percent or more of the circuits are turned on the RCD (not an RCBO) always trips out ? it does not seem particularly dependant on the actual circuits that are on (larger circuits may cause the tripping slightly sooner but it is difficult to tell). Note there are other circuits (not CBus) e.g ring main sockets, domestic kitchen equipment downstream of the same RCD but on a different MCB.
The system is in a domestic installation in the UK, with a power supply of 230/240v a.c, 50 Hz, single phase. It was fitted by a Part P certified electrician (but they are not a CBus installer). The power supply to the building does fluctuate, when windy the light level varies, although the CBus system itself seems to cope well. CBus units are DIN rail dimmers and relays types L5508D1A, L5508D2A, L5512RVF (9 units supply power to CBus)
There was a power cut and the RCD also tripped ? can the power supply quality cause an imbalance and trip an RCD?
Any help is welcome e.g. redesign, fault finding, experience gained in this matter.
More details of the setup and equipment can be provided if required.

 

I dont know the answer but I install each CBUS module on its own RCD (usually a combined single pole unit with an over-voltage protection module (970RM).

This way I am isolating the power demands of each CBUS unit from all of the other units. Some installers also place 1AMP or as needed the balanced load MCB on each load channel.

Professional CBUS dimmer/relay modules have all of these features already integrated.

I think my attitude favours protection of the CBUS because switches are cheaper than removing and installing a replacement module. The only problem is that you need significantly more space to house all those extras.

 

Mate, I have had heaps of dramas with RCDs nuisance tripping as an electrician. Best solution is to limit the number of items per RCD. electronic ballasts and computer gear by Australian standards for example can legally leak quite a bit of current and the accumulation effect causes the RCD to trip(inrush on start up seems to be a killer).

You should have a number of RCDs installed rather than a single one, I have never seen power problems cause tripping because RCDs work off difference between active and neutral conductors current flow which irregular voltage should not effect.

 

It may well not apply to your setup but I have found that a power board with built in surge protection will trip an rcd due to surges in the supply bleeding some current to earth.
So if someone popped one of these into a lighting circuit it could do some random tripping.
If you put surge protection after an rcd it is going to trip the rcd when you get an overvoltage.
As others have said, one rcd per cbus unit output supply is a better way to go since if there is a fault it will only take out the lights for that unit and also have less problems with accumulated leakage.
Use a seperate MCB for the CBus power supplys since you dont want the CBus power supply to drop out and bring down the Cbus network.
You will also then need individual neutral links for each CBus units rcd protected loads.

 

Oh and get the power circuits off the rcd you are using for lighting for a start.

 

RCD tripping

First thing is to test your circuits for insulation resistance, make sure there are no wiring faults. You can have 48 50watt down lights on a circuit running at once for a whole hour before it will trip out a 10 amp circuit breaker so if you have a large amount of RCDs they aren't needed. Power blackouts can trip the RCDs, not sure why but it can happen. Also make sure you don't have any circuits crossing over using one neutral from one circuit and a different active from another.

end of the day there is an inbalance somewhere you just need to find what is causing it.

 

Thank you for all the input. Further experimentation has shown that if the ground floor ring main is switched off at the MCB (downstream of the same RCD that is tripping) is switched off, then all lighting can be run without tripping.

So it looks like there may be some leakage in that circuit (this includes an outside waterproof socket supplying a sump pump - but it makes no difference if the pump is running or not).

It may be possible to split the supply to the 3 CBus boards with two boards running downstream of one existing RCD in the first consumer unit and the third board running downstream from another existing RCD in a second consumer unit, but in each case there would still be other household circuits on the same RCD's. Suppling each of the 15 CBus units with it's own RCD would be quite a modification but I appreciate the benefits - it this often done?

Perhaps the best thing is a third consumer unit with it's own RCD supplying only the CBus system.

In the UK, is it permissible to somehow take a feed downstream of the main 100 amp red incoming switch (upstream of the existing RCD's in two consumer units) and feed it through suitable cabling to one of the CBus cabinets where the MCB (or RCBO) woudl be located, so the CBus has it's own MCB exclusively (or must RCD's always be immediately adjacent the red main switch in the same consumer unit)?

From all the comments so far is it correct to sum up that it's fine to have RCD's more or less anywhere without tripping other RCD's as long as there are no surge suppressors downstream? With a single phase supply how is it possible to 'cross the neutrals'? (is there a diagram of exactly what the latter is?).

 

Crossed boarders and mixed neutrals...

Hi Opto
You need to be mindful that all the responses are form Australian registered users whereas you are in the UK, and we have different rules of what we can and can't do.
Obvioulsy the rules of electricity do not change so much!

Here in the Lucky Country we would typically have a Main switch the first item inline of an incoming supply after the utility meter. Down line from the main switch we break into sub circuits for different uses such as Power, lighting, etc. ideally each controlled by a combo MCB/RCD. (Project homes seem to have 2 high current RCD's and supply up to 3 MCB's for sub circuits downstream of them to save a few dollars) Those subcircuits are for each lighting or power circuit that originates from a single supply point in a branch topology, we are not allowed to ring main as you are.
This should NEVER happen, but if you mix or cross the neutrals in a subcircuit, say the neutral from RCD#1 some how ends up on RCD#2 they will trip (because they are unbalanced, this is how an RCD works measuring the current on the active and neutral equal each other). On old wiring where there are no RCD's they stay mixed until some one finds it hopefully by testing and not being zapped.

I would say Yes, within your local regulations. The C-Bus (pink) signal cable is isolated from the mains and is not an issue.

It is the ideal way to wire them, so if that RCD trips, you also know where abouts the fault is, also it does not leave the house in complete darkness.

As others mentioned, electronic control gear (as used in modern fluorescents) has leakage current so you are limited to how many you can put on each RCD. I always put a surge suppressor on each RCD protected power circuit and have not had a problem with them tripping.

 

C-Bus power fluctuation

I am trying to install a M2M router and I have setup the router in workshop and it works fine, but when I taken to site whereas the site uses a C-Bus system I am finding the power is dropping out of router and and returning power back to the router. Hence resetting the router an the 3G M2M router has to establish the connection again and customer losing Internet access.

I have returned the router back to workshop to test on normal power distribution to make sure router's power supply or device not faulty. The router works normally and does't lose power nor Internet connectivity.

My question does C-bus affect the power points i.e reset power to them?

Also, if I place a UPS before the router as so router works on the UPS and when power resets it will not upset my router. Will this trip anything out on the C-Bus end?

I am not an electrician, just want answers from an electrician as so I can resolve my issues.

Thank you.

 

Hello spkc2680

I can't quite understand the set up.
Are you saying that the power supply for your router is switched by CBus?
In my experience very few installations have power outlets which are switched by CBus.
If they did the power would only switch on and off when told to.

Why is the router connected to a CBus output rather than an unswitched supply?
Are you supplying power to your router via a lighting circuit which is switched on and off because that was convenient?
If so a UPS may well exceed the rating of the CBus relay outputs and would also be poor practice.