Can an upstream fault cause an RCBO to trip?

[LlandrilloSpark]

Fellas

Scenario - 1 main three phase board feeding 3 further three phase boards with each of those feeding 15 single phase boards containing only two final circuits each.

The fault is on the final circuits, ive tested the final circuits and all clear, can a fault on the distribution circuits upstream cause the RCBO to operate?

cheers

 

[telectrix]

i suppose a poor connection upstream of a RCD could cause an imbalance

 

[Marvo]

I've heard of sodium/mercury lighting switchgear like streetlighting causing RCD's to trip. Not sure if it's a harmonics issue or if some residual current devices are more prone than others.

 

[pushrod]

It is my understanding that certain circumstances upstream of an rcd/rcbo can cause tripping eg voltage spikes, switching of large inductive loads. Are you confident that the rcbo is working correctly - what does a ramp test show and are you certain that nothing being used on the circuit in question is not allowing an earth leakage

Edit also heard the other day of walkie talkies causing rcds to trip.

 

[GLENNSPARK]

It is my understanding that certain circumstances upstream of an rcd/rcbo can cause tripping eg voltage spikes, switching of large inductive loads. Are you confident that the rcbo is working correctly - what does a ramp test show and are you certain that nothing being used on the circuit in question is not allowing an earth leakage

Edit also heard the other day of walkie talkies causing rcds to trip.

Walkie talkies...."BREAKER...BREAKER"....lol........

 

[LlandrilloSpark]

nothing leaking to earth as the final circuits power 3 light fittings,2 leds, and 2 sockets only between them!, rcbo trips as 21mA, so i changed to a c type tripping at 27mA but i clamped the earth and under full load there isnt 2mA leakage, im just weighing up if i am going to have to test all the distribution circuits also

 

[i=p/u]

clamp all the earths and see which circuit has highest earth leakage current,, beware of what i say!!!! but beware of my future knowledge

 

[LlandrilloSpark]

none of the final circuits leak anything at all so thats why im asking about the upstream fault, I think for the time it takes i will test the distribution circuits

 

[pushrod]

Is there any electromagnetic/radio interference near the rcbo in question? Is it tripping all the time immediately or at specific times or just occasionally.

 

[i=p/u]

sorry for being dumb there

 

[platty1005]

Hi llandrillo you are talking about an RCBO it trips on overcurrent like an MCB and on earth fault like an RCD. Don't concentrate on earth leakage it could be an insulation fault on the final circuit
I suggest start from scratch R1+R2, IR, polarity, Zs then function of the RCBO
Once you are convinced final circuit is OK then look upstream

 

[Knobhead]

An up stream fault can cause tripping but the usual cause is one of the up stream breakers tripping, which I think you’d notice. Are there any inductive loads being switched up stream?

 

[LlandrilloSpark]

went back today, everything fine since i changed a few accessories and the most troublesome room which tripped daily hasn't tripped since i changed the RCBO from a type b Eaton Mem tripping at 21mA to a Type c crabtree tripping at 27mA, i didn't change any lamps or accessories in that room, its very strange that only four rooms are effected, also that the distribution circuit supplying each room is on a different phase, so no one phase has a problem there.
One thing i did find though is that there is a three phase lift upstream, big motor, might cause the trip.

 

[LlandrilloSpark]

platty i have pre comm tested the two worst rooms, completely clear of any faults on the wiring mate

 

[malcolmsanford]

Any problems with dampness in these rooms??

 

[LlandrilloSpark]

Nothing apparent on a visual of the room malcolm, the building is a 12 month old travelodge, essentially in mint condition and a new build not a renovation of an old property, ccu's for the rooms are situated in service risers alongside every other service like HVAC controls ect ect, but there are 40 db's in this place, one per room and only these 4 are effected.

 

[Knobhead]

Surge suppression on the lift springs to mind, but a bit drastic if only 4 rooms are affected. These rooms wouldn’t happen to be near the lift motor room would they? Or possibly off the same branch feeder? Just ideas.

 

[LlandrilloSpark]

this block of rooms is nearer to the lift than any other rooms Tony, basically the lift is at the same end of the corridor as these rooms

 

[Knobhead]

Either get the lift company in and put the ball in their court.

Otherwise look a surge suppression at the board involved, the suppression will have to be on the live side of the lift supply.

Suppression works both ways it can stop a spike coming back in to the system. Depending on where it’s fitted.

 

[LlandrilloSpark]

I'll look into that Tony, I was told this morning that they had an emergency evacuation about two weeks ago as there was an electrical burning smell coming from the floor in question, customers thought it was the lift, the lift company came out and said it wasnt the lift.

 

[Knobhead]

I don’t know how long you’ve been in the game Llandrillo but you’d better get used to being told things in little bits.

There are times when you have to be like Sherlock Holms to find a fault. A bit of information here, a bit from there and eventually you get the full picture. (If you’re lucky).

 

[LlandrilloSpark]

Prob not as long as you Tony!, Thats the thing with this job, 5 different staff members and lots off different guests telling them what happened, I asked the main manager to open up a faults log and ask the customers the usual Q'S, what did you press, what did you hear, did you smell anything, what was on in the room when it tripped.........2 weeks later no log so im changing little things each visit to see if they have an impact, bottom line is this company use cheap crap in their installations i have found faulty lamps ect, but like ive mentioned the biggest effect has been switching the RCBO type, the other problem is the contract is not mine, im working on behalf of a much bigger firm and i dont have the authority to change all the lamps, switchgear or accessories so i have to ask, also because the place is full i have a limited window each day im available to get in to the rooms.......nightmare.

 

[pushrod]

Just a real longshot - intercom in the lift or staff walkie talkies?

 

[LlandrilloSpark]

both present in the building pushrod, but cant be the walkie talkies as they are used through out the building

 

[Rockingit]

I'm REALLY reaching at a guess, here, BUT... if this is a hotel scenario (having spent enough time living in the damn things myself) is there any possibility that you could have equipment brought in by guests (thinking laptops and phone chargers) which have inherently higher leakage, together with the possibility of some shoddy earthing?

Either that, or are these the type of rooms where guests are inclined to swing from the chandeliers???

 

[LlandrilloSpark]

Nice try but i reckon a long shot as guests bring items in to all 40 rooms and only 4 effected!

 

[Rockingit]

Nice try but i reckon a long shot as guests bring items in to all 40 rooms and only 4 effected!

Appreciated, but my thoughts were more towards the possibility of those four rooms having some commonality of earthing, hence just those rooms affected.

 

[LlandrilloSpark]

Quick update

The room which tripped on a daily basis has not tripped since the RCBO was changed from type B TO C, and its been fully occupied for 8 days, with no earth leakage on the final circuits its a bit of a mystery?!, faulty RCBO or as suggested hight start up current upstream.

 

[nickblake]

Bet you its the coffee machine ......it would be if i was there lol

 

[pushrod]

One of the world's great unsolved mysteries - maybe all of the suicidal spiders that lived near the CU are now all dead.

It certainly shows the downside of rcbos compared to rcd+Mcb. Yes they might minimise inconvenience, but when it comes to a problem you don't know whether you are starting with an overload or an earth fault.

 

[LlandrilloSpark]

Nick the Coffee machine is situated in reception and was £2 a pop.......no chance!!