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.