Fluorescent fault overcurrent trip?

[SpannerSpark]

4ft old style starter/ballast type fitting which when powered does nothing at all (not a flicker) but trips the 6A/30mA RCBO after maybe 3-5 secs. I didnt have my clamp meter with me when i went to see the fault but assume due to the time delay that its the overcurrent part of the RCBO rather than the current leakage part thats making it come out.
The fitting is min 20 years old i would guess, some heating marks on the ballast but other than that the tube looks ok , no blackening. Removing the tube only no trip. Removing the starter only and no trip. Fitted a new starter now RCBO trips immediately. Customer happy to replace whole fitting, but i wouldnt mind knowing what the fault possibly is. Any theories welcome

 

[GLENNSPARK]

4ft old style starter/ballast type fitting which when powered does nothing at all (not a flicker) but trips the 6A/30mA RCBO after maybe 3-5 secs. I didnt have my clamp meter with me when i went to see the fault but assume due to the time delay that its the overcurrent part of the RCBO rather than the current leakage part thats making it come out.
The fitting is min 20 years old i would guess, some heating marks on the ballast but other than that the tube looks ok , no blackening. Removing the tube only no trip. Removing the starter only and no trip. Fitted a new starter now RCBO trips immediately. Customer happy to replace whole fitting, but i wouldnt mind knowing what the fault possibly is. Any theories welcome

what makes you say this?

could be a neutral-earth fault

whats the earthing arrangements?

 

[Darkwood]

Ballast partial collapse(high inpedence fault) internally or short depending on what part of the cycle the power is on when the starter opens and recloses could give a delay on a short....
If the tube gives an extra bright flash and refuses to work again the tube elements will have blown out too .

As you have already guessed it sounds like a new fitting or ballast swap.

 

[Darkwood]

what makes you say this?

could be a neutral-earth fault

whats the earthing arrangements?

A Neutral/Earth fault is highly unlikely as the OP said taking out the starter stops the rcbo tripping this means the only culprit that could cause this (If not a ballast fault) is a short to earth on the wire to the starter from the tube end fed by the ballast and as this has the tube elements in series too and this wouldn't actually be classed as N as the Neutral point ends at the pin on the other end of the lamp.

 

[GLENNSPARK]

A Neutral/Earth fault is highly unlikely as the OP said taking out the starter stops the rcbo tripping this means the only culprit that could cause this (If not a ballast fault) is a short to earth on the wire to the starter from the tube end fed by the ballast and as this has the tube elements in series too and this wouldn't actually be classed as N as the Neutral point ends at the pin on the other end of the lamp.

yes....
thanks Dark

 

[Darkwood]

yes....
thanks Dark

Soz Glen thought i best correct you and better from a fellow yorkshire man than one of those southern lot

 

[GLENNSPARK]

Soz Glen thought i best correct you and better from a fellow yorkshire man than one of those southern lot

well...its just that he was mentioning about how the RCBO held for 5 secs or so..then let go...

can be a symptom of neutral-earth faults....but i was wrong..you were rite....lol..

 

[Darkwood]

The delay is most likely due to ballast short as weird as it sounds ...if the ballast can still provide enough field collapse to strike the lamp it should then act as a current limiter (choke) but a internal short will allow overcurrent which will either trip the circuit after a time delay or destroy the lamp as it get warmer the internal resistance falls which is also another reason for delay to occur.

We lack enough info to know exactly what is tripping the mcb/rcbo but i think i covered with this posts most of the possibilities with what he has given us.

Re-reading the OP it doesn't strike so its likely the ballast can't build enough field to give back EMF but still may let overcurrent through and the starter completes the circuit but still will have 2 elements in series (lamp caps).. the starter may well weld with overcurrent stopping the bimetallic strip from opening you get your delay again ... a new starter could open and still send a partial back EMF into the rcbo and trip it until it also welds

I bet the ends glowed with the old starter and not with the new one.

 

[SpannerSpark]

Blimey, thanks for the replies all

 

[Darkwood]

How a Fluorescent Light Works - Schematic Animation - YouTube

Watch this Spanner to remind you how the ballast and starter play their role its the easiest one i can find to follow just keep pausing the video as the wording does move by before you can relay it to the diagram.

You'll understand why telling the customer the fitting is knackered is the best way rather than trying to explain to them.