Intermittent faults...

[ElectroChem]

Intermittent faults are the spawn of the devil. Their mission on earth is to torment electricians and confuse apprentices.

Just wanted to make that clear.

 

[Octopus]

I like a challenge - add long as the customer will pay!

 

[Jonspark]

just replace part by part till the fault disappears

 

[telectrix]

I like a challenge - add long as the customer will pay!

i challenge you to a duel. voltsticks at dawn.:49:

 

[Bobster]

Is this in a control panel?

We used to set up latching relays wired into the control system so that say a drop in voltage in one part would set one off. Nicknamed them mousetraps.

I remember a fault on one of our overhead cranes, before they were PLC controlled I had nearly 30 relays wire in! Found the fault in less than a day with them installed a contact was not quite making properly, so with the crane bouncing around it would unlatch every now and then.

 

[ElectroChem]

Yeah we've done similar for a freezer unit throwing errors, set up a load of latches in the PLC and caught a low pressure alarm coming and going.

I originally thought this fault was in the panel, turned out to be a heater element (barely) pushed up against it's support bracket, as it thermally cycled it would occasionally short to earth.

 

[Guest125]

I always thought here was a magic 'fault' switch under the matt. As soon as you step inside the property the fault stops. As soon as you step back on your own matt at home the fault starts again.

Similar to the 'call me now' button on cafe chairs.

 

[Bobster]

Yeah we've done similar for a freezer unit throwing errors, set up a load of latches in the PLC and caught a low pressure alarm coming and going.

I originally thought this fault was in the panel, turned out to be a heater element (barely) pushed up against it's support bracket, as it thermally cycled it would occasionally short to earth.

A lot easier and quicker now everything doesn't have to be hard wired.

Same principal though.

 

[Geordie Spark]

Intermittent faults are the spawn of the devil. Their mission on earth is to torment electricians and confuse apprentices.

Just wanted to make that clear.

NOT just electricians bonny lad.

Have you ever tried to find one on a Combi gas boiler???

Just wanted to make that clear!

 

[ferg]

I've had a few recently and you are right they are the spawn of Satan.

It doesn't help when customers are slightly less than truthful.

Why is it that they think not telling you about hidden DIY bodges is a good idea?

 

[ruston]

NOT just electricians bonny lad.

Have you ever tried to find one on a Combi gas boiler???

Just wanted to make that clear!

A boiler is a plumbers 3036 board lol. sorry madam it's........................

 

[VoltzElectrical]

Tell me about it! The veterinary surgeon I use for my dogs asked me to install some outside lights that he had bought. He had removed the old ones and left the cables in connectors, taped and bagged.

I installed the new lights, the cables looked ok, tested and left.

A couple of months later, he called to say the RCD was tripping occasionally, but would reset when the outside lights were left off. He switched them back on, and would hold for up to a couple of weeks, then trip again.

I went back around for another look. These were cheap Orange shed fittings and I suspected water ingress even though I had siliconed them up, as one was on a weather facing wall.

I took the fittings off, tested, visually inspected, and everything looked ok, put it all back together, reset the MCB that was tripping the RCD, function tested, and agreed to monitor the situation.

A couple of weeks later and another phone call. Now I'm starting to look like a muppet, so I take another forum member with me as another 'fresh' pair of eyes.

Anyway, to cut a long story short, the problem was the original installer had been a little bit enthusiastic with the side cutters and had 'just' nicked the live as it exited the brick wall. It could barely be seen, and every couple of weeks with a bit of bad weather, enough moisture would short the cable to the 'mass' of earth (as opposed to the cpc), and trip the RCD.

The lesson I learned from it, was to leave the cpc in the earth bar when testing IR so as to not only test between conductors, but between conductors and the general mass of earth.

I was lucky that on the final visit, the fault was still present on the circuit.

It was a great learning curve, and thanks to those who helped at the time, you know who you are.