Block of 200+ flats, eleven single channel hot water timers blown this week alone.

[marconi]

I’ll add this to my long list of other things I have got wrong. Yours humbly……

 

[Mike Johnson]

Don't think it's been asked, but did all eleven flats loose their timers at the same time, or was it cumulative over a period.

 

[marconi]

Don't think it's been asked, but did all eleven flats loose their timers at the same time, or was it cumulative over a period.

Following MJ’s theme - MOVs do degrade each time they react to over voltages. It is not unknown for them to eventually suffer thermal runaway which is when their quiescent current rises over time, the MOV warms up, its resistance reduces, it passes more current, it warms up even more…until it cannot dissipate the heat quickly enough to its surroundings and it destructs. All of which can happen in the absence of any overvoltage.

 

[GBDamo]

Don't think it's been asked, but did all eleven flats loose their timers at the same time, or was it cumulative over a period.

That is a good question but impossible to get a definitive answer as we don't know when they "went" only when the tenant discovered and reported them.

The first was reported on Tuesday, I was called on Thursday and by then there were eleven.

All we've got is the times they were reported.

But judging by the crazy disco lights I witnessed the issue is still ongoing and more will go.

 

[Lucien Nunes]

@marconi I'll let you off if you can find a SIL through-hole bridge rec in a white package made in the last 25 years.?

We can now confirm from the PCB pics that the failed part is across the mains input. In theory it could have been a small filter capacitor but:
a) The part shape and burst pattern are more consistent with an MOV
b) A cap of those dimensions would typically be a Y-class part of a few nF which is not appropriate there.
c) An MOV is not a bad idea where a capacitive dropper is tapped off the supply to a relay-switched 16A load of unspecified characteristics.

What it will hopefully have been doing, before it popped, was shaving off transients likely to damage the dielectric of the X2 dropper cap, that would otherwise cause a progressive loss of capacitance to the self-healing process.

But judging by the crazy disco lights I witnessed the issue is still ongoing and more will go.

Somebody needs to switch this lot off now.

 

[GBDamo]

Somebody needs to switch this lot off now.

Twice I have told them it needs attention, verbally and in writing via the job card.

I will chase it up on Monday as the lass who I was dealing with didn't convince me she understood the potential gravity of the situation.

 

[UNG]

Just curious if you did any more voltage checks when you went back although I think to catch any major voltage peaks or dips you would probably need to put some logging equipment in across all three phases


Had a similar problem to this at a business premises I used to work from many years ago although no equipment was damaged the voltage would very often dip to 170 - 185v on one phase around 8:15 - 9:00 in a morning and around 17:30 - 18:30 in an evening but not everyday, after a few weeks we got the DNO involved who put a voltage logger in for a week who told us there was no problem found, a week later 4 DNO vans appeared one afternoon and dug up the link box at the end of the street about 50m away, talking to the DNO lads they said that the box was close to failing due to thermal damage and was being replaced with a resin joint, The voltage problem disappeared after that

 

[Dave OCD]

Could it all have been caused by a one off surge as the power was restored following the reported mains failure across the entire block ?

 

[roper_ni]

They are rated at 16A. The hot water cylinders are on a dedicated circuit off their own 16A MCB, isolated via a 20A double pole switch, length is a couple of meters.

Couldn't see a rating on the element but looking into that now.

Edit to add,

The elements are 3kW but looking at the plumbing I think they're on a central hot water system as there seems to be a coil on the cylinders.

I'm back there tonight two replace a couple and grab some more info.

Time to get the Megger out and 1000v dc @ the heater could be cable or heater.

 

[roper_ni]

Time to get the Megger out and 1000v dc @ the heater could be cable or heater.

Sorry wrong post