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

[littlespark]

Might be hard to tell now, but what were the terminations like?
im thinking these were all fitted when the block was new, just wondering if maybe the same- not very effective- electrician did the connecting and left a loose screw in these particular flats.

clutching at straws, but always something to think about if all other avenues of investigation are exhausted.

 

[LukeD]

Might be hard to tell now, but what were the terminations like?
im thinking these were all fitted when the block was new, just wondering if maybe the same- not very effective- electrician did the connecting and left a loose screw in these particular flats.

clutching at straws, but always something to think about if all other avenues of investigation are exhausted.

Has to be a factor.... The ability for someone to just make a mistake/miss something is super high

 

[GBDamo]

I would also see if the affected units are on the same phase still can’t rule out floating neutral

If love to, I fact already discussed the possibility with site but that is a herculean task without drawings, access and someone on site who has a clue.

 

[GBDamo]

Might be hard to tell now, but what were the terminations like?
im thinking these were all fitted when the block was new, just wondering if maybe the same- not very effective- electrician did the connecting and left a loose screw in these particular flats.

clutching at straws, but always something to think about if all other avenues of investigation are exhausted.

Possible but it's the time frame that leads me away from workmanship, coupled with the recent other electrical issues.

I don't know for sure but the block looks to be ten year old and for bad workmanship to start to show up so late in the day then all within a week makes me think other factors are at play.

 

[Mikegh]

If love to, I fact already discussed the possibility with site but that is a herculean task without drawings, access and someone on site who has a clue.

Wander lead




Joking

 

[GBDamo]

Here's some photos @Lucien Nunes and others.

The terminals and cables are clean as a whistle.

This is the culprit

Capacitor(?) has blown.

 

[plugsandsparks]

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.

Would definitely clamp it , you may get over 14 Amps if lucky...lol but is stuff that good nowadays. BTW i only use Timeguard products for this type of stuff as fed up changing crap out after a few years

 

[freddo]

Looks like a metal oxide varistor connected across the supply, If several blew at once this is a sure sign of overvoltage on the supply. A MOV is normally high resistance, but it's resistance drops as the voltage increases to stop voltage spikes. A sustained overvoltage such as from a supply fault will quickly overheat and destroy an MOV.

 

[Yozza19]

Looks like a metal oxide varistor connected across the supply, If several blew at once this is a sure sign of overvoltage on the supply. A MOV is normally high resistance, but it's resistance drops as the voltage increases to stop voltage spikes. A sustained overvoltage such as from a supply fault will quickly overheat and destroy an MOV.

Would definitely put my money on a floating neutral as some stage some Dno have a search function on there site to advise if there have been any incidents in the locality

 

[Lucien Nunes]

Yup, it sure does look like an MOV that wasn't big enough absorb the available energy in the overvoltage event. When that happens, it can initiate an arc that lasts until the fuse blows, which can dissipate so much more energy that it makes it hard to identify whether the trigger event was an impulse or a prolonged excursion above clamping voltage.

Assuming the building is served by conventional urban underground distribution the latter seems the most likely and I would say the likelihood of a cable fault causing both the timer damage and the flickering / outage events was very high. Other items in the properies with MOVs (and even SPDs) might also have been compromised, but if the MOVs in the timers had a slightly lower clamping voltage then they might have all gone phut before many of the remainder showed signs of distress.

The sub might be specific to the estate or building, in which case any information you can get from the DNO about recent faults might nail it.