What could have caused this 😮

[Crofter]

Think I had a close shave here. 

Plug now replaced and I'm keeping a very close eye on it. 

Any suggestions for why this would have happened?

[dpmiller]

too much for too long. There's always a small amount of heating effect at a contact point- which in the case of a plug tends to weaken the sprung contacts that hold the fuse. Vicious circle then...

 

Tumbledryer? Immersion heater?

[Crofter]

8 minutes ago, dpmiller said:

too much for too long. There's always a small amount of heating effect at a contact point- which in the case of a plug tends to weaken the sprung contacts that hold the fuse. Vicious circle then...

 

Tumbledryer? Immersion heater?

Yup it was running an immersion heater. In theory it should have been sufficient for the current. This bodge only came about because the sparky didn't realise we had two immersions on the tank.

I think I'll need to get it done properly...

[dpmiller]

Nope, 3kW continuous is too much for a 13A plug.

[ProDave]

The fuse, which by it's nature is a bit of resistance wire, will also have got hot and looks to be the culprit.

 

Feed it directly from a 20A double pole switch, not a fused switch unit or you will just be moving the next failure to the FCU.

[Crofter]

2 hours ago, ProDave said:

The fuse, which by it's nature is a bit of resistance wire, will also have got hot and looks to be the culprit.

 

Feed it directly from a 20A double pole switch, not a fused switch unit or you will just be moving the next failure to the FCU.

Ideally I'd be setting it up with a WiFi enabled timer, so that it could run on the E7 off peak rate, and we could turn it back or off when we're away. Not sure how to go about this though.

[NailBiter]

24 minutes ago, Crofter said:

Ideally I'd be setting it up with a WiFi enabled timer, so that it could run on the E7 off peak rate, and we could turn it back or off when we're away. Not sure how to go about this though.

 

You need a Wi-Fi (or Bluetooth / Thread / Zigbee / Zwave) relay / contactor capable of handling the load you are putting through it.

Something like:

https://shellystore.co.uk/product/shelly-plus-1/ (but only rated up to 16A so be careful)

 

or

https://itead.cc/product/sonoff-pow-elite-smart-power-meter-switch/ (one of them is rated up to 20A)

Personally I'd flash ESPHome on whichever device I chose (super easy to do) so I knew they were secure.

You can also program the timer at the device level so even if Home Assistant / ESPhome is down the timer will still run fine locally on the device. There are various ways to make this nicer to use e.g. using the screen to display auto / manual mode, next timer run and current time 

Edited May 4 by NailBiter

[Mattg4321]

I’d use one of those wifi devices if you want another potential fire. 
 

If you really want to use one, then get it wired in via a contactor. 

[Nickfromwales]

Contactor all day long matey. The plug is rated 10a continuous…… you dodged a bullet there 🙁

[JohnMo]

4 hours ago, Crofter said:

Ideally I'd be setting it up with a WiFi enabled timer

Maybe a Shelly relay as linked above, but use that to switch a suitably rated relay. Set up a schedule and have a manual override switch. The shelly is then just doing the low energy side of things.

[Crofter]

1 hour ago, Nickfromwales said:

Contactor all day long matey. The plug is rated 10a continuous…… you dodged a bullet there 🙁

Funny, it says 13A on it... which it obviously couldn't handle!

[FuerteStu]

People just assume they can plug anything into a socket and it be OK because 'if there's a problem the fuse will blow'. 

 

 

Nope. 

 

Manufacturers instructions will always tell you how things should be connected and there are good reasons for it. 

 

Even the correct contactors need to be selected to allow for suitable loads. 

 

 

Edited May 4 by FuerteStu
Typo

[Nickfromwales]

23 hours ago, Crofter said:

Funny, it says 13A on it... which it obviously couldn't handle!

13a peak, 10a constant. Resistive heating can suck full power for sustained periods, and everything warms up really quickly. 
Fuses will run ‘molten’ where the metal is borderline melting point, and the heat then spreads and it goes terminal.

 

Use a timer to fire a pair of contactors, and make sure the 2 immersions are fed independently, and things will be less ‘toasted’ looking   

Edited May 5 by Nickfromwales
I can’t spell contactor

[NailBiter]

8 hours ago, Mattg4321 said:

I’d use one of those wifi devices if you want another potential fire. 
 

If you really want to use one, then get it wired in via a contactor. 

The Sonoff device is likely already using a contactor as it's rated up to 20A. I can't find any explicit documentation though.

Teardown (20A version): https://youtu.be/O1HvycrP4s4?t=457

You can also get big monsters like this (switches up to 5500W): https://tech.scargill.net/sonoff-powr3-powerful-controller/

 

Edited May 4 by NailBiter

[Crofter]

Of course I could swap out the 3kw immersion element for a smaller one, it's got all night to heat a 200l tank so probably doesn't need to be that big?

[JohnMo]

If you are still thinking solar, why not pre prepare for that with a PV diverter that does two immersion heaters, with a timer and WiFi if you need it. It doesn't care if you actually have PV or not, its just a CT clamp doing the the reverse detection.

[Crofter]

5 hours ago, JohnMo said:

If you are still thinking solar, why not pre prepare for that with a PV diverter that does two immersion heaters, with a timer and WiFi if you need it. It doesn't care if you actually have PV or not, its just a CT clamp doing the the reverse detection.

That's an interesting idea, not really sure where to start though.

[JohnMo]

The shelly is just a wifi relay with manual switch input as well. You can use the shelly app to set timers to open and close the relay contact. Use the output of the shelly to control a second relays  open and closing solenoid - choose a relay that can happily take 13A continuous load, it can be a dumb relay. You can just use a light switch to do the manual override.

[Nickfromwales]

2 hours ago, JohnMo said:

The shelly is just a wifi relay with manual switch input as well. You can use the shelly app to set timers to open and close the relay contact. Use the output of the shelly to control a second relays  open and closing solenoid - choose a relay that can happily take 13A continuous load, it can be a dumb relay. You can just use a light switch to do the manual override.

I’d say you should look for min 16a or a comfortable 20a continuous load device, 13a is still cutting it a bit fine imho. Shelly’s can do this and seem well suited to this application. It’ll need a separate 16a or 20a supply for each ‘channel’ / immersion, so don’t take both feeds off one breaker (so you’ll need 2 positions in the CU to do this properly too). 

[Mattg4321]

A contactor and a relay are basically the same thing, but a contactor is generally more heavy duty.

 

I wouldn't be trusting those shelly or sonoff devices to consistently handle 13 amps, regardless of what it says on the box. You can see from the video that the relay is pretty puny. A decent DIN rail mounted contactor is peanuts and will reliably operate a 13 amp load for years, probably decades, and take the heavy lifting away from the IoT device.

[Nickfromwales]

2 hours ago, Mattg4321 said:

A decent DIN rail mounted contactor is peanuts and will reliably operate a 13 amp load for years, probably decades, and take the heavy lifting away from the IoT device.

Yup, what he said 👆

[NailBiter]

Yeah that sounds like a much better idea thinking about it thanks guys. Also decouples the smart bit (more likely to fail or need upgrade but also cheap if only being used to switch a contactor) from the more expensive and longer lasting contactor. 

[Crofter]

Funny thing is, the whole place recently went through a new EIC and the immersion setup was never mentioned.