Grade of wire for immersion to electronic timer

Damien360

Caught this little mess this evening in my home. Immersion and tank about 12 months old. I had the thermal cutout on the top of the immersion cut out three times last year but last event was 6 months ago. Live wire plastic shielding had melted back and the core of the.wire contacted the plastic of the timer. I got a TCP smell (burning plastic) but it didn't trip the RCB. It's thin core but not solid. Left hand side is immersion in and right side is electrical in off a fused spur. That didn't trip either. Neutral to ground measured at about 2V. That seems high to me but you guys may know better.

My question. Do I need a solid core wire and what gauge to wire from immersion to that switch. Getting a electrician in anyway to check if wiring is ok.

10-10-20

Fed off a fused spur? Fused at what, 13A?

Damien360

https://www.boards.ie/discussion/comment/121587274#Comment_121587274

Yes. Fused at 13A

10-10-20

Your incoming and feed to the element are both burnt at the clock and that says to me that they are likely to be undersized. What rating is the element, 2kW or 2.87kW? Only the former would be acceptable to be run off a 13A spur, but it should be on its own circuit rather than a spur.

Damien360

https://www.boards.ie/discussion/comment/121588850#Comment_121588850

Not 100% sure which size element is in it. I suspected the cable gauge wasn't good enough when I saw the burns. Thanks very much for your post. I'm getting a good electrician we dealt with in the past to have a look in the next few days. Plumber put it in when the last cylinder gave up after 20 years.

2011

Most immersions are 3kW (so it will draw around 13 amps). I am not familiar with the timer in the photo, but I would guess that it is not rated to switch a load as large as this. I suspect that it is designed for switching a boiler which is a far smaller load (<3 amps). If the timer was overloaded the issue may have started at that point. If you can see the make and model a quick google will tell you what it is rated for.

Typically an immersion will be fed from the distribution board with a 2.5 mm sq. cable. From the immersion switch to the element a 1.5 mm sq. heat resistant cable is generally used. It is best to have the immersion switch and timer located outside of the hot press.

10-10-20

https://www.boards.ie/discussion/comment/121590428#Comment_121590428

Looks like it's the LAP timer from B&Q/Screwfix:

https://www.screwfix.ie/p/lap-digital-immersion-timer/1804r#product_additional_details_container

Rated at 16A/240V.

I'm still thinking that the wire could have been over-tightened or over-flexed at the screw-terminals causing the strands to fail as it's multicore stranded.

DublinDilbert

I would always use 2.5sq in and 2.5sq out, solid or stranded. I would always bend the solid cable over so the connector is grabbing the conductor doubled over.

I have the same timer here myself for the last year or so, i just checked my own one there. Your cables look to be only 1.5sq, which although not great you shouldn't see burning to that extent.

Serious amount of heat there, especially on the RSH, I suspect that the terminal/termination on the cable wasn't great. Is there any chance that the screw terminal was grabbing onto the insulation and the wire might just have been touching the inside of the connector?

Looking at the image the heat was going from right to left, worst burning is on the far RHS.

Damien360

Update. Electrician came and said the wire was way too small for the load. He has replaced the wires with much thicker wiring and the controller with a EPH immersion controller. Thanks for your help here.

Bruthal.

Interesting how it only roasted at the terminals of the timer.

Damien360

https://www.boards.ie/discussion/comment/121620313#Comment_121620313

That might have been luck. I happened to be upstairs and chased the strange smell. Probably just happened.

10-10-20

https://www.boards.ie/discussion/comment/121620313#Comment_121620313

It think it was the clamps, they weakened the undersized wire and the remaining copper just acted like a resistor.