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I've had my shower fitted for about 3 years and just yesterday it went bang and stopped working. (My wife was using it and says there was a blue flame!)

When I checked inside the unit I saw that the neutral wire was burned out along with the adjoining section of the connector block. The wire had become so hot it had actually melted into the casing.

I'd like to know why this might have happened, after it had been running fine for so long. How dangerous was it- could I have been given a shock if I'd been touching the casing when it blew up? Also I'd like to know whether repairing it is a job it is safe for me to undertake myself or do I need a qualified electrician.

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    If you're asking this question, I'd be happier if you found an electrician... but you can start by defining "burned out". A photo of the damage, as you found it, would be tremendously useful. This sounds like a bad connection, but... (This would be the reason Americans find the concept of an "electric shower" so weird.) – keshlam Sep 7 '14 at 22:55
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    Current causes heat, heat causes expansion. Over time, the heating and cooling cycle can cause connections to loosen. This is especially true for higher drawing appliances, such as heaters and stoves. The documentation for some such appliances, suggest inspecting and tightening connections from time to time. If the connection wasn't properly tight to begin with, this problem can lead to catastrophic failure (as you've seen). I'm guessing the wire heated to the point that it broke, then ended up coming into contact with the "hot" terminal. Which caused the spark. – Tester101 Sep 7 '14 at 23:07
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    Of the breaker/fuse didn't do its job, it could have been much worse. – Tester101 Sep 7 '14 at 23:08
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Rip that thing out of the shower. You do not want mains power in a shower even on a good day.

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    How else can an electric shower work? – Urbycoz Sep 8 '14 at 6:50
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    These seem to be fairly common in the UK; can't vouch for anywhere else in Europe. I've presumed it's some sort of retrofit for old houses that originally had cold-water-only showers or that Yes, it surprised me too, but "if it happens, it must be possible." – keshlam Sep 8 '14 at 12:50
  • Had a missionary friend nearly die of one of these in Peru. He found it's quite common for something to come unstuck and let you be the ground conductor there. He became an advocate of cold showers unless there was a central water heater. – Fiasco Labs Sep 8 '14 at 14:12
  • I reset my case despite the fact that someone saw fit to down vote my answer. – Michael Karas Sep 9 '14 at 3:55
  • @MichaelKaras Really? Your solution for "why did the wire blow in my electric shower" is "don't have an electric shower"? Seriously though, I'd guess nowadays electric showers outnumber standard showers at least 5 to 1 in the UK. I can't actually think of anyone I know who doesn't have one. They're not the death-traps you imagine. – Urbycoz Sep 9 '14 at 19:23
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yes, it can burn after long time. I do not see your setup, but I guess (and hope) that your connection block is in a sealed box, this sealant is aging and water can end up going in.

it could have been dangerous (fire hazard) if there were some flammable material around it. You could have got an electric shock while touching it when it happened but most likely you would have got a burn.

repairing should be safe (given that you put it off the grid while doing it), but take care of the wire gauge you are using and most importantly, investigate to understand what happened, if you just repair without knowing the cause, you might simply have it burn again later as you did not fix the real issue. and that time, you might be not so lucky.

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    Thank you. Sounds good advice. Yes it is all in a sealed box, and I can't see any moisture inside. Any advice on diagnosing the cause? I'm guessing it's a loose connection, but it's tricky to say which one now that it's all burned out and melted. – Urbycoz Sep 8 '14 at 10:34
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    well, seeing only the burnt connection box, that is hard to help further as it can be virtually anything. The loose connection is a good explanation, I have no idea what you call an electric shower (in my country, they work with water :) ) maybe a malfunction as well generated an extreme current leading to heat generation at the weakest point of the circuit... all that is just guess work, if you really can not pinpoint the cause, seek for professional advice. – Memes Sep 8 '14 at 12:40
  • That's my own guess. Setscrews worked loose or weren't tightened properly in the first place, loose connection caused resistance/sparking/heat and made things worse, eventually heat got bad enough to melt the plastic and let the wire really disconnect which caused the big arc, blue flash, and "loss of magic smoke". – keshlam Sep 8 '14 at 12:52
  • the comment from Tester101 below your question is also a good explanation (the heat cycles) – Memes Sep 8 '14 at 12:54
  • Hadn't realised "Electric Showers" weren't a universal concept. Here's a little diagram I found, if you're interested. (Obviously they've got a case over the front when they're actually active.) – Urbycoz Sep 8 '14 at 12:59
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A Loose connection at the neutral pole/junction is many times the first suspect.

Unfortunately you will not notice this until the circuit breaker trips due to overheating because of the loose connections (or overrated amps flowing through it).

And its a definite fire hazard in waiting. Consider yourself lucky if the Circuit breaker trips. Don't reset it immediately, just give a thought before as to why it happened (or call a qualified electrician). If it keeps tripping, something is really wrong.

As a rule of thumb, if you have appliances using heavy amps (ACs, Induction Stoves, Ovens...you know what i am saying), its a good investment to periodically open your Main Switch Box and check for any signs of burns/chars at the circuit breaker joints. A visual inspection sometimes reveals any potential damage.
Avoid using heavy appliances all at once (unless you have a properly distributed electrical (2/3) phase connection. This is another reason why the circuit breaker would trip with a potential to cause fire.

Better safe than to be sorry.

There are many here who have answered to the point (tester101 gave a quick short and perfect explanation)

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neutral cable is the return path for current, so when the heater is switched on it draws a lot of current and flows through the coil then to the neutral cable is the size of the cable is small definitely the cable will got burned

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  • I seriously doubt this is a case of the neutral wire being undersized (that's a rather major factory defect if it were to be the case) – ThreePhaseEel Dec 14 '17 at 12:37

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