Burnt out 6mm on 8.5kw shower

[JohnS888]

Hi all

Just checked job and 6mm live supply is burnt out on 8.5kw shower. Run is 4 metres clipped direct with no insulation my calcs are that this should be perfectly fine. Was also on a 40 amp wylex push type mcb. Terminations seemed fine. Has anyone got any possibilities what may be causing this? I was also getting 115v across disconnected live feed and load neutral. My understanding is that this can be normal but can someone clear up the theory behind this. Thanks

 

[James]

any pictures??

 

[JohnS888]

any pictures??

No sorry James didn't take any

 

[radiohead]

Are you saying the entire cable has burnt out or just at a termination?
It's very common for shower/switch terminations to burn out due to poor connections.

 

[Lucien Nunes]

115V measured with what? What exactly was disconnected and where?

As above, normally the damage is caused by heat conducted from high-resistance terminations or contacts. Was there any damage to the cable that was more than a foot away from the ends?

 

[JohnS888]

Are you saying the entire cable has burnt out or just at a termination?
It's very common for shower/switch terminations to burn out due to poor connections.

It was about an inch up from termination radiohead. Thing that makes me bit more dubious though is that shower has recently gone in to replace a previous faulty one and that customer reported that shower would seems to alter temperature quite extremely even when using same temp setting on dial. I suppose this could perhaps still be down to the loose connections on pull cord if voltage and current being affected by the loose connection
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115V measured with what? What exactly was disconnected and where?

As above, normally the damage is caused by heat conducted from high-resistance terminations or contacts. Was there any damage to the cable that was more than a foot away from the ends?

Hi Lucien

115v was measured between disconnected live supply at pull switch and the still terminated load neutral to shower. The signs of burnout were only about an inch up from termination. As post above though do you think that this loose connection could have been affecting the dramatic changes in water temperature that customer reported

 

[Lucien Nunes]

Yes, absolutely. The terminal was probably arcing causing the voltage to fluctuate at the shower and heating the cable instead of the customer.

Still not sure what was disconnected; was the line cable disconnected at the CU, or disconnected from the switch but still live, or what?

 

[Baddegg]

Yes, absolutely. The terminal was probably arcing causing the voltage to fluctuate at the shower and heating the cable instead of the customer.

Still not sure what was disconnected; was the line cable disconnected at the CU, or disconnected from the switch but still live, or what?

Live at switch I think he means?....? or I hope he does ??

 

[ChrisElectrical88]

If the cable was been overloaded to the point it burnt out the line conductor in the pull switch I would expect to see some kind of thermal damage at all the MCB aswell? Worse case is it’s pulling 37 amps, so should be more than suitable.

 

[JohnS888]

Live at switch I think he means?....? or I hope he does ??

Live at switch I think he means?....? or I hope he does ??

lol I am mate
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Yes, absolutely. The terminal was probably arcing causing the voltage to fluctuate at the shower and heating the cable instead of the customer.

Still not sure what was disconnected; was the line cable disconnected at the CU, or disconnected from the switch but still live, or what?

Thanks for confirmation Lucien. The line just disconnected at switch and tested across this the still connected load neutral
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If the cable was been overloaded to the point it burnt out the line conductor in the pull switch I would expect to see some kind of thermal damage at all the MCB aswell? Worse case is it’s pulling 37 amps, so should be more than suitable.

Thanks Chris that's what my calcs came out with so no concerns about cable size and yes signs of thermal damage at MCB

 

[ChrisElectrical88]

Get a clamp meter on it then, cause it’s... poor connections/products, cheap as anything cable, 4mm cable or not a 8.5kW shower.

 

[JohnS888]

Get a clamp meter on it then, cause it’s... poor connections/products, cheap as anything cable, 4mm cable or not a 8.5kW shower.

That meant to say no thermal signs at MCB ? sorry mate