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Has anyone had this experience or could offer advice please? I have a 9.5Kw shower, it is fed from the DB in 10mm T&E, a run of approximately 4mtrs to a pull switch then around 3mtrs to the shower. It is protected by a 40amp MCB (I know its close but has never tripped) on the RCD side of a split load board. The shower, a "Triton Enrich" is about 4 1/2 years old.

About six months ago I was called because the pull switch had burned out and stopped working. On investigation I found the nuetral on the switched side was charred and welded into the switch. I pulled some spare cable and reterminated into a new switch (rating of pull switch 50amps). I did a full test of the circuit and everything was fine, I put the fault down to a loose connection in the pull switch.

I was called again yesterday to the exact same fault. I have tested everything and even been through the loft space doing a visual inspection as I thought maybe a compression fault or water ingress but evrything is fine.
All test results are perfect, IR/ELI,continuity.

The only thing I can think of is to condemn the shower unit but I have stripped it down, checked every connection for tightness, checked insulation resistance across P/E and N/E and continuity/resistance of element. There is no sign of arcing or water ingress, in fact it looks like brand new! I dont want them forking out for a new shower and being called back again in 6 months and personally I would like to know the cause.

Anybody have any ideas?
 
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James

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Was it a good brand of switch?
Is it being turned on and off under load?

I would not condem a customers equipment unless I had tested it and found a fault with it.

Could the termination of the cable have been loosened by pushing it in to a tight space and flexing the cable on installation?
 

darkwood

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It is a common issue and regardless of switches tbh but cheaper one will promote the effect, the issue is the cable can be terminated very tightly but the act of trying to get the cover on to the backbox actually buckles and bends the cables in the process and this exerts high twisting forces onto the terminals you have just made off as you offer the cover up to the backbox, being 10mm it is often very stiff which exaggerates the effect.

Solutions to reduce the risk -

-Use switches/pullcords that have double terminals on each of the connections.
-Form the cables into the final shape they will take, terminate them, offer them up to the box several times to ensure you have reduced the resistance, then before you do the final offer up to secure the cover you tighten the terminal again.
-Where possible when 10mm is used try to find a wall switch option instead of a pull cord as you can double the size of the back box reducing this risk.

All cables on all terminations like switches and sockets etc should be preformed to their final shape to avoid loosening of the termination on final fixing of the cover, now the smaller the cable the less likely the forces acting on the terminals will loosen the connection but it does happen even on switches.
 
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Thanks Darkwood. I am experienced, been doing it 43 years but am never too old to take on board good advice. I have formed the cables and used an extra deep pattress but even so they are still tight to get back into the box and your suggestion of dual terminal type pull switch is an excellent idea. My concern was that it being the same cable on both occasions, even though I re-dressed them to a different configuration is a bit too much of a coincidence for my liking.
 

telectrix

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use a Crebtree or a Click switch. termination is far better and no struggling to bend 10mm into a box. and educate the customer that it's an isolator, not an on/off switch:
 

darkwood

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Thanks Darkwood. I am experienced, been doing it 43 years but am never too old to take on board good advice. I have formed the cables and used an extra deep pattress but even so they are still tight to get back into the box and your suggestion of dual terminal type pull switch is an excellent idea. My concern was that it being the same cable on both occasions, even though I re-dressed them to a different configuration is a bit too much of a coincidence for my liking.
No intention of teaching you to suck eggs, just a generic reply to cover the issue, to note though, when the cable welded in it will have been glowing hot, this changes the characteristics of the cable where the overtemp' occured, this can impact on future retermination so be careful you have stripped back enough to remove all the affected cable, it might not be visually obvious but often a clear indicator is you want the shiny copper back that bends and flexes like it should do, overtemp' copper can cause it to become brittle and is noticeable to anyone with experience that it doesn't move the same... I have replaced copper busbar in the past for the same reason and you can literally bend it with ease where the bar got too hot when in reflection a new busbar needs a vice and a hammer to form it.
 

darkwood

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only one i ever come across was one that i had installed 15 years previously. that had not suffered burn up, but just stopped working.
I take it the guarantee had run out then?
 

Pete999

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With such a short distance of cable, think outside the box. Use a contactor and standard switch for the contactor coil.
The switch is there for isolation purposes, a contactor is in my opinion nonsensical, as automatic control shouldn't be used for isolation purposes.
Post automatically merged:

With such a short distance of cable, think outside the box. Use a contactor and standard switch for the contactor coil.
To elaborate, just goes to show some of the gulfs between, Engineering and Electrical safety issues, over engineering can be dangerous.
 
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telectrix

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I take it the guarantee had run out then?
as it was my best mate, he paid by paying for lunch - 16oz. steak and chips with a couple of pints.
 
The switch is there for isolation purposes, a contactor is in my opinion nonsensical, as automatic control shouldn't be used for isolation purposes.
Post automatically merged:


To elaborate, just goes to show some of the gulfs between, Engineering and Electrical safety issues, over engineering can be dangerous.
Pete think you find that contactors with BS EN 60947 markings can be used for 'Isolation', it's in the Regs!
 

Pete999

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Pete think you find that contactors with BS EN 60947 markings can be used for 'Isolation', it's in the Regs!
I suppose, I should have explained my thoughts a bit more clearly, it's not the contactor it's the control circuit controlling the coil I was referring to, being as it's operation is not controlled, I suppose the sane could be said regarding Pull cord and wall isolator, neither which is lockable.
An argument which will continue no doubt.\. but thanks for your input.
 

pc1966

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A contactor seems overkill here, trying one of the Crabtree switches suggested above would be the obvious place to start!
 

Pete999

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I suppose, I should have explained my thoughts a bit more clearly, it's not the contactor it's the control circuit controlling the coil I was referring to, being as it's operation is not controlled, I suppose the sane could be said regarding Pull cord and wall isolator, neither which is lockable.
An argument which will continue no doubt.\. but thanks for your input.
Although not a reply to my own re[ly, some xrea info for discussion:
Each device -for switching OFF for mechanical maintenance MUST
a) Where practicable be inserted in the main supply
circuit.
b) be capable of switching full load current
c) be manually operated
d) have either an externally visible contact gap, or a clearly and reliably indicated OFF position. An indicator lamp should not be relied upon.
e) be designed and/or so as to prevent inadvertent or unintentional switching on.
f) be installed and durably marked so as to be readily identifiable and convenient for use

In my opinion a contactors to a), b),
Contactors are lacking sadly in c),e),d)
and f), e) especially so.
Discuss!
 
Although not a reply to my own re[ly, some xrea info for discussion:
Each device -for switching OFF for mechanical maintenance MUST
a) Where practicable be inserted in the main supply
circuit.
b) be capable of switching full load current
c) be manually operated
d) have either an externally visible contact gap, or a clearly and reliably indicated OFF position. An indicator lamp should not be relied upon.
e) be designed and/or so as to prevent inadvertent or unintentional switching on.
f) be installed and durably marked so as to be readily identifiable and convenient for use

In my opinion a contactors to a), b),
Contactors are lacking sadly in c),e),d)
and f), e) especially so.
Discuss!
My understanding is that 'switching off for mechanical maintenance' only covers a task when contact with live parts is not possible.

Re-lamping a fitting (even know most will re-lamp with the power still on!)

Changing out a ballast or gear tray, then a full 'isolation' is then required.

Also from above, as all control circuits should be protected by an OCPD, then this is where the isolation for the contactor can be physically locked out, as can the OCPDs feeding the contactor. The controlling switch certainly will not be capable of being LOTO.
 

Pete999

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My understanding is that 'switching off for mechanical maintenance' only covers a task when contact with live parts is not possible.

Re-lamping a fitting (even know most will re-lamp with the power still on!)

Changing out a ballast or gear tray, then a full 'isolation' is then required.

Also from above, as all control circuits should be protected by an OCPD, then this is where the isolation for the contactor can be physically locked out, as can the OCPDs feeding the contactor. The controlling switch certainly will not be capable of being LOTO.
My understanding is that 'switching off for mechanical maintenance' only covers a task when contact with live parts is not possible.

Re-lamping a fitting (even know most will re-lamp with the power still on!)

Changing out a ballast or gear tray, then a full 'isolation' is then required.

Also from above, as all control circuits should be protected by an OCPD, then this is where the isolation for the contactor can be physically locked out, as can the OCPDs feeding the contactor. The controlling switch certainly will not be capable of being LOTO.
Are you using the contactor to switch ON load? can't see the contacts lasting very long in that scenario, same as using the pull cord or wall switch to do the same job. If you lock the control circuit Off what's to stop the operating via a fault in the control circuit?
 

James

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personally I don't like the idea of using a contactor as a means of isolation.

most switches are spring close and positive break contacts. (good)

most contactors are positive make and spring break (not good)

if you are using a physical switch you can be sure that the only place it can be changed from off to on is at the switch itself (good)

if you are using a contactor then unless you can see the entire control circuit, it could be operated from somewhere else as well. (not good)

JUST A PERSONAL OPINION, not quoting regs etc. at you
 
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