Shower Problem

[Russell Moss]

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?

 

[Pete999]

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!

 

[timbobelfast]

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]

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]

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