My contact in the social housing provider's maintenance team has reported back that there is indeed a sizeable number of shower pullcord switches with thermal damage with a disproportionate number where the neutral is burned back. He tells me that often bubbling is evident on the surface face of the pullcord.

I am sure that if someone in IET wanted to establish more precise facts, he would be willing to engage.

I have replaced a few of these in my own home (around one every couple of years), such is the paranoia I actually keep a new one in stock in my garage. When I change them the cores are not found loose. When the new one goes in I take time in manipulating the cores in the box for the least stress, push the switch into the box then lower it just enough to get a screwdriver on to recheck the terminal screw tightness. I have taken old switches apart and generally the switch contact faces are blackened, mostly on the neutral.

Interestingly if you consider the operation of the shower; current breaking at the ceiling switch should not be a problem because everyone turns the shower off at the shower then at the ceiling switch. Logically at the time the ceiling switch is operated you are only switching off the neon lamp within the shower that indicates the power is on.

Not sure if anyone else has taken an old shower apart for fun, sadly I have. When you switch it on a solenoid valve operates which admits the water to the heater and this has a pressure switch on it that switches the heater elements in. This is done for safety so that the heaters cannot be on unless the water flow will be adequate to prevent overheating.

From memory inside the shower unit only the live is switched on the heater and solenoid valve and the wiring in there is not particularly large, certainly smaller than the 10mm^2 supply cable. I am wondering if there is something else going on, perhaps due to the inductance/capacitance of the heater elements, is the damage to the neutral contacts occurring when the switch is opened?

I have replaced a few of these in my own home (around one every couple of years), such is the paranoia I actually keep a new one in stock in my garage. When I change them the cores are not found loose. When the new one goes in I take time in manipulating the cores in the box for the least stress, push the switch into the box then lower it just enough to get a screwdriver on to recheck the terminal screw tightness. I have taken old switches apart and generally the switch contact faces are blackened, mostly on the neutral.

Interestingly if you consider the operation of the shower; current breaking at the ceiling switch should not be a problem because everyone turns the shower off at the shower then at the ceiling switch. Logically at the time the ceiling switch is operated you are only switching off the neon lamp within the shower that indicates the power is on.

Not sure if anyone else has taken an old shower apart for fun, sadly I have. When you switch it on a solenoid valve operates which admits the water to the heater and this has a pressure switch on it that switches the heater elements in. This is done for safety so that the heaters cannot be on unless the water flow will be adequate to prevent overheating.

From memory inside the shower unit only the live is switched on the heater and solenoid valve and the wiring in there is not particularly large, certainly smaller than the 10mm^2 supply cable. I am wondering if there is something else going on, perhaps due to the inductance/capacitance of the heater elements, is the damage to the neutral contacts occurring when the switch is opened?