Shock from switch due to dampness

[LastManOnline]

Does it happen?.Is it even possible.?.I ask the question because I have never experienced the issue professionally and have become increasingly convinced that with a standard plastic switch it is not even possible.The traditional reasoning behind mounting a light switch outside a bathroom is due to the perception that a credible risk of shock due to dampness/condense exists if it is mounted inside.However I have repeatedly tested the resistance between the live terminal of a switch and the outside of the switch (where a finger would be positioned) while submersing the switch in water and not got a resistance lower than 20,000 ohms.

 

[littlespark]

Not to the same extent, but by your reckoning, you wouldn’t need weatherproof switches for outside?

Water creates rust, along with any other impurities can get into the switch and create a path between parts that should be separate.

A lot of times an electric shock is more “shock” than electricity felt by the user. The big bang, a flash of a spark as the current finds the shortest route through moisture.

 

[loz2754]

As a low reading ohm meter test would be insufficient to conduct this test, I presume you used an insulation resistance tester?

 

[pc1966]

Was that pure water, or one with anything ionic dissolved in it (like salt, etc)? Makes a big difference to conductivity!

The other issue with doing a quick test on a given switch is it will not prove that all makes or models of switch are going to be the same. That is what the standards and/or manufacturer's specifications cover.

Personally I think switches should be inside the bathroom to stop a-holes messing about when someone is in there, but suited to the location (i.e. how close to any likely source of water, if rated for high humidity operations, etc).

 

[LastManOnline]

As a low reading ohm meter test would be insufficient to conduct this test, I presume you used an insulation resistance tester?

Yes.Used 500 volts

 

[LastManOnline]

Water creates rust, along with any other impurities can get into the switch and create a path between parts that should be separate.

This is the point I wanted to address.(prompted by the current thread "Mains electric shock from plastic light switch").Even by creating a direct water path between parts that "should be separate",I still cannot get a resistance lower than 20,000 ohms.And I am erring on the conservative side.I,m not wanting to make an argument here for using plastic switches in bathroom or anywhere else.Its more to be able to electrically analyse potential faults more accurately and to be able to confidently rule out whether dampness is an issue or not.The post I quoted above is from a gentleman who's light switch is not in a bathroom

 

[LastManOnline]

Was that pure water, or one with anything ionic dissolved in it (like salt, etc)? Makes a big difference to conductivity!

Used tap water.I would imagine moisture damp would probably be purer again and have a higher resistance

The other issue with doing a quick test on a given switch is it will not prove that all makes or models of switch are going to be the same. That is what the standards and/or manufacturer's specifications cover.

Valid point.I am referring only to the standard plastic MK or Click type switch with a centimetre gap from live terminal to outside of switch

Personally I think switches should be inside the bathroom to stop a-holes messing about when someone is in there,

Agreed

but suited to the location (i.e. how close to any likely source of water, if rated for high humidity operations, etc).

Agreed.

As an aside I was recently in a holiday home in the north of Sweden.3 mts x 2 Mts.It had a light switch 30 cms from shower.A socket 60 cms from shower.Two other double sockets and the house distribution board all included in the room

 

[brianmoooore]

Does anywhere else in the world have this nonsense attitude regarding switches in bathrooms?

 

[DPG]

Does anywhere else in the world have this nonsense attitude regarding switches in bathrooms?

I don't think it's wise to use some of the other foreign electrical systems as a reference - if you start doing that we'd have all sorts of dodgy ideas.

Not saying they're all bad obviously, but there are some distinctly poor practices around

 

[Lucien Nunes]

Was that pure water, or one with anything ionic dissolved in it (like salt, etc)? Makes a big difference to conductivity!

Used tap water.I would imagine moisture damp would probably be purer again and have a higher resistance

The switch suspected of causing a shock through dampness in the recent thread, had been connected to an energised circuit and is suspected to have been leaking between contacts before the shock (evidenced by the light flashing). If liquid within the switch was passing the leakage current for a time, a significant concentration of ions could have dissolved into it through electroysis of the live metal components. A smear of this liquid escaping over the surface might have created a much more highly conductive path than submersion in clean water, where any solutes would be much more dilute.

 

[LastManOnline]

The switch suspected of causing a shock through dampness in the recent thread, had been connected to an energised circuit and is suspected to have been leaking between contacts before the shock (evidenced by the light flashing). If liquid within the switch was passing the leakage current for a time, a significant concentration of ions could have dissolved into it through electroysis of the live metal components. A smear of this liquid escaping over the surface might have created a much more highly conductive path than submersion in clean water, where any solutes would be much more dilute.

 

[LastManOnline]

The switch suspected of causing a shock through dampness in the recent thread,

According to the OP from post 26

"There was no sign of moisture inside the switch found by me or the electrician"

"I have never seen any other signs of damp or water leaks "

had been connected to an energised circuit and is suspected to have been leaking between contacts before the shock (evidenced by the light flashing). If liquid within the switch was passing the leakage current for a time, a significant concentration of ions could have dissolved into it through electroysis of the live metal components. A smear of this liquid escaping over the surface might have created a much more highly conductive path than submersion in clean water, where any solutes would be much more dilute.

Agree with all the above.But until evidence for moisture been present is established it remains speculation.I think checking his earthing remains the most practical next step.

 

[happysteve]

Apologies for digging up a 9 month old thread, but was going to post about a fault-finding job I did today where I can confirm that it is possible to get a shock off the plastic bit of a plastic switch, and this seemed as good a place as any to put it.

Client reported getting a shock off the switch after cleaning it (getting rid of mould nearby), and also that the landing light (LED GLS) was glowing dimly when off (normal brightness when on). House is COLD - really cold, can see your breath cold - elderly resident cannot afford to put the heating on (and no heating in the 3 foot square hallway anyway). Switch is 2G in hall: 2-way for landing, and 1-way for hall lights. No L link wire between hall and landing switches - on the face of it, separate. 2x lighting circuits, neither RCD-protected. Client had turned off both lighting circuits at the DB.

Checked:

• Zs@DB fine (0.20Ω), TN-C-S, incoming polarity good
• Bonding good
• R2 to switch back box/lugs: 0.10Ω (to MET)
• Confirmed polarity on switches
• Confirmed earth continuity to upstairs switch (for and on the landing).
• No cpc at landing light, pendant set, loft boarded above.
• IR (L+N) to E for upstairs and downstairs circuits in parallel 1.06MΩ but a little variable
• IR upstairs N to downstairs N 3.39MΩ

However:
- Continuity upstairs L to downstairs L ~33kΩ

~scratches head~

So upstairs and downstairs lighting circuits are linked "somehow" possibly via a lamp...? Resolve to put both up and down L on one MCB (2 circuits to 1). Having confirmed earthing, polarity, IR, and joined two circuits together (which were "somehow" linked) I restored power to the circuit(s).... and got a shock off the plastic bit of the switch.

• Voltage MET to pattress screws: <10V
• Voltage MET to the plastic bit of the switch: ~ 34V
• landing light glowing dimly

Ah! So downstairs permanent L is tracking across the 2G switch to the upstairs switched L. Gotcha.

Power off, chuck the 2G switch in the bin. New 2G plastic switch...:

• IR upstairs L to downstairs L: now >10MΩ
• Back to 2 separate circuits
• No more tingly tingly, landing light now turns properly off.

So yes, shock off a plastic switch is apparently a thing. Marvellous.

 

[DPG]

Apologies for digging up a 9 month old thread, but was going to post about a fault-finding job I did today where I can confirm that it is possible to get a shock off the plastic bit of a plastic switch, and this seemed as good a place as any to put it.

Client reported getting a shock off the switch after cleaning it (getting rid of mould nearby), and also that the landing light (LED GLS) was glowing dimly when off (normal brightness when on). House is COLD - really cold, can see your breath cold - elderly resident cannot afford to put the heating on (and no heating in the 3 foot square hallway anyway). Switch is 2G in hall: 2-way for landing, and 1-way for hall lights. No L link wire between hall and landing switches - on the face of it, separate. 2x lighting circuits, neither RCD-protected. Client had turned off both lighting circuits at the DB.

Checked:

• Zs@DB fine (0.20Ω), TN-C-S, incoming polarity good
• Bonding good
• R2 to switch back box/lugs: 0.10Ω (to MET)
• Confirmed polarity on switches
• Confirmed earth continuity to upstairs switch (for and on the landing).
• No cpc at landing light, pendant set, loft boarded above.
• IR (L+N) to E for upstairs and downstairs circuits in parallel 1.06MΩ but a little variable
• IR upstairs N to downstairs N 3.39MΩ

However:
- Continuity upstairs L to downstairs L ~33kΩ

~scratches head~

So upstairs and downstairs lighting circuits are linked "somehow" possibly via a lamp...? Resolve to put both up and down L on one MCB (2 circuits to 1). Having confirmed earthing, polarity, IR, and joined two circuits together (which were "somehow" linked) I restored power to the circuit(s).... and got a shock off the plastic bit of the switch.

• Voltage MET to pattress screws: <10V
• Voltage MET to the plastic bit of the switch: ~ 34V
• landing light glowing dimly

Ah! So downstairs permanent L is tracking across the 2G switch to the upstairs switched L. Gotcha.

Power off, chuck the 2G switch in the bin. New 2G plastic switch...:

• IR upstairs L to downstairs L: now >10MΩ
• Back to 2 separate circuits
• No more tingly tingly, landing light now turns properly off.

So yes, shock off a plastic switch is apparently a thing. Marvellous.

What brand was the switch, and how old was it?

 

[happysteve]

What brand was the switch, and how old was it?

Crabtree. "Made in England". BS 3676. 5AX 2352. 250V AC ONLY.

Old. But not ancient.






Edit: State of my hands! Mucky pup. Need a bath!

 

[brianmoooore]

That's a Crabtree 2172, and the 2000 series were known to be susceptible to 'shocking' in a damp atmosphere. Crabtree virtually admitted to this when they emphasised the improved resistance to water entry in the publicity blurb, when the 4000 series was introduced.

 

[happysteve]

That's a Crabtree 2172, and the 2000 series were known to be susceptible to 'shocking' in a damp atmosphere. Crabtree virtually admitted to this when they emphasised the improved resistance to water entry in the publicity blurb, when the 4000 series was introduced.

Fantastic! Thanks for the information, that's superb!

It's all coming out now....

 

[LastManOnline]

That's a Crabtree 2172, and the 2000 series were known to be susceptible to 'shocking' in a damp atmosphere. Crabtree virtually admitted to this when they emphasised the improved resistance to water entry in the publicity blurb, when the 4000 series was introduced.

Very interesting.I would add that ,since plastic is technically a non-conductor of electricity, would it be more correct to describe these Crabtree makes as "non-plastic"? They must have contained a component or additive that allowed for conduction.

 

[DPG]

Very interesting.I would add that ,since plastic is technically a non-conductor of electricity, would it be more correct to describe these Crabtree makes as "non-plastic"? They must have contained a component or additive that allowed for conduction.

Could be poor quality or contaminated plastic maybe. I've seen that happen in a production environment where the plastic body of a batch of mains inlet sockets failed, although admittedly that was during 3kv flash tests.

 

[brianmoooore]

Water isn't technically a conductor either, but we all know that in most cases it is and this was the problem with 2000 series switches. There was a small and fairly short route between the plastic of the switch body and the plastic of the rocker, all the way into the live contacts. This drew water in by capillary action, causing the rocker to bite whoever touched it. Once dried out, they were fine again.
The promotional stuff when the 4000 series was introduced, referred to 'increased labyrinth design' or something like that, around the rocker.