Shocks from new washing machine. (Un earthed)

[spynage]

Hi.

Did a call out just this morning as customer was getting shocks from Kitchen sink. On arrival I could see the sink was earthed and had good continuity back to the main bond. The client told me that it was when he was using the washing machine underneath that he had the shock when he touched the sink.The machine as I discovered was plugged into a socket spur that had a loose CPC. My question is why would the shock be produced? Does a washing machine produce earth leakage that needs to be discharged during normal use? It was a brand new machine but I didn't PAT test it.

Cheers

 

[pc1966]

Most stuff these days is electronically controlled so it will have an EMC filter that typically puts some current in to the CPC under normal use, but usually of the order of 0.5mA

 

[Darkwood]

As above, dependent on the model and brand some washers now use VSD controlled motors as well as all the electronic gear in displays etc, a reliable earth is a must and it would bring about the question that if this was a new washer then who installed it? If it was some kind of company 'Engineer' from the supplier then they have walked out leaving a dangerous install, if they fitted it themselves then this shows why DIY can be dangerous. I would expect anyone contracted to install any appliance would verify the socket/spur is safe and functional.

 

[Lucien Nunes]

Washing machines and other appliances have had interference suppressors such as delta caps across their inputs since before variable speed drives. They help to minimise the escape of transients from motors, heaters, solenoid valves etc being switched on and off. Also appliances with sheathed heating elements tend to leak even without the suppressor.

 

[spynage]

Thanks for your replies. So it's reasonable to assume that 'shock' was coming from potential energy stored in the washing machine going back to earth via person and sink? What would you call a build up in charge like that? It's not static is it?
I was initially wondering before I arrived wether the sink had a raised potential as it was on a PME supply. But being on the first floor I expect there was no real path to true earth. Would I be correct?

 

[Lucien Nunes]

If the source of the shock current is AC leakage there can't really be a build-up of charge, it is more likely to be a small steady current that is most noticeable as a shock when the person first makes contact with it.

Static is an often-misused word, which correctly refers to electrical energy stored as net or displaced charge on isolated bodies that is not free to flow around a circuit. Often it is used to mean specifically triboelectricity generated by friction between insulators, as this is the way many people encounter it e.g. by walking on a synthetic carpet or driving on dry tyres.

There should not indeed be a path to true earth of relatively low resistance (i.e. an extraneous conductor) that is not bonded to the MET. But if the bonding were absent and an extraneous metallic service were connected to the sink, then your initial suspcion could well have been correct in that there could be a potential between the sink and the MET, although I would rather say that the MET was at elevated potential than the extraneous service, since drop along the CNE conductor would be the likely source of the potential.

 

[spynage]

If the source of the shock current is AC leakage there can't really be a build-up of charge, it is more likely to be a small steady current that is most noticeable as a shock when the person first makes contact with it.

Static is an often-misused word, which correctly refers to electrical energy stored as net or displaced charge on isolated bodies that is not free to flow around a circuit. Often it is used to mean specifically triboelectricity generated by friction between insulators, as this is the way many people encounter it e.g. by walking on a synthetic carpet or driving on dry tyres.

There should not indeed be a path to true earth of relatively low resistance (i.e. an extraneous conductor) that is not bonded to the MET. But if the bonding were absent and an extraneous metallic service were connected to the sink, then your initial suspcion could well have been correct in that there could be a potential between the sink and the MET, although I would rather say that the MET was at elevated potential than the extraneous service, since drop along the CNE conductor would be the likely source of the potential.

Thanks.

Yeah I mean't if the sink was at a raised potential as it WAS bonded to the MET then you still wouldn't receive a shock as a person would be relatively insulated on the first floor of a building from true earth?