Problem with grounding??

[snowsuit]

I live in a rented terrace house which was built c.1890 but has been substantially updated.

we've lived here for six months and about a month ago my laptop started to feel strange. i have a macbook with a metal case. the case felt almost magnetic, or sticky. it was mild, but noticeable enough to be annoying. the effect only happens if i have one hand on the casing - if i put the other hand on it goes away. it only happens when the laptop is plugged into the wall, and it happens with more than one outlet. i'm pretty sure this is a new development as, like i said, i find it annoying to the point that i can't use my laptop while it's charging, and i can't imagine not having noticed it for the last 5 months.

i have also noticed the same problem with the edge of my ipod when it's in its dock and the dock is plugged in and the edge of the metal electric kettle when it's on.

so my question is - what's going on here? are these appliances ungrounded and therefore live? if so is it dangerous to use them? is it dangerous to be in the house?

we have documentation that the electrics were checked just before we moved in and no problems were found then - is it normal for grounding problems to appear suddenly like this? or would the electric checks not necessarily show up a grounding problem?

i want to gather as much information as i can before i contact the agent because they are terrible and do nothing unless you pester them. if this isn't really a big deal, i probably won't bother with all the calls and letters it would get to make them sit up and take notice.

thanks in advance for any help!

 

[jj4091]

I'm not sure what you mean by feeling "magnetic or sticky" but if you are getting any sort of tingling sensation when you touch an electric appliance it does tend to indicate some sort of potentially dangerous fault especially if it happens with more than one appliance. It could of course be static electricity discharging from you through the appliance, but this tends to be more of a short sharp shock. This is more likely caused by you building up a charge from nylon carpets or some such thing & discharging it through any earthed appliance, but if it is the former you are well within your rights to demand that your landlord check this out, it would not take long nor be expensive to establish if you have an earthing fault. Alternatively you might call your supplier although I am not sure if they are as concerned about safety as the gas companies.

 

[xr4x4]

Check your water and gas pipe are earthed/bonded with earthing cable, these should be on clamps connected to the pipes where they enter the property.

Edit.

Could be a problem with TT earth, do you have an earth cable running outside to a metal spike in the ground? These will be around the outside wall, normally otherside of fuse box.

 

[Spark123]

What type of power adaptor are you using with the mac? I noticed mine came with two plugs - one which is a mains lead and one which is a clip on plug. Whilst the mains lead is which connects to the PSU is earthed the alternative plug which the PSU can clip to isn't

 

[JBR]

...about a month ago my laptop started to feel strange. i have a macbook with a metal case. the case felt almost magnetic, or sticky. it was mild, but noticeable enough to be annoying. the effect only happens if i have one hand on the casing - if i put the other hand on it goes away. it only happens when the laptop is plugged into the wall, and it happens with more than one outlet.
i have also noticed the same problem with the edge of my ipod when it's in its dock and the dock is plugged in and the edge of the metal electric kettle when it's on.

so my question is - what's going on here? are these appliances ungrounded and therefore live? if so is it dangerous to use them? is it dangerous to be in the house?

I have just found this thread and it describes what seems to be exactly the same phenomenon I experience.

The 'sticky' feeling that the OP describes, and which I might describe as a slight 'vibration', occurs when I gently slide my finger along the metal upright of a standard lamp and also a metal table lamp. Like the OP this ceases when I touch the lamp with my other hand. To clarify, it also stops with the standard lamp when turned off at the foot switch (so the cables within the upright are isolated from the mains), but does not when the table lamp is turned off at the bulb holder (so the cables within are still at mains potential). Neither lamp has an earth connection, so I am assuming they are double-insulated. The standard lamp is brand new from House of Fraser and is not a 'cheap Chinese import'! The phenomenon also occurs on the metal case of a Panasonic DVD player which was provided with a 2-core cable (no earth).

I am wondering whether this could be due to induction, by the electricity in the mains cables, of a potential into the metal upright surrounding the cables (eddy currents?).

I am not an electrician, so I hope that this assumption is not met with derision from any of you more-qualified people here! However, I am intrigued as to what the cause actually is. Also, I hope that you can assure me that there is no danger here. Having looked at other replies, I can confirm that earth bonding is present on water and gas pipes in the house. I can also confirm that the feeling is not a static discharge - I am familiar with that feeling and this is quite different.

 

[bernardgreen]

You are feeling the very small amount of charge that is being capacitively coupled from the Live wires to the casing. While un-loaded this capacitively coupled voltage can be anywhere between 0 and 230 volts but is most often around 120 volts as neutral and live both affect the voltage on the case which tends to the mid point of them.

But because the capacity is very small the amount of current that can pass though it is very small and is ( provided the insulation is intact ) not a hazard.

If the tingle is strong then have the lamp tested for safety as insulation failure does happen.

 

[JBR]

Thank you Bernard. I am particularly grateful because my wife can't feel this and thinks I am making it up. Perhaps I am more sensitive than she is!

Capacitive coupling - is that the same as a current being 'induced' in the casing? As a layman, I am not sure about correct terminology.

How is it that the feeling disappears when I touch the casing with both hands?

 

[martinxxxxxx]

You are feeling the very small amount of charge that is being capacitively coupled from the Live wires to the casing. While un-loaded this capacitively coupled voltage can be anywhere between 0 and 230 volts but is most often around 120 volts as neutral and live both affect the voltage on the case which tends to the mid point of them.

But because the capacity is very small the amount of current that can pass though it is very small and is ( provided the insulation is intact ) not a hazard.

If the tingle is strong then have the lamp tested for safety as insulation failure does happen.

I am preparing myself for another public humiliation - but surely live and neutral don't come anywhere near the laptop if the PSU is functioning correctly?

Is there enough capacitive coupling through a healthy PSU to have this effect, I suppose is what I am asking, as I get a tingling feeling but only when I am in the bath ( )

 

[bernardgreen]

I am preparing myself for another public humiliation - but surely live and neutral don't come anywhere near the laptop if the PSU is functioning correctly?

The stray capacity between live conductors and the ELV ( 18 volt ) supply inside the PSU is adequate to bring the ELV ground towards the mid point of Live and Neutral voltages. Hence the laptop floats at that voltage until there is path for the trace of current to leak away.

 

[bernardgreen]

Capacitive coupling - is that the same as a current being 'induced' in the casing? As a layman, I am not sure about correct terminology.

Not quite. The stray capacity at 50 Hz ( mains frequency ) acts like a very high resistance.

How is it that the feeling disappears when I touch the casing with both hands?

The strength of the tingle depends on current density ( the amoung of current per square mm of skin ). Touching with one finger tip puts all the stray current through a small area while touching with both hands spreads the current over a larger area of skin hence lower current density and less tingle.

 

[ericmark]

While I think bernardgreen is correct I do wonder if it should be physically checked rather than just assumed to be correct.

I know when we test a house we should do things like disconnect the earth bonding from earth rod and check the reading of the rod its self but we do tend to get lazy and just take an earth loop impedance reading with everything connected.

One only has to look at some of the readings to know this is the case. 0.8 ohms on a TT supply just does not happen we all know earths are also supplemented by water and gas pipes plus any other metal bonded and in the ground.

So there is always a chance that gas or water supplies are changed to plastic and as a result the earth is lost. It takes a few seconds to plug in an earth loop impedance meter and verify the earth is still there. Not talking about a full check just a quick one which would give the guy piece of mind and know nothing has gone wrong.

I have found loose connections in the past and although the lap top may have some capacitive or inductive coupling quite often connected with the filters that is not the case with a kettle.

I am sure if he asks a local electrician to pop round and do a quick test it will not cost much.

 

[bernardgreen]

What I have said about capacitive coupling to a case does NOT apply to the tingles from the kettle.

If the kettle gives a tingle then the earthing is suspect and needs to be checked. It might be a fault in the kettle, its lead or plug or it might be an indication that the earth in the socket and /or house has failed. That does need to be checked.

As it is a rented property you can request to see the electrical safety certificate for the property. Not all landlords / agent will have one.

Point out to the agents that there seems to be a problem that could be a present risk of electrocution and you fear this unknown fault might develop into a risk of fire.

Dubious land lords and agents often take a bit more notice if they fear the property may be at risk of serious damage.

 

[JBR]

Thanks for all this interesting information.

I am not the guy in the rented accommodation; we have our own house. Nevertheless, your advice to have the earthing checked is well received. Looking at my CU, I see a green and yellow cable connecting the CU to a metal conduit through which comes the mains supply from outside. I've been doing a lot of reading on here and I think this must be a TN-S method of earthing.

Will the power supply company check the earthing for free?!

 

[SimonH2]

I get this with my Macbook Pro as well if I use the "duckhead" adapter which doesn't earth the PSU. The cable that's also supplied does earth the PSU and the problem doesn't occur.

This isn't just about "stray capacitance". Just about most modern switch mode PSU have filters on the input - and that typically means fitting capacitors from L&N to E. Without the equipment earth connected to supply earth - this means you have a potential divider making the equipment earth float at something around have the supply voltage.

I find it odd that this is allowed. The voltage is most definitely higher than would be allowed for SELV, and the capacitors used would not count as "insulation". So the effect is to make equipment where the chassis/exposed metalwork is directly connected to the supply live via something that isn't proper insulation.

 

[JohnW2]

This isn't just about "stray capacitance". Just about most modern switch mode PSU have filters on the input - and that typically means fitting capacitors from L&N to E. Without the equipment earth connected to supply earth - this means you have a potential divider making the equipment earth float at something around have the supply voltage.

I'm not sure that I understand that argument. The filter capacitors will be between L&N and the supply earth. The PSU output (hence equipment) will, indeed, be floating but, in the absence of any capacative (or other) coupling between input and output of PSU, I don't really see why the presence of the filter capacitors should influence what voltage the equipment will be floating at. Am I missing something?

Kind Regards, John