Keep getting zapped !

[mdrandall]

I'm not sure which forum to post this on but I hope someone can help.

I have a 1 year old house which seems to have some weird things with the electrics.

Shortly after moving in I noticed that the phone line was not as clear as it should be. Using dial-up internet access gave a rubbish connection speed. Also, the noise on the line disappeared if I switched off the boiler at the wall fused switch. I then got broadband and thought nothing more of it.

Then I was emptying the washing machine, steadying myself by holding the utility room steel sink. When I reached into the machine I got an electric shock. Using a multi-meter I could not detect any voltage but did find that the sink was not connected to the normal wall socket earth. The boiler is attached to the wall in the utility area. Again this has not repeated.

Last week I was mounting an LCD tv to the wall in the bedroom above the utility area. I found the metal stud in the wall, checked there were no cables behind it etc. All went well until I was holding the tv bracket while plugging in the coax aerial lead - I got a shock and the boiler blew the 3A fuse in the switch in the utility area! The main consumer unit did not trip its RCD.

I have measured between the bedroom wall socket earth and the aerial coax and there is about 12 to 16 volts ac and a few but rising mV of dc. This is with the lcd tv switched off and disconnected. The tv picture has a herring bone effect when the tv is first switched on but disappears after a few minutes (maybe just the tv warming up).

Also there is no continuity between the tv stand (therefore the metal stud) and earth.

I checked another room and there is a much smaller ac voltage between that rooms aerial feed and a local wall socket earth.

Last night I tried tapping the aerial outer metal part of the coax connector onto the tv stand, there was a spark and it blew the boiler fuse again!

The aerial comes from a multi-way amp in the loft which has sky bypass. I think the installer powered it from the adjacent smoke detector supply so it may not be earthed (?).

Sorry for the long winded post but I am struggling to even think what can cause these shocks.

1) Should the metal vertical studs in a partition wall be connected to earth?

2) What could cause the 12 to 16 volts ac between the aerial feed and earth?

3) What would cause the boiler to blow the fcu fuse?

4) Should the RCD have tripped when I got my shocks?

5) There is steady 8v dc between the coax outer and inner but I think this is power for a sky tv link device.

6) Should radiators have continuity to earth? The pipe work from the boiler does but not the rads themselves.

7) I intend to get the builder to end round the electrician but what can I get him to check and how?

Thanks for any advice...................................

 

[bathjobby]

Contact the builders under your NHBC cover..... Why do you feel the need to instruct the electrician ? Tell him you are getting shocked everywhere and can see that units aren't earthed.....

 

[Big_Spark]

1) Should the metal vertical studs in a partition wall be connected to earth?

No, there is no requirement for metal stud partitions to be Earthed. They are physicaly attached to the building fabric, and as such should be at the same potential as the walls etc, not such charge should build up in them to recieve a shock from them. However a static charge in your body will ground to earth using a metal stud, so this is a potential source of the shock

2) What could cause the 12 to 16 volts ac between the aerial feed and earth?


How do you think the recieving equipment gets the signal for the transmission, it is a potential difference or voltage. If you have an amplifier on the system this type of voltage is quite common.

3) What would cause the boiler to blow the fcu fuse?

A Fault on the Boiler causing the circuit to draw more load than the fuse is capable of handling, probably unconnected and should be investigated by a quailifed person

4) Should the RCD have tripped when I got my shocks?

This is a common urban myth. RCD's do not prevent electric shocks, they simply reduce them to no fatal levels by disconnecting the circuit, normally before the shock is felt, but not always. Further DC shocks, such as static, will not operate the RCD unless it is a DC sensing type and the static travels down an earth path that returnes to the distribution board the RCD is installed in.

5) There is steady 8v dc between the coax outer and inner but I think this is power for a sky tv link device.

This is the potential difference of the signal being recieved from the dish.

6) Should radiators have continuity to earth? The pipe work from the boiler does but not the rads themselves.

Radiators should have continuity to earth, however if you mean should they be cross bonded, there is no need for this so long as all the pipework is copper and of the soldered joint type. The radiators will have some form of earth continuity as they are attached to the building fabric.

7) I intend to get the builder to send round the electrician but what can I get him to check and how?

He is a professional, simply explain where you have recieved electric shocks and then leave him to investigate and if required, find solutions

 

[andy]

1) Should the metal vertical studs in a partition wall be connected to earth?
dont think so

2) What could cause the 12 to 16 volts ac between the aerial feed and earth?

a fault. could be anything

3) What would cause the boiler to blow the fcu fuse?

more than the current rating flowing

4) Should the RCD have tripped when I got my shocks?

depends. uf you got a shock from something on the non-RCD side then it wont trip. if it was from something on the RCD side then the RCD could be faulty

5) There is steady 8v dc between the coax outer and inner but I think this is power for a sky tv link device.

yup

6) Should radiators have continuity to earth? The pipe work from the boiler does but not the rads themselves.

the pipes at the boiler should be cross bonded. the main gas and water should also have a 10 (maybe 16)mm earth from the MET. radiators are not elecrtically connected to the main pipes, since the PTFE tape can insulate them

7) I intend to get the builder to end round the electrician but what can I get him to check and how?

you could get an electrician round to find out whats causing the problem. we can only guess since were not there and the fault could be anything. it could even be the meter tails...

 

[Lectrician]

With the boiler FCU out, or fuse blown, do you still get shocks/measure volts?? If you don't, and the fault vanishes........you have a dangerous problem!

The 8v from centre to outer on aerial is for you magic sky-eye.

Many TV's will cause a frighteningly high voltage to appear on the screen of the aerial due to internal capacitors inside the TV. This will be spread across ALL aerial coax's in the home if the coax isn't earthed anywhere - it should be. This will cause a tingle from aerial lead to earth.

The metal stud has no requirement to be earthed.

The radiators don't either (bathrooms require seperate consideration).

The sink in the utility doesn't require earth bonding, nor the pipes beneath.

So, if your TV in the lounge is connected to the aerial lead from the loft, there is a high chance that it will put some tingle volts onto the coax screen. This voltage will spread to all other outlets. You will get a shock from coax to anything 'earthy' (even if not directly connected to earth).

 

[mdrandall]

Thanks guys,

I thought a number of my findings were spurious and not related. I will get onto the builder about the boiler fuse blowing etc (it definately blew at the same time as I got a shock in the upstairs bedroom or at least very close as my Wife was in the utility area and heard it "crack").