We`ve been having a new boiler fitted in our house and the electrician found that the earthig system had not been connected correctly at the service head. Apparently it`s a PME set up and the earth block should be linked to the neutral within the head unit rather than just floating in space as it was.
Am I correct in assuming that this is the responsibility of the electricity company and should I raise merry hell with them? How dangerous was this?
It's your responsibility to test the earthing. The electricity company is under no obligation to provide you with any earthing at all, and even if they do, you don't have to use it. It may have been deliberately disconnected to turn the system into a TT system for example.
You would need to ask the electricity company to reconnect it if you want it reconnected as it should be under the protection of a seal, and they would need to verify the local supply network still meets the requirements of a TN-C-S (PME) supply before allowing you to use their neutral as a PEN (Protective Earth and Neutral).
That depends on lots of things, including the state of your own earth bonding. In the worse case, it could be very dangerous.
If it's anything like some installations around here, what has probably happened is that your installation has / had an earth rod (TT) system and that at some point the supply company upgraded the incoming to be
*capable* of PME (TN-C-S). If you read the little sticker on the incoming supply you will see a dire warning along the lines of "the installation earth should not be connected to this supply earth unless the installation fully conforms to the PME earthing requirements of BS7671".
Leaving all else alone would leave you with a TT system which can be (relatively easily) upgraded to PME at a future date, and in fact a lot of houses around here have that. Some appear to have no system earth rod, just an ELCB with rod. I have also just come across one (with PME incoming but E not attached) which has a 30mA RCD providing the only protection against indirect contact due to the earth loop impedance of the installation being some 220 Ohms. I can't find an earth rod anywhere, so possibly this 220R is down to paths through the water pipes (there is no main bond to the gas). Needless to say, in these circumstances it is well worth upgrading to PME.
BEFORE you connect to the supply earth you *must* ensure that all main and supplementary bonding us present and correct. If you are confident of this then quite often it is a job the supply company will do for free. They may even have left an earth block ready for you to connect.
If you are in *any* doubt, don't take your plumber's advice for granted: consult an electrician.
That depends. It was probably quite dangerous, but there is a possibility that it was quite safe.
Sometimes the electricity company provides no earth, but a local upgrade results in them later providing an earth terminal, such as through upgrading overhead lines to support TN-C-S. However, the householder is under no obligation to use the new terminal. It often happens that to use the new terminal safely, the main equipotential bonding needs replacing at great expense (under slate floor, etc.) so the householder declines to use it. If this is the case, then the main earthing terminal should be connected to an earth rod and the whole installation should be RCD protected (preferably by a time delay 100mA RCD, but more likely a 30mA immediate).
If this doesn't apply and the house should have been using TN, then the main equipotential bonding (if present) may have reduced the risk somewhat, although earth loop impedences may have been marginal for instantaneous disconection of MCBs in the result of an earth live short. Again, a whole installation RCD (if present) would have mitigated this risk, although it would still have been a failure.
If it was never connected at the start and not just become disconnected, then there is no excuse. The electrician should have performed an earth loop impedence check which would have brought up such a major earthing issue.
The main equipotential bonding to gas and water is present and correct.
The electrician did an earth loop impedance check which is is how he discovered the problem.
I`m not too familiar with the the ins and outs of the various earthing systems but the earth block in the cutout was not connected to anything at all - neither the neutral or the cable sheath which I understand from my limited grasp of the system, it should be.
If so, then it was non-compliant, but probably reasonably safe with < 200 ohms ELI.
With no-RCD, it was a fire and electrocution hazard waiting to happen. However, if < ~5 ohms ELI (unlikely), an earth fault would probably have finally tripped the fuse/MCB on thermal operation. If < ~1.5 ohms, it would have actually have been electrically safe, but non-compliant and subject to ground resistance changes.
If you're interested, there's information about the different types of systems at:
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is an excerpt from John Whitfield's book, which is well worth owning if you plan to do your own electrics.
It sounds to my non-professional ear as if the electric board made quite a moderately serious mistake here. You should thank your plumber/electrician profusely...
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