earthing

[thompsk]

Just been doing a contract job for a contractor that is working on an NHS site, senario: two story block student flats, two D.B's one on each floor, fed in pyro some 50 m run no bigger than 6mm, only earth was of inadequate size off the conduit box terminal, so this contractor has put in two 16mm earths but taken them to two earth spikes therefore mixing earthing arrangements ie its now earthed as a tt would be but mis supply at source is tnc-s.

And one other thing a new water heater has been fitted and it required 3 x 3.3 immersions wiring to it, in the haste of the job their gaffer forgot and when we told him it required this he told us to wire these off the ring main...which we did not, that aint right in my eyes is it ?

 

[Spark123]

Just been doing a contract job for a contractor that is working on an NHS site, senario: two story block student flats, two D.B's one on each floor, fed in pyro some 50 m run no bigger than 6mm, only earth was of inadequate size off the conduit box terminal, so this contractor has put in two 16mm earths but taken them to two earth spikes therefore mixing earthing arrangements ie its now earthed as a tt would be but mis supply at source is tnc-s.

What, if anything does he think he is gaining by using electrodes? If anything he has made the situation worse (the electrodes will now be part of the PME system tying the neutral to ground). Why is the current earth too small?

And one other thing a new water heater has been fitted and it required 3 x 3.3 immersions wiring to it, in the haste of the job their gaffer forgot and when we told him it required this he told us to wire these off the ring main...which we did not, that aint right in my eyes is it ?

Not a good idea to have fixed loads of that sort of magnitude on a ring circuit, won't leave much room for anything else.

 

[Space cat]

a new water heater has been fitted and it required 3 x 3.3 immersions wiring to it, in the haste of the job their gaffer forgot and when we told him it required this he told us to wire these off the ring main...

Do you mean 3 x 3.3kW heaters? A quick calculation should tell you that 10 kW will take over 40 amps.

 

[thompsk]

Thanks Spark123 and Space cat, it is exactly what I thought and the other subbie I was working with.

The existing earth is the sheath of the M.I. but there is no earth tail so the contractor thought he'd run these 16mm's in and put them onto electrodes rather than do a complete run back to source. We both thought it would be mixing earthing systems which cant be good news.

On the whole the installation was/is a complete mess and in our eyes it should have been a total rewire, the existing cables are early pvc which are showing signs of deterioration some of the lighting isnt earthed the list goes on.

Glad ive a different job on Monday, thank goodness I havent touched the damn installation, I just installed the fire alarm.