TT System??

[leckydee]

thanks for the post Eric, i can't touch anything yet, until I'm qualified , i will be looking at the NICEIC domestic installer scheme , and a job like this would be a great one for assessment when the time comes, ill keep you all in the loop

 

[JohnW2]

I had assumed with single RCD it would be 100mA specially since talking about TT with 30mA there is a problem should there be any faulty equipment working out what is faulty but that does not really cause a danger.

In the first era of general use of (30mA) RCDs (in TN installations), it was fairly common to just have a single 30mA RCD protecting all circuits in an installation, wasn't it? I lived with such an arrangement for many years, and at least a couple of members of my family still have such an arrangement.

As to two line supplies likely had economy 7 or similar at one point.

The OP's supply is very confusing- at least to me. There appear to be two DNO fuses, suggesting that there are two phases, but the OP says that there are only two overhead cables coming to his property. It therefore sounds as if a single phase feed for some reason splits somewhere before it gets to the fuses, which seems extremely odd. Furthermore, even if it were two phases, I've never heard of an E7 (or suchlike) supply utilising two phases - have you? Conversely, if it's single phase, it would seem very odd (and, again, definitely a new one on me) for the supply to split before two DNO fuses - have you ever seen that?

Kind Regards, John

 

[leckydee]

17th regs is that circuits need to be separately controlled so remaining circuits remain energised, says preferred arrangement is whole installation protected by 100ma RCD and install a split load protecting the sockets with a 30ma RCD , ill check for an Earth Electrode and install one at the same time if not there, cheers guys for all the comments, as for the split from DNO thats what baffled me here

 

[securespark]

You could call the DNO and say there is no earth on their incoming supply and ask for an engineer visit. Look to see if there is any crumbling insulation on the incoming rubber cables. That will need attention too.

Get it all assessed when the eng. comes round.

As for the incoming supply, I can see the one tail coming from the LH corner with the final circuit cables that goes into the top of the L service block used by the meter.

Then there's the tail on the RH side going into the bottom of the service block beneath that one.

Then the tail to the left of this one goes into the bottom of the L service block, which feeds the incoming side of the meter.

My eyes (as usual!) may be missing something...

I can't see anything else attached to the bottom service block, so is this unused phase?

If so, where does the incoming neutral to the meter come in?

 

[JohnW2]

17th regs is that circuits need to be separately controlled so remaining circuits remain energised, says preferred arrangement is whole installation protected by 100ma RCD and install a split load protecting the sockets with a 30ma RCD....

It is true that most people interpret the current regs as saying that operation of an RCD should not take out all of the circuits. However, what you describe would not achieve that. If there are any final circuits which are not protected by RCDs or RCBOs, then a fault on such a circuit will cause an up-front installation-wide RCD to operate (even if it is a 100mA time delayed one), hence taking out the entire installation. Similarly, a N-E fault on any final circuit will take out such an upfront 100mA RCD (hence whole installation) even if protected by a single-pole RCD or RCBO, since the single-pole device will not clear the N-E fault. The best solution (IMO) for a TT installation is to either have a dual-RCD (or 'high integrity') CU, with all final circuits protected by an RCD or RCBO, or to have an all-RCBO CU - in either case, you then don't need the up-front 100mA RCD.

Don't forget that if you wanted complete compliance with current regs (even though no-one is forcing you to bring an old installation up to current regs standards), it's not just sockets that would need 30mA RCD (or RCBO) protection. Any circuit in a bathroom (e.g. lighting, shower) needs RCD protection, even if outside of bathroom 'zones', and any unprotected cable buried <50mm deep in a wall also requires RCD protection.

... ill check for an Earth Electrode and install one at the same time if not there, cheers guys for all the comments, as for the split from DNO thats what baffled me here

It's probably worth talking to the DNO before you install an earth rod - it's just possible that, amidst that confusing supply, they could offer you a TN-C-S earth. Someone also needs to get to grips with what's actually going on with that supply!

Kind Regards, John

 

[JohnW2]

I can't see anything else attached to the bottom service block, so is this unused phase?

As you will have seen, that's something we've been speculating about. However, the OP says there are only two overhead (I assume 'single') cables supplying his property.

Kind Regards, John

 

[securespark]

Time for more piccys!!

We love piccys!™

 

[westie101]

You could call the DNO and say there is no earth on their incoming supply and ask for an engineer visit

As said many times the DNO is not obliged to provide an earth connection in this case. They might but it is at their descretion.

BUT
Looking at the ohotos I don't think either of them are actually fuses, they look more like neutral blocks that have been used as Henley type connectors..
I strongly suspect the cut-out is elsewhere and we can see tails from this feeding to the location in the picture.
i.e. 2 lives coming down from above to the blocks, one live from one block to the meter and one unused. The neutral enters on the left with the circuit wiring and goes straight to the meter.

For large E7 loads it was often that 2 livesa were available to reduce the load on the cut-out fuse, but joined onto the bottom side as that is rated higher han the fues carrier/contacts

 

[JohnW2]

As said many times the DNO is not obliged to provide an earth connection in this case. They might but it is at their descretion

Sure, but in this case it would be useful for the OP to know whether the DNO could/would supply an earth.

The other DNO-related question concerns the rather odd appearance of the supply - seemingly two DNO fused (one with output not connected) but apparently only two overhead cables come to property - do you have any thoughts/ideas about that?

Kind Regards, John

 

[westie101]

there were 2 cables running from the street pylon to the house (i presume phase and neutral), then that ran into some partitioned external stud work and 3 cables on th either side, i could not get access to the external stud work so i guess the phase has just been split and the neutral ran solo, I'm assuming

As I said I'm not sure that the two connectors even contain fuses.
Reading this earlier post the OP needs to gain access to that area where I think a cut-out will be found

 

[JohnW2]

As I said I'm not sure that the two connectors even contain fuses.

Ah - but you only said that (slipped it in!) after I replied to what was originally the one-sentence post from you Whatever, thanks for that assessment - which certainly would make a lot more sense of what we are looking at.

Reading this earlier post the OP needs to gain access to that area where I think a cut-out will be found

It seems that may well be the case.

Kind Regards, John

 

[Spark123]

i was looking at the Kewtech KT65 or the Megger MFT1720 cheers peeps

I personally like Megger stuff, it is reliable and their service is good. If you stick to a reputable make such as Megger, Fluke, Metrel or Kewtech you won't go far wrong.
Don't forget to buy yourself a set of isolation testers too.

 

[leckydee]

sods law here, this will be one of my first jobs upon legally qualified, i knew this one would be an open wound ;o(O)

 

[leckydee]

View media item 82390

 

[JohnW2]

View media item 82390

Yep, that's certainly consistent with what westie suggested. You clearly need to try to find the cutout and see if there is any earth anywhere - like investigating that green wire! Good luck.

Kind Regards, John