Global IR testing on RCBO populated CU

[Midwest]

I shall be replacing my dual RCD CU, for a all RCBO populated CU. A question or two about technique for IR testing.

For the IR test, I've read here before that a global IR test is preferable. With older types of RCBO's that wasn't possible, without disconnecting cables, which ended up with the testing of each individual circuit.

I'm installing a Hager CU, with their miniature ADA RCBO. The MI state an IR test can be carried out on the RCBO terminals, circuit connected with the RCBO turned off. As I've a few different sorts of luminaire connected, I will be doing live/neutral to to earth.

How do you carry out such a test? I've seen some stackable MFT leads, so you can combine live & neutral together?

 

[Mike Johnson]

Single width with plug in busbars for L & N sounds like a good way forward...

Ah, but to do that you would have to mix and match. ?

 

[loz2754]

Ah, but to do that you would have to mix and match. ?

Aaaaagjhghjkh!!!!! No........

 

[nicebutdim]

Ah, but to do that you would have to mix and match. ?

Way forward for manufacturers... ?

 

[pc1966]

I did once enquire about a 3 phase supply for a workshop at the same property, but the costs were astronomical - new poles, transformer, underground cables etc ?

For our current project we initially assumed a 60-100A single phase supply as all our equipment is single phase, and we assumed we would have a lot more to pay for getting 3-phase in. Then we actually got to see the supply arrangement and to speak to the sparky who normally deals with it and found we could get 500A 3-phase if we needed it all for the same price!

OK, our cable cost to get there would vary a lot...

 

[nicebutdim]

At the time I just accepted the quote from our electricity supplier and gave up on the idea. Can't remember the actual figure, but it was much larger than I could ever have imagined.

 

[pc1966]

Once they start talking about laying cable you are in to the £100/m or more just the the duct work

Probably others here know more for specific areas, etc, but they know how to charge!

 

[nicebutdim]

I'd proposed a separate new supply coming into a shed that was within 10' of the existing transformer, but it wasn't quite that simple. I think they needed to bring power from another line.

 

[Simon47]

Many years ago I got asked by a friend for ideas about getting lecky to a couple of isolated holiday cottages. They'd asked about a new mains supply and been quoted £70k ?
Then they tried buying a little petrol generator. The sparky had to rewire it (I imagine is was some variation of non-earthed neutral), and when they tried it ... the BS4343 plug melted as the small shed had insufficient ventilation. The final nail in that idea was when I pointed out that if they ran it continuously, it would be wanting two oil changes and a new spark plug per week - not to mention all the petrol it would drink (or perhaps gas, can't remember now).
In the end, they ran their own submain from a property 1.3km away and accepted that running anything "heavy" would make the lights dim. The DNO refused to provide a supply via that route as they said the network didn't have the capacity.

Look out for RCBO with functional earths as they show up when doing global or L+N to E testing. The Hager commercial RCBO have them but I don't know about the domestic ones.

The Pro-Elec (CPC's own brand) RCBOs I used in our rental properties test out at (from memory) 165k one way, but open the other way - L+N to functional earth fly lead. Can't do a whole installation test with my MFT as it doesn't run the test long enough to charge up capacitors - but the trusty old Megger BM10 works a treat holding the button down for a few seconds.

The only problem with switched neutral RCBO's is they are dual module, not a problem in a continental type CU but very restrictive in a normal UK domestic board, I had to use single module RCBO's for the lighting circuits due to lack of room.

There are single module compact RCBOs available - some of them without flying neutral leads. I can understand why somsone might have reasons not to use SBS - but at least they do have single module RCBOs with switched neutrals and N busbar.

Why not test N-earth and then test live - earth. What are you gaining/preventing by joining them together?

Convenience - and getting one result.

 

[Risteard]

In the case of ROI I would not be surprised if it was a mix of the single-pole OCPD based on the historic ties with the UK regs, and the move to double-pole switching from more recent EU influence and/or historical use of TT or similar, leading the 1P+N being normal for RCBO.

Might explain the difference in part number for the same basic module size between the Hager .ie and .fr sites.

Maybe @Risteard knows more on the background?

The southern Wiring Rules are a sort of strange mix of German and British Standards. I think much of the reason for this is that the ESB (Electricity Supply Board - the DSO) had historic ties with Siemens if I'm not mistaken in their early days. So Diazed and later Neozed fuses were the usual fuse standard here rather than BS 88s or BS 1361s as an example, and multi-row DBs are used in domestic premises.

 

[LastManOnline]

The southern Wiring Rules are a sort of strange mix of German and British Standards. I think much of the reason for this is that the ESB (Electricity Supply Board - the DSO) had historic ties with Siemens if I'm not mistaken in their early days. So Diazed and later Neozed fuses were the usual fuse standard here rather than BS 88s or BS 1361s as an example, and multi-row DBs are used in domestic premises.

Yes, Germany had a huge influence on our electrical system. After the war a decision was taken here to electrify the entire country regardless of how remote a dwelling was located.A massive project, It was completed in the 1970,s. More by accident than design, an Irish engineer working for ESB but who previously worked for Siemens got them involved in the project. Germany was undergoing its own regeneration at the time, so the relationship worked well.
Overall, I would describe the system as robust, streamlined and standardised. The regulators here tend to keep a very open mind on what works well in other countries and then apply same. I would describe their approach as by and large progressive (exception being adoption of TNC-S). A 2 row CU in every home. RCD, s have always had a valued place in domestic installs. A UK spark would feel totally comfortable working here within a day or two.
Ironically you mention fuses (neozed etc). Well, in five years time, only place you will see a fuse in this country is likely to be a museum

 

[pc1966]

Ironically you mention fuses (neozed etc). Well, in five years time, only place you will see a fuse in this country is likely to be a museum

What about the incoming protection for the installation?

 

[LastManOnline]

What about the incoming protection for the installation?

A 63 amp mcb for a standard 12kva supply. As of February this year, new regs stipulate that now becomes a double pole 63amp

 

[pc1966]

A 63 amp mcb for a standard 12kva supply. As of February this year, new regs stipulate that now becomes a double pole 63amp

That is interesting. Certainly makes it easier to disconnect the CU supply to do any work!

It is just a regular MCB (not MCCB)?

Typically the use here of a BS88 fuse gives selectivity with many down-stream MCB characteristics as well as far higher braking capacity and fault current-limiting characteristics, but probably in most cases they are not essential (though some cities' supply points can deliver over 10kA PFC).

 

[Mike Johnson]

Wouldn't a S type RCD be better?

 

[nicebutdim]

Ironically you mention fuses (neozed etc). Well, in five years time, only place you will see a fuse in this country is likely to be a museum

Is this on the supply side or is Ireland moving away from fused plugs on domestic appliances?