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Some differences in opinion regarding EIC records

IronFreely

Those of you who’ve been kind enough to discuss things with me in the past will know that I like to get to the bottom of why different sparkles choose different ways of doing things so that I have a large arsenal of tactics at my disposal and to make sure I’m doing what is best rather than just going through the motions.

I recently attended a little additional training, we went through a number of different scenarios and I was surprised that the trainer insisted we record things on an EIC in a way that I believed to be inaccurate. It made made me wonder how the fine people of the forum approach similar situations? I’ll list them below.

1) The first thing is that he insisted that where we find a 1361 type 2 DNO cut out fuse that we absolutely must record it as a BS 88-3, he said that the 1361 fuse had been renamed BS88-3 and their characteristics are exactly the same for both. Now I’m a time served sparkie and was taught all those years ago you write down what’s in front of you (if the DNO label says 1361 then that’s what you record). I was also once given a chart for fuse comparison a long time ago and it says that the 1361 type2  was not renamed it was replaced and that thier characteristics are slightly different, in particular one has a 16.5KW breaking capacity and the other a 33KW capacity. Was I just taught to keep inaccurate records? I can’t see any danger in this but still it didn’t seem right.

2) The second is how one would record the supply characteristics and details at the origin. The scenario was the creation of a TT island where it is not preferable to export PME/TNCS outside for either an electric vehicle charger or shed and where an additional consumer supplied via an MCB in the original consumer unit is installed to facilitate this.. Again back in the day I was taught to record what you see. If it’s TNCS at the origin of supply you record that and it’s Ze, in the description of the installation you would indicate that you have separated the TNCS earthing and created a separated TT installation, and that the RA of the Ze of the separated system be recorded on the schedule of test results with the distribution board details. What the trainer insisted on is that the TNCS system should be totally ignored on the records and only details of the the TT system should be recorded on the particulars and supply characteristics section. This didn’t go down well with me as I would want anyone reading my EIC to fully understand that the main installation is connected to the PME network and that it and it’s bonding should be kept entirely separate from the TT system. What particularly bothered me is that having made us fill out a mock EIC (based on mock up on a test wall) with no mention of the TNCS/PME aspect we were then expected to record confirmation of equipotential bonding arrangement to gas and water on this EIC which by rights was not connected to the TT system at all. This really seemed bizarre to me. How do others make these records where a TT system is separated from a TNCS installation?

3) The last thing that irritated me is I was questioned in depth as to why I had recorded max permissible Zs on a TT circuit as 1667Ω instead of the figure from table 41.3 for the over current device. I had to very carefully explain that as the distribution board supplying circuit was part of a TT system where Ze far exceeds max Zs figures in table 41.3 and thus the 30mA RCD was providing both fault and additional protection, and that I felt anyone qualified to be looking at my schedule of test results would note that the R1+R2 value was a mere 0.01Ω and should be able to determine (without additional notes being made) that the circuit was not a sufficient length to require further consideration in terms of disconnection times or voltage drop. Personally I think it’s a bit pedantic and that any genuine sparks would get it either way.

Any way, I thought it’s a worthy discussion as I feel our aim with keeping records is to allow those who come after us to quickly determine our design decisions and without inspections determine the precise situation on site, possibly in advance before a site visit.

still running freely.

  • Interesting, I wonder who the training provider was?

    1. It doesn't matter, put what you see!

    2. Assuming an EICR, fill out 2 forms, 1 for the island one for the main installation. The TT one should contain comments about the Earth isolation and the Earth electrode. This is again a very pedantic bit of training. If new the EIC (For the new TT bit ) would say TT and again have details of the Earthing, and its isolation from the point of supply. You cannot ever provide too much information to guide the next guy. The Zs and PSCC would be at its point of supply (Zdb) wouldn't it, that is what controls the selection of equipment as it is fed by a submain?

    3. The trainer is an idiot, as the CPD doesn't provide Earth fault protection, it is only the RCD that matters. You might have to consider the max Zs for the CPD if the circuit is long to decide that it can break other types of faults quickly enough, but unlikely in your situation. You already know that the CPD for the submain can meet 5 seconds, but you might need a quick check for the final circuits. Many people don't even realise that these external circuits with switchgear at the end in the shed etc. even are submains!

  • in reply to David Stone

    I’m not going to call out the the provider, mostly because I haven’t got my money back yet!

    I’ve thought of another interesting conundrum with the test rigs they had there. So in case of the TT island…. The main DB1 was on the TNCS supply, and MCB within supplied DB2 via T&E. Within DB1 the CPC for the T&E Submain supplying DB2 was insulated in a chock block. DB2 was directly next to DB1 and had a dedicated earth rod and 1 final circuit supplying an external appliance, in this case an EV charger. Now both DBs were metal of course, so that makes DB2 an extraneous conductive part and an exsposed conductive part which should be connected to the MET of the TNCS installation via equipotential bonding. Thus the dedicated earth rod should not have been installed on DB2, nor should DB2 earthing have been separated from DB1. I feel that TNCS earthing should have been separated from the EVSE at the point of entry to the charger and the dedicated earth rod should have been installed directly to the charger thus ensuring the metal case of DB2 would not introduce a dangers earth potential under fault conditions.

    Or don’t separate the TNCS at all and install a charger that incorporates an Open PEN device, which also negates the need for a complex risk assessment to ensure all exposed and extraneous parts of surrounding TNCS installations don’t cause a potential danger. Damn! I should be teaching that course!

  • IronFreely said:
    The first thing is that he insisted that where we find a 1361 type 2 DNO cut out fuse that we absolutely must record it as a BS 88-3, he said that the 1361 fuse had been renamed BS88-3 and their characteristics are exactly the same for both.

    That is FALSE. The characteristics are NOT identical, as you can CLEARLY see from Tables B4 and B5 of the On-Site Guide ! Yes, BS 88-3 replaces (on paper) BS 1361, but BS 1361 fuses are still available, widely used, and have different max (and max measured) loop impedances, even for the 80 A and 100 A which do align in the preferred values.

    IronFreely said:
    ow I’m a time served sparkie and was taught all those years ago you write down what’s in front of you (if the DNO label says 1361 then that’s what you record).

    I would go with the fact that you can't see the fuse itself, so write down what you can see ("Labelled as ... but can't verify" if you can't withdraw the fuse and look inside the holder.

    IronFreely said:
    2) The second is how one would record the supply characteristics and details at the origin.

    This depends on how you define "the installation" - in the case of a circuit separating out to TT, the source of the "installation" is surely the overcurrent protective device supplying the circuit, which is not necessarily the source of supply for the premises.

    IronFreely said:
    3) The last thing that irritated me is I was questioned in depth as to why I had recorded max permissible Zs on a TT circuit as 1667Ω instead of the figure from table 41.3 for the over current device.

    Agreed, Table 41.5 ... provided of course earth electrodes are stable for circuits on TT.

  • IronFreely said:
    The first thing is that he insisted that where we find a 1361 type 2 DNO cut out fuse that we absolutely must record it as a BS 88-3, he said that the 1361 fuse had been renamed BS88-3 and their characteristics are exactly the same for both.

    That is FALSE. The characteristics are NOT identical, as you can CLEARLY see from Tables B4 and B5 of the On-Site Guide ! Yes, BS 88-3 replaces (on paper) BS 1361, but BS 1361 fuses are still available, widely used, and have different max (and max measured) loop impedances, even for the 80 A and 100 A which do align in the preferred values.

    IronFreely said:
    ow I’m a time served sparkie and was taught all those years ago you write down what’s in front of you (if the DNO label says 1361 then that’s what you record).

    I would go with the fact that you can't see the fuse itself, so write down what you can see ("Labelled as ... but can't verify" if you can't withdraw the fuse and look inside the holder.

    IronFreely said:
    2) The second is how one would record the supply characteristics and details at the origin.

    This depends on how you define "the installation" - in the case of a circuit separating out to TT, the source of the "installation" is surely the overcurrent protective device supplying the circuit, which is not necessarily the source of supply for the premises.

    IronFreely said:
    3) The last thing that irritated me is I was questioned in depth as to why I had recorded max permissible Zs on a TT circuit as 1667Ω instead of the figure from table 41.3 for the over current device.

    Agreed, Table 41.5 ... provided of course earth electrodes are stable for circuits on TT.

  • in reply to gkenyon

    This depends on how you define "the installation" - in the case of a circuit separating out to TT, the source of the "installation" is surely the overcurrent protective device supplying the circuit, which is not necessarily the source of supply for the premises.

    But as this MCB is within a DB which is a TNCS installation the “origin” and “characteristics” in terms of earthing remains the same it’s TNCS at the origin. The new DB2 is TT and I feel it’s important record both earthing arrangements with a description detailing the separation of the two earthing arrangements, that way if someone down the years gets sent my documents in order to provide an estimate before visiting on site they know exactly what they’re getting into. They can also easily determine what’s going on and don’t end up stupidly quoting to install for example a class 1 light on the front drive…

  • in reply to IronFreely

    Quite right. I hope you get your money back, but if not publish the provider!

  • Firstly how do you know what Type and Rating of the fuse is given that you are not allowed to interfere with the suppliers equipment? Of course you could have contacted the DNO but they do not keep records so how would they know?

    Your instructor is wrong. BS 1361 fuses are not the same as BS88-3 fuses as they have different maximum fault current ratings.

  • Your instructor is wrong. BS 1361 fuses are not the same as BS88-3 fuses as they have different maximum fault current ratings.

    Not to mention different actual ratings - e.g. 63A rather than 60A.

       - Andy.

  • Worrying., rather gives the nod to the old joke about

    'Those who can, do; those who can't, teach' from George Bernard Shaw's 1905 stage play Man and Superman.

    Shame actually as there seems to be a shortage already of folk who actually understand stuff without creating a new generation.

    I hope the rest of the sessions  were better and you are quoting only the low bits. 
    Exactly how you record things can be  partly a matter of choice, but reality has to take precedent over fiction and it does all have to be there somewhere, and clear to whoever picks up after you. I'd have no problem with your approach.

    And yes, touchable metal from the two earth zones really should not be within reach of each other.

    Mike.

  • in reply to mapj1

    Thanks Mike, neither JP or I should attempt teaching again then?

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