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.
