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John ^ I don't think formulae are magic, and I'm not that arsed, just asked what I thought was a simple question. Seems the way breakers work and the physics of fuses blowing mean that it's not too simple or reliable to have a formula, I got that from the original thread I linked to and the...

nah i think i screwed up a multi-quote and it was a bot wot did it, you're awfully paranoid!

In response to your last question ELFI, excel fits in my pocket, the regs book does not and I find it quicker to enter things into excel than flick through the regs book to remind myself of formulas, rewrite them, and work things out with a pencil and calculator, but each to their own!

well my last reply is awaiting moderator approval apparently, what's with that?

I haven't myself but under 200 is considered stable for TT, and I've measured 20-80odd before myself. I've have had a 7ohm Ze (and various other very wrong readings) on TNS supplies. The DNO come out pretty quick and dig up the road usually. I found a 44Ω TT supply protected only by 3x100A...

I haven't myself but under 200 is considered stable for TT, and I've measured 20-80odd before myself. I've have had a 7ohm Ze (and various other very wrong readings) on TNS supplies. The DNO come out pretty quick and dig up the road usually. I found a 44Ω TT supply protected only by 3x100A...

It was a 1.25 I think, the most typical size for 13A extensions. It was the C16 protected temporary installation that has the 1.5. The relatively common melted cable reel extension proves that the fuse will not protect the cable in all situations. yeah typo i meant max Zs!

Some installations aren't designed properly, but they are still put in to service and used. For RCD protected circuits the EFLI can be a lot higher than was traditionally permitted (1667 ohms is bandied around). I'm not ignoring the possibility of LN faults my query is about exactly that. For...

"Zs is the earth loop impedance and for the purposes of my enquiry that's not relevant" Zs can be many even hundreds of ohms if the circuit is RCD-protected but large L-N loop impedances (what I was calling Zx) mean low short circuit fault currents which means longer disconnection times and...

Well Zs is the earth loop impedance and for the purposes of my enquiry that's not relevant, I'm looking at L-N faults. Quite, but 127A was just an example, and virtually instantly is not a time that may or may not be less than 0.4s for example That's OK John you don't need to know everything...

You mean Zx? Yes, I was wondering if there's a formula for Zx/disconnection time if you prefer that to fault current/disconnection time. So what's the disconnection time if the fault current is 127A as I recently measured at the end of a long extension, and would that trip the breaker or blow...

Not every installation has been designed though, some have just been chucked together! And when assessing existing installations and temporary installations it would be useful to know whether the fault current would be sufficient to operate the cpd before the cable overheated, for example (at...

Are there formulae to calculate fuse/mcb disconnection times at a given fault current instead of having to look up graphs? The same question as being asked here: https://electronics.stackexchange.com/questions/129632/can-i-determine-a-formula-for-fuse-disconnection-times

Am I right in thinking that at the moment (under the 17th) it is prohibited to connect a local earth rod to the PME installation earth?

they only tested ceilings. Plastic plugs into solid walls with a decent length screw are fine, imo.

I've seen bells of this age wired in cotton insulated cable, the black moulded bit may unscrew from black base section, but don't attempt unless required for fixing that surface cable bodge as wood can split. Transformer maybe cream or brown thing the size of a small remote control (and...

Probably more likely to exceed 40deg indoors, it's not likely at all. Presumably it can be 40deg ambient temperature outside the cabinet and a fully loaded board with all breakers carrying their full load (with the heat that generates), and that is never going to happen in a normal domestic...

If you get an electrician not only will they do the work, they will be able to test their installation and do the work in accordance with the regs, so it won't be 'money for nothing'. The responsibility for obtaining a warrant lies with you, not a contractor you employ to work in your property...

All work should comply with building regs - https://beta.gov.scot/publications/building-standards-technical-handbook-2017-domestic/ (technical handbook) and BS7671

There is no restriction on what you can or cannot do yourself in Scotland. Some works should have a building warrant in place. In reality nobody actually obtains a building warrant for adding a socket or 2.