Yes. It all depends upon the installation though. I recently added an isolator between the meter and the CU, working live. As the CU is plastic cased and the isolator switch input side could be wired outside its enclosure and then clipped in, I didn't have the risks of trying to get a bare, live wire through a metal enclosure. With basically nothing to short to, I felt comfortable enough doing it.
I wonder if there is a specific sequence of disconnecting L & N from old switch and then a sequence of connecting L & N to new switch in a similar way where one would connect a "live" battery on a car to another car with a 'dead' battery requiring a jump start?
Smart meter dumb installer.
Genius! Great idea, I'll use that!
Yes, or both! Unfortunately, my old earth loop impedance meter is somewhat out of date and doesn't have those features. The fact that the instructions tell you to leave five seconds between tests and not to hold the button down too long provide a pointer to a rather more crude approach involving *lots* of current! The aforementioned meter (a Robin if you remember those) is giving me readings of just under 100 ohms from all the outlets in the house and that seems way too high for my liking. I'd have expected sub 5 ohms, but I guess it depends on the earthing system here and I'm not sure what mine is off-hand. :-/
Why do you think there would be an arc if you've isolated all the loads? When I've done this I switch off the CU, check the condition of the fuse carrier (don't do it if it looks old, cracked, etcetera), wear a rubber glove, stand on a rubber mat (sometimes), and am careful not to touch anything else while pulling the fuse carrier. The precautions are to protect against the carrier disintegrating.
With nothing but L&N to short to each other, it should make little difference which way around you do it.
With putting them into a metal enclosure, I would think L, then N and both before earthing the enclosure.
oh and full face protection gear plus a heat resistant jacket!
There used to be an old adage from my YEB days. Something like 'Neutral is first to make and last to break' meaning always connect the neutral first and disconnect it last' ( where 'reasonably practical' of course!)
If the fuse carrier looks dodgy in any way, that is good grounds for asking the DNO to change it anyway!
It's a TT supply, and the 100 ohms is probably correct. That's why you have an upfront RCD. It's to protect the circuits, as they'll never trip the ciruit breakers with a 100 ohms fault loop unless it is a dead live to neutral fault.If you stand there holding the live in one hand, and the other hand is touching earthed metalwork, you'd be buzzing a long time until the circuit breaker tripped.
I presume you have had the CU changed at some point, and it has RCD protection on all circuits? If so, then you should be ok, but I wouldnt put an isolator switch in place of the RCD, I'd put a 100mA, or even
300mA, time delayed RCD in its place, that means your tails from there are protected for fault current, which with a switch, they wouldnt be. You can also use the RCD for isolation of the install.
I think you've got the wrong end of the stick, mate.
So pull the fuse.
OK, you've alerted them to your intentions, but the holder doesn't look like it's out of the ark, and as long as you don't f*ck-up, they won't nip round to have a little look whether you did fiddle with it.
Yup I have an old Megger LT5 that does that - uses something like 20A of test current. While not RCD friendly, it does prove that the earth system is actually robust enough to clear a fault in real life, and not just in theory.
Well if it is anything other than TT you have a major fault to report to the supplier!
Here is how you can tell:
I might be tempted to be a little bolshy. Say I told you the fuse was going to be removed. And after ring them up to say the work has been done and suggest they might want to replace the seal! What's the worst they are going to do?
I might suggest that is done first or together if the RCD in your photo is the only protection.
Bypassing the current RCD is a little foolhardy if there is no other RCD protection. The cable you have used is well below the required rating.
I strongly suggest the issues are dealt with in quick time.
Indeed. I did mention it's only a temporary expedient way back up the thread. It's 20A cable, which is more than enough for me given my personal circs at this time of year and I won't be using any of the workshop equipment til it's all properly sorted out. The missus has been informed and instructed not to use more than one power appliance at a time yadayadayada. And finally, yes, I'm aware that 12V cable doesn't have 240V standard insulation and all that, but see above, yadayadayada....
Sounds like it's TT, local earthling rod.
I'd bin off the RCD if I could and replace it with a 125A double pole isolator. If I had to keep the RCD (e.g. TT earthing) I'd fit one with a 100mA trip.
It might be a TN supply and the suppliers earth is not been used (for various reasons) and so is wired up as a TT supply.
I have known that to have happened before.
A closer look at the RHS of the cut out might help as that is where the earth terminal usually is.
Adam
A 100mA trip is only adequate for equipment protection, not shock protection. So you would need downstream RCDs for all circuits that are
30mA trip. That kind of negates the point of having the single RCD upstream.(it was more common in the 16th edition days to use a 100mA type S as the main switch on a split load CU, with a normal 30mA RCD protecting the socket circuits only. Lighting etc did not at the time need shock protection. Since the 17th edition it is far more common to need 30mA RCD protection for all circuits).
These days you might just as well go for RCBOs on all circuits.
Yup could be...
Yup, here :-) I have a TN-C-S supply but the house is TT (I would guess the supply was upgraded after the house was last rewired).
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