Pulling a main fuse safely

[John Rumm]

The fuse has no bearing on the amount of current that is available - that is a function of the supply loop impedance. All a fuse can do is interrupt the flow of current some time after the fault becomes apparent. So if you have a loop impedance ~ 0.04 ohms[1], then you will get close to 6000A fault current. That will be likely enough to take out the substation fuse for that phase - but it might take it a tenth of a second. (in which time it could deliver 3.6MJ of energy!)

[1] That would be pretty low unless very close to a sub station or in an area with a very high capacity supply. 0.1 to 0.3 ohms would be more typical.

[GB]

Ours was installed in 1971. Some sort of plastic, clearly in good nick still. So, I think his risk was small.

Nevertheless, I don't blame the guy for taking precautions, although I was a bit surprised at the time.

[Chris J Dixon]

After I pulled the fuse to change a CU some considerable years ago, there was an issue that I didn't spot affecting the contact surfaces. Subsequently I experienced occasional supply dips, and eventually noticed overheating of the fuseholder.

They were round to sort it in very short order.

Chris

[Tim+]

Was it after a power cut? ;-)

This self sorting phenomenon seems quite common and I?ve often wondered if it?s been a power cycling caused by a brief power cut that is ?rebooting? the modem.

Anyhow, it would seem that Octopus must spy on Usenet as just this morning I?ve had an email with dates for an engineer?s visit. (I had also badgered them yet again by email so the Usenet spy theory might not be correct.). ;-)

Tim

[Tim+]

Well my present tariff is the modern equivalent of Economy 7 and if you have an EV it?s definitely worthwhile being on a variable tariff.

If you don?t have a significant load that you can timeshift then probably not worth the bother.

As I have an EV it very definitely is worthwhile.

Tim

[Mark Carver]

Ha, no, my router has been up since the last known power cut on July 7th last year, so no, that didn't do it !

Well that's interesting because given the poor CS over this, I'm considering switching to Octopus !

Perhaps not then ! ?

[Mark Carver]

I had  a new DNO point installed 18 months ago. As part of that they fitted a double pole 100 A switch (downstream of the meter, but obviously upstream of the CU) Is that a new policy to avoid folk 'meddling'  with the fuse  ?

[Theo]

I'm not sure if it's policy, but it's good practice and simple to do. Electricians can fit an isolator if the cutout is removed, as can the supplier (who own the meter). It would seem to make sense to do it as part of a new install.

Theo

[John Rumm]

Which you can cut off, and no one will seem to care...

[Mark Carver]

I'm trying to remember now whether it was actually the meter man from OVO who fitted it, or the DNO. It might have been the meter man, (seeing as his bit was downstream of the 100 A fuse) I didn't take a photo between the DNO lads leaving, and Mr OVO arriving.

Anyway, it will prove very useful at some point in the future.

[Adam Funk]

Is that because theft of electricity is a lot less common than it used to be?

[Pancho]

I've got the same, apart from I had ignored it up until today, but it explains why my Home Display stopped displaying electricity.

Still works for gas, just not leccy. Stopped working about 5 months ago. The actual meter display shows a sensible number. I just get estimated electricity bills and no electricity figure on the Home Display.

Strange:

"Gas meters send their readings through the electricity meter. When they're more than 10metres (32 feet) apart, the gas meter won't be able to communicate with Bulb or the smart network."

So the electricity box is responsible for networking. Mine can report gas figures just not its own internal figures.

Smells like a software bug, rather than network issues. Might be a bug at Bulb, rather than my meter.

[Dave Plowman (News]

It's a criminal offence to steal electricity. And they'd know if the seal was removed to do this.

[Mark Carver]

My electric smart meter, and dumb gas meter are about 8 or 9 metres apart, but on the same wall, so there's 8 or 9 metres worth of bricks, insulation, and breeze blocks between the two.  OVO want to upgrade the gas meter to a smart one, but I'm not sure whether the comms would work anyway ?  Anyway, I keep rejecting the idea, telling them I want to witness a full 12 month period of reliable operation from the electric one.

[John Rumm]

Probably not. More likely to be a combination of the supplier using historical data and algorithms to spot fraud rather than fuse seals, and the meter readers no longer technically clued up people who are part and parcel of the organisation actually responsible for billing.

(there is also a slight distinction between meter seals and fuse seals, where the latter will be more broken commonly anyway for reasons of isolation of supply).

[newshound]

Mine is similar. The leccy board man is of course doing it all the time, unlike you. Also, he'll be aware that if he has an accident while not wearing the stipulated PPE it will screw his chance of compensation (and could get him fired).

[Adam Funk]

Good points, thanks.