Company fuse.

[westie101]

At the end of the day there is a means of isolation at the main fuse, which is the equivalent position as the gas isolation point.

The difference is that access to the electricity equipment is restricted for good reason (to the industry anyway)

Now I can see your point but would suggest wiser folk than ourselves have decided to maintain the status quo with no need to fit an isolator anywhere else.
If others wish to lobby for a change that is their right.

So one reason could be if the CU isolator catches fire, so would you then suggest there needs to be a means of isolating somewhere if the cutout catches fire? How far should we go?

It's been like this for over 100 years with no major issues so why do we need to change something that may not be an issue (I regularly talk to local electricians, non have suggested that isolators are needed.
A final point in this post, there seem to be agreement that connections are a weak point in an installation, yet here we are discussing adding a further 4 connections at the point of highest load of an installation!

 

[JohnW2]

At the end of the day there is a means of isolation at the main fuse, which is the equivalent position as the gas isolation point. The difference is that access to the electricity equipment is restricted for good reason (to the industry anyway)

As you say, the difference is access. If one views the presence of an isolator at the origin of a 'dangerous supply' as being their at least partially for use in emergencies, it's essential that they are accessible to consumers - unless you propose to have a member of DNO staff hidden away permanently in each and every 'meter cupboard'

So one reason could be if the CU isolator catches fire, so would you then suggest there needs to be a means of isolating somewhere if the cutout catches fire? How far should we go?

Yes, it's always going to be possible to extend the argument. However, as I've said, I think it would be reasonable to have isolation at the point where the supply becomes the responsibility of the consumer (i.e. at output terminals of meter). A meter with built-in isolator is, I suppose, the most obvious way of achieving this (and, in response to one of you other comments,a method which would not involve any additional non-factory connections). My LPG supplier insists on an isolator before the supply enters my property. That would also be ideal for electricity, but you've said that is not possible because of concerns about tampering with meters. Of course, if you were starting afresh, maybe you'd have meters external to the property (like many 'underground' water meters), and more-or-less immune from tampering.

Kind Regards, John.

 

[stillp]

It would be quite easy to design a "one-shot" isolator that would allow the householder to isolate the incoming supply to his premises, but not allow him to turn it back on. That would satisfy the "safety" need and not encourage tampering. Would there be any demand for such a device? Clearly not.

 

[JohnW2]

It would be quite easy to design a "one-shot" isolator that would allow the householder to isolate the incoming supply to his premises, but not allow him to turn it back on. That would satisfy the "safety" need and not encourage tampering. Would there be any demand for such a device? Clearly not.

True, but that's the case with any number of things which exist only for 'safety' reasons, in all sorts of walks of life - unless mandatory, there is going to be little demand.

Amidst all these discussions, the thing I probably understand least is why meters with built-in isolators (such as BAS and two members of my family have) are not much more common. If all new meters were of that type, then they could be installed at virtually no cost (the marginal cost of the actual isolator would probably be trivial) in the course of routine meter changes. Westie has said in the past that they result in 'problems' - but unless the manufacturers of meters are incapable of manufacturing reliable isolators, I find it hard to understand what sort of problems they might be.

Kind Regards, John.

 

[DavidWard]

It says nothing about qualifications - if you are competent you may do the work.

Yes but I cant self certify can I!

(I was going to go low voltage with individual transformers).

//www.diynot.com/wiki/electrics:voltage-bands[/QUOTE]

I forgot I was talking to electricians, terminology with general public understanding Low Voltage to be 12 to 24 volt. A hang over of fitting electric curtain tracks for customers. Although I am aware that it is extra low voltage since my course. Thanks

 

[333rocky333]

Westie has said in the past that they result in 'problems' - but unless the manufacturers of meters are incapable of manufacturing reliable isolators, I find it hard to understand what sort of problems they might be.

Well i was always taught isolators are for isolating off load, as opposed to main switches that can switch loads.
Whether there now made similar i dont know.
so called isolaters ive seen appear to be just a main switch within an enclosure, but I may be wrong.

If the consumers are unaware and did not switch off the loads and frequently used the isolator on and off under load possible damage to the contacts could occur i suppose.

 

[westie101]

It would be quite easy to design a "one-shot" isolator

I know I'm cynical but anything designed like that and folk will try and find a way round it

6 inch nails replacing main fuses that have blown, claw hammer replacing cut-out fuses and carriers that have burned out (honest).

A lot of HV supplies have such a device in the form of an emergency trip button that trips the HV switchgear, only we can switch back on, so we get accidental operation (they can only been reset with a key, I've seen one dismantled by an electrician to get it to reset. They still couldn't understand why the supply had not come back on) and suspected deliberate operation!
I have never known one operated for the original purpose!

 

[Wontdothatagain]

Just incase anyone is wondering what type of meter is being talked about, here is the inside of an ampy single phase disconnecting meter

Untitled

• Wontdothatagain
• 8 Jul 2011
• 2

 

[rebuke]

I'm intrigued by the photos of people wearing gauntlets and visors etc to pull the fuse - when I had my supplier (British Gas, though the guy they sent was from Siemens) come out and fit an isolator (and in fact a subsequent meter change that they randomly decided they needed to do), he didn't have any PPE to speak of (well, he might have been wearing glasses but I don't think they were safety ones) - he just switched the load off at my main switch, then cut the seal with some side cutters and pulled the fuse with his bare hands. He then did the necessary work, put the fuse back in and redid the seal, then plugged one of those socket testers in to a nearby socket to check the polarity.

I wonder if the lack of PPE on isolation is just the guy from Siemens not following procedures he's meant to, or whether they just don't have them in the first place...

 

[westie101]

I wonder if the lack of PPE on isolation is just the guy from Siemens not following procedures he's meant to, or whether they just don't have them in the first place...

Probably the former, but the latter wouldn't surprise me. If they get caught they generally never work on a DNO system again!

 

[JohnW2]

Well i was always taught isolators are for isolating off load, as opposed to main switches that can switch loads. Whether there now made similar i dont know. so called isolaters ive seen appear to be just a main switch within an enclosure, but I may be wrong.

I was taught exactly the same but it's always seemed a bit odd to me, except in very special situations. As you say, at least in the domestic setting, things installed these days called isolators seem to simply be switches rated to be able to break the full potential load. If, per this discussion, one of the desired functions of such an 'isolator' is to be as an 'emergency cutoff', it obviously ought to be rated for breaking the maimum possible current.

If we were talking about kA loads, then the cost saving of having a true isolator makes some sense, although that would have to be balanced against the risk that it might be operated on-load and hence damaged. I suppose that it could be designed such as it could not be operated if an appreciable current were flowing.

If the consumers are unaware and did not switch off the loads and frequently used the isolator on and off under load possible damage to the contacts could occur i suppose.

It's a little difficult to see why they would be operating it frequently, but I suppose that could be an answer. In the 'sample of two' that I've seen, if the operating lever is anything to go by, the switches/isolators in meters certainly are unlikley to be very meaty. However, if one is going to have them installed in meters, at the mercy of consumers, then I don't think it would make sense to have a switch/isolator which was not rated to break the maximum possible current.

Kind Regards, John

 

[JohnW2]

I'm intrigued by the photos of people wearing gauntlets and visors etc to pull the fuse -

Same here. I've witnessed several meter changes, and have never seen any significant PPE being used.

Kind Regards, John.

 

[sparkticus]

Iv'e seen a demo 2.5KA short circuit with 16mm copper tails. It is a very generous process. Everyone would have received a nice piece of molten copper had it not been for the safety screens.

 

[EFLImpudence]

Westie

As I said, I don't want to appear complacent or arrogant but...

... I find the majority of your reasons and arguments a bit fatuous and not really addressing the issue. It is obvious that you think an isolator unnecessary with answers ranging from it's been that way for 100 years (that is irrelevant and certainly wouldn't hold sway with any other products in the modern world) to you'd need a new pair of pliers.

The only reason which I may find acceptable is the one regarding additional joints being a weakness but even this fails when Henley blocks abound. The isolator could be fitted to the board with your torque drivers at the same time as the rest of the fittings.

I know people are conditioned by the job they do but you do not seem to care about the other side of the argument nor the people who have to put up with hassle from giant corporations which set the rules, write the contracts and do what they want with only themselves in mind.

We are NOT allowed to work live so rather than implement a simple solution we have (to do it legally) to wait for a man to turn up, pull cut-out, do work, man come back, replace cut-out and probably charge the customer getting on for fifty per-cent of my charge for changing a consumer unit; let alone a smaller job.


Another idea - Make the out-going terminals of the meter accessible under a separate seal which we can replace with our new pliers. Still live but easy to remove tails.

 

[westie101]

EFL
I actually do sympathise with you as I am fed up of going to properties with unsealed meters and cut-outs where it is obvious the CU has been changed.

I was shocked to attend a fire where that had been done and a poor connection the cause of the fire.
It was an obsolete cut-out of a type that should have been changed and would have if an authorised person had attended to remove the fuse.
The poor connection was the fuse carrier that had been disturbed!

I was shocked by the incident some years ago where a competent electrician got the polarity wrong making his own connections after pulling the main fuse and nearly killed someone

All I am doing is laying it on the line why isolators are not fitted, was it not Wontdothatagain posted a few pictures of burned out isolators recently.

At the end of the day the DNOs/suppliers are not interested in the concept so will do nothing to change, which is why I have twice suggested it needs your trade associations to start lobbying to change things

I have tried at a senior level to get the company interested in dealing with this problem without success.

And I absolutely condemn the practice of suppliers/DNOs charging for to remove/replace the main fuse!