Is this genral knowledge

[1stfix2ndfix]

Or is it in the book (regs) ?

I was helping on a job today and paid particular attention to the fact that when the cutout fuse was 100a and the main switch was 100a we had to upgrade the size of the tails to 25mm

When it was 60a we didn't! Now I'm not 100% sure if the main switch was 100a 80a or 60a which might make a difference!

At what point do you have to upgrade the tails?

it was the last job of the day, after a near 400 mile round trip for 3 jobs so I didn't want to hold up proceedings by ask a million and one questions ...

 

[davesparks]

I don't think it is possible to get a main switch less than 100A in a CU these days.

The size of the tails can be calculated exactly the same as any other cable based on the size of the company fuse.
OR if the tails are feeding something like a switchfuse then the rating of the fuse in the switchfuse can be used for the calculation. So if you have a 32A switchfuse you could use 6mm tails.

 

[Octopus]

Or is it in the book (regs) ?

I was helping on a job today and paid particular attention to the fact that when the cutout fuse was 100a and the main switch was 100a we had to upgrade the size of the tails to 25mm

When it was 60a we didn't! Now I'm not 100% sure if the main switch was 100a 80a or 60a which might make a difference!

At what point do you have to upgrade the tails?

it was the last job of the day, after a near 400 mile round trip for 3 jobs so I didn't want to hold up proceedings by ask a million and one questions ...

So you cut the seals on the meter then?

I don't always upgrade the 16mm tails to 25mm - especially if the house isn't likely to draw much over 40A! jmo. Tin hat on

 

[GLENNSPARK]

So you cut the seals on the meter then?

I don't always upgrade the 16mm tails to 25mm - especially if the house isn't likely to draw much over 40A! jmo. Tin hat on

common sense...

i mean come on fellas...how many houses are pullin close to 100A?

unless they`v got a grow goin on or summat like that.......

 

[Richard Burns]

The tails need to be rated for the current they will take and so this is based on the rating of the protective device if you have a 100A fuse and the installation is taking 100A then the tails need to be able to cope with 100A.
The rating of the main switch is dependent on the load it will take, it should be rated equal to or higher than the design current, generally if you have a 100A fuse then the switch after it should be rated to 100A, though if the installation is divided then each switch may not need the full 100A capability.

 

[telectrix]

think i've posted before that i've had 16mm T/E running at 110A for about 30 minutes, at which time the 63A MCB let go. measured the temperature of the insulation at 39deg. hate to think what i'd have had to shove through it to get to 70.

 

[davesparks]

70degrees is max conductor operating temperature not the max surface temperature of the insulation !

 

[telectrix]

so why is xlpe higher rated temp for same conductor size? copper melts at around 1000 deg.

 

[Marvo]

With 6mm volt drop would probably be the downfall rather than exceeding the temperature rating.

 

[D Skelton]

70degrees is max conductor operating temperature not the max surface temperature of the insulation !

Max conductor operating temperature to ensure that its insulation is not degraded

 

[Knobhead]

so why is xlpe higher rated temp for same conductor size? copper melts at around 1000 deg.

1085°C

I don't always upgrade the 16mm tails to 25mm - especially if the house isn't likely to draw much over 40A! jmo. Tin hat on

So if the load is liable to be high would you replace the tails from the head to the meter? If you don’t it makes a mockery of replacing the tails from the meter.
Yes it’s their property and they work to their own rules. But technically they should be replaced to be of equal CSA.
The DNO’s own specification states 25mm for 100A in a new install.

 

[telectrix]

normally, you select the size according to the OCPD for the tails, but in a domestic situation where the load will never approach any where near 100A, 16mm tails, if showing no sigh of damage, can be left in. on a new installation, obviously, you fit 25mm.

 

[HappyHippyDad]

See Best Practice Guide number 6.

"16mm² meter tails with a 100A cut-out fuse could be adequate if the maximium demand of the installation (taking into account diversity and load profile) does not exceed the current-carrying capacity of the tails, AND also provided that the requirements of the Regulation 434.5.2 for protection of the tails against fault current are met."

In other words... excatly whats already been said!! But nice to see it in black and white!

 

[Geordie Spark]

See Best Practice Guide number 6.

"16mm² meter tails with a 100A cut-out fuse could be adequate if the maximium demand of the installation (taking into account diversity and load profile) does not exceed the current-carrying capacity of the tails, AND also provided that the requirements of the Regulation 434.5.2 for protection of the tails against fault current are met."

In other words... excatly whats already been said!! But nice to see it in black and white!

Careful now .. that could be bordering on being a Racist Comment.

 

[Deleted member 26818]

My understanding, is the requirement for 25mm tails is something to do with the DNOs, not something that is a requirement of the Regs.
In the majority of cases, 16mm tails are more than adequate for loads up to 100A.

 

[Knobhead]

See Best Practice Guide number 6.

"16mm² meter tails with a 100A cut-out fuse could be adequate if the maximium demand of the installation (taking into account diversity and load profile) does not exceed the current-carrying capacity of the tails, AND also provided that the requirements of the Regulation 434.5.2 for protection of the tails against fault current are met."

In other words... excatly whats already been said!! But nice to see it in black and white!

As far as I know the best practice guide isn’t issued by the IET but by the NICEIC. It therefore doesn’t really carry any weight. It’s just the NIC making things up as they go along. (As per normal.)

HHD, if you blithely follow everything you read in black and white, could I recommend the two excellent publications by Mr. D. W. Cockburn.

I was taught to question things, find out the reason why things are done. Not just blindly follow everyone else.
If you look how I phrased the 2[SUP]nd[/SUP] part of #11, I said “But technically they should be replaced to be of equal CSA.”

 

[davesparks]

so why is xlpe higher rated temp for same conductor size? copper melts at around 1000 deg.

Because XLPE insulation can cope with a higher conductor operating temperature.

PVC is only specified to cope with a 70degree conductor operating temperature. the inner surface of the insulation will be in contact with the conductor which is at 70degrees, the outer surface will be at a lower temperature due to the fact that the insulation will also insulate thermally as well as electrically.

 

[Engineer54]

In all the decades i've been working in this industry, i have yet to see a single circuit let alone an installation approaching anywhere near to operating normally at 70c!! The only person here that may have is Tony, working in the steel foundry industry.... (With appropriate insulation method/material in place)

A conductor operating even remotely near 70c, the PVC insulation will be showing definite visual signs that something is very wrong!! ....

 

[shanky887614]

As far as I know the best practice guide isn’t issued by the IET but by the NICEIC. It therefore doesn’t really carry any weight. It’s just the NIC making things up as they go along. (As per normal.)

HHD, if you blithely follow everything you read in black and white, could I recommend the two excellent publications by Mr. D. W. Cockburn.

I was taught to question things, find out the reason why things are done. Not just blindly follow everyone else.
If you look how I phrased the 2[SUP]nd[/SUP] part of #11, I said “But technically they should be replaced to be of equal CSA.”

I was brought up the same way tony, not many people seem to have been brought up like that now adays.

Electrical Trainee :You need a new fuseboard
average Client: how much?

They dont question anything to makesure its valid for some reason, when my pc was goosed did I go and buy another?

No I just bought new psu etc

 

[Knobhead]

In all the decades i've been working in this industry, i have yet to see a single circuit let alone an installation approaching anywhere near to operating normally at 70c!! The only person here that may have is Tony, working in the steel foundry industry.... (With appropriate insulation method/material in place)

A conductor operating even remotely near 70c, the PVC insulation will be showing definite visual signs that something is very wrong!! ....

The only time I’ve used MICC was directly above an iron ladle, kiln tops were done in cambric.

Otherwise find a route around the heat source. All cable runs were coated in ganister cement as a precaution against metal splash. But normally you avoid heat whereever possible.

 

[1stfix2ndfix]

Cheers for all the answers it looks like Ive got lucky and asked a good question for a change!
Im sure I've lost jobs in the past by asking to many questions (possible at the wrong time in fairness) but you can't be sure, It would be a shame if it did but it does slow things down bit!
Still I've been educated here and left to ponder if I want which is the main thing so thanks for that. Hopefully any other questions are just as good


As far as I knot the tag was already cut, but I think I would sooner cut it of if it was on and pull the fuse if I had to upgrade the tails or change a cu. I'm trying to think of a way to do that that means I won't get electrocuted and no one has shown me a way yet and I can't think of one

Even if you didn't pull the main fuse say and put the tails into a temporary board wouldn't that be a bit risky if it was live as there so stiff. Surely you can't leave em live and make sure you don't brush against them either

 

[PEG]

..."As far as i know,the tag was already cut"...your going to fit in a treat,pal :clap:

 

[Geordie Spark]

Cheers for all the answers it looks like Ive got lucky and asked a good question for a change!
Im sure I've lost jobs in the past by asking to many questions (possible at the wrong time in fairness) but you can't be sure, It would be a shame if it did but it does slow things down bit!
Still I've been educated here and left to ponder if I want which is the main thing so thanks for that. Hopefully any other questions are just as good


As far as I knot the tag was already cut, but I think I would sooner cut it of if it was on and pull the fuse if I had to upgrade the tails or change a cu. I'm trying to think of a way to do that that means I won't get electrocuted and no one has shown me a way yet and I can't think of one

Even if you didn't pull the main fuse say and put the tails into a temporary board wouldn't that be a bit risky if it was live as there so stiff. Surely you can't leave em live and make sure you don't brush against them either

"Someone" once told me that an unused nozzle from a silicone tube fits nicely over the bare end of a meter tail just jam it on then secure it with a bit of insulting tape to make sure that it doesn't drop off.

 

[shanky887614]

"Someone" once told me that an unused nozzle from a silicone tube fits nicely over the bare end of a meter tail just jam it on then secure it with a bit of insulting tape to make sure that it doesn't drop off.

Thats interesting I wonder who told them that

 

[tidyboiler]

"Someone" once told me that an unused nozzle from a silicone tube fits nicely over the bare end of a meter tail just jam it on then secure it with a bit of insulting tape to make sure that it doesn't drop off.

Jeez, even your tape's offensive!!!

 

[Geordie Spark]

Thats interesting I wonder who told them that

It was a long time ago and I'm not sure that I remember now and not even sure if I have ever done it, but I can see it being a lot easier and safer than trying to wrap insulting tape around the live bare ends or shoving them into a choccy block.

 

[Geordie Spark]

Jeez, even your tape's offensive!!!

Yes pet.

 

[shanky887614]

It was a long time ago and I'm not sure that I remember now and not even sure if I have ever done it, but I can see it being a lot easier and safer than trying to wrap insulting tape around the live bare ends or shoving them into a choccy block.

Is that then connecting into henley block then new tails from there because as far as I can see it the fuse would need to come out to uprate the tails in a lot of cases

 

[Geordie Spark]

Is that then connecting into henley block then new tails from there because as far as I can see it the fuse would need to come out to uprate the tails in a lot of cases

Don't ask me ...... I'm only a plumber.

BUT .... I'm a plumber who knows that silicon cartridge nozzles fit very nicely on the live ends of meter tails.

 

[shanky887614]

Don't ask me ...... I'm only a plumber.

BUT .... I'm a plumber who knows that silicon cartridge nozzles fit very nicely on the live ends of meter tails.

Dont look at me im just an amateur musician honest

Dont have a clue where grade 4 one is and stopped lessons cause of work just before was going to do 5.

Could have joined raf etc as musican sigh the contracting life for me then

 

[Geordie Spark]

Dont look at me im just an amateur musician honest

I used to be one of those but there was nothing honest about it.

 

[shanky887614]

I used to be one of those but there was nothing honest about it.

Im a musician not an electrician XD

 

[1stfix2ndfix]

So although they say don't pull the main cut out, you haven't got a lot of choice if u decide to opt for 100per cent not electrocuting yourself? So why do people tut when it's done, I just don't get that If I'm honest!

 

[shanky887614]

So although they say don't pull the main cut out, you haven't got a lot of choice if u decide to opt for 100per cent not electrocuting yourself? So why do people tut when it's done, I just don't get that If I'm honest!

Because they would rather pay the dno to turn up pull the fuse then come back later to put it back in


Edit changed breaker to fuse

 

[Engineer54]

Because they would rather pay the dno to turn up pull the breaker then come back later to put it back in

Pull the Breaker?? Posh round your way then is it?? lol!!

 

[Knobhead]

If he’s pulling the breakers at Castle Donnington it’s going to get bloody dark around large area on the midlands.

 

[shanky887614]

If he’s pulling the breakers at Castle Donnington it’s going to get bloody dark around large area on the midlands.

Lol I meant fuse

Im right next to substation on new estate so no problem XD

 

[Knobhead]

I’ve spoken to grid control at Castle Donnington a few times when we needed our 33KV supply switching.
They used to moan if we wanted a breaker put in to circuit earth. Opening and closing was remote, they had to send someone out for anything else.

 

[shanky887614]

I’ve spoken to grid control at Castle Donnington a few times when we needed our 33KV supply switching.
They used to moan if we wanted a breaker put in to circuit earth. Opening and closing was remote, they had to send someone out for anything else.

Lol I know one of people in the call centre there tony? a right mouthy woman

 

[Geordie Spark]

Lol I know one of people in the call centre there tony? a right mouthy woman

It's not Your Lass is it??

 

[shanky887614]

It's not Your Lass is it??

No, one of the regulars in a local pub

 

[Knobhead]

Grid control isn't a call centre. It's the operations room, call them, they answer the phone. It's staffed by engineers you can have a sensible conversation with.

 

[shanky887614]

Grid control isn't a call centre. It's the operations room.

The only one I have ever seen was the one in Ratcliffe on soar.

On a tour

 

[Knobhead]

They did upset me one night.

I’d had a 20MVA 33/11KV transformer go out on Buchholtz surge. They phoned, didn’t even ask what was wrong “Do you want us to reclose?” “No I bloody well don’t!”