Property: 3 flats to one house

[Dambo]

As has been said several times in this thread, you need to protect the cables in the installation. The DNO's provide guidelines on what you can do with tails, and downsizing them\running them across the house (usually classed as anything over 3m) isn;t something you can do.This isn;t some secret piece of info that only elite electricians learn, it is mentioned in the OSG (I think, sure it's mentioned somewhere prominent in a popular document). Also, common sense should tell you that the 100A fuse will be fine protecting a 2m piece of 25mm 6181Y but not a 20m piece of 16m 6242Y.

What name do you trade under?

Sorry, I wasn't aware of the 3m restriction. So is asking for advice on something you're not sure about now out of the question? I thought that was one of the main reasons for these forums.

 

[Dambo]

Hi DamienAre all the Consumer Units and Existing Meters in the same location?

If they are then NO switch fuses are required if all tails are less then 3 mtrs, they can all come from a double pole Henley type block off one set of tails from One Meter.

If however each Consumer Unit is at a remote location then the Distribution circuit must be provided with Over current protection, RCDs do not protect cables from overload or short circuit type faults.

Each of the consumer units is on a separate floor sparkytim. I know that RCDs don't detect overload or short circuit but I wasn't aware of the 3m rule.

 

[Lurch]

Regardless of the 3m rule, the general principles and basics of overload protection and cable sizing along with submains and their use seems to be something you don;t know anything about. Now the submains thing, maybe that could be overlooked if it's not something you've covered in detail in your training but cable sizing and overload protection should be something you know at least something about.

And I'm not saying that everyone should know everything about the subject, I'm saying someone who is a self employed electrician, supposedly registered as an NICEIC DI should know about fuses and cables.

 

[Dambo]

I rest my case.

[quote name='Andy

 

[Lurch]

It'd be more helpful if you tried to answer the question instead of trying to make me feel embarrassed for asking.

To be fair, you should be. And I think the question has been answered.

 

[Dambo]

Regardless of the 3m rule, the general principles and basics of overload protection and cable sizing along with submains and their use seems to be something you don;t know anything about. Now the submains thing, maybe that could be overlooked if it's not something you've covered in detail in your training but cable sizing and overload protection should be something you know at least something about. And I'm not saying that everyone should know everything about the subject, I'm saying someone who is a self employed electrician, supposedly registered as an NICEIC DI should know about fuses and cables.

Contrary to what you might think or what I may have portrayed I'm well aware of cable sizing and overload protection. But having not had any exposure to this type of submain work yet I just wanted to come on here and pick peoples' brains. And what's this 'supposedly registered as an NICEIC DI'? This forum seems to have turned from a great place to come and ask about things you're not sure about to a bit of a character assassination.

 

[Lurch]

Forget the submain bit specifically, it's just concerning that the general principles of fusing cables seemed to have been lost on you. That's it, that's what has been portrayed, that is what I'm basing my posts on. I can;t really see what else I can say.

 

[Dambo]

Forget the submain bit specifically, it's just concerning that the general principles of fusing cables seemed to have been lost on you. That's it, that's what has been portrayed, that is what I'm basing my posts on. I can;t really see what else I can say.

Fair enough. I'm not really interested in getting into this tit for tat posting Lurch. Since i've been coming on here your posts have been really helpful so I don't want to now seem ungrateful. Maybe sometimes some of the things I ask about I should already know but if I don't, i'll ask. I wouldn't do a job if I wasn't completely sure what I was doing, hence why I've come on about this topic. But believe me, my general understanding of fuse and cable sizes is fine.

 

[Chr!s]

Damien

You need to design the system to you maximum demand, once you have decided on that you can get cracking, the distribution circuit need protecting the same as any other, and theres nothing wrong with using the dnos fuse to protect the cable, though id stick a double pole isolator in the tails.

For me unless reasonable discrimination would be achieved between the dno fuse and switch fuse there's not much point fitting one.

Without more info its difficult to help

 

[batty]

I think this is the problem nowadays there seem to be more and more doing electrical work that don't know the basics. No offence Damian just glad you have come on here and asked at least your job will be done correctly.

 

[batty]

I think this is the problem nowadays there seem to be more and more doing electrical work that don't know the basics. No offence Damien just glad you have come on here and asked at least your job will be done correctly.

 

[steptoe]

DamienYou need to design the system to you maximum demand, once you have decided on that you can get cracking, the distribution circuit need protecting the same as any other, and theres nothing wrong with using the dnos fuse to protect the cable, though id stick a double pole isolator in the tails.

For me unless reasonable discrimination would be achieved between the dno fuse and switch fuse there's not much point fitting one.

Without more info its difficult to help

yes there is, the DNO fuse is to stop you overloading their cable,

nothing to do with your cable.

you must fit a switch fuse.

 

[Chr!s]

yes there is, the DNO fuse is to stop you overloading their cable,nothing to do with your cable.

you must fit a switch fuse

No you dont, the regs allow it

 

[steptoe]

where?

and more importantly,

will the DNO.?

 

[Lurch]

If the DNO say tails should be 3m max then that is that. They can refuse to supply if they see fit, doesn;t matter if it complies with 7671 or not. I think most say 3m max, none say do what you want with the distribution cables.

 

[Apache]

No you dont, the regs allow it

You mean where you could [theoretically] spur off a 2.5mm 32A ring using 1mm protected by a 13A fuse? Protect the cable before the power could be used as such?

No good if DNO won't connect!

 

[Lurch]

My maximum demands 95 amp, dno fuse 1361 100 ampill stick a 100 amp switch fuse in at 3 meter's whos fuse is protecting the distribution circuit?

While we are there do use the dnos fuse for fault current protection, answer yes, all the standard circuits in the onsite guide use the current limiting properties of the dnos fuse for their designs.

So we are happy to the dnos fuse for fault current protection but not overload?

You've lost me, if the DNO says 3m maximum tails before a switch fuse is needed then that's it. I'm not interested in what the OSG, BRB or anything else says on the matter.

 

[Chr!s]

You've lost me, if the DNO says 3m maximum tails before a switch fuse is needed then that's it. I'm not interested in what the OSG, BRB or anything else says on the matter

Well, the dno in my area is eon, they are only responsible upto the main cut out, the tails and the meter are the suppliers responsibility.

They have no issues using there fuse for overload and fault current protection, and as i I've already stated we've always been using it this way.

This 3 meters does not exist with eon the installation from the cut out needs to comply with Bs7671 and if the installation does then there happy.

 

[Lurch]

This 3 meters does not exist with eon the installation from the cut out needs to comply with Bs7671 and if the installation does then there happy.

Regional variations can differ. I'm saying the DNO says what's what, you're saying your DNO says what the whole country can do. Not quite sure what you're trying to achieve here?

 

[Chr!s]

Regional variations can differ. I'm saying the DNO says what's what, you're saying your DNO says what the whole country can do. Not quite sure what you're trying to achieve here?

Whos your dno Lurch, do they insist on the 3 meters?

Aslo i know edf have are the same, all they require is that if the tails are greater than two meters then an isolator is required.

It was my understanding that dnos only guarantee protection to the tails if the tails are no greater than three meters, beyond this you need to calculate.