dno fuse question that isn't can i pull it

[highpockets]

hello all, if a customer wanting a consumer unit upgrade has a dno fuse of 100 amp and 16mm tails approx 3m long and passing through walls, can i leave in the 16mm tails and ask the distributor to replace the fuse with an 80amp? also, how much could they charge for this?

 

[Zeespark]

You can certainly ask the DNO, though I wouldn't know how much they may charge for this. Why not ask the DNO to fit a DP isolator for you at the same time?

Just a quick question, how do you in fact know that the fuse is rated at 100 Amp?

AndyGuinness

 

[cadspark]

I was at a customers house last week doing an EICR when Scottish Power turned up to replace an ancient cutout. I asked them what size fuse they would be putting in and they told me they only fit 80 amps because the meters are only rated for this.

 

[Technician]

Is there not something in the new OSG about 25 mm

tails minimum, and if so, is this retrospective and

can it be applied to upgrades as well as new installs?

 

[Andy™]

Is there not something in the new OSG about 25 mm tails minimum, and if so, is this retrospective and

can it be applied to upgrades as well as new installs?

im not aware of anything in the regs stating min 25mm for tails. if something is said in the OSG, then its just guidance anyway

 

[ProDave]

I was at a customers house last week doing an EICR when Scottish Power turned up to replace an ancient cutout. I asked them what size fuse they would be putting in and they told me they only fit 80 amps because the meters are only rated for this.

That's at odds with Scottish Hydro. One if their linesmen I met on a new build told me they only ever fit 100A fuses.

but if you haven't pulled the fuse how do you know the rating of what's in there? :innocent Just because it says 100A on the carrier does not mean that's what is inside.

Personally I would fit an isolator and 25mm tails from the CU to the isolator, then phone the DNO to report sub standard tails and see if they will upgrade the meter tails to 25mm to match.

 

[Theorysparky]

The way i see it...

what is the estimated maximum current that will be pulled by the installation ????

is it ever going to exceed 80 amps ????

do the 16mm tails look as though they are over heating ????

personally i would be more worried about ensuring there was a 16mm main earth............

just me..........

 

[Doc Hudson]

[quote name='Andy

 

[highpockets]

to be fair, 80 amps would be easily cover the maximum demand. i haven't opened the carrier as yet, i was just wondering what i could do if it did turn out to be 100 amp. i got told today that there is a nationwide drive to replace all the 100A fuses with 80A, to help with the apparently impending energy crisis. it seems to make sense, but as ever, it can depend on who you ask.

 

[SPECIAL LOCATION]

to be fair, 80 amps would be easily cover the maximum demand. i haven't opened the carrier as yet, i was just wondering what i could do if it did turn out to be 100 amp. i got told today that there is a nationwide drive to replace all the 100A fuses with 80A, to help with the apparently impending energy crisis. it seems to make sense, but as ever, it can depend on who you ask.

It is the DNO's responsibility to protect their tails adequatly.... Not yours!

Are there existing signs of overheating on the cables???

If you are never realistically going to drawn 80amps + then it is to some degree irrelevant!!

 

[kerching]

Have a look at the 'scary graphs', see what a 100Amp and an 80Amp will actually carry before lifting...hardly worth the worry........ :coat

 

[Adrian41uk]

........nationwide drive to replace all the 100A fuses with 80A, to help with the apparently impending energy crisis....

There is a general trend towards downgrading to 80A but its got nothing to do with any "energy crisis" ... more to do with the fact the the DNOs have realised that for a large number of installations Ze is to large to allow a 100A BS fuse to open quickly enough, so, instead of doing the necessary work to reinforce the network and lower the earth loop impedance they take the easy way out and down grade the fuse!

 

[Doc Hudson]

There is a general trend toward downgrading to 80A but its got nothing to do with any "energy crisis" ... more to do with the fact the the DNOs have realised that for a large number of installations Ze is to large to allow a 100A BS fuse to open quickly enough, so, instead of doing the necessary work to reinforce the network and lower the earth loop impedance they take the easy way out and down grade the fuse!

How does that concept work with TT installations supplied via a 100A (or even 80A) cut out fuse with an Ra up toward 100ohms?

Doc H.