Departurtes

[ricicle]

The 100A fuse in the service head (or whatever size it is) does not protect the DNO cable entering your property, this is protected by the next DNO fuse upstream wether it be a 315A fuse I don't know. Only they can answer that.

Might have to argue a bit with you on that one spark ( ). The DNO's LV cables in the path are usually of larger CSA than the spur off to the property. The fuse at the s/s protects the larger cable, but the fuse in the property protects the cable from the joint in the ground (overload only of course) even though it is further along from the change in CSA.

 

[duncanhead]

You won't find an RCD protecting the DNO service cable though.
You'll get the full 560A if the cable faults, how the cable behaves is another matter.

I'd think that you'll be surprised, the DNO feeds are very good - so is thier protection, as I said I wouldn't want to try it in practice, 2 reasons, it'll take the whole block out, and the DNO may then want to replace thier feed to my system board, (would require digging up 2 rooms and a nice driveway)...

.. and to create this sort of fault is (death), I know it as I've heard from a colleague that some one dropped a spanner ( but don't site me) and "melt down" occured, the person died a week later.... not a "nice" "picture"...

hmmm.. it'll actually be a 100 Amp fuse, need to check out the specs for the DNO fuses and what mm2 thier supply actually is, (I'm not going to try and measure it (each core) with my micrometer though) but as you rightly know fuses "run" at overcurrent" for quite a few seconds if not an hour (depending on the over current) as relating to the "nominal" rating.... Why do you think that I wouldn't what to "upgrade" to a 100 Amp fuse if I knew that 80-100Amps+ were regularly loaded thru it ( the original 60 Amp fuse)?




If the supply is for the block I don't think it will be 100A

do you mean thay supply 100 Amps, or they provide a "fusable" link at the DNO supply head at 100 Amps

Can't wait for Sunday...

 

[RF Lighting]

I've worked in DNO substations.

The fuses are generally BS88, rated upto 560A per ring main.

I'm quite happy to publicly disclose this. Hardly official secrets stuff

 

[Spark123]

The 100A fuse in the service head (or whatever size it is) does not protect the DNO cable entering your property, this is protected by the next DNO fuse upstream wether it be a 315A fuse I don't know. Only they can answer that.

Might have to argue a bit with you on that one spark ( ). The DNO's LV cables in the path are usually of larger CSA than the spur off to the property. The fuse at the s/s protects the larger cable, but the fuse in the property protects the cable from the joint in the ground (overload only of course) even though it is further along from the change in CSA.

Was talking fault current i.e. from page 7.
When the BS951 clamp bites into the cable and it goes bang the upstream protective device is the one doing the protection

 

[ricicle]

The 100A fuse in the service head (or whatever size it is) does not protect the DNO cable entering your property, this is protected by the next DNO fuse upstream wether it be a 315A fuse I don't know. Only they can answer that.

Might have to argue a bit with you on that one spark ( ). The DNO's LV cables in the path are usually of larger CSA than the spur off to the property. The fuse at the s/s protects the larger cable, but the fuse in the property protects the cable from the joint in the ground (overload only of course) even though it is further along from the change in CSA.

When the BS951 clamp bites into the cable and it goes bang the upstream protective device is the one doing the protection

Yeah, sorry we are talking short circuit here (note to myself -must read posts properly)

 

[duncanhead]

I've worked in DNO substations.

The fuses are generally BS88, rated upto 560A per ring main.

I'm quite happy to publicly disclose this. Hardly official secrets stuff

hmmm... that's an overload for quite a considerable period, if it's 560 Amps per "installation" .... so it could take 1000 Amps for say 30 secs with no "issue"...

 

[duncanhead]

You won't find an RCD protecting the DNO service cable though.
You'll get the full 560A if the cable faults, how the cable behaves is another matter.

I'd think that you'll be surprised, the DNO feeds are very good - so is thier protection, as I said I wouldn't want to try it in practice, 2 reasons, it'll take the whole block out, and the DNO may then want to replace thier feed to my system board, (would require digging up 2 rooms and a nice driveway)...

.. and to create this sort of fault is (death), I know it as I've heard from a colleague that some one dropped a spanner ( but don't site me) and "melt down" occured, the person died a week later.... not a "nice" "picture"...

hmmm.. it'll actually be a 100 Amp fuse, need to check out the specs for the DNO fuses and what mm2 thier supply actually is, (I'm not going to try and measure it (each core) with my micrometer though) but as you rightly know fuses "run" at overcurrent" for quite a few seconds if not an hour (depending on the over current) as relating to the "nominal" rating.... Why do you think that I wouldn't what to "upgrade" to a 100 Amp fuse if I knew that 80-100Amps+ were regularly loaded thru it ( the original 60 Amp fuse)?




If the supply is for the block I don't think it will be 100A

do you mean thay supply 100 Amps, or they provide a "fusable" link at the DNO supply head at 100 Amps


no, my DNO "head" fuse is/will be 100 Amps
Can't wait for Sunday...

 

[Spark123]

In your case, if it is protected at the sub station by a 560A fuse and the BS951 clamp crushes the cable so the earthed metal meets the live conductor, the fuse at the sub station may never blow. It might pop and bang a lot inside your property.

 

[RF Lighting]

Yes, this is the point we are trying to make, and why it is so dangerous to attatch BS951 clamps to PILC supplies.

There was a photo of a fuseboard on here a little while ago.

An arc struck in the main switch and burned up must of the board for quite some time before the 100A supply fuse operated.

Now imagine that, but nearly six times more ferocious.

 

[Spark123]

I had a look at what was left of a switch room the other week where water (and bird poo) had got into an isolator causing it to arc over. It took out the 315A fuses feeding it and all but obliterated the isolator, the porcelain of one of the 315A BS88 fuse actually cracked in half.

 

[duncanhead]

Yes, this is the point we are trying to make, and why it is so dangerous to attatch BS951 clamps to PILC supplies.

There was a photo of a fuseboard on here a little while ago.

An arc struck in the main switch and burned up must of the board for quite some time before the 100A supply fuse operated.

Now imagine that, but nearly six times more ferocious.

yes point taken, the "damage" could be at/around my board, I'll "consult" with EDF 1st thing tomorrow as to BS951 clamps, if they need to "upgrade" the CPC to the earth "bus" then they can do that. I'm welcome.... I just think that 6 or 8 mm2 is "not up to it" - but that's a legacy cpc connection and as I've tested the Ze is only 0.4 Ohms so, good....

 

[duncanhead]

There's scope for using RCBOS on non-cpc lighting circuits, but I believe the niceic guidance phrases it "if the customer cannot be convinced of the need to rewire". IE a very last resort, now like RF says you're the installer and client, how's it gonna look that you couldn't convince yourself to do the job to the basic minimum standard?

the client is actually "my wife" and as she is funding the "project", I've written to her (with the official wording/recommendations) etc and more than 90% of the issues have been agreed to be "sorted" by myself as the Installer to the agreed timescales and my charges, and of course to the necessary compliancy/regulations, so I believe that I've "done the utmost" for complete compliancy and have reached a compromise that "meets " the recommendations as to a new CCU installation - this is all in accordance with the Electrical Safety Council Guide, a full risk assessment and recommendations have been corresponded, all class 1 fittings "departures" will be "sorted" leaving only 3 fittings that are of minimal risk and that the client states that the cost and/or disruption cannot be borne to rectify these, I've been asked to proceed with these "remedial" tasks prior to the CCU installation...

 

[duncanhead]

The 100A fuse in the service head (or whatever size it is) does not protect the DNO cable entering your property, this is protected by the next DNO fuse upstream wether it be a 315A fuse I don't know. Only they can answer that.

hmmm, again my telephone call to EDF tomorrow may answer this, if they give me a reply I'll post it in this Forum...

 

[duncanhead]

You are dangerous please never touch anything electrical again.

NICE PIC!!

I've been "told that" many times in business (IT), my "enthusiasm" has "done the biz" despite not the "technical expert" - as to a Project success...

 

[ban-all-sheds]

Nah - it's definitely a fishy smell:

It's a wanda lead...