Are DNO cables fused?

[Cookie]

Are DNO cables in the UK fused before going into a building? And if so how? What happens if you were to short the cable out before the cutout main fuse?

View: https://youtu.be/HQSohl-C_nk?t=180

 

[Pete999]

Yes at the feeder Pillar you could be in deep do dos

 

[Cookie]

Yes at the feeder Pillar

Any idea on the amps, type of fuse, time current curve?

 

[Lucien Nunes]

It depends on the type and size of service. Normal urban domestic and light commercial supplies are not individually fused outside the building; they are tapped off a distributor cable that might be fused at a pillar or link box. My street, for example, has ~150 houses and is fed in two sections, one each side of a crossroads, each fused at 315A with IIRC BS88 part 5, 80kA J-type fuses. E.g.: Lawson 315A JSU

There is a box in the road at each end of each section, with the fuses present in one but removed from the other, to allow for two alternative sources of supply in case of cable or transformer failure. The main is 3-phase but most services taken from it are single-phase, fused at 60-100A within the premises. There are a few 3-phase service cables feeding new builds that will have a multi-service head, plus a few of the larger houses (mine included) which have two of the three phases using the old 3-wire cables from the days when it was a 240-0-240 DC supply.

I don't know under what specific conditions or current ratings an LV service cable to a single consumer would be individually fused. Perhaps one of our ex-DNO guys will chime in with more info.

 

[davesparks]

Any idea on the amps, type of fuse, time current curve?

Normally J type BS88 fuses for normal supplies, bigger supplies may be fed from ACCBs.

I think, from memory, UKPN (try to) standardise at 400A 630A or 800A

 

[Cookie]

Normally J type BS88 fuses for normal supplies, bigger supplies may be fed from ACCBs.

I think, from memory, UKPN (try to) standardise at 400A 630A or 800A

How do their time current curves compare with regular indoor fuses? Do they coordinate with the cutout fuse below the consumer unit?

 

[Cookie]

It depends on the type and size of service. Normal urban domestic and light commercial supplies are not individually fused outside the building; they are tapped off a distributor cable that might be fused at a pillar or link box. My street, for example, has ~150 houses and is fed in two sections, one each side of a crossroads, each fused at 315A with IIRC BS88 part 5, 80kA J-type fuses. E.g.: Lawson 315A JSU

There is a box in the road at each end of each section, with the fuses present in one but removed from the other, to allow for two alternative sources of supply in case of cable or transformer failure. The main is 3-phase but most services taken from it are single-phase, fused at 60-100A within the premises. There are a few 3-phase service cables feeding new builds that will have a multi-service head, plus a few of the larger houses (mine included) which have two of the three phases using the old 3-wire cables from the days when it was a 240-0-240 DC supply.

I don't know under what specific conditions or current ratings an LV service cable to a single consumer would be individually fused. Perhaps one of our ex-DNO guys will chime in with more info.

Any idea of the distributor cable's size (mm2) and the size of the tap (mm2)?

I am wondering 1) how fast a short circuit below the cutout fuse will take to clear 2) will the BS88 fuse blow before any thermal damage to the tap cable.

I like the idea of normally open tie points. Very elegant. I can see why cable faults do not persist in the UK.

You have what are called Lucy cutouts in the UK correct? And links to a UK pedestal by chance?

 

[davesparks]

Any idea of the distributor cable's size (mm2) and the size of the tap (mm2)?

I am wondering 1) how fast a short circuit below the cutout fuse will take to clear 2) will the BS88 fuse blow before any thermal damage to the tap cable.

I like the idea of normally open tie points. Very elegant. I can see why cable faults do not persist in the UK.

You have what are called Lucy cutouts in the UK correct? And links to a UK pedestal by chance?

Distributing mains are usually either 185mm or 300mm I think (again based on memory from UKPN specs, other DNO's have their own rules)
Service cables are sized according to the size of supply, a typical 100A SPN supply will be 35mm concentric.

DNO's tend to stick to a few select cable sizes rather than using the full available range of cable sizes.

Service cables are protected from overload at by the cutout fuse.

Lucy is a company which makes cutouts, feeder pillars and other equipment. Other brands of equipment are available.

I believe some DNO's use Merlin Gerin's SAIF type feeder pillars,
[automerge]1597509572[/automerge]

How do their time current curves compare with regular indoor fuses? Do they coordinate with the cutout fuse below the consumer unit?

I think they are the same fuses just in a different physical package.

BS88 fuses will generally discriminate as long as their is a gap of 2 standard sizes between them.

 

[Lucien Nunes]

My service (tap) cable is 19/.064 paper-insulated lead-covered which is quite typical of its time. 19/.064 is Olde English for 0.0225 sq. ins, i.e. about 14.5mm². It was probably put in for 60A but my fuses are probably 80A BS1361s, possibly 100A, I can't remember. None of the cutouts on this street are likely to be above 100A so will be fine for selectivity with the main fuses. I don't know the size of our main, 0.3 sq. Ins or 185mm² would be typical.

Lucy Electric are a manufacturer of equipment widely used by DNOs for over a century, other main UK brands are Henley and (historically) Isco and BICC.

Distribution cabinet: Lucy 1600A cabinet

 

[davesparks]

Lucy Electric are a manufacturer of equipment widely used by DNOs for over a century, other main UK brands are Henley and (historically) Isco and BICC.

I thought ISCO was a W.T. Henley product line?

 

[Lucien Nunes]

Good point!

<rhubarb />

 

[Micktw68]

Are DNO cables in the UK fused before going into a building? And if so how? What happens if you were to short the cable out before the cutout main fuse?

View: https://youtu.be/HQSohl-C_nk?t=180

London area are fused in the local secondary sub station (11kv-415), occasionally fused in the link box in the street .Not many pillars in London as most of the secondary subs are indoors (small block buildings ) Or package subs - link to SP doc with some photos of current pillars and subs . Interesting photos of open LV boards which are still in use. (skeltag “suicide” board My personal favorite. ) https://www.spenergynetworks.co.uk/userfiles/file/OPSAF-12-007.pdf

 

[pc1966]

Interesting photos of open LV boards which are still in use. (skeltag “suicide” board My personal favorite. )

Wow - it give me the willies just thinking about working on something like that!

 

[Lucien Nunes]

In my post #9, for "19/.064" please read "7/.064". I was writing a report on something wired in the larger cable and have 19/.064 on the brain now. 7/.064 is 0.0225 sq. ins.

 

[Cookie]

Distributing mains are usually either 185mm or 300mm I think (again based on memory from UKPN specs, other DNO's have their own rules)
Service cables are sized according to the size of supply, a typical 100A SPN supply will be 35mm concentric.

DNO's tend to stick to a few select cable sizes rather than using the full available range of cable sizes.

Service cables are protected from overload at by the cutout fuse.

Lucy is a company which makes cutouts, feeder pillars and other equipment. Other brands of equipment are available.

I believe some DNO's use Merlin Gerin's SAIF type feeder pillars,
[automerge]1597509572[/automerge]


I think they are the same fuses just in a different physical package.

BS88 fuses will generally discriminate as long as their is a gap of 2 standard sizes between them.

Do you know the rated burial current of 185mm2, 300mm2 and 35mm2 concentric cable?

Alright.

 

[Cookie]

My service (tap) cable is 19/.064 paper-insulated lead-covered which is quite typical of its time. 19/.064 is Olde English for 0.0225 sq. ins, i.e. about 14.5mm². It was probably put in for 60A but my fuses are probably 80A BS1361s, possibly 100A, I can't remember. None of the cutouts on this street are likely to be above 100A so will be fine for selectivity with the main fuses. I don't know the size of our main, 0.3 sq. Ins or 185mm² would be typical.

Lucy Electric are a manufacturer of equipment widely used by DNOs for over a century, other main UK brands are Henley and (historically) Isco and BICC.

Distribution cabinet: Lucy 1600A cabinet

Any idea what a 185mm2 trunk might be fused at?

 

[Julie.]

Wow - it give me the willies just thinking about working on something like that!

Open frame distribution panels like that remain pretty normal at 400v for most dno I think, the protection from contact is keeping the substation door closed.

In circ 1978 I had to carry out my first "real" live switching at 6.6kV - it was an open panel similar to that 400v one, but at 6.6kV - officially one had to stand 2m away and pull each phase separately (just like expulsion fuses on ohl).

However, the substation was under Picadilly train station in Manchester in a room less than 2m wide!

Scariest thing I have ever done in my life!

In fairness every live line switching after that was a piece of cake in comparison.

The engineers were dreadfully disappointed when the station was upgraded and proper switchgear put in place - it had been the test of new engineers for as long as anyone could remember.

 

[Cookie]

London area are fused in the local secondary sub station (11kv-415), occasionally fused in the link box in the street .Not many pillars in London as most of the secondary subs are indoors (small block buildings ) Or package subs - link to SP doc with some photos of current pillars and subs . Interesting photos of open LV boards which are still in use. (skeltag “suicide” board My personal favorite. ) https://www.spenergynetworks.co.uk/userfiles/file/OPSAF-12-007.pdf

Is there anyway these could be put underground? Does such a thing exist?

I just want to say I'm amazed at the level of fusing.

Can I ask? Why does the UK fuse everything on the DNO side?

 

[pc1966]

Open frame distribution panels like that remain pretty normal at 400v for most dno I think, the protection from contact is keeping the substation door closed.

It is not the contact that worries me, it is the potential arc-flash from dropping something!

 

[Julie.]

It is not the contact that worries me, it is the potential arc-flash from dropping something!

The issue really is people breaking into substations, thinking it's just the same as any other place, that's why dno are moving away from substation buildings towards package substations, or fully enclosed panels in bigger substation buildings