Minimum distance between DNO feed and another protected circuit.

[epsilonGreedy]

I am planning to install two hockey stick conduits in the same area of a cavity wall.

 

1. One conduit will take the unprotected 100 amp DNO feed from underground up through the wall which will terminate in the cavity wall mounted meter box. All as per regs.
2. The second conduit will take a protected SWA high amp cable from the consumer unit out down the conduit and underground to the garage.

 

The relatively close proximity of the meter box and CU mounted in the same wall could result in the two conduits being very close inside the cavity wall and also by implication in the ground below. Would I be correct in thinking there is a minimum safe distance between the live DNO feed and other protected circuits originating from the CU?

[Jeremy Harris]

They are both double insulated LV power cables, and there's no specified separation distance requirement.  Also, both circuits are protected, as the incomer will be fused upstream, albeit with something like a 400 A to 800 A fuse.

[epsilonGreedy]

7 minutes ago, Jeremy Harris said:

They are both double insulated LV power cables, and there's no specified separation distance requirement.  Also, both circuits are protected, as the incomer will be fused upstream, albeit with something like a 400 A to 800 A fuse.

 

When I got my static caravan connected the electrician was not happy that I had the DNO feed and RCD protected caravan cable crossed and touching in a service trench. In retrospect I can see his point.

 

A 400amp fuse is of no benefit to a living creature.

 

In the absence of any safety standard I will fit the conduits 400mm apart.

[Jeremy Harris]

9 hours ago, epsilonGreedy said:

 

When I got my static caravan connected the electrician was not happy that I had the DNO feed and RCD protected caravan cable crossed and touching in a service trench. In retrospect I can see his point.

 

A 400amp fuse is of no benefit to a living creature.

 

In the absence of any safety standard I will fit the conduits 400mm apart.

 

 

Not sure where your electrician has made that up from, but I've just leafed through the blue book and there's nothing in the regs stating that.  There's no requirement for separation of double insulated power cables, and even if there was 400mm is completely OTT.  Get you bloke to read his copy of the blue book and confirm to you which section he thinks specifies this, as I can't find it anywhere.  Electrical separation and the requirements for basic protection are in sections 413 and 416 respectively.

 

FWIW, a 1A fuse is of no benefit to any living creature, either.  1A is several times more current than is needed to kill you.  Anyway, fuses and over-current circuit breakers are not there to protect from electric shock, they are there to prevent cables over heating and causing fires.

[epsilonGreedy]

1 hour ago, Jeremy Harris said:

FWIW, a 1A fuse is of no benefit to any living creature, either.  1A is several times more current than is needed to kill you.  Anyway, fuses and over-current circuit breakers are not there to protect from electric shock, they are there to prevent cables over heating and causing fires.

 

 

No, which begs the question why did you associate a 400amp fused DNO cable with any notion of householder electrical safety? RCDs are significant and this is the point, crossing cables where one is not RCD protected. As has been mentioned here before DNO supply cables are not armoured so one forceful plunge into soil with a sharp spade or over eager grab with a digger bucket and...

 

1 hour ago, Jeremy Harris said:

Not sure where your electrician has made that up from, but I've just leafed through the blue book and there's nothing in the regs stating that.

 

 

Surely you can comprehend the common sense in his concern even if there is no matching chapter in the regs. My electrician was over 50 and during the job he complained about the £20k he had spent on a paddock for the family horses, so we can infer some some commercial success and competence as an electrician.

 

1 hour ago, Jeremy Harris said:

There's no requirement for separation of double insulated power cables, and even if there was 400mm is completely OTT. 

 

 

How wide is a digger bucket? Perhaps my guy was applying real world experience and knows building sites can be chaotic and dangerous places hence he did not want any chance of a live 400amp feed getting through to the static caravan post an accident elsewhere onsite.

 

I find it odd that you feel motivated to deride the safety advice of a time served professional electrician because you cannot find a matching paragraph in the regs and yet you have spent an excess of £300 on your double pole RCBO consumer unit to obtain a small incremental increase in safety that is not required in the regs. 

[Jeremy Harris]

1 hour ago, epsilonGreedy said:

No, which begs the question why did you associate a 400amp fused DNO cable with any notion of householder electrical safety? RCDs are significant and this is the point, crossing cables where one is not RCD protected. As has been mentioned here before DNO supply cables are not armoured so one forceful plunge into soil with a sharp spade or over eager grab with a digger bucket and...

 

 

Because the hazard associated with cables that might somehow get some sort of short between them requires over-current protection, nothing to do with the risk of electric shock, really.  If you look at the way concentric/split concentric cable is constructed you will see that the PEN, or PE and N, conductor(s) form a concentric protective layer around the well-insulated line conductor.  The reason for this is so that anything conductive that may cut through the cable hits the conductor(s) that are at, or very near, earth potential before contacting the line conductor.

 

RCD protection is for outlets, rather than cables.  It's there to protect (by reducing the electric shock risk from touching an exposed conductive part) in the event of there being an excessive earth leakage, usually via a connected appliance.  It's worth doing a bit of research to get a feel for why the various protective devices are used where they are, what each can and cannot do, and the specific risk each is intended to reduce.

 

1 hour ago, epsilonGreedy said:

 

Surely you can comprehend the common sense in his concern even if there is no matching chapter in the regs. My electrician was over 50 and during the job he complained about the £20k he had spent on a paddock for the family horses, so we can infer some some commercial success and competence as an electrician.

 

 

What common sense concern?  You can safely run your hands along the outside of a double insulated cable carrying LV, after all.  Where's the hazard?  If something cuts through the DNO cable it matters not one jot that there may be an adjacent domestic cable, the risks and outcome will be the same.

 

 

1 hour ago, epsilonGreedy said:

 

I find it odd that you feel motivated to deride the safety advice of a time served professional electrician because you cannot find a matching paragraph in the regs and yet you have spent an excess of £300 on your double pole RCBO consumer unit to obtain a small incremental increase in safety that is not required in the regs. 

 

You might find it odd, but the issue re: using an all-RCBO CU has nothing to do with enhanced safety at all.  A standard split board with two RCDs provides the same level of protection.  The reason for using an all-RCBO board is simply the reduced nuisance factor, and easier fault finding, in that only the faulty circuit will trip in the event of an earth leakage fault, not half the board.  FWIW, our all-RCBO board didn't cost close to £300, either.

[epsilonGreedy]

On 17/02/2020 at 10:34, Jeremy Harris said:

What common sense concern?  You can safely run your hands along the outside of a double insulated cable carrying LV, after all.  Where's the hazard?  If something cuts through the DNO cable it matters not one jot that there may be an adjacent domestic cable, the risks and outcome will be the same.

 

 

I am aware a live DNO supply cable can be touched, I spent a few hours at the weekend exposing my DNO supply cable in its trench prior to the meter box being lifted into the wall tomorrow as the wall goes up. Because of previous comments on this forum I was alert to the fact I was handling a potentially lethal cable with just a few mm of plastic protecting me from the live copper core, so I exposed the cable with the same level of care as an archaeologist uncovering the burial site of Queen Boudica.

 

Where is the hazard you ask. The hazard is in the random unanticipated event.

 

Think of it this way, many decades ago an MOD boffin was asked to assess whether it was safe to fit a deep fat fryer in the galley of a Type 42 Destroyer. Viewed in myopic isolation it was a reasonable safe thing to do, except the boffin did not anticipate an exocet missile ripping into the side of the ship, the jet engine consuming its remaining propellant and then the deep fat fryer igniting thus contributing to the conflagration leading to the demise of HMS Sheffield.

 

The exocet missile missile on a building site is a digger. You cannot predict with any certainty what random lethal circuits might form should a digger bucket slice through both a DNO cable and other cable downstream of the CU. Your hostility and suggestion that a foot of separation between such cables is a dubious idea is unfathomable.

Edited February 18, 2020 by epsilonGreedy

[Jeremy Harris]

15 minutes ago, epsilonGreedy said:

 

I am aware a live DNO supply cable can be touched, I spent a few hours at the weekend exposing my DNO supply cable in its trench prior to the meter box being lifted into the wall tomorrow as the wall goes up. Because of previous comments on this forum I was alert to the fact I was handling a potentially lethal cable with just a few mm of plastic protecting me from the live copper core, so I exposed the cable with the same level of care as an archaeologist uncovering the burial site of Queen Boudica.

 

Where is the hazard you ask. The hazard is in the random unanticipated event.

 

Think of it this way, many decades ago an MOD boffin was asked to assess whether it was safe to fit a deep fat fryer in the galley of a Type 42 Destroyer. Viewed in myopic isolation it was a reasonable safe thing to do, except the boffin did not anticipate an exocet missile ripping into the side of the ship, the jet engine consuming its remaining propellant and then the deep fat fryer igniting thus contributing to the conflagration leading to the demise of HMS Sheffield.

 

The exocet missile missile on a building site is a digger. You cannot predict with any certainty what random lethal circuits might form should a digger bucket slice through both a DNO cable and other cable downstream of the CU. Your hostility to the suggestion that a foot of separation between such cables is a dubious idea is unfathomable.

 

 

An exposed incoming live conductor is an immediate cause for reporting the installation as being unsafe.  There is a mandatory requirement that there shall be no exposed live conductors, ever, and live in this context means both the line and neutral conductors,

 

The incoming cable from the DNO is double insulated, as are all other exposed cables anywhere in an installation (or they should be, if correctly installed).  The reason for this requirement is specifically to reduce the risk of accidental shock.

 

If a digger goes through a cable there is probably going to be a bit of a bang.  It matters not one jot whether there happens to be 1, 2 or 10 cables in the same spot, the outcome will be the same.

 

What is the risk you believe to exist here?  There's always a risk that an incomer can be hit by a digger.  This risk is mitigated in several ways.  Firstly, no one should dig without checking with a CAT, that's just common sense, and it would be gross stupidity to ignore doing this.  Secondly, there is a requirement for marker warning tape to be laid above cables, to provide an early warning to someone digging that there's a cable, or cables, buried in that location.  Finally, the design of cables for direct burial is such that if something conductive (like a digger bucket) does cut the cable, the first conductor(s) that it will contact is one at, or very near, local earth potential.  This acts to protect the operator when the line conductor gets cut. 

 

Not at all sure why you want to try and make new safety rules up when the IET etc see no requirement for them.  Do you happen to know something that the regulation writers don't?

 

BTW, every warship I've ever worked on has had deep fat fryers in the galley.  The risk from those is absolutely trivial compared to what's in the ship's bunkers and magazine.  Arguably, the aluminium topsides on a modern warship are far more of a fire hazard than a couple of fryers in the galleys.  As a footnote I lost three good friends in HMS Sheffield, a ship that I knew fairly well at the time.

[epsilonGreedy]

6 minutes ago, Jeremy Harris said:

BTW, every warship I've ever worked on has had deep fat fryers in the galley.  The risk from those is absolutely trivial compared to what's in the ship's bunkers and magazine.  Arguably, the aluminium topsides on a modern warship are far more of a fire hazard than a couple of fryers in the galleys.

 

 

The Admiralty did not agree with your opinion, hence the immediate instruction to the fleet during the Falklands War to decommission the deep fat fryers in the combat zone.

 

 

10 minutes ago, Jeremy Harris said:

An exposed incoming live conductor is an immediate cause for reporting the installation as being unsafe.  There is a mandatory requirement that there shall be no exposed live conductors, ever, and live in this context means both the line and neutral conductors

 

 

Why did you post this? What do you imagine happened on my site at the weekend?

[Jeremy Harris]

30 minutes ago, epsilonGreedy said:

 

The Admiralty did not agree with your opinion, hence the immediate instruction to the fleet during the Falklands War to decommission the deep fat fryers in the combat zone.

 

 

That's rubbish.  When I was doing sea trials prior to the acceptance into service of HMS Norfolk in 1989 I can assure you the deep fat fryers were alive and well in the galleys.

 

The spread of the fire in HMS Sheffield was due to failings found in the fire and smoke control systems on the ship and there were a lot of injuries from flammable synthetic clothing that was used in uniforms at that time.  There were also some early reports that suggested that the warhead hadn't detonated, when in reality it had.  Somewhere I have a copy of the non-redacted version of the report, as I stayed in touch with my late friend's family for some time afterwards, and they obtained a copy.

 

 

30 minutes ago, epsilonGreedy said:

Why did you post this? What do you imagine happened on my site at the weekend?

 

Because you wrote this:

 

Quote

I am aware a live DNO supply cable can be touched

 

That implied exposed conductors.

 

 

[epsilonGreedy]

15 minutes ago, Jeremy Harris said:

That's rubbish.  When I was doing sea trials prior to the acceptance into service of HMS Norfolk in 1989 I can assure you the deep fat fryers were alive and well in the galleys.

 

 

The Falklands War finished 7 years earlier and HMS Norfolk was not in a combat zone when you were onboard.

 

Any sentient Briton over the age of 50 with a passing interest in the Royal Navy knows the Admiralty issued a stop order on using deep fat fryers after the loss of Sheffield.

 

34 minutes ago, Jeremy Harris said:

That implied exposed conductors.

 

 

Why am I still able post on this forum if I had been fondling the live exposed copper core of a DNO cable last weekend?

 

Earlier in this thread you mentioned it was possible to touch a live DNO cable and I did not assume you meant the live copper core. Why were you not able to apply the same degree of rational interpretation of human dialogue that I applied?

[Jeremy Harris]

26 minutes ago, epsilonGreedy said:

 

The Falklands War finished 7 years earlier and HMS Norfolk was not in a combat zone when you were onboard.

 

Any sentient Briton over the age of 50 with a passing interest in the Royal Navy knows the Admiralty issued a stop order on using deep fat fryers after the loss of Sheffield.

 

 

Why am I still able post on this forum if I had been fondling the live exposed copper core of a DNO cable last weekend?

 

Earlier in this thread you mentioned it was possible to touch a live DNO cable and I did not assume you meant the live copper core. Why were you not able to apply the same degree of rational interpretation of human dialogue that I applied?

 

 

How much time have you spent at sea in RN warships?  Between 1976 and 1990 I spent an average of two to three weeks a year on sea trials. 

 

FWIW, the fire in HMS Sheffield had sod all to do with deep fat fryers, they aren't even mentioned in the BoE report.  I've dug out my old typed copy of the CINCFLEET BoE report and that states clearly that the fuel for the main fire was, quote:

 

Quote

Burning missile propellant and Dieso from the FAMR service and Ready Use Tanks were the main sources

 

 

 

I suggest that, rather than try to justify some mythical electrical regulation that either you, or someone you know, has led you to believe is true, you take the time to look at reality.  The regs generally err on the side of caution, so when there is nothing in them to support your view that a risk exists, I suggest that may be because there is no appreciable risk. 

 

If further evidence is needed, then we have a 95mm² Wavecon DNO main (not the supply to our house) running in the same trench alongside two runs of SWA running from what was our TBS  CU.  The DNO main supplies the house across the other side of the lane, one of the SWA runs is a 6mm² run that goes a bit further around the edge of the plot to supply our garage, the other is a run of 2.5mm² that turns off that boundary trench to supply our treatment plant.  Also in that trench, but spaced to the opposite lower corner, is a run of Duct 56 that carries a 28 pair 'phone cable, that connects to several houses further up the lane.  The DNO laid their cable at the same time as we laid our cables and the Openreach duct.  No one had the slightest problem with it, nor did they need to, as there's no appreciable risk from doing this.

 

 

 

[PeterW]

27 minutes ago, epsilonGreedy said:

Any sentient Briton over the age of 50 with a passing interest in the Royal Navy knows the Admiralty issued a stop order on using deep fat fryers after the loss of Sheffield.

suggest you check your source on this as JSP456 clearly states that deep fat fryers should only be drained as part of the state 1 readiness for action ... otherwise they are used daily. 

[Jeremy Harris]

11 minutes ago, PeterW said:

suggest you check your source on this as JSP456 clearly states that deep fat fryers should only be drained as part of the state 1 readiness for action ... otherwise they are used daily. 

 

 

My experience is that there might well be a bit of an outcry amongst the ship's company if fry ups were off the menu!

[epsilonGreedy]

4 minutes ago, Jeremy Harris said:

How much time have you spent at sea in RN warships?  Between 1976 and 1990 I spent an average of two to three weeks a year on sea trials. 

 

 

The hard won experiences of the Falklands War are still enshrined in Royal Navy operational procedure today, here are the standing orders for a Ship's galley:

 

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/799484/20190502-20_04_03-_JSP_456_DCM_Pt_2_Vol_1_-_Ch_13_-_Royal_Navy_Catering_Management_Amndt_019.pdf
 

Quote

 

1340. Securing for Action.

 

Deep Fat Fryers. Due to the hazards associated with deep fat fryers they must be correctly isolated and drained of oil during state 1 preparations.

 

 

[epsilonGreedy]

16 minutes ago, PeterW said:

suggest you check your source on this as JSP456 clearly states that deep fat fryers should only be drained as part of the state 1 readiness for action ... otherwise they are used daily. 

 

 

"state 1 readiness for action" sounds a lot like a combat zone to me.

 

@Jeremy Harrishas imagined that I claimed deep fat fryers have been banished for evermore in the Royal Navy.

[Jeremy Harris]

6 minutes ago, epsilonGreedy said:

 

The hard won experiences of the Falklands War are still enshrined in Royal Navy operational procedure today, here are the standing orders for a Ship's galley:

 

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/799484/20190502-20_04_03-_JSP_456_DCM_Pt_2_Vol_1_-_Ch_13_-_Royal_Navy_Catering_Management_Amndt_019.pdf
 

 

 

 

Note the wording carefully.

 

How often does a warship ever go to State 1?

 

1 minute ago, epsilonGreedy said:

 

@Jeremy Harrishas imagined that I claimed deep fat fryers have been banished for evermore in the Royal Navy.

 

That's because you wrote this:

 

1 hour ago, epsilonGreedy said:

 

The Admiralty did not agree with your opinion, hence the immediate instruction to the fleet during the Falklands War to decommission the deep fat fryers in the combat zone.

 

No such thing happened.  Ships sail within active conflict/combat zones all the time without being at State 1.   At the time that HMS Sheffield was attacked she wasn't even at State 1, despite being on patrol within the TEZ during an armed conflict.  She was on Defence Watches, Air Warning State Yellow and Damage Control State 2 at the time of the attack, according to the BoE report.  That's a pretty relaxed state, and one of the BoE report observations was that boredom by some members of the crew, due to the apparent lack of action, may have played a role in the response to the attack.

[epsilonGreedy]

Just now, Jeremy Harris said:

Note the wording carefully.

 

How often does a warship ever go to State 1?

 

 

Quite often when an Argentinian warplane is inbound with Exocet ready to fire.

 

These days with just 9 RN surface warships ready for action at 2 weeks notice, then the chances of the Royal Navy getting embroiled in anything like the Falklands War again is looking remote. In 1982 we had 65 commissioned frigates and destroyers, today there are 19 in theory though due to an horrendous procurement design error by the MOD the 6 newish Type 45s are lame ducks awaiting a substantial upgrade.

[Jeremy Harris]

2 hours ago, epsilonGreedy said:

 

Quite often when an Argentinian warplane is inbound with Exocet ready to fire.

 

These days with just 9 RN surface warships ready for action at 2 weeks notice, then the chances of the Royal Navy getting embroiled in anything like the Falklands War again is looking remote. In 1982 we had 65 commissioned frigates and destroyers, today there are 19 in theory though due to an horrendous procurement design error by the MOD the 6 newish Type 45s are lame ducks awaiting a substantial upgrade.

 

 

You really need to read up on what really happened, rather than rely on half truths you've picked up from unreliable sources.  No one knew that the Super Etendard had the range it did, as there was a false assumption that the Argentinians didn't have AAR, when it turns out they did.  That's why the section of the Task Force that HMS Sheffield was in was only at Air Warning State Yellow; the assumption was that, at their range from the Argentinian bases they were outside the effective range of the Super Etendard.  HMS Sheffield never went to Actions Stations or DC State 1 Condition Zulu, as the attack was not detected until there was visual contact with two incoming missiles (one hit, one missed and ditched).

[MJNewton]

Only on the Internet can a discussion on 'Minimum distance between DNO feed and another protected circuit' lead to a pissing contest about deep fat fryers on warships.

 

Whilst it is mostly making me cringe, a small part of me is in sheer admiration of the impact of the Internet on mankind... and how actually I wouldn't want things any other way!

 

?

Edited February 18, 2020 by MJNewton

[epsilonGreedy]

5 hours ago, Jeremy Harris said:

You really need to read up on what really happened, rather than rely on half truths you've picked up from unreliable sources.

 

 

This is a perfect description of the initial official Royal Navy report on the loss of the Sheffield. It took another 25 to 30 years for the Royal Navy's halve truths to be exposed in a subsequent investigation demanded by veterans and families.

 

We now know:

 

Prior to the conflict the Sheffield had an establish reputation as an unlucky ship with a discontent crew. Her origin as the first of production batch vessel goes some way to explaining this. HMS Astute is a modern day example.

 

Her captain had been appointed to that command a few months earlier and of more concern, he had recently transferred from the submarine branch and was considered inexperienced with surface warfare operations. Senior officers have subsequently questioned why a more suitable commander was not substituted before the ship was dispatched south.

 

Let's fast forward to the 48 hours upto the missile strike.

 

5 hours ago, Jeremy Harris said:

No one knew that the Super Etendard had the range it did, as there was a false assumption that the Argentinians didn't have AAR, when it turns out they did.

 

 

Admiral Woodford the fleet commander was concerned about something. He was positioned well East of the Falklands with a destroyer radar picket line between his fleet and Argentinian air threats. His main fleet was 20 miles further back than the radar picket line. Clearly his actions demonstrate he was extremely worried about air attacks which torpedos your assertion.

 

Moving on...

 

Admiral Woodford knew Sheffield was his weakest air defence ship which was why he positioned the more capable HMS Coventry in the hot seat of the picket line.

 

Eventually after an intense period Coventry needed to fix some equipment and the crew rested, so Coventry took up Sheffield's quiet end of the picket line and Sheffield switched into the hot spot.

 

A few minutes before missile impact a radar operator on one of the carriers called an air threat alert after seeing a brief ping, this was heard by the fleet but then countermanded by someone more senior on the carrier.

 

Even so two ships on the radar picket line called actions stations including the Coventry in the quiet spot but the third ship the Sheffield did not.

 

5 hours ago, Jeremy Harris said:

That's why the section of the Task Force that HMS Sheffield was in was only at Air Warning State Yellow; the assumption was that, at their range from the Argentinian bases they were outside the effective range of the Super Etendard.  HMS Sheffield never went to Actions Stations or DC State 1 Condition Zulu, as the attack was not detected until there was visual contact with two incoming missiles (one hit, one missed and ditched).

 

 

Absolutely not true as is now well established.

 

It took many decades before the reason that Sheffield was ambling along in a lower state of readiness was revealed. At the time the carrier broadcast an air threat the 5 most senior officers on the Sheffield were absent from their posts. The captain was lounging in his private cabin and the warfare control room head was having a cup of tea & chat at the galley. The 5 officers most likely to have responded and called action stations, as did the other two destroyers, were not at their posts to make that call.

Edited February 18, 2020 by epsilonGreedy

[Jeremy Harris]

There's loads of critical content missing from your summary.  I have in front of me the unredacted CINCFLEET BoE report, as a photocopy of the original typewritten report.  What you've written is not in that report, and distorts many of the facts.  Where it came from I don't know, I suspect a bit of dodgy journalism from the sound of it.  This is events as reported by CINCFLEET in the BoE report:

 

In the days prior to the attack the TG had been achieving reliable airborne detections out to 160 miles, and as a consequence of this, together with attacks being concentrated on the NGS group closer inshore, they stopped going to Actions Stations and State 1 Condition ZULU when at Air Warning YELLOW.  The decision was made for the TG to only go to Action Stations when the Air Warning state was RED.

 

On the day of the attack, the two attack aircraft were detected at a range of about 40 miles by the 965 on HMS Glasgow.  HMS Glasgow went to Action Stations and fired Chaff D, believing the detections to be valid and reported them to the rest of the TG.  HMS Invincible had radar paints at 30 miles and 50 miles range but CAP subsequently failed to find them.  The AAWC onboard HMS Invincible did not accept HMS Glasgow's target classification as valid (perhaps because there had been many false classifications that they believed were induced by ESM) and declared the contacts to be spurious.  This was relayed to the other ships in that group, including HMS Sheffield.  ZIPPO 4 was not called by AAWC and the Air Warning remained YELLOW (YELLOW was the normal operational state for the TG within the TEZ).

 

At about 15 miles range the two Super Etendards passed HMS Glasgow and turned towards HMS Sheffield.   At the time of the attack, HMS Sheffield was operating overtly, with all systems transmitting.  It was later suggested that this could have had an impact on the ability of her passive sensor suite to detect the AGAVE radar on the Super Etendard.  The false detections the fleet had been experiencing had led the AAWC on HMS Invincible to believe that the supposedly false AGAVE detections were really Mirage III radar detections (Mirage III was not considered to be a threat at their position).   Both CTG and HMS Sheffield had intelligence suggesting that an AM 39 attack from a Super Etendard was possible, but Capt. Salt disagreed with CTG on the level of this threat, and was convinced a submarine attack was more likely.  At the time of the attack HMS Sheffield was running an anti-submarine attack course, regularly turning through 90° on a zig-zag course.

 

Just before the attack, HMS Sheffield's AAWO was in the Wardroom, and his deputy had gone to the head.   The captain was in his cabin.  There was no exec officer to make anti-air warfare decisions in the ops room.  Some of the anti-aircraft weapons were unloaded and not ready for use.  When the anti-air warfare officer was recalled to the ops room he was convinced the air attack wasn't real, as he believed that they were beyond the range of the Super Etendard.  He failed to alert the captain and get him to come to the ops room.  He later admitted to not having read the intelligence confirming that the Super Etendard now had an AAR capability, which significantly increased its operational range.  The AAWO took no action to defend the ship, no chaff was fired and the ship was not ordered to turn head on to the oncoming threat, but remained on her anti-submarine attack course.  He was found negligent by the BoE.  The BoE also found that the PWO was negligent, in not taking defensive action to protect the ship earlier.  Neither of these charges was made public at the time, for fear of impacting on morale and public opinion.

 

The AM 39 hit HMS Sheffield amidships, and destroyed the computer room, the FAMR / FER area and breached the Firemain water pipe to the fire fighting systems.  The fire that developed from the burning propellant and Dieso from the FAMR Service and Ready Use tanks that had been hit by the missile created large amounts of smoke that hampered fire fighting.  Of the four fire pumps, C was damaged by shock, K was running but stopped at impact and would not restart, L stopped at impact but was restarted and N was defective.  This left HMS Sheffield with minimal fire fighting capability.   The lack of the Firemain pressure left just external boundary cooling with buckets and portable pumps as the only means of fighting the fire.  The fire burned out of control until 041750Z when, aware of the tactical situation, and aware that the Sea Dart magazine was at risk of exploding, Capt. Salt gave the order to abandon ship.  At that time HMS Arrow and HMS Yarmouth were alongside trying to assist with external firefighting, and they took off what remained of HMS Sheffield's crew.

 

Only one body was recovered, the remaining nineteen, including three friends of mine, went down with the ship when she sank whilst under tow four days later.  For pretty obvious reasons this is an incident that remains close to my heart.  On the night that we heard that HMS Sheffield was hit, I went to a club with about a dozen others who knew members of her company.  We sat in complete silence for the whole evening, just drinking.  Not one word was spoken about those we had known, nor about the attack.  I clearly recall being outraged a few days day later, when the manufacturer published an advert in a defence magazine for the AM 39 declaring it undetectable, with a photo of HMS Sheffield, on fire, in the background.

 

AFAIK, the only major difference between the redacted report issued at the time and the unredacted version that was given a limited distribution (my copy was originally marked Secret - UK Eyes B, but it has now been officially declassified) was mention of the ship's company being bored, the negligence of the AAWO and PWO, some confusion as to whether the missile warhead had exploded or not (it had, but it suited PR at the time to suggest that it may not have), the prior experience of Capt Salt (a submariner) and his number 2, a FAA Officer, and the various details of the technical shortcomings in the fleet air defence systems. 

 

A later analysis of events suggested that MI had underestimated the capability of the Argentinian Air Force, by unfairly comparing it with the, largely conscript manned, Argentinian Army.  The Argentinian Air Force were highly professional, well-trained and very capable.  As it happened I'd flown with them in the UK a few years earlier, at the time that they had placed an order for some Mk 23 Lynx helicopters from Westland.  We were still doing weapon acceptance trials on the RN HAS Mk 2 at the time, and some of their guys came down to Culdrose to see the A/C first hand.  They seemed pretty competent to me.  As a side note, about fifteen years after the loss of HMS Sheffield I flew with one of the pilots from HMS Invincible who had flown the CAP, looking for the aircraft that HMS Glasgow and HMS Invincible's radars had detected.  He was still kicking himself because they didn't find and engage the Super Etendard's when they were still beyond attack range.  He did get a DFC for his part in the attacks against the missile batteries in the Falklands, though.

 

 

 

 

[Markblox]

Getting away from warships for a moment, perhaps we should have a poll for the qualified electricians on here to ascertain the truth to the burning question about DNO cables and non DNO cables in the same trench and the proximity to each other. 

 

Edited February 18, 2020 by Markblox

[Jeremy Harris]

As mentioned earlier, it's not an issue.  We have a DNO main, plus two runs of SWA that feed our garage and treatment plant respectively, plus a run of Openreach Duct 56 with a 28 pair cable, all running in the same trench.  The only separation requirement is the 100mm between the power cables and the 'phone cable.  We put the power cables in one corner of the trench, the 'phone cable duct in the other corner, so they were well over 100mm apart.

[Markblox]

25 minutes ago, Jeremy Harris said:

As mentioned earlier, it's not an issue.  We have a DNO main, plus two runs of SWA that feed our garage and treatment plant respectively, plus a run of Openreach Duct 56 with a 28 pair cable, all running in the same trench.  The only separation requirement is the 100mm between the power cables and the 'phone cable.  We put the power cables in one corner of the trench, the 'phone cable duct in the other corner, so they were well over 100mm apart.

Yes, I know it's not an issue.  Can't see the point of asking for advice and then arguing about it but TBH I think you two just clash! I clash with one of my sisters, same thing really. 

I don't know how long you two were writing your ever expanding answers but it took me half an hour to just read it.