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Grafton Va School Complex - fire in main electrical distribution room.
2

Grafton Va School Complex - fire in main electrical distribution room.

Grafton Va School Complex - fire in main electrical distribution room.

(OP)
February 3 at 1:38 PM · Just before 4 pm today, school administrators initiated evacuation procedures due to reports of an electrical issue in the main electrical room. As emergency responders arrived, an active fire was discovered. The fire was contained to that electrical room though smoke did spread through parts of the building. Due to the nature of this incident, power to the building remains off and Dominion Energy is on site assessing the situation. We do not yet have an estimate for power restoration or a timeline for necessary repairs.

Background
The Grafton complex houses a Grafton Middle School and Grafton High School. Location 403 Grafton Dr, Yorktown, VA USA, Aerial Photograph https://www.google.com/maps/@37.1638862,-76.469773... Complex opened in 1996.

While I do not have specifics it is usual practice here for buildings of this size to distribute electrical power at 480V 3phase, building loads are 480/277 or 208/120, with transformation to 208/120 near using panelboards. The Dominion Power would provide a transformer close to the electrical room. At this voltage level arcing faults can be sustained for a long time.

Sprinkler system did it's job, fire contained to the electrical room, no injuries.

Grafton Va School Complex Update Feb 6, 2020 - good pictures of destroyed main electrical panel.
https://www.youtube.com/watch?v=_TfbMCDJ9i0&fe...

Restoration of power to the complex will take months.
Soot is now considered a Hazardous Material, cleanup in progress.
Students will now share space with York Highschool, and Tabb Middle school.

Friday, February 7, 2020 – Letter from the Superintendent York County Schools
https://www.facebook.com/yorkcountyschoolsva/posts...

Disrupted students - will be sharing school space in shifts for several months.
Grafton Middle School 882
Grafton High School 1185
York High School 1075
Tabb Middle School 921

Disaster? depends on definition - for sure disruptive and costly.

RE: Grafton Va School Complex - fire in main electrical distribution room.

480 Volt distribution in a large complex is common and is good engineering, economically for both installed cost and for line losses.
480 volt distribution, stepped down to 120/208 Volts may be argued as safer than a higher voltage distribution.
Anecdote alert:
I may have avoided a similar disaster in a school complex.
There were four dormitories, a school building, a main administration building including a kitchen and mass hall/assembly hall.
I had done a lot of volunteer work at the school and had much more leeway to take action than would be normal for a visitor.
I was walking though the boiler room with the maintenance chief when I felt a blast of heat radiating from the main switch.
I opened the switch and saw several mini-arcs inside the switch.
The arcs were between the movable switch blades and the contacts that the blades closed into.
The arcs were only a pin point of intense light.
I measured several Volts drop across each arc. Incoming was a couple of hundred Amps at 120/208 Volts.
From the heat radiated I estimate that a few thousand Watts was being lost.
It was on the weekend, no parts were available nearby.
There was no budget.
The school was empty but classes were due to start in a week or so.
Step one. Measure and record voltage drops across the arcs and across point that were not arcing for comparison.
Step two. Call the utility emergency number for an emergency disconnect. I requested and they agreed to leave the high voltage fuses in my possession as an added safety measure.
Step three. Dismantle the switch and scrape, file and polish the blades and the contact clips including the pivot points.
Memory fails but I probably cleaned up the fuse holders as well.
Step four. Work harden and re-tension the contact clips.
Step five. Call the utility for a re-energization.
Step six. Measure and record the voltage drops across the switch terminals.
Step seven. Prepare and submit a report to the owners trying to indicate the seriousness of the situation and recommending replacement of the main switch ASAP.
While this was not as large as the Grafton Complex, I am sure that we were just a couple of weeks away from a similar, though smaller, meltdown.
A similar micro-arc in one or more connections may have been the root cause here. As the damage escalated to and through complete failure any evidence of the original cause may have been destroyed. Maybe not.
Anecdote two. A failure in a new safety switch on the first day.
Root cause: The installer left one of the main terminal connections loose to the point that heat was developed.
Point of failure: The heat was transmitted up the copper conductors so that the insulation was softened.
A conductor pushed through the softened insulation and made contact with the grounded entry conduit.
There was no significant damage to the loose connection other than slight surface discoloration, but it was obvious that the loose connection was the source of the heat that caused the damage elsewhere.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Grafton Va School Complex - fire in main electrical distribution room.

(OP)
WoW That's a scary close shave.

RE: Grafton Va School Complex - fire in main electrical distribution room.

Why the big issues in the USA with medium voltage?

I see this on solar panel installations as well.

My setup runs at between 400 and 550v but the USA users seem absolutely terrified of that. They are more than happy to run at 40-50 amps compared to my 9 amps. I use 6mm2 solar cable rated at 1000v. They are all using 21mm2 or more and running hurrenous losses and hot.

My house supply is 22kW 3ph 400v 32amp breaker.

I do have 10mm2 from the main distribution panel to the subs. But I could use 6mm2 if I wanted to. Just didn't seem worth not spending an extra 30 euro on cable.

The solar lot are talking 100amp circuit breakers on heating/Aircon radials and main breakers of 300 amps. There are numerous pics of earth bolts cherry red in distribution panels. Quiet why they are using M6 bolts as earthing bus bars is also a bit strange to me. I have a length of copper bar with holes drilled through it and grub screws to hold the wires in.

I was always taught voltage is shocking current kills.

I am under cultural shock at the moment anyway after being brought up in the UK with electrics. And am now building a house in the EU, sockets and switches which are utterly cheap shite if you get the local ones. Thankfully Amazon UK will deliver UK standard gear through the post. And you can get UK standard EU fit mk sockets. And the switches are good anyway. They cost three times as much but fixing the local crap every couple of months will hopefully not need doing.

PS I don't think we can use blade main power switches legally any more and haven't been for some 30 odd years due to this inherent risk of arcing followed by fire, I don't have a single one.

RE: Grafton Va School Complex - fire in main electrical distribution room.

Quote (Alustair)

I was always taught voltage is shocking current kills.
Quite right, but the current that kills is generally less than 1 Amp.
600 Volts against 120 Volts to ground._ In the event of contact with your body, 5 times as much current that kills.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Grafton Va School Complex - fire in main electrical distribution room.

As you say it's milliamps that kill.

1 amp or 5 amp is the same as falling 10 meters or 50 meters.

Have 300 amps going to earth is a load of extremely hot wire. In fact why are they using M8 bolts for earth? They would be needing M40 at least. winky smile

Edit to had thinking about it over the last 30 years I have had two unintended zaps. One was 220v across a finger and the other I was fixing an ossicilascope. First one resulted in swearing, second I ended up on my back 1 meter away from the work bench with the old boy say, that's why you always keep one leg on the foot rest.

Intended zaps to many to count. I used in old days my right hand clenched fist knuckle to check cables to see if they live on 220v . Clench fist with index finger knuckle slightly out and then swipe down brushing end of wire. These days with glow when hot screwdrivers I use them instead.

RE: Grafton Va School Complex - fire in main electrical distribution room.

Mainly because I am bored stuck in a hotel.

USA has 330 million people and in 2002 20 000 deaths were due to electicution.

UK has 60 million people and it's 70 deaths per year.

This for in the home.

Haven't looked yet at electrical induced house fires.

Looks like I am going to be sticking to my medium voltage, low current setup.

Wood house 15 meters of 1000v 6mm2 cables inside a fireproof channel inside the wall. No connectors between roof and inverter just 4 cables. Running max 10 amps at 570 volts versus 120V running at 40 amps plastic channel inside internal walls...

Not that your going to be able to change things now away from how things are in the USA. Just seems particular silly. And the stats seem to prove the excuse for having it that way don't give any safety benefit.

RE: Grafton Va School Complex - fire in main electrical distribution room.

Not sure I'd call a small fire in a small school a disaster, much less an engineering disaster.

RE: Grafton Va School Complex - fire in main electrical distribution room.

550V isn't medium voltage....

RE: Grafton Va School Complex - fire in main electrical distribution room.

AH: "Edit to had thinking about it over the last 30 years I have had two unintended zaps."

I still remember being zapped by the anode wire on a colour TV circuit about 60 years back... it was a real 'eye opener'. When people used to throw out TVs, we used to scrounge the parts... I could tear the flyback system out in a short time and had a relatively safe source of 20K volts... just what every kid needs.

Dik

RE: Grafton Va School Complex - fire in main electrical distribution room.

I had a Neon transformer at about 15,000 Volts.
It powered a nice Jacobs ladder.
As well I had an old foot X-ray machine from a shoe store, 100,000 Volts.
I tried making a capacitor with sheets of window glass and tinfoil, encased in paraffin wax.
After a couple of failed capacitors I gave up on that.
Safety? NO, I was extra careful around those two.
The third prize was a very old distribution transformer.
I never back energized that one. I stripped the wire to use for other projects.
Hands up if you remember when transformers were wound with DCC, Double Cotton Covered wire?
I just googled and was surprised to see that DCC wire is still available.
Here's what the Neon transformer looked like.



This is what my other toy looked like.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Grafton Va School Complex - fire in main electrical distribution room.

I only used the term medium because that's what the solar lot call it.

Low voltage to them is 12/24/48 V with the string voltages at sub 140 V.


RE: Grafton Va School Complex - fire in main electrical distribution room.


Quote (LionelHutz)


550V isn't medium voltage....

My general (entirely personal) rule is as follows:

Human body resistance can be as low as 500 Ohms (wet skin). Ventricular fibrillation can start occurring at 100mA. So 50V is about the limit I'd want to risk touching without taking extra precautions (PPE). And I try to keep it below 30V.

So anything under 50V is "low" voltage: probably don't need too much care to be safe from the direct electrical hazard.

IEC defines high voltage as 1000V AC or 1500V DC. US NEC defines high voltage as >= 600V. Other organizations are similar, usually the cutoff is around 1kV. So I tend to go with 1kV (either AC or DC) as "high".

The rest is "medium". So 550V does make sense as medium, though I'm not aware of an electrical safety code that uses the term "medium voltage" that is probably just because I don't work in power systems. NEC would call it "low voltage"!

RE: Grafton Va School Complex - fire in main electrical distribution room.

2
ANSI C84.1-1989 defines 5 voltage levels
Low < 600
Medium 2400 to 69kv
High 115kv to 230kv
Extra high 345kv to 765kv
Ultra high 1100kv

Link

RE: Grafton Va School Complex - fire in main electrical distribution room.

Must admit to me as a mechie and I know I am not the only mechie that thinks this way.

low voltage is anything under mains 220/400V and you need something to bring it down.

High voltage is anything on the grid side of things above mains that the local transformer brings down.

And Medium is anything between Low and High... With Mains at 220/400V. very low current is anything under 5amp, low 5 to 16 amp, medium 16 to 32 and high anything over 32amp.

I realise and expected that this doesn't comply with any known standard. For me the currents which are normal on 110V domestic systems are mind boggling high and so must be the wire losses.



RE: Grafton Va School Complex - fire in main electrical distribution room.

When you work with the various voltage levels, you use levels lik ANSI defines. Otherwise, you tend to make up some definition that varies depending on the person and overall means little.

You lost all credibility on your voltage level arguments when you posted a ridiculous number like 20,000 home deaths per year in the USA due to electrocution.

Solar systems in NA can run at 400-600VDC into a single inverter that converts it to 240VAC for grid connection.

RE: Grafton Va School Complex - fire in main electrical distribution room.

That's what the stats sites say. Although you seem to collect labour accidents federally and the domestic stuff by state if at all. And there is no consistent definition, so some of those could be dead in an electrical house fire.

Its not really surprising UK is lower by a large margin. Its always had quiet strict electrical codes and standards. Plus we tend to live in brick houses. Mainland Europe is about the same as the USA with variations between countries.

RE: Grafton Va School Complex - fire in main electrical distribution room.

LOL, because it makes perfect sense that 55 people are being electrocuted to death at home per day.

RE: Grafton Va School Complex - fire in main electrical distribution room.

https://www.nickleelectrical.com/safety/electrical... Seems like 400 as the top range for estimates of USA household electrocution deaths, more on job sites; this from 5 years ago, so even more GFCIs should mean even fewer in-home electrocutions.

I was originally going with the fact that the UK has so many Lucas electrical components that there isn't any electricity to escape.

Why do Brits drink warm beer - Lucas refrigerators. Many more: http://www.mez.co.uk/lucas.html

RE: Grafton Va School Complex - fire in main electrical distribution room.

Lucas also built braking systems for trucks.
The motto of their brakes division;
WE PRESS ON WHERE OTHERS HALT.
No joke.
A customer brought a Ford school bus into my friend's shop with factory original Lucas brakes.
Any one familiar with North American air brakes knows the yellow button on the dash that sets or releases the spring applied, pressure released parking brakes or Maxi Brakes.
Lucas made a spring applied, hydraulic pressure released parking brake for hydraulic brake systems.
Quite rare. Almost impossible to source repair seals.
Oh, the same yellow button on the dash. Instead of being mounted on a special air valve, a rod went through the fire wall and operated a hydraulic dump valve.


Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Grafton Va School Complex - fire in main electrical distribution room.

Ya, a realistic number in North America would be around 1 death per million population each year.

RE: Grafton Va School Complex - fire in main electrical distribution room.

(OP)

The 20,000 deaths statistic is wrong, but an understandable mistake. The source is likely this document published by the National Center for Biotechnology Information, U.S. National Library of Medicine, where 30,000 non fatal electrical shock incidents per year is the statement. US Population is 327.2 million (2018), so 9000 non fatal shock incidents per million. From below if lightning is excluded 400 fatalities is about 1.2 per million per year.

Electrical Injuries
Michael R. Zemaitis; Lisa A. Foris; Richard A. Lopez; Martin R. Huecker.
https://www.ncbi.nlm.nih.gov/books/NBK448087/
The statement is
In the United States, there are approximately 1000 deaths per year, as a result of electrical injuries. Of these, approximately 400 are due to high-voltage electrical injuries, and lightning causes 50 to 300.
There are also at least 30,000 shock incidents per year which are non-fatal.

Another source indicates close to 200 workplace electrical fatalities per year.

Report: NFPA's "Fatal Electrical Injuries at Work"
Author: Richard Campbell
Issued: May 2018
https://www.nfpa.org/News-and-Research/Data-resear...
Report highlights 2012 to 2016 (4 years)

739 died from exposure to electricity.
By occupation, workers in construction and extraction occupations (47%) and installation, maintenance, and repair occupations (22%) accounted for the largest number of deaths.
80% of fatal injuries from direct exposure to electricity occurred while workers were engaged in constructing, repairing, or cleaning activities.
Workers who were fatally injured as a result of indirect exposure to electricity were most often engaged in construction, repairing, or cleaning activities (37%) or were using or operating tools or machinery (32%) at the time of injury.

My this thread has wandered to a number of interesting places.
====================
February 11, 2020 Here’s an update on the Grafton School Complex
https://wydaily.com/local-news/2020/02/11/heres-an...
Answers are going to take a while.
===========
Fred

RE: Grafton Va School Complex - fire in main electrical distribution room.

That's fair comment,

But still there doesn't seem to be any major reduction or increase in survival by running lower voltage so you take all the hit for wire loss for no gain. As I said your just as dead dropping from 10 meters as you are from 20 meters or 2km.

And hot wire domestic fires are not accounted for. 200 amp main CB's that's a load of heat that can be produced before it trips.

I still reckon I am more than happy running 500-600V on my solar with sub 10 amp currents and a 32 amp max supply on my 400V 22kW mains supply. Just have to factor internally from behind the main distribution box I can have 41.5 Kw going through the copper.

BTW 70 is the UKs total number of deaths both industrial and domestic. Most of them are similar to the US and industrial accidents involving over head power lines including people getting zapped on train lines.

240V 50hz V 110V 60hz there is no statistically proven benefit for running at lower voltage domestically.

To be fair it is an interesting topic..... Huge target group.. Not that anything will ever change in the USA. But the wire losses are become huge factor as electricity becomes more expensive. Not that I pay anything at all for my electricity since I had the panels installed but 1000 euro a year is a normal bill in the area with maybe 2% wire losses. I would prefer 20 euro in my pocket compared to heating the environment and running at 110V.

Am I right in thinking that 22Kw single phase is 200 amps 110v? compared to my 22 kW 3ph 400V being 32 amps? So I have more than 6 times less wire loss if I pull max that I can?

I still don't get this running a M8 bolt though as a earth bus. It is F'ing stupid in my setup never mind the currents the USA runs. My copper bar is 180 amps with a supply of 32 amps. What's a mild steel bolt of M8/M10 good for?

As a scotsman running 28mm2 to 35mm2 copper wire is bum clenching expensive. I run mostly 6mm2 apart from the connections I am likely to put a TIG welder on the end of and then its 10mm2. 10 meters of 35mm2 is extremely expensive.


RE: Grafton Va School Complex - fire in main electrical distribution room.

I understand that most single phase circuits in the UK are derived from a 400 Volt star connections and are 230 volts.
Most of our residential circuits are based on a center-tapped 240 Volt supply.
With a reasonable balance between the 120 Volt circuits there is little or no current in the neutral and the losses are based on a 240 Volt circuit.
With a given load, the current will be a little less at 240 Volts than at 230 Volts but not enough to argue about.
Losses are about the same, but our system uses 120 Volts to ground rather than 230 Volts to ground.
If you have a 230/400 Volt industrial service than we would compare that to our 277/480 Volt service with less loss or, in Canada, a 347/600 Volt service with even less loss.
Our code mandates that many residential circuits be limited to 5% voltage drop.
When two 120 Volt circuits are combined in a three wire circuit with a shared neutral the 5% drops to 2.5%.
Do the UK codes specify any maximum voltage drop?

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Grafton Va School Complex - fire in main electrical distribution room.

Show of hands: How many think residential power in the US will be switched to UK standards before the Sun runs out of fuel?

RE: Grafton Va School Complex - fire in main electrical distribution room.

I don't as I have already said believe it will ever change.

That's good background information about the differences though.

I don't have a clue if there is a voltage drop specified.

UK is a bit strange anyway compared to most because we use ring mains instead of radials lighting circuits are radials though as are cookers and that sort of thing. The reason for that is something to do with world war 2 and copper shortages I believe. Complete PIA to trouble shoot.

We also use individually fused plugs which are none reversible.

The star supply is something to do with the water mains going plastic, We used to earth everything off the water mains pipe. And there was a huge PIA factor of ensuring all piping and metal in the house was bonded to earth including kitchen sinks etc. So when the water mains got replaced by plastic most houses lost their earths. They dropped the piping bonding requirement I think 10 years ago. Personally I still do it because I don't like the modern plastic piping inside walls. Everyone with it seems to have a major leak every couple of years. Where as the copper pipe I put in with my dad 30 years ago for a heating system and water is still fault free. So I think I am the only person in Estonia to put copper pipe in a new build this decade. I had to teach the young plumber how to solder it. It was good fun building it. We did use plastic though for the UFH loops but after the manifold it was all copper. But I still earth strap everything mainly for corrosion reasons. It probably doesn't make any difference though.

The rest of Europe runs on radials for everything, reversible unfused plugs. And my mains supply is a delta supply. I have 3 proper earth spikes on my farm. But most of the electrics in the area date from soviet times and most places the earth is rather suspect.

RE: Grafton Va School Complex - fire in main electrical distribution room.

20% heavier and slower Dave? grin

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Grafton Va School Complex - fire in main electrical distribution room.

Alistair,

You get around a bit. Thought you were in Scotland, but now Estonia? I like Estonia. Your Eng-Tips profile shows SE, which is Sweden, but that is not exact, just an indicator of your ISP.

RE: Grafton Va School Complex - fire in main electrical distribution room.

Born and Educated in Scotland.

Worked in the UK as an Engineer. Then did 2 years in Germany contract work. That paid for Pilot training.

First job flying was up in Inverness then ended up at as a contract training Captain floating about Europe and the Middle East enjoying life with Inverness as my go home base.

Last contract was in Estonia which I ended up with a wife and kid.

And now have screwed the nut and got a proper stable job. She comes from the south next to the Russian Latvian border and you can pick up property for next to nothing barely 5 figure euro sums for 10000 m2 of land and a house. A shell property came up next to her relatives, weather sealed with a new roof but inside empty apart from one of those massive Russian stove woodburners. So I bought it to save us having to stay at the MIL's. Its turned into a bit of a labour of love hobby doing it up. I do most of it myself, its good to get back on the tools and think about something other than aviation and keeps the kid exposed to his second primary language. The poor little sod speaks 5 languages already and he is only 4.

Todays job is designing a log sauna.... which like most scotsmen I have absolutely zero clue about


As for the profile location, I maybe change country location ip addresses 4 times in a day sometimes more. I might have joined up when I was bored in a Hotel in Arlanda and it took my location from there.

RE: Grafton Va School Complex - fire in main electrical distribution room.

Hi Alistair. Changing from 120v to 220v strikes me as similar to changing from imperial to metric measure. We went metric in Canada decades ago but in construction it was really only a pretense, it wasn't actually reasonable to change. Products are now labelled in metric but a tape measure shows they are still the same dimensions as the old imperial products. Nephew-in-law finished school in our metric era and immediately had to learn imperial in order to work in construction. Even grocery store products are the traditional container sizes with new labels. You've probably seen the same pretense in Europe where railway track is described in millimeters but still matches the feet and inches English gauge and threaded pipe sizes descend from American designs of more than a century ago.

Back to voltages I think the long life of utility distribution and home wiring would force a prohibitively expensive dual stocking of consumer products and so prevent either of our hemispheres from ever changing.

Bill

RE: Grafton Va School Complex - fire in main electrical distribution room.

More than 90% of the stuff I do is Imperial, still...

Dik

RE: Grafton Va School Complex - fire in main electrical distribution room.

I was in the first batch that didn't get taught imperial at Uni.

About the only thing left imperial round here is pipe sizes but everything is BSP. But you do get a load of Din fittings as well.

But its a mess because the pipe diameters are all metric. So I have 22mm and 15mm copper pipe going onto 3/4" and 1/2" tank fittings. You just can't get those tapered American threads as I found out when I got a optical pressure switch for the well pump. The local way is to wrap it to death with PTFE tape and ram it in. I managed to get an adapter to BSP from AliExpress.

All other materials are metric.

In the UK anyway you did used to get differences in wood sizes but all under the description of 4 by 2. But that's pretty much gone now as most construction wood comes from Scandinavia.

I agree they won't change. And Airport hotels round the world will continue to have a burned out socket marking the death of a 60Hz 110v American hair care product.

RE: Grafton Va School Complex - fire in main electrical distribution room.

Worth mentioning that EU/UK have been through the nominal voltage change process already.

Standard UK used to be 240V 50 HZ and standard European used to be 220V. On 1st Jan, 1995, we converted overnight to a "Harmonised" supply of 230V +10% / - 6%. You can guess how much actual difference that made in practice.

A.

RE: Grafton Va School Complex - fire in main electrical distribution room.

The indication that we see of an internet is for the most part showing where you are connected to the backbone of the 'net.
If I log in at home I am correctly shown as in Alberta.
If I log in from my smart phone, anywhere in Canada, I am shown as in Quebec, where my phone plan provider connects to the internet backbone.
In Honduras, my internet provider piggybacked on a larger provider and my location was shown as in Guatemala.
Another strange thing happened.
Some years ago, the Baltimore Sun did a series of articles about some nasty things that were done in Honduras by ...........
I made the mistake of mentioning online, some of the nasty stuff done by the ......., in Honduras.
For a few years after, no matter where I logged in, my location was shown as Virginia, US.
What company in Virginia could have an interest in my internet traffic?
Then it hit me; Company, in Spanish CompanIA.
That hasn't happened for years now, so the question now is;
Am I off the radar or have they got a better hacker?
Gotta go now, someone is coming.
Who do I know that drives a black Suburban?.......

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Grafton Va School Complex - fire in main electrical distribution room.

My VPN allows me to set my country... If I set it for Mexico, web pages often come up in Spanish... or whatever country I choose. Never any black Suburbans around here.

Dik

RE: Grafton Va School Complex - fire in main electrical distribution room.

Quote (Bill West)

Nephew-in-law finished school in our metric era and immediately had to learn imperial in order to work in construction.
It confuses me why this is the case. Just as it continues to boggle my mind that US engineers work in imperial.

Here in Australia plenty of our products in clearly imperial sizes, measure in metric. Big deal. It is stay FAR easier as an engineer to use the metric system even if your readily available structural members and mechanical fitting may still be based off an imperial size.

Nobody here in construction or engineering finds it useful to use imperial units even if supplies are imperial.

RE: Grafton Va School Complex - fire in main electrical distribution room.

I believe the USA is the last bastion of the Farenheit scale as well. The cranes I work on were all built in Europe or Asia so the prints are all metric I love it, never any fractions. All though stopping the mechanics from cross threading a imperial bolt into a metric threaded hole is a never ending struggle. The metric thread system is beautiful as well, it's so easy to figure out the drill bit size you need for a given thread. (Diameter - pitch = drill size) no letter sized drill bits.

RE: Grafton Va School Complex - fire in main electrical distribution room.

909 -It has been a long transition era, half of those he would have been working with would not have known metric. Keeping the old dimensions but using metric would have really weakened metric's simple math. Instead of how many studs on standard 16" centers will back a 48"x96" (4'x8') plywood sheet you would have 406mm stud centers and a 1219 x 2438mm sheet. All of a sudden the mental arithmetic goes above the average carpenter's assistant. And you can't round by more than about 4mm over a distance or you will start having gaps in the work.

In the early '70s my company started buying internationally and I got quite used to working in both systems. We were lucky to get some things to align automatically. We had just consolidated our switchboard cubicles to a standard 24" width so adopting 600mm (23-5/8") allowed us to mix and replace cubicles in a line up without a problem.

The one thing that still hasn't changed for me is my sense of physical values, my long learned ideas of what I can lift, how far I can walk and how hot/cold is it is still based on Imperial and I translate any time such a question comes to me in metric. It's not just the absolute figures, it's also the judgement of how much I can fudge those figures to one side. At what cold temperature is stepping out the door in a shirt for two minutes okay? Walking 10 minutes to the corner with a light jacket? Going for two hours without adding a sweater under a heavy coat? The need for these numbers comes up randomly over years and so it's not like I could pre-memorize them.

Cool -one tiny tiny counterpoint that Imperial has is the pressure on dimensional consistency in developing unfamiliar formulas. Because of the conversion factors for the units it's harder to construct an incorrect formula whose dimensional inconsistency doesn't make it glare as garbage. Yes you can still make mistakes because of a missing a conversion but in Metric the formulas can easily nice look nice even when the components have incorrect relationships. For instance in force x crank length x rotational speed = power, entering an inches to feet conversion would expose a forgotten length. In metric, erroneous thinking leading to leaving out the length wouldn't draw as much attention because there isn't a conversion to be written in. Worth zero points in the pro-metric argument but still an observation, logical reasoning can be eccentric at times.

Bill

RE: Grafton Va School Complex - fire in main electrical distribution room.

A whose team is better discussion doesn't seem to be worth continuing too far.

But suffice to say most of the world has gone through unit system transitions and come out the end just fine. Your sense of physical values just requires the use of the system. No different to moving to another country with a different currency. At first you spend time converting to your old currency then you eventually get used to it.

RE: Grafton Va School Complex - fire in main electrical distribution room.

Sorry 909, I took "confused"' and "boggle" to be an invite for insight rather than a "whose ....better" challenge.

Bill

RE: Grafton Va School Complex - fire in main electrical distribution room.

Sorry Bill. I didn't meant that comment to be direct at myself as much as anybody else. As you rightly point out I invited the insight.

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