When the Institution of Electrical Engineers decided to "go mettric" they didn't hang around. (For those not aware of the IEE, it is the body in the U.K. which publishes regulations for the electrical installations of buildings, along with associated activities.)

The IEE handbook had always used only Imperial measures, but in 1969 the IEE issued a supplement on the use of metric equivalents.

The changeover to metric-only was quick. The IEE published a new edition of the regulations in 1970, and EVERYTHING was just cut straight over to metric -- No dual-measurements in sight anywhere. The amended measurements were rounded where possible, e.g. the previous minimum spacing of a light switch from a bathtub changed from 6 ft. to 2m.

At the same time manufacture of electrical equipment changed to metric specifications, so that the old British cable sizes of 1/.044, 7/.029 and so on were replaced with 1.0, 1.5, 2.5 sq. mm. etc.

I'm sure there are those who will applaud the IEE for (a) being an early adopter of the metric and (b) changing over in such a "direct cut" method with no real dual-measurement period.

Problems were caused by this approach, however. I'll save an explanation until you've all congratulated the IEE on their stance of going over to metric in such a fashion. ;)

I congratulate them.

Now tell us what the problems were?

Sounds too direct. In such a technical field it is not sensible to make such severe roundings.

One of the biggest problems in my opinion was the metrication of the cable rating tables.

These are the tables which set out the maximum current which can be safely carried by different size cables under different conditions.

Clearly, with the introduction of new metric-sized cables, it was necessary to draw up new tables giving the calculated ratings. New buildings would be wired with the new cables, so there would be no problem.

But to simply drop the existing tables completely from the regulations was a very bad move. It meant that the new regs. contained no reference for the millions of existing installations using Imperial-sized cable. It would be important to be able to look-up the correct ratings when extending or modifying the wiring.

I think it's become a greater problem as time has gone on. There are *still* many systems in use with cables dating from the 1950s and 1960s, yet most electricians now have no reference for these cables, unless they've tracked down an copy of the old 1966 regs. for themselves.

I believe that the IEE should have retained the Imperial tables for this reason.

There are plenty of other niggles at the changeover as well. For example, the fixtures screws used to attach switches and outlets to boxes were always a 4BA thread, but metrication changed that to 3.5mm.

The bolts look almost the same at first glance, but they're different enough to result in either loose fittings or jammed and stripped threads. Again, this is a problem with attaching new devices to old boxes.

"There are *still* many systems in use with cables dating from the 1950s and 1960s, yet most electricians now have no reference for these cables, unless they've tracked down an copy of the old 1966 regs. for themselves."

Wouldn't thirty year old wiring simply be replaced during any refurbishment works ?

I can't comment on the wonderful world of electrical engineering but in my particular field (structures) the change over wasn't quite as rapid.

I think there was a five year phased change over period that ended in 1975. All I can say is, I'm glad I wasn't arround for that one. I bet it was a most "interesting" time. Knowing the construction industry everybody would have carried on in the same old way for the first four and a half years and then panicked in the last six months.

Of course, when you're dealing with a refurbishment of an old building it's vital to know the "old ways" so that you can make a proper assesment of the structure.

That's why there are numerous referance books dealing with historic steelwork (for example) that tell you all about what steel and iron sections have been available since the mid 19th century and how it would have originally been designed in the days before modern methods were developed. Luckily for me, conversions of lbs/sq ft and tons/sq ins into useable units are given.

No self respecting engineer should be without them. I'd be suprised if there weren't equivalents for electrical engineers.

By the way, you would be suprised at the confusion caused to one of my colleagues by a 1960's concrete
design table a couple of weeks ago. Does "lbf" mean "pounds-force" or "foot-pounds" ?

He should have known better, this guy is in his fifties! Give me "kN" and "kNm" any day.

With regards to your fixture screws, be thankful that the change over was so fast and final. If the IEE had adopted the "use whatever system you like" approach that you advocate then it wouldn't just be thirty year old switches that you'd have problems with !

"Wouldn't thirty year old wiring simply be replaced during any refurbishment works ?"

For a full refurbishment then yes, but where only part of a building is being remodeled then this wouldn't necessarily be the case. To rewire the remaining sections as well could entail major expense, and it is not necessary.

Old vulcanized rubber cables still in service will almost certainly need replacing by now, but PVC cables from the 1950s onward are still perfectly serviceable.

If a new section has to take its feed from existing cables, then it's important to be able to calculate the maximum loading.

"Of course, when you're dealing with a refurbishment of an old building it's vital to know the "old ways" so that you can make a proper assesment of the structure."

I agree with you there. A criticism I often level at some of the new electrical books and courses is that they cover only current, modern techniques. They frequently make no mention whatsoever of the way things were done in the past.

"No self respecting engineer should be without them. I'd be suprised if there weren't equivalents for electrical engineers."

There were, but I think you'd be hard pressed to find any in current publications. The IEE and similar organizations probably think that metric cables have been around long enough that nobody needs to bother about pre-1970 wiring, but that's just not the case.

"By the way, you would be suprised at the confusion caused to one of my colleagues by a 1960's concrete
design table a couple of weeks ago. Does "lbf" mean "pounds-force" or "foot-pounds" ? "

Well I'm no structural engineer, but I know the difference. The fact that in practical day-to-day matters we still need to deal with Imperial measures shows that they SHOULD be taught, even if everything is now officially metric.

"With regards to your fixture screws, be thankful that the change over was so fast and final. If the IEE had adopted the "use whatever system you like" approach that you advocate then it wouldn't just be thirty year old switches that you'd have problems with !"

In practice all the manufacturers pre-1970 made boxes to the appropriate British Standard, which specified a 4BA thread, just as they now make all their boxes to the current standard which specifies M3.5.

PaulEOS wrote

<<
In practice all the manufacturers pre-1970 made boxes to the appropriate British Standard, which specified a 4BA thread, just as they now make all their boxes to the current standard which specifies M3.5.
>>

The 4BA thread boxes were not around all that long. In 1978/9 I rewired a house of 1958 vintage. Thje boxes were wooden!

Do you know what?

I haven't the faintest idea of what you lot are on about!

Steve, it is quite clear that many metrication issures go over your head.

The point I was trying make was that here is a bloke in his 50's who has grown up with imperial and has used it professionally. And yet, even he now has trouble with the odd units that imperial throws up on a regular basis.

I can tell you now, you won't find many engineers of any age that want to go back.

Any system that can't make a proper distinction between mass and force isn't much good in my books.

Martin: "The 4BA thread boxes were not around all that long. In 1978/9 I rewired a house of 1958 vintage. Thje boxes were wooden!"

The 4BA fixture threads were around for a long time. The "box made from wood blocks" technique was employed by those who were too cheap to buy the proper metal boxes. I still see that dodge in old houses around here.

SteveH: "I haven't the faintest idea of what you lot are on about!"

The cable specifications I'm referring to are just the way of quoting the physical size of the wire.

The metric size just specifies the overall cross-sectional area of the conductor in square millimeters. The old British system gave the size by number and diameter of strands, e.g. 7/.029 specified a conductor made up of seven strands, each 0.029" diameter.

In electronics work the SWG (Standard Wire Gauge) system was used. A similar system known as AWG (American Wire Gauge) is still the standard in the United States, and works in the same way in that the larger the gauge number the smaller the wire (there's no direct correlation between the two however). Very large cables are measured in circular mils in the U.S.

BUMP!

The BA thread system is actually metric, although not part of the ISO metric thread system.

Perhaps not completly relevant to metrication, but in the 50s and 60s, before they changed to ISO threads, the BA thread was supposedly obselete, to be replaced with the UNF/UNC sizes (equivalent to 4BA is 6-32), but, looking at old equipment, it seems most manufacturers didn't bother to change from BA to UN sizes, even if they were reasonably quick to change from whitworth to unified threads.

The US is not quite so far along with the National Electrical Code.

The NEC has used dual units for a long time (I can't determine the introduction date). Beginning in 1997, metric was listed first, but was generally a hard conversion of an inch value.

In 2002, metric was declared "preferred," had to be first, and a rational metric value was introduced wherever practical. Values were chosen such that compliance with either the metric value or the FPS value satisfied the code.

There is a 2005 edition, but I am not aware of any change to the metric policy.

Like all of our duality, it is possible to comply with NEC using either metric or FPS units.

<<
Like all of our duality, it is possible to comply with NEC using either metric or FPS units.
>>

That's good. That means that those who want to metricate can do so without messing up the rest of the industry. Then they will soon realize that they are alone, and change back. But the metric standards will stay there, just in case anyone else wants to try.

I think this is a good approach. It satisfies those who advocate metrication without causing problems for the industry.

I'm not sure which of us is the "wishful thinker." But for now, I am glad to get the camel's nose in the tent.

I will point out there is some metric construction going on (new Federal construction is required to be, and a little private construction is). I will also point out that some standards organizations are dropping dual and going "metric only." The IEEE has published new and revised standards in metric only, since 2000. (Metric is "more natural" for electrical engineers as all our electrical units are metric anyway.)

If metric materials are available without a huge premium, reports are that most construction workers like metric after working a job or two. However, there are some issues with material availability, suppliers.

Bud said:

That's good. That means that those who want to metricate can do so without messing up the rest of the industry. Then they will soon realize that they are alone, and change back. But the metric standards will stay there, just in case anyone else wants to try.

I think this is a good approach. It satisfies those who advocate metrication without causing problems for the industry.


Dan says:


Except that those making the change are more likely to be foreign businesses selling to the US market. They will never feel alone and never change back. Those still doing it the English way will be the ones that have to deal with two methods and be the ones cussing under their breath.

The changes were made to accommodate powerful interests both inside and outside the industry. The outcome will be an eventual full metric conversion.

It is a great way to allow metric to enter the industry by stealth, overwhelm the English system and convert the industry completely without government interference that opposer's of metric blame for increase of metric anyway.

<<It is a great way to allow metric to enter the industry by stealth, overwhelm the English system and convert the industry completely without government interference that opposer's of metric blame for increase of metric anyway>>

Yes, I'd go along with that.
Let the market choose metric on its own benefits, superiority, popularity etc.

Unfortunately the UK is an example of where letting evolutionary changes change things on their own goes wrong. So force became necessary because people kept using the "wrong" and "inferior" system.

And still do.