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Phased out: IT architect plugs hole in clean-freak admin's wiring design

Rich 11 Silver badge

Plot twist? What plot twist?

"I looked at the installation and realised the sysadmin had meticulously wired all the servers to the same phase," Oscar said.

I'm going to go out on a limb here and say that we all saw this coming.

defiler Silver badge

Re: Plot twist? What plot twist?

Yarp. Still, whilst working in an old building we were proudly told by the beaming electrician who'd just finished a rewiring job that the three phases had been nicely isolated so that one carried the lights, the second all of the sockets, and the third the high-drain devices such as aircon, the kitchen appliances and the server cabinets...

Those UPSs took a beating smoothing out that load.

Neil Barnes Silver badge

Re: Plot twist? What plot twist?

Built a radio studio in a flat in Bangladesh once. Turned out that the habit there was (is?) to distribute the three phases coming into the building by lights, sockets, and aircon... but instead of rotating between flats they rotated between rooms to spread the load. Made for some interesting hunting down of earth loop hum.

(as an aside, they would frequently black out one phase - not always the same one - to save power, which also made things interesting.)

Richard 12 Silver badge

Re: Plot twist? What plot twist?

That makes no sense. Blacking out a single phase in a TPNE system increases the load on the neutral and means you either need a much bigger wire or you destroy equipment. Up to and including the entire building.

John Miles

Re: That makes no sense.

since when has sense or reality ever got in the way of some manager's idea to save monry

Prst. V.Jeltz Silver badge

Re: Plot twist? What plot twist?

"I'm going to go out on a limb here and say that we all saw this coming."

Yup . just the mention of 3 phase...

But its the on call section.

Similar to if you're watching You've Been Framed and somebodys on a rope swing over a river ..... you know whats going to happen.

Yet Another Anonymous coward Silver badge

Re: Plot twist? What plot twist?

"I'm going to go out on a limb here and say that we all saw this coming."

I was going for - he somehow managed to use an extension lead to join two phases.

We had a server basement broom cupboardroom where somebody needed a couple more 240v outlets and so had knocked a hole in the drywall and run an extension from another room - on a different phase. Server and monitor on 415V difference in supply - strangely nothing went wrong.

Evil Auditor Silver badge

Re: Plot twist? What plot twist?

strangely nothing went wrong

What should go wrong there? Even in my home installation I run the peripherals (screens and stuff) on one phase and workstations/servers distributed over all three phases. Strangely, I haven't been electrocuted yet ;-)

Yet Another Anonymous coward Silver badge

Re: Plot twist? What plot twist?

>What should go wrong there?

I'm old enough to remember TVs on 2wire leads where the chassis ground was connected to live or neutral at random.

Antron Argaiv Silver badge
Thumb Up

Re: Plot twist? What plot twist?

Not at random, it depended on which way you put the plug into the power socket.

It was called "hot chassis" design and it saved a winding or possibly an entire transformer.

You had nothing to complain about, the pressboard back of the cabinet served as an insulator, and as long as you didn't go poking around where you didn't belong, you were safe. Until your screwdriver slipped or your kids lost one of the knobs on the front. Made life more interesting.

That's why we have polarised plugs and a ridge down one wire of the zip cord now.


Re: Plot twist? What plot twist?

Having worked on these, the chassis was normally hot 100% of the time, because the oncoming mains went through a bridge rectifier with no isolating transformer. The chassis was connected to the -ve side of the rectifier, so you have a nice half-wave 240V potential on the chassis.

I was taught to work on these beasts with one hand in your pocket, as it minimized the chance of through body contact. More exciting was using a scope on these units, as connecting the shield (grounded) to the chassis (with 240V half wave) was a big no-no. The exciting approach was to let your scope float (plastic knobs only), the more sensible approach to use an isolating transformer for the TV, and then ground the chassis.


Re: Plot twist? What plot twist?

"home installation"

Unusual to have 3 phase in domestic premises.

razorfishsl Bronze badge

Re: Plot twist? What plot twist?

No it's not

In Hk & China it is REALLY REALLY common.

The they do something stupid , like split it 1 phase per floor.

But aircons are 1 phase....


Re: Plot twist? What plot twist?

I've got it. Previous occupants ran a pottery studio and kiln in the shed out the back. Gently slope was a bastard to cover with a floating floor ...

Clive Harris

Re: Bridge rectifier?

These must have been more recent than the old valve TV's I worked on, way back in the last century. These ones had one mains terminal (hopefully neutral) connected directly to the chassis, with the HT provided by simple half-wave rectification of the mains. (No-one worried about mains waveform distortion in those days). This rectification was invariably done with a massive selenium rectifier about 8 inches long. Valve heaters were connected in series and driven directly from the mains via a big dropper resister. This generally had taps on it to adjust to different mains voltages.

These selenium rectifiers were notorious for the stink they made when they failed, which has been compared with a robot farting. Often a TV repairman would be greet with profuse apologies from the householder who couldn't work out the source of the smell and generally blamed their cat or dog.

Daniel 18

Re: Plot twist? What plot twist?


If single phase power is 120V, three phase will come in at 208V.

Instead, homes usually have a centre tapped feed, giving a choice of 120V or 240V single phase. The latter is used for things like clothes dryers, water heaters, central air conditioning, and stoves.

Other things - stuff plugged into wall sockets, furnace motors, lights, sump pumps, garage doors, etc. are generally 120V.

As a result connection is simpler and more compact than 240V, with no need for things like fuses in appliance plugs and the option of designing for a two prong plug.

Also, it seems like 120V doesn't bite as hard as 240 - the few times I've had undue excitement with 120V, it wasn't too bad, but rather startling.

The 208V stuff shows up in some moderately heavier commercial and industrial installations like store refrigeration systems, large AC units, I susect for elevators, some computer gear, and so on.

The 'big stuff' may use higher voltages like 400, 600, or 800V... steel mills, motors moving 1100 tonne bridges, lock gates, subways, and the like generally go for higher voltages.

(And while it may be a bit odd, if you put me in the motor room of a big lift bridge, I will actually go over and read the specification label on the motors...)

As for frequencies, originally it was 110V at 25 Hz, but back somewhere around the 1930s, they decided that was inefficient and changed to 60 Hz - much better for transformers.

When I was a kid, antique radio gear sometimes showed up with 25Hz transformers, which were way bigger and could be used at much higher loads on the newer 60 Hz current.

Daniel 18

Re: Bridge rectifier?

"This rectification was invariably done with a massive selenium rectifier about 8 inches long."

This sounds like some kind of transitional technology to me. What year were these built, roughly?

I remember taking apart old TVs - no solid state rectifier though, that part was done with a vacuum tube, and the right tube gave you a full wave rectifier.

Glen 1 Bronze badge

Re: Plot twist? What plot twist?

Re: hot chassis

Reminds me of the old Usenet yarn.

Magic/More magic

Don't get me started on the Story of Mel

H in The Hague Silver badge

Re: Plot twist? What plot twist?

"Unusual to have 3 phase in domestic premises."

Depends on the country. Here in NL it's usually 3 phases into the consumer unit/distribution board, with single outgoing phases to the house wiring. (Though you could fit a 3-phase breaker if you want to install some nice large machine tools in your home workshop :)

Talking of breaker panels, had a beer a while ago with a chap who refurbished an old house (in the UK I think),he turned the power off at the first fuse box and at the second one. Then started cutting the old cables, cue flash, bang and molten wire cutters. Eventually he found the third fuse box behind some wallpaper.

Here's one for the weekend.

Unicornpiss Silver badge

More wiring follies..

A friend of mine bought a house, and she asked me to take a look as every time she plugged in her computer monitor (CRT type) into a certain outlet, the circuit breaker would trip instantly. The monitor worked fine when plugged into any other outlet, and anything else plugged into the suspect outlet worked fine too.

The outlet was a standard 3-wire duplex outlet, like billions of others in the US. The house was somewhat older and parts of it still had 2-prong outlets. Upon pulling the outlet out of the wall, I found that to make this a 3-wire outlet, someone had wired the neutral and ground together, as there were only 2 conductors available from the panel. While this was a code violation, and a safety issue, it would have been mostly okay if the idiot that wired it hadn't mixed up the hot and neutral wires. So the neutral and ground were both hot, and her monitor apparently had some internal fault that led to the discovery.

This could have been lethal, if for example, someone was using an older power tool that had the metal case grounded for 'safety', then touched a pipe or similar with their other hand. A metal-cased power strip could have been shocking too..

Unicornpiss Silver badge

Re: Bridge rectifier?

"These selenium rectifiers were notorious for the stink they made when they failed, which has been compared with a robot farting."

Everything in that column of the periodic table forms stinky compounds and reeks when burned. (Eg. sulfur, selenium, tellurium, and presumably polonium too)

If you're bored, google "tellurium breath". Apparently it only takes a very small exposure to tellurium to make the breath, urine, sweat, etc. reek horribly of garlic for a very long time.

bobajob12 Bronze badge

Re: Plot twist? What plot twist?

In many parts of the world, Bangladesh included, the concept of make-it-work trumps adherence to "code", or saftey, or anything we take for granted in the developed world. See for an example (from Pakistan). You see it and you are simultaneously impressed and horrified!

bobajob12 Bronze badge

Re: Bridge rectifier?

Check out Derek Lowe's chem blog for more on this. Like: "Imagine 6 skunks wrapped in rubber innertubes and the whole thing is set ablaze. That might approach the metaphysical stench of this material"


Re: Plot twist? What plot twist?

"Unusual to have 3 phase in domestic premises."

You clearly don't live in Belgium! Our house built in the 1950s runs on 240v 3 phase 15A, and we consider that an improvement! As until a few years ago it was on the original 110v Split phase!


Re: Bridge rectifier?

I remember getting old throw-out 405 line tellies to play with in my early teens (~1970), with selenium rectifiers. In one, I remember accidentally shorting out >1/2 the segments by mis-routing one of the connecting wires and letting it rest against one of the fins. The remaining segments objected to the over voltage went pop. And yes it really did stink. I wasn't very popular at home...

Drawing arcs with a screwdriver off the EHT was fun too. Until you got your finger too close to the edge of the insulated handle, and the arc jumped from blade to flesh!

Robert Forsyth

Re: Plot twist? What plot twist?

The aerial lead made the aerial not the thing to grab in the loft or on the roof; may be an anti-theft measure?


Re: Plot twist? What plot twist?

Everyone around me has 3 phase. How else do you run a 4.5kw air conditioner? You're probably thinking of somewhere like the UK where ice is still considered a luxury item...


Re: Plot twist? What plot twist?

No, in the civilized part of the world that is entirely normal


Re: Bridge rectifier?

Be glad they were not using Tellurium, compound smelliness apparently increase as you go down that group of the periodic table S -> Se -> Te. I assume that Polonium compounds would be even worse, but there you have other problems to contend with that are more worrying then smell..


Re: Plot twist? What plot twist?

In NZ, quite happily from the normal 240v single phase on a 20? amp circuit. Ovens are usually on a 32 amp breaker. (Actually IIRC it a 4.2kw unit)

We only use one voltage for household stuff here.

Unless you have a machine shop in the basement

Anonymous Coward
Anonymous Coward

Re: Plot twist? What plot twist?

"As a result connection is simpler and more compact than 240V, with no need for things like fuses in appliance plugs and the option of designing for a two prong plug."

I think you are confusing "240V" with "the crazy stuff they do in Britain". Pretty much the whole world runs 230/240V just fine without fuses in plugs and with 2-pin plugs for unearthed devices.

Even in Britain probably 90% of those ridiculous plugs nowadays have a plastic third pin and no fuse, for the simple reason they are just a cheap localisation measure fitted to something that was designed to have a 'normal' 2-pin unearthed plug.

This post has been deleted by its author


Re: Plot twist? What plot twist?

Moi, aussi....

The previous owner of my flat was rather prone to doing random bits of DIY that really should have been done by a professional, so I have multiple plug sockets in rooms in random places, and mixes of wall and ceiling lights running off multiple circuits. When I first moved in, my dad was up helping me replace a nearly-antique fluorescent tube in the kitchen with something more modern that I could actually still but bulbs for. We worked out that there were two separate circuits in the main fuse box and switched off all the fuses to cut the entire power supply into the property, and dad picked up the drill. At which point the penny dropped that the mains-powered radio in the kitchen was still active....I've never yet worked out where that circuit comes into the property or how to turn it off. I've also never put a drill into any wall myself and warn any tradesman coming in - they've never solved it either but they've all survived.

JulieM Bronze badge

Re: Plot twist? What plot twist?

Have you never watched Casualty? It's usually pretty obvious within the first five minutes, who's going to be in the ambulance and why. Doesn't make it any less interesting, though.

Anonymous Coward
Anonymous Coward

Whilst the overload wasn't clever...

I would have expected the UPS to detect this and do something other than "let out the grey smoke that makes the chips work" - drop into bypass (to help clear fuses if there is a hard fault) or drop the load if that's not possible.

Anonymous Coward
Anonymous Coward

Re: Whilst the overload wasn't clever...

I have seen exactly that problem with one of the big UPS manufacturers that it could not handle severely unbalanced loads.

Captain Scarlet Silver badge

Re: Whilst the overload wasn't clever...

In my youth when a UPS had tripped because of a fault, the management card screamed about an input fault. Being a PFY, I went and thought thats odd and pressed the button to reset the UPS power input without thinking the UPS itself could be faulty.

What followed was a lightshow from the 16Amp power input cable which had melted before my eyes and hoping it would retrip itself which is did shortly after. So for me its possible the UPS may have tripped but someone inexperienced might have commanded the device to try again, as thats exactly what I did and I will never ever do ever again.

Anonymous Coward
Anonymous Coward

Reminds me of a time...

...that an airport I was working at had a water leak in the middle of the night. The contractors went under the check-in desks and isolated the individual UPSs in the area that was affected, just to be on the safe side (they weren't actually wet). Having stopped the leak and cleaned everything up, they plugged the UPSs back in again.

About half an hour later, check-in started, everything was going fine, until that entire bank of check-in desks all died within 2 minutes of each other, and chaos ensued in the middle of the morning rush.

Turns out the contractors hadn't plugged the UPSs back into the mains - they'd plugged them into themselves...

Prst. V.Jeltz Silver badge

Re: Reminds me of a time...

I heard tell of a desktop support guy under a desk looking at a tangle of power cables. the problem turned out to be the "4 gang" adaptor was plugged into itself....

The Oncoming Scorn

Re: Reminds me of a time...

Last UK house, I put in spot lights (GU10) in the bathroom, the end light in the harness "failed" yet showed continuity when I used my DVM on the connector.

I ended up making the harness into a loop which solved the issue, there were four lights*.

*Icon ST-TNG

Yet Another Anonymous coward Silver badge

Re: Reminds me of a time...

>. the problem turned out to be the "4 gang" adaptor was plugged into itself....

Of course if you can make it work you are in the money


Re: Reminds me of a time...

On a similar note, it was my daughter's 10th birthday and the I'd taken the afternoon off, however some guy in sales had noticed that a network cable had come lose behind his computer and kindly plugged it back into the shared router under his desk.

Unfortunately, he didn't tell anyone at the time, also, the cable was supposed to go into the back of his PC, so what he did infinite looped the router which took the whole network down.

We ended up disconnecting everything from the main switch and plugging the cables back in one by one until we discovered the one connection that took everything down.

Needless to say, I was late for the party. :(

Stevie Silver badge

Re:Of course if you can make it work

Gallon of liquid helium, a magnet and you are sorted.


JimboSmith Silver badge

Re: Reminds me of a time...

One showroom I was at trying to run cable to a new location for the PDQ (card machine). I had used two four socket extension leads to create seven sockets coming off one 13A wall socket. I needed the PDQ to have a wall socket to itself and had labelled the extension sockets as for lighting only. The manager was worried that the wall socket might get overloaded with seven ornamental table lights plugged in. The bulbs on these things were a maximum of 40W and in a few of them they were low energy ones. The total came to under an amp of current from memory. I explained this and showed my working out because she wasn't 100%. I said it would be a different story if you had the microwave the kettle, a heater etc. on the same extension cord. She went white and showed me into the staff area where there was just that sort of thing going on despite ample power sockets being available. Some education followed with the staff about what not to do and new single socket extension cords were bought.

John Sager

Surprised the sockets on different phases were close enough together to connect the servers like that. I thought there were rules about spacing. A server installation I visited once had the cabinets on different phases far enough apart so you could not touch 2 at the same time.


That's my understanding as well.

We had issues "back in the day" with Apricot networking not being cross phase tolerant. A new build for one of our clients was specified with turned-earth-pin plugs and sockets for the computers being all on a single phase.

Despite this being accepted by the architects when we actually got in there (with only a couple of days to complete the installation) we found that firstly they hadn't supplied the special plugs (a motorcycle courier was arranged to bring them from Birmingham) and secondly that they hadn't wired them all to the same phase as "they're too close to the other sockets". They'd also totally ignored the instructions on the network cable install but we managed to work around that.

This would all have been avoided if our request for a site meeting with the sparkies before they started work had been accepted but we were assured that the architect knows best!

Richard 12 Silver badge

That's a myth. It was a requirement added in the 14th ed of the UK wiring regulations, and removed in the 15th edition for being pointless - before BS7671 existed.


Thanks for the clarification. Obviously the contractors we had were working to 14th Edition standards then, even though 15th Edition had been introduced a few years before!

Chunky Munky

NEVER assume the architect knows best! The school I work at has just had a building erected, one of the prime features is a light & airy glass walled atrium. As this was to be used as a meeting point/social area for older students, good WiFi coverage was essential. I requested a minium of 4 access points, one in each corner of the room, 2 - 3 metres from ground level. The architect knew better and instructed the builders to install them at roof height (2 storey building) & behind the false ceiling so they couldn't be seen as they would ruin the buildings asthetic (?). Unfortunately, the false ceiling had aluminium covered tiles and so formed a lovely Faraday cage.

The builders were less than happy with having to move them :)

frank ly Silver badge

All architects care about is building 'aesthtics' and will insist on anything if they think it maintains or improves their 'vision'. I've worked with people who install large scale systems (Power, HVAC, etc) and they've told me horror stories about architect decisions putting installation costs up and reducing the efficiency of installed systems.


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