NEC Crossbar

By the late seventies it became obvious to the PO engineers that NZ would have to update it’s phone systems FAST! Customers were wanting new features and reliability, so the standard supplier adopted was NEC Japan and their range of NEC Crossbar exchanges. Exchanges from this supplier were installed in their hundreds in sizes ranging from small rural ones to huge ‘Tandems’ like the Airedale Street HTX A and B exchanges that occupied the entire third floor of this building.

Crossbar switch

I worked on these exchanges for a time and if we thought that SxS was a noisy system, a large crossbar handling hundreds of calls a minute were in a class of their own! These were extremely complex exchanges that while mostly reliable, were a bugger to fault find on. NEC had included automatic test equipment that madly printed out punched paper strips of fault-related information that could (in theory) be used to track down problems, but I never enjoyed or really mastered this process.

Wirespring relays in their thousands were employed in the (much higher than SxS) frames as well as the crossbar switches and these were basically maintenance-free, so the systems were designed to run unattended for periods. Of course, installation work done by our group often caused the maintenance techs grief when we made a wiring error. If we were working on one of the translators we could easily put the whole place off the air until the problem was fixed and it happened more than a few times.

All connections were made using wire-wrapping guns and this was certainly better than soldering, but the technique of getting a reliable connection needed practice. I became a bit of an expert in using the special wirewrap gun bits that cut, stripped and then wrapped the joints when we had to install new equipment.

Calls were routed through these exchanges in a completely different way to SxS as they used a ‘common control’ method with markers, translators as well as the crossbar selectors. The Markers could only switch one call at a time and some exchanges just had 2 of them, so it meant they worked hard during busy hours. Each call processing procedure only took under a second but in a large exchange like the HTX they were banging away like mad involving hundreds of relays working in sequences to keep up with the calls being made.

One year I was on shiftwork as at that time a skeleton staff of 2 looked after the whole Airedale St building and had to look after the HTX’s. We slept on the 3rd floor on stretchers as after midnight not a lot happened unless we had a 111 call trace to do or there was an alarm to tend to and sometimes I managed a few hours kip. One joker I remember used to do his ‘Kashin the Baby Elephant Walk’ around the exchanges when he was bored – pulling his pockets out of his shorts and a part of his anatomy out as well. What can I say? It was sometimes so bloody boring! You had to watch out for the ‘nice boys’ up on the 7th floor who used to summon you up for a bogus fault and try to chat you up when they got bored… One senior tech I remember used to bring in binoculars in his bag full of Penthouse mags to see if he could find any passionate couples ‘at it’ in the surrounding hotels and apartments. Ralph would mutter ‘keep an eye on things for an hour’ and just disappear.

They came in godawful colours too…

A new range of very modern phones was made available to the subs around this time to replace the old dial phones. They had real push buttons which caused many wrong numbers as people were so used to ‘dialling’ the number. Also, they were so much lighter than the old phones that we were used to and many a new push button phone was accidently pulled off the desk and smashed while in use! They had new sensitive microphones as well and quite a few of us got caught out slagging off about a caller only to find out he had heard every word!

As an aside, people often used to ask me why the emergency code in NZ was 111 not 999 as in the UK or 000 as in Australia. Here’s the reason: the old-fashioned phones with dials sent out a number of pulses depending on each number dialled. The pulses would operate the switchgear to connect the calls. Kiwi phone dials had the numbering ‘arse about face’ for some reason – instead of going from 0-9-8-7 etc back to 1, they went 0,1,2 to 9 with the number 0 being 10 pulses and the number 9 being 1 pulse.

Kiwi dial phone

If a customer’s line developed a fault (usually lines that banged together in the wind) it was common for the exchange to get a lot of slow single pulses which would actually have dialled a ‘999’ code. If the emergency number had been set to that then the operators would have had to handle hundreds of false calls a day! Hence the change to ‘111’. This was virtually impossible for a fault condition to cause. I have no idea why the NZ Post Office got special dials made up. Of course the British made and later Japanese switching equipment had to be modified as well to handle our unique dials.

The crossbar era came and went and within 10 years the equipment that took hundreds of thousands of man hours to painstakingly assemble and get working was unceremoniously yanked out to be replaced by SPC (Stored program Controlled) computerised exchanges – again made by NEC. It was such an unbelievable waste of money and time, but I guess it was a sign of times to come – the only thing certain was that things would keep changing.

Found this video of a working LM Ericsson Xbar exchange. This was the same type that I worked on when based at the Airedale Street Telex exchange. Brings back great memories of a better (IMHO) crossbar system than the NEC ones. A lot quieter too (note the xbar switches are behind perspex covers).

I have many memories of working on crossbar systems, one humorous one was ‘Marvin the Joker’, one of the ratbag installation blokes who used to hide up in the overhead racking and wait for an unsuspecting maintenance tech (usually me) to replace an Ericsson fuse. These fuses were designed by a sadist. They were strings of fusewire with metal beads at intervals of around 5-8mm that you had to hook one end onto a spring loaded terminal, gently pull down (or up I can’t remember) on the fusewire string to catch the other end onto the live main bar connection. The 80 volt fuses were the most hair-raising ones to replace because you not only worried about accidentally touching the live end onto the metal frame of the equipment (which of course would instantly fuse leaving a nice burn mark across your palm) but also getting a shock from 80 volts. So, anyway Marvin would wait with a nice heavy aluminium plate in his hands which he would drop from above behind you just as your shaking hands were installing the fuse…
He got me more than a few times and I can still remember his cackles of delight from above!

1 thought on “NEC Crossbar

  1. I remember working on the LM Ericsson Telex exchange in the mid-80s in Airedale street. The plus/minus 80 VDC was far more shocking than the mere 50VDC of the telephones!

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