When did seperate earth's in trunking become fashionable?

[davesparks]

Next question on the date my install game.

When did the practice of installing seperate cpcs in trunking become the norm?
The 'original' part (the rewire when the VIR was replaced) of the install I am trying to establish an age for is entirely in enameled trunking which has been used as the CPC.

I guess another pertinent question would be when did enamelled trunking stop being made/installed?

 

[freddo]

When did the practice of installing seperate cpcs in trunking become the norm?

About the time people installing the stuff were too unskilled to install it properly enough to make a reliable connection.

 

[davesparks]

About the time people installing the stuff were too unskilled to install it properly enough to make a reliable connection.

So never then? There have always been bad installers, and some of these installations were not put together well enough to make reliable connections.

 

[freddo]

A lot of older installs are far better than many of the newer installs I've seen!

 

[ipf]

So never then? There have always been bad installers, and some of these installations were not put together well enough to make reliable connections.

Yep......but these days they just throw them in. Some I've seen with trunking not even flanged, just bushed and not fixed.

 

[Julie.]

It started to come into good practice around the time the 15th edition was trying to be accepted (released in '81, it was reluctantly accepted in mid '80s as it was a substantial change from the previous).

It was a big talking point, the issue is that the conduit is iron, so is magnetic, thus when the current flows in an earth fault the impedance changes significantly, mainly due to reactance, so at low currents or DC the impedance is purely resistive, however as the current increases the reactance increases to some saturation value (circ 60A for 20mm conduit) at which point the overall impedance is around 3x the DC resistance, and of course has a very reactive phase angle, above this the relative impedances go down, and the overall impedance falls back down again.

So for estimating, it's 4.5miliohm per metre when the fault current is less than 100A, but 2.5miliohm per metre for fault current above 100A (20mm conduit)

Of course if you run additional earth cable within the conduit, then this dominates the parallel impedance (cable // conduit) and the impedance stays more constant.

 

[davesparks]

A lot of older installs are far better than many of the newer installs I've seen!

I’ve noticed this too, but you have to remember that the worst of the older installs will have failed/been replaced/ended their life a lot sooner than the good ones. So there S a lot less of the bad one should around.

The same is true for old Wylex fuseboards, people now use the surviving ones as examples of how they’d never had loose connections or suffered faults, but they forget about the countless ones that did have these problems but got repaired or replaced much sooner because of this.

 

[ipf]

The same is true for old Wylex fuseboards, people now use the surviving ones as examples of how they’d never had loose connections or suffered faults, but they forget about the countless ones that did have these problems but got repaired or replaced much sooner because of this.

Numerous thousands of those, in pretty decent condition, were removed due to property rewires or because extra circuits were required. Whilst I'm not against this, I feel the double screw connections at fuse connections were much more secure than some of those involved in current CU's. It's down to cost effectiveness as much as safety. Some DB's, these days, ARE a joy to work on....others are just an absolute mess. I wouldn't like to see the state of them in 40 years or so.

 

[R-fur]

Have never seen a burnt connection on a wylex board, brass blocks with two screws rarely gave problems. When cage connectors were introduced in the early 80's I was an installation inspector for the local board, testing and metering new builds and rewires, we soon learned that after fitting the meter we had to open the CU and retighten the tails connection before energising or they would burn.
We all knew they were not good but the manufacturers said they had been type tested and the sparks were not tightening properly, so we got torque screwdrivers, that had to be calibrated, still they burned so we got metal consumer units, all because of cage terminals.
Having said that, I think the metal CU's are a better job and the stuffing glands for tails are a big help in holding the tails firm to give the cage terminals a chance.