IET's new Guide to Consumer Units

[Iggifer]

Metal consumer units pose a great risk of becoming live due to overheated cables loosening up and touching the box, which hasn’t been properly earthed. Therefore there is a need for an insulation material to be placed inside the unit to prevent this from happening

Whilst this is strictly true, you'd have to be a complete numpty to not terminate your main earth properly into the earth bar - which is then directly bolted to the chassis.

Maybe the guy who can't tighten his earth up properly, IS the guy who has overheating cables in MCBs. I've never seen an overheated cable escape from an MCB though; maybe I just don't get out enough

 

[JohnW2]

Metal consumer units pose a great risk of becoming live due to overheated cables loosening up and touching the box, which hasn’t been properly earthed. Therefore there is a need for an insulation material to be placed inside the unit to prevent this from happening

Whilst this is strictly true, you'd have to be a complete numpty to not terminate your main earth properly into the earth bar - which is then directly bolted to the chassis.

I agree. However, the concern I have often voiced relates to the situation in which a metal CU is properly earthed. In the context of a less-than-competent or less-than-careful-enough DIYer (or 'electrician', or even electrician) who is 'fiddling' inside a CU, I fear that all that earthed metal around will present a potential hazard. The LFB presumably are not all that concerned about electrical injuries and electrocutions, but it would not surprise me if an increase in them due to the move to metal CUs more than balances any decrease in injuries/deaths due to CU-related fires (which do concern the LFB).

Kind Regards, John

 

[Iggifer]

Metal consumer units pose a great risk of becoming live due to overheated cables loosening up and touching the box, which hasn’t been properly earthed. Therefore there is a need for an insulation material to be placed inside the unit to prevent this from happening

Whilst this is strictly true, you'd have to be a complete numpty to not terminate your main earth properly into the earth bar - which is then directly bolted to the chassis.

I agree. However, the concern I have often voiced relates to the situation in which a metal CU is properly earthed. In the context of a less-than-competent or less-than-careful-enough DIYer (or 'electrician', or even electrician) who is 'fiddling' inside a CU, I fear that all that earthed metal around will present a potential hazard. The LFB presumably are not all that concerned about electrical injuries and electrocutions, but it would not surprise me if an increase in them due to the move to metal CUs more than balances any decrease in injuries/deaths due to CU-related fires (which do concern the LFB)

I'm not sure I disagree, but I definitely don't agree 100%. At least if it's earthed, you're gonna know pretty quickly if something live touches down. And, all being well, the OPD, be it MCB or Main Fuse, is hopefully going to open. If it doesn't, the flash and bang is going to be enough for you to move out the way pretty quickly. The same just wouldn't happen with a plastic consumer unit, if you were that incompetent you wouldn't know.

That being said, at least with the Hager boards we fit, the epoxy coating on the casing is pretty thick, and I haven't tested it, but I wonder if it would actually pass voltage or whether it does have some insulating properties...

 

[JohnW2]

I'm not sure I disagree, but I definitely don't agree 100%. At least if it's earthed, you're gonna know pretty quickly if something live touches down. And, all being well, the OPD, be it MCB or Main Fuse, is hopefully going to open. If it doesn't, the flash and bang is going to be enough for you to move out the way pretty quickly.

I wasn't thinking of live things coming in contact with the earthed enclosure - but, rather, of 'earthed metal all over the place' for someone to touch at the same time as touching something live (like the incoming terminals of the main switch).

That being said, at least with the Hager boards we fit, the epoxy coating on the casing is pretty thick, and I haven't tested it, but I wonder if it would actually pass voltage or whether it does have some insulating properties...

Yes, that could be the saving grace, but the coating is (or may be) presumably breached by nuts/bolts, rivets etc.

Only time will tell.

Kind Regards, John

 

[PBC_1966]

In the context of a less-than-competent or less-than-careful-enough DIYer (or 'electrician', or even electrician) who is 'fiddling' inside a CU, I fear that all that earthed metal around will present a potential hazard.

Metal casing is the norm here, and there hasn't been as much emphasis on shielding busbars and other live internal parts as has happened in the U.K. over more recent years. Below is a picture I posted elsewhere of a new panel I bought recently. I do sometimes wonder if the extreme level of shielding which is present in modern U.K. boards in an attempt to provide protection might actually lead some people into complacency and carelessness.

 

[Echo the husky]

Anyone who has worked on an old Ottermill 3 phase board with the power on will be glad the newer ones are more shielded. Old Dorman Smith boards are often exciting too.

 

[JohnW2]

Metal casing is the norm here ....

I don't really know enough statistics to even guess at particularly meaningful US/UK comparisons - and the voltage differences are clearly a major issue. Do you have any idea how many domestic electrocutions there are in the US?

Kind Regards, John

 

[kai]

Just bring back traditional Twin Terminal Screw Connections - problem solved!
(Have YOU ever encountered a burnt Wylex Standard Range unit which was burnt, but has NOT been subjected to some misuse??)

 

[Iggifer]

Anyone who has worked on an old Ottermill 3 phase board with the power on will be glad the newer ones are more shielded. Old Dorman Smith boards are often exciting too.

Working on (well it's gone now) a Federal Electric Stablock 3P board this week. They're thrilling. The disconnection times on them is in the seconds rather than milliseconds too

 

[PBC_1966]

Do you have any idea how many domestic electrocutions there are in the US?

I don't think I've ever really looked for the national statistics. OSHA (America's equivalent of the British HSE) would no doubt have statistics for occupational electrocutions, but I'm not sure about domestic.

 

[JohnW2]

Do you have any idea how many domestic electrocutions there are in the US?

I don't think I've ever really looked for the national statistics. OSHA (America's equivalent of the British HSE) would no doubt have statistics for occupational electrocutions, but I'm not sure about domestic.

There are similar issues in this country, with all types of accidental injuries/fatalities - if they are 'occupational', they tend to be reported/ recorded/ investigated, in a manner which is not generally the case for domestic accidents. At least with fatalities we have death certification records (albeit they are notoriously inaccurate), but there is no reliable source at all (of which I am aware) of statistics regarding non-fatal domestic electrical injuries. The ESC's attempts to do (small) surveys have resulted in figures which tend to stretch credibility!

Kind Regards, John

 

[JohnW2]

I've found this ....

This report provides: ... information about the estimated number of unintentional non-work related electrocutions associated with the use of consumer products in 2008 ... There was an estimated average of 53 electrocution fatalities associated with consumer products per year over the three-year period from 2006 through 2008,

Pro-rata to population, that's approaching half of the total UK domestic electrocutions.

However, I suppose priorities (and 'concerns') are a little different over there, given that those 53 electrocutions by consumer products per year has to be seen in the context of ...

Some 13,286 people were killed in the US by firearms in 2015

... which is about 50% higher than the pro-rata number of people killed on UK roads!!

Kind Regards, John

 

[PBC_1966]

Pro-rata to population, that's approaching half of the total UK domestic electrocutions.

But it does say "associated with the use of consumer products," so presumably that doesn't include somebody playing around in a distribution panel, hitting overhead lines with a ladder, etc.

 

[JohnW2]

Pro-rata to population, that's approaching half of the total UK domestic electrocutions.

But it does say "associated with the use of consumer products," so presumably that doesn't include somebody playing around in a distribution panel, hitting overhead lines with a ladder, etc.

Exactly. I would guess that, of the 20-30 UK domestic electrocutions per year, less than half are probably "associated with the use of consumer products" - so I was implying that total US domestic electrocutions is (pro-rata to population) at least as high as in UK, despite a lot of the voltages being lower..

Kind Regards, John

 

[stillp]

I wouldn't believe the UK statistics and doubt the US ones are any more accurate.
I did some research into the reporting of electrical accidents some years ago. One involved a toddler who had stuck a button cell up his nose. The same incident had been recorded by the A & E receptionist, a triage nurse, and the discharging doctor, so appeared 3 times. Another concerned an elderly gent who'd stood a kitchen chair on top of a settee and climbed on it to change the battery in his clock. He fell, breaking his hip. Because he was intending to change a battery it was recorded as an electrical accident. There were also some fatalities wrongly recorded as electrical.