metal Cu earth straps

[binky]

proper fuse boards :slap

I took apart an old wylex board yesterday, proper insulated fuse carrier ( din rail) , decent size copper bus bars, proper fire retardent plastics and I dare say the fuse holders would survive a fire quite happily.

 

[Rob_the_rich]

My concern is that due to the design of Amd3 boards, householders are being exposed to a danger which before Amd3 they weren't. The act of holding onto the lid connects the householder directly to the earthing system, we like to think that the whole house is within the equipotential zone, but this is not always the case, and the householder could also be in contact with something which has a potential other than that at the source of the supply. In a broken PEN situation, whether in the supply to the property, or a neighbouring property, the earthing conductors might be carrying more load than intended, that's why I introduced into the discussion.

 

[Blue Duck]

So if you are fitting a non combustible consumer unit then you must also fit an isolator in a combustible enclosure incase of the non combustible unit becoming live under fault conditions and you can't lift the lid to isolate the supply.

Seems a bit shortsighted but unlikely? 

:coffee

 

[phil d]

My concern is that due to the design of Amd3 boards, householders are being exposed to a danger which before Amd3 they weren't. The act of holding onto the lid connects the householder directly to the earthing system, we like to think that the whole house is within the equipotential zone, but this is not always the case, and the householder could also be in contact with something which has a potential other than that at the source of the supply. In a broken PEN situation, whether in the supply to the property, or a neighbouring property, the earthing conductors might be carrying more load than intended, that's why I introduced into the discussion.

That's a valid point,maybe the powers that be will come up with something, like the board being isolated electrically from the metal case and the case being connected to an earth rod, sounds mad but the way things are going you never know. I've had conversations with people who clearly don't understand things, they make sweeping statements like, "if everything is bonded and rcd'd then you can't get a shock" if only that were true, I don't think we'll ever come up with a way of totally preventing shocks, merely as we have now where we try and limit the time and level of the current that will flow. I must admit it would be nice though, lets be honest we've probably all had a belt at some point by touching something live and simply standing on a floor.

 

[Lurch]

The front covers usually have a drop-down flap which would be held up by the householder when re-energizing a tripped mcb/rcd. The extra bonding, I assume, is provided by the OEM to try and mitigate the effects of holding on to a bit of metal connected to the earth when doing so

The bonding is just from the rear case to the front cover, not directly to the flap, and the issue is that the front cover will be bonded via the screws anyway so the earth strap is unnecessary in most cases.

My concern is that due to the design of Amd3 boards, householders are being exposed to a danger which before Amd3 they weren't.

That's not right. I have fitted loads of metalclad boards, no different to the current crop of Amd3 boards.

The act of holding onto the lid connects the householder directly to the earthing system, we like to think that the whole house is within the equipotential zone, but this is not always the case, and the householder could also be in contact with something which has a potential other than that at the source of the supply.

You could say this about anything metal, the board isn't suddenly more metallic than anything else connected to the earthing system.

In a broken PEN situation, whether in the supply to the property, or a neighbouring property, the earthing conductors might be carrying more load than intended, that's why I introduced into the discussion.

That's a completely separate issue, and the argument for that also applies to anything metal anywhere in the installation.

 

[Sidewinder]

Remember, if the case of the board comes into contact with a line conductor and a fault current flows, then ADS must operate as per the requirements of BS7671, just in this case you are relying on the DNO fuse, the EFLI between the incoming line conductor and the body of the board must meet the requirements for ADS.

If it does not occur due to an increase EFLI based on the DNO fuse, then you must, do something to ensure that ADS does occur, & take action to prevent as far as reasonably practicable the board coming into contact with the line conductor.

 

[kerching]

And what about continuity across the hinge?...some of the  'hinges I have seen have been 'slacker than a Wizards sleeve'

just musing

 

[Sidewinder]

The DB hinges are covered by EN 61439-1 & EN 61439-3, so that is sorted, no matter what the hinges are like!

 

[binky]

 I've had conversations with people who clearly don't understand things, they make sweeping statements like, "if everything is bonded and rcd'd then you can't get a shock" if only that were true, I don't think we'll ever come up with a way of totally preventing shocks, merely as we have now where we try and limit the time and level of the current that will flow. I must admit it would be nice though, lets be honest we've probably all had a belt at some point by touching something live and simply standing on a floor.

in theory the touch voltage is limited to less than 50V if everything is bonded and earthed correctly

 

[Andy™]

in theory the touch voltage is limited to less than 50V if everything is bonded and earthed correctly

not if you have a TT supply at the incoming tails / busbar were to touch the case, then it would be 230v

 

[M107]

Who earths back boxes via cover screws?

Errrrm me

 

[binky]

not if you have a TT supply at the incoming tails / busbar were to touch the case, then it would be 230v

 but then the incoming tails are suppossed to be fixed in a way they can't do that, and if they did short to the casing it would blow the main fuse

 

[Sidewinder]

 but then the incoming tails are suppossed to be fixed in a way they can't do that, and if they did short to the casing it would blow the main fuse

It won't blow the main fuse with a TT though will it, well highly unlikely even with a 60A DNO fuse I doubt most domestic TT's get an EFLI low enough.

60A BS1361 5s disconnection Zs < 0.7 Ohms, or there abouts.

Doubt you'd see that with a domestic TT.

 

[Andy™]

 but then the incoming tails are suppossed to be fixed in a way they can't do that, and if they did short to the casing it would blow the main fuse

not on TT. it would happily sit live at 230v until, in the case of a job last year, the electric meter kept using all the credit and switching off. no idea how he wasnt dead (L-E short on sockets, no RCD, fault current around 20A)

 

[datadiffusion]

This sounds almost as good as a mate of a mate who kept complaining of 'tingling' when he touched the sink if the dishwasher was running.

Eventually I was persuaded to take a quick look as I was in the area. His Dads 'sparky' mate had come all the way from London 6 months ago to change the

CU. And there was NO main earthing (or cross bonding) whatsoever....

 

[binky]

so in that case, we should really be fitting 100mA TD RCD prior to boards to ensure full safety of customer

 

[Andy™]

so in that case, we should really be fitting 100mA TD RCD prior to boards to ensure full safety of customer

which would also have to be in an LFB approved metal CU so still the same problem

 

[binky]

just worked out 200 Ohm rod at 240V gives roughly 1.2A fault current. Just trying to think if an individul RCD / breaker needs fire rated enclosure, or whether that non-sense only applies to full board?

 

[Sidewinder]

The "industry approved" solution as put forward & agreed by all the scams, the IET & Electrical Safety First etc. in fact all of those listed as contributing to the Electrical Safety First BPG's is as follows:

Insulating gland on entry to the consumer unit, e.g. a plastic Wiska type gland with the 3 hole insert.  Yes plastic.  Other brands than Wiska are available.

The sheathing of the tails is taken all the way to the entry of the main switch, none of the basic insulation is on show, except perhaps a very tiny bit at the entry to the main switch tunnel terminals. Code the tails with tape or another means if you feel that this is required.

The tails must be clamped in place at the entry to the main switch so that they cannot simply come out of the electrical connection and then be free to move.

Most CU manufacturers offer this kind of clamp.

The main switch itself must be a 100mA time delay two pole RCD.

For reference, I know that Hager do a ready made split load board with all of these features as standard, if all goes to plan we will be using one shortly so I'll try to get a report back on it.

It was a private conversation between myself & Mark Coles after this was presented at an Elex show got me a row of said Mr Coles for using the term "fireproof" when if comes to the so called Amd3 compliant boards.

It was a slip of the tongue, and easy to make, but there is no requirement for fireproofing in BS7671, as I was so succinctly reminded!

The requirement is that the CU body is made from a "non-combustible" material, this has been taken by BEAMA members to be steel.

It seems that even non BEAMA member companies have gone the same way, bar one, who has also made a die cast Aluminium alloy material.

However, I have yet to discover of this allow contains Magnesium, if it does, then it may well not meet the requirements for "non-combustible" under the building regulations description.

The term "non-combustible" has its roots in building regulations and construction materials where there is a test for "non-combustibility".

As far as sealing penetrations to the CU, the requirement is the same pre-Amd3 as it is post Amd3, that they meet the IP rating requirements specified in BS7671, .g. IP4x for accessible top horizontal top surfaces etc.

I trust this covers the matter.

 

[datadiffusion]

For reference, I know that Hager do a ready made split load board with all of these features as standard, if all goes to plan we will be suing one shortly so I'll try to get a report back on it.

Or perhaps using. Or maybe suing as well

As every other manf sells out to the LCD, I still rate Hager.