Watch out I'm fitting a plastic DB in domestic.....

[Lazlo]

It's a TT so I reckon I'll sleep better at night knowing that if there was a fault to earth upstream of the RCDs the customer wouldn't get a brutal/possibly fatal belt. Just going to put it in the departures section of cert and discuss it at my annual inspection with my assessor.

I know I have till Jan anyway......Stupid reg should exclude TT installs, much more risk associated with electric shock than a possible loose termination resulting in a fire within DB. If it was so dangerous surely every night the news would be filled with stories of consumer unit infernos burning civilisation as we know it to the ground.:devil:

 

[Dave OCD]

I agree 100%, although I've fitted many metal CUs in the past in places such as workshops I won't be doing any amendment 3's until January. :smiley2:

 

[Octopus]

I fitted a plastic CU just last week on a TT system. Naughty me!

 

[Deleted member 9648]

The risk of a fault to the metal case of a CU from the tails is nil if the right precautions are taken. How many times do you see a fault from the tails on any metal CU,regardless of earthing type?....virtually never,and most tails are unsecured and simply pass through a rubber grommet. The risk on TT's is grossly exaggerated IMO.

 

[amlu]

we will have double insulated metal units for 18 edition regs ;-)

 

[Dave OCD]

The risk of a fault to the metal case of a CU from the tails is nil if the right precautions are taken. How many times do you see a fault from the tails on any metal CU,regardless of earthing type?....virtually never,and most tails are unsecured and simply pass through a rubber grommet. The risk on TT's is grossly exaggerated IMO QUOTE]

So's the risk of an insulated CU bursting into flames IMO :rolleyes2:

 

[Deleted member 9648]

The risk of a fault to the metal case of a CU from the tails is nil if the right precautions are taken. How many times do you see a fault from the tails on any metal CU,regardless of earthing type?....virtually never,and most tails are unsecured and simply pass through a rubber grommet. The risk on TT's is grossly exaggerated IMO QUOTE]

So's the risk of an insulated CU bursting into flames IMO :rolleyes2:

Yes indeed....but I wouldn't mind betting there's been more CU fires than tails shorting out on metal cases. I've had a think about this, and I can recall a number of burnt out internals in CU's ,(not mine I hasten to add!)...at least 2 in the last couple of years. Most editions of the picture gallery in PE mag show a burnt out component in a CU. I cant recall one single instance of tails shorting onto a metal case in 35 years.

 

[Lazlo]

I think the manufacturers should offer tail clamps within the CU and all should have clip on insulated covers on busbars. I suppose the fact that a risk is rare does not make the magnitude of the consequences any less severe, it would likely be fatal in both cases (house fire or getting in contact with circa 20 amps).....Makes you wonder if the powers that be have really considered this scenario............

 

[Deleted member 9648]

The risk of a fault to the metal case of a CU from the tails is nil if the right precautions are taken. How many times do you see a fault from the tails on any metal CU,regardless of earthing type?....virtually never,and most tails are unsecured and simply pass through a rubber grommet. The risk on TT's is grossly exaggerated IMO QUOTE]

So's the risk of an insulated CU bursting into flames IMO :rolleyes2:

I don't believe the A3 requirement has that in mind, it is to prevent the escape of fire from the internals of a CU to flammable materials around it. Given the position of most CU's in understairs cupboards with piles of junk stacked around them there is some merit in this.
That said proper training and better quality components are required here....not shutting the barn door after the horse has bolted as has been implemented.

 

[Risteard]

getting in contact with circa 20 amps

You will be in contact with the same current as supplied by a lighting circuit as the resistance of your body will dictate this.

 

[HappyHippyDad]

I have to admit, I've been umming and arrhing whether or not to fit a plastic CU. Its a TT at present but will be changed to TNCS. However it will be before January so I dont see any issue.

However, if I was to fit it on january 1st I believe the regs state it will spontaneously combust so I will avoid the risk of a fire by fitting it in December.

 

[Midwest]

I don't believe the A3 requirement has that in mind, it is to prevent the escape of fire from the internals of a CU to flammable materials around it. Given the position of most CU's in understairs cupboards with piles of junk stacked around them there is some merit in this.

That depends on who you listen to or read advice from on the subject. The IET blur on it suggests preventing the escape of fire or fumes, whereas manufacturers & others like niceic & Elecsa, are suggesting the reg change is to remove a source of fuel (plastic CU) from any resulting fire. Nice to know they are all singing from the same song sheet!

 

[Lazlo]

You can get in contact with any number of amps, whatever ends up flowing through you would depend on numerous variables. Anything over 30mA is considered bad news, 1, 2, 6, 20, 33&1/4 the numbers are somewhat academic. The HRC fuse (60/80/100A) is intended to provide fault protection to the tails and discrimination from the substation and does not provide any additional protection therefore touching any earthed element of a TT install with a fault to the casing of a metal enclosure upstream of any RCDs is a situation to be avoided.

Anyway plastic DB fitted today, Ra of 5.87 Ohms with an 8ft rod.....I'd do the same if I were carrying out the job on the 2nd January.

I glued the DB on the wall with wallpaper paste and did the terminals up with a butter knife, I hope it doesn't catch on fire.....

 

[Octopus]

I think the manufacturers should offer tail clamps within the CU and all should have clip on insulated covers on busbars. I suppose the fact that a risk is rare does not make the magnitude of the consequences any less severe, it would likely be fatal in both cases (house fire or getting in contact with circa 20 amps).....Makes you wonder if the powers that be have really considered this scenario............

Not sure they really considered anything other than new books, and the manufacturers thought about higher value products and higher margins!

I still think a mains powered smoke alarm in the same location as the CU would have been a better answer, and if the CU was under the stairs, then this would have to be interlinked with the upstairs smoke!

 

[baldsparkies]

Not sure they really considered anything other than new books, and the manufacturers thought about higher value products and higher margins!

I still think a mains powered smoke alarm in the same location as the CU would have been a better answer, and if the CU was under the stairs, then this would have to be interlinked with the upstairs smoke!

Shudder to think you would use a plastic smoke alarm, surely they also should be of non combustible material !! lol.

 

[DNO]

This is an excellent post, well thought out and logical. Fires? perhaps overheating of terminations yes, and if it happens our poster is correct in stating that the shock risk from bare tails needs protection by a plastic RCCD up front. In any event all the outfits giving their "recommendations" will disappear when a real issue develops, ie death or a severe incident. If have seen not one of the trade associations giving guarantees of safety-well they wont will they? So, plastic up front, a note to customer and you can sleep at night,

 

[Deleted member 9648]

This is an excellent post, well thought out and logical. Fires? perhaps overheating of terminations yes, and if it happens our poster is correct in stating that the shock risk from bare tails needs protection by a plastic RCCD up front. In any event all the outfits giving their "recommendations" will disappear when a real issue develops, ie death or a severe incident. If have seen not one of the trade associations giving guarantees of safety-well they wont will they? So, plastic up front, a note to customer and you can sleep at night,

Pointless and poorly thought out. The am3 regulations don't just apply to CU's, but to associated switchgear as well. An RCD in a plastic enclosure would be a departure, if you are going to do that you may as well just use a plastic CU!