Quite nervous doing this... - Page 1
Forum section: electronics / general

author: paulca
author_rank: Super Contributor
timestamp: January 23, 2020, 07:39:21 pm
content: So my house has loads of underfloor "ventilation". The meter cupboard had bare floor and was allowing cold air in. Literally it was like 5*C in there at night time and cold air pouring in so much that if you open a window the meter cupboard door would blow open.So I decided to put thermal underlay down to cover all the cracks and holes.Thing is... it has a conductive upper layer! No point turning the power off either. Just had to nervously make sure it didn't hit anything. I don't think there is any exposed live, but it was still a bit daunting.Of course I did bump the trip test button and it's got such a heavy spring on it, it went CRACK! and darkness. Scared the living sh1t out of me.Done now though, phew!

author: andy3055
author_rank: Super Contributor
timestamp: January 23, 2020, 09:07:50 pm
content: That looks pretty dangerous and could be against the local code!You could line the floor with plywood instead and seal off all the edges with silicone sealant - the kind used for sealing bathroom sinks. For better insulation, line up foam sheets under the plywood.Just my thoughts.

author: thinkfat
author_rank: Unknown
timestamp: January 23, 2020, 09:36:15 pm
content: What on earth is THAT? Your house mains wiring??

author: dmills
author_rank: Super Contributor
timestamp: January 23, 2020, 09:45:41 pm
content: Yup, older style UK incomer, meter, RCD and breaker box, not the neatest job I have seen but fairly typical of what you find in older housing stock, and FAR from the worst job you will see.Current rules would need non flammable materials and a metal cased breaker box, but you only got to make those changes if doing major work.Regards, Dan.

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: January 24, 2020, 12:55:14 am
content: Quote from: thinkfat on January 23, 2020, 09:36:15 pmNice timber backboard. Classy.

author: TerraHertz
author_rank: Super Contributor
timestamp: January 24, 2020, 04:59:12 am
content: So that's just some lightweight foam with a foil layer, sitting there unattached?Won't make any difference. If air draft came up through gaps in the floorboards before, it still will. And lift that foam up like a piston.I'm guessing that 'solution' was chosen because you don't have any means of cutting to shape something solid, like plywood?How about this instead: Some old heavy felt carpet underlay, with a layer of something like linoleum or rubber floor matting on top. Those are all things that can be cut with scissors. Then seal any gaps around the edges with silastic. But if you cut the underfelt a bit oversize that won't be necessary.End result: a relatively non-flamable, electrically insulating layer, heavy enough to hold down against draught pressure.Or, just seal all the floorboard gaps with gap-filler.

author: paulca
author_rank: Super Contributor
timestamp: January 24, 2020, 08:21:42 am
content: Quote from: TerraHertz on January 24, 2020, 04:59:12 amYes, it's regulation compliant foam underlay for putting under hardwood flooring. I believe it's fire retardant. The upper layer is mica or something, probably not actually conductive on it's surface as it's laminated in plastic.I weighted it down with stuff. But, yes the air still gets round it and I can still feel a draft under the door.I might just seal the door surround.On my meter box. This is a late 1960s house. Looks like the meter box has been updated maybe 10 years ago. Not sure if house has been rewired, but it is using black/red twin and earth and has way too many double plugs for a 1960s house. However it's still out of date, if it was rewired it was 10 or 20 years ago.A rewire is on the long finger, but at approximately £3000 it will need to wait for other work first.

author: BillyD
author_rank: Regular Contributor
timestamp: January 24, 2020, 09:25:01 am
content: I imagine it should at least reduce air flow through the floor of that compartment which should be some help.Just wondering about the boards that the electrics are mounted on, could there also be draughts coming through the gaps in these boards and around the edges, etc.Assuming that the door the cupboard doesn't get opened very often, it might be more effective to tackle the cupboard door - put a good seal around it, a latch to ensure it doesn't spring open, maybe even insulate it.

author: janoc
author_rank: Super Contributor
timestamp: January 24, 2020, 10:59:21 am
content: Hum, if anything goes wrong in that closet, you have at least a well prepared electrocution chamber now. You feeling nervous about doing this is a pretty good indication that it is a terrible idea.Sealing the holes and cracks with either silicone or foam is a much better (and safer) way.

author: ebastler
author_rank: Super Contributor
timestamp: January 24, 2020, 01:41:19 pm
content: Looking at your original post, I had not realized that you meant that to be the complete job!?!As you state, this stuff is meant to go underneath hardwood floor. Please do yourself a favor and put something on top of it — pine board, cheap laminate, whatever.

author: paulca
author_rank: Super Contributor
timestamp: January 24, 2020, 02:57:11 pm
content: Yes, I'm currently considering laying heavy underfelt over it and putting a draft strip around the door. It doesn't have to be pretty, it's an under stairs cupboard.Also I think the "foil" is just metalized plastic sheet, it's probably only 1 or 2 atoms of aluinium thick to create the thermal mirroring.

author: TK
author_rank: Super Contributor
timestamp: January 24, 2020, 03:12:53 pm
content: Quote from: paulca on January 24, 2020, 02:57:11 pm

author: paulca
author_rank: Super Contributor
timestamp: January 24, 2020, 03:48:10 pm
content: Quote from: TK on January 24, 2020, 03:12:53 pmYou know how mirroring of surfaces works in the modern world and how they can use silver to coat mirrors and not have it cost thousands? They vapourise the metal (or metal compound) and allow it to condense onto the electrically charged surface forming a layer with is literally only a few atoms thick but creates a perfect mirror effect.Even electroplating can be done to produce extremely thin layers. Food packaging with "foil" is quite often actually plastic with an extremely thin layer of metal to make it look like foil. Crisp packets for example.

author: Monkeh
author_rank: Super Contributor
timestamp: January 24, 2020, 03:52:59 pm
content: Quote from: andy3055 on January 23, 2020, 09:07:50 pm?!Double insulated cabling, what's the problem?

author: Twoflower
author_rank: Frequent Contributor
timestamp: January 24, 2020, 04:05:29 pm
content: A telescope mirror has a coating about 100nm a diameter of an Al atom is about 125pm. So I think that's a bit more than 1 or two atoms.An Al is cheap, so even a 1mm layer wouldn't cost a fortune compared to the whole thing.If interested spend some time watching this (Recoating a Giant VLT Mirror):

author: NivagSwerdna
author_rank: Super Contributor
timestamp: January 24, 2020, 04:07:04 pm
content: An isolation switch just after the meter. That's quite novel?

author: andy3055
author_rank: Super Contributor
timestamp: January 24, 2020, 04:11:39 pm
content: Quote from: Monkeh on January 24, 2020, 03:52:59 pmThe problem is what he has done. We are not addressing the cables in this post.

author: paulca
author_rank: Super Contributor
timestamp: January 24, 2020, 04:33:06 pm
content: Quote from: NivagSwerdna on January 24, 2020, 04:07:04 pmAs I understand it, this is common. It is also a requirement in some houses depending on the type of earthing.If you are replacing a consumer unit/breaker board in a house you need to disconnect the mains, however the main inlet in the UK is usually sealed with metal seals and you are not allowed to break the seals. Breaking the seals is considered "tampering with ultility equipment" and a criminal offense, since you could have been installing a meter bypass loop, yes that's a thing! Some areas it's just a matter of calling up the distributor and getting authorisation to cut the seals and pull the main fuse, in others it requires the distributor send out an engineer to do it. Either way the distributor has to come back out to replace the seals later. All this costs money and time.So in a lot of places a sensible spark will install some form of 80/100A isolator between the meter and the consumer unit making it easier in future to isolate the board to do work on it.

author: paulca
author_rank: Super Contributor
timestamp: January 24, 2020, 04:43:06 pm
content: Quote from: andy3055 on January 24, 2020, 04:11:39 pmHis point is, there is no exposed mains. As discussed elsewhere, (a) the flooring is not actually conductive in it's current state (I can test that) and (b) it should/will be covered with something else.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: January 24, 2020, 04:51:24 pm
content: Quote from: paulca on January 24, 2020, 04:33:06 pmIndeed. I'm a bit jealous. I'm pretty sure my consumer unit cannot be isolated without pulling out the company fuse.

author: Monkeh
author_rank: Super Contributor
timestamp: January 24, 2020, 05:59:42 pm
content: Quote from: andy3055 on January 24, 2020, 04:11:39 pm... and what is it he's done? Placed an object next to a cable?

author: paulca
author_rank: Super Contributor
timestamp: January 24, 2020, 07:32:38 pm
content: Quote from: Monkeh on January 24, 2020, 05:59:42 pmIt's a lot more funny if you think about all the things that you would normally find in the understairs cupboards. Examples:The hoover.Your wellie boots.The kids wellie boots.The tent.Camping gear.The boxes of biscuits from Christmas that nobody likes.Your sons first bike that he's well outgrown but you still keep in case you have another kid.The ironing board.The spare car battery.Engine oil / washer fluid.Shovel for the drive and car window scraper.Your old HiFi the wife hated.Usually it's piled so high that to read the meter you need to pull a load of junk out first.It used to be a favourite place to play hide and seek when I was a kid.

author: Bud
author_rank: Super Contributor
timestamp: January 24, 2020, 07:46:21 pm
content: Quote from: paulca on January 24, 2020, 07:32:38 pmUsually that goes along with your sons carseat that was hoarded before the bike

author: coppice
author_rank: Super Contributor
timestamp: January 24, 2020, 07:57:20 pm
content: Quote from: paulca on January 24, 2020, 07:32:38 pmIt amazes me people get away with this kind of thing as much as they do. The terminals on most meters, and some of the other items used for consumer wiring, are not well shielded, and its very easy for some piece of metal amongst the junk in a cupboard to poke into one of those recesses.

author: jogri
author_rank: Frequent Contributor
timestamp: January 26, 2020, 12:37:28 am
content: Quote from: paulca on January 24, 2020, 03:48:10 pmHigh-end mirrors are treated this way (or any mirror that shouldn't suffer from thin film interference), but normal household mirrors are created using chemical deposition: The metal you want to use as a coating is dissolved, if you add something that has spare electrons your metal will get reduced and you get a layer of pure metal on everything the metal will stick too. If you want to coat a mirror, you just dip the warm, clean glass surface into a pool containg the solution of your dissolved metal and the reducing agent (some form of sugar) and wait a few minutes. This process is way faster, cheaper and less complex than vapour deposition, but the surface finish won't be nearly as good.Today, mostly aluminum is used (it is cheaper than silver), but even a silver coating is rather inexpensive: The silver is going to cost you roughly 500 bucks per kilo, and since you can use a 0.1 molar solution (~15g of silver per liter) you are looking at roughly 10 bucks per liter.Btw, a "mirror" with a 2 atom thick coat would be completely black. The metallic character necessary to get a reflection starts to kick in at a few hundred layers.But btt: I would suggest using a vapour barrier (basically just a fancy PE foil) and vapour barrier tape and making sure to get an airtight seal. If you can stop the air movement, the air between the floor and the door should provide a rather decent insulation.

author: TerraHertz
author_rank: Super Contributor
timestamp: January 26, 2020, 06:25:31 am
content: On the topic of Aluminized insulating sheet (as in the photo), a few years back (2010) there was a big government scandal in Australia.A famous singer, Peter Garrett of Midnight Oil, had been elected to Australian federal parliament and became minister for the environment. He then oversaw a government scheme to subsidize improvements in home energy efficiency, by installing thermal insulation. Mostly in roofs.Great, but the problem was he ignored advice that one form of insulation being used was unsafe. Metalized foil...Something like 93 house fires and four deaths later, Peter Garrett took the blame.The danger lay in installation methods. Installers would roll the stuff out in attics, then use staple guns to fix it down to the ceiling joists. But typically the electrical wiring in ceilings is also fixed to the joists, and a person on top of the insulation can't see if he's going to be stapling into wiring. The wires are only PVC insulated, not metal conduit.So anyway, turns out the metalization IS electrically conductive.

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: January 26, 2020, 10:43:02 am
content: Quote from: TerraHertz on January 26, 2020, 06:25:31 amNo he bloody well didn't.

author: GlennSprigg
author_rank: Super Contributor
timestamp: January 26, 2020, 12:34:04 pm
content: 'Legal' doesn't always mean 'Right'/'safe'...Generally here in Australia, if power is supplied from Poles on the street, then on the poles,they havemain fuseson the pole for the premises, (or gutter riser), before the main S/B feed.(Sometimes, these are underground from the street).However, I've seen small factories where the street supply traverses inside the roof for say 50mbefore being terminated in the main switchboard with supply fuses, on the other side of the building!Meanwhile, there is unprotected "street fault current" on the supply through the roof!!!(Sorry... I just remembered that)

author: SeanB
author_rank: Super Contributor
timestamp: January 26, 2020, 05:01:35 pm
content: Street fault current is typically handled by the 400A per phase fuse on the secondary of the distribution transformer. If the transformer is bigger, and feeding more loads, then there will be a few outgoing cables at low voltage, each with it's own set of 400A fuses per phase. They take around 2 seconds to blow if there is a short at the far end of the cable, but can blow faster if you have somebody put a pickaxe through the cable closer to the transformer.The cable to the factory would have to be rated for the fault current, so they will almost always also have a set of pole mounted fuses at the tap off point, even if the factory has fused disconnects inside by the meter. Might be 100A per phase inside, and 160A per phase outside, with the cable able to not fail before the fuse blows. Overhead cables can stretch quite a bit on overload, especially the bare copper ones on old installations, which are pretty well insulated by the thick copper oxide layer on them.

author: Zero999
author_rank: Super Contributor
timestamp: January 26, 2020, 06:31:54 pm
content: Quote from: Monkeh on January 24, 2020, 05:59:42 pmPlacing a metal/conductive object next to some cables is not dangerous, as long as the cables are double insulated, which they are in this case.It seems like many people see cables laying on aluminium foil and panic about it being dangerous, without actually thinking about it. If it were unsafe to put aluminium foil under those cables, then they be exposed like that, so anyone can touch them. In reality there are no exposed, live conductors, so there's no additional risk of electrocution by putting aluminium foil there. You'll see a similar type of thing inside a double insulated, metal cased appliance, such as a DVD player.

author: james_s
author_rank: Super Contributor
timestamp: January 26, 2020, 06:45:13 pm
content: Quote from: TerraHertz on January 26, 2020, 06:25:31 amThe wires are run across the top of the joists? Here they're run either along the side of a joist or if they need to cross they are run through a hole drilled through the middle. On the side the sheetrock is attached you have a nail plate that is stuck to the joist or stud to prevent a nail or screw from damaging the wire. Normally you wouldn't have anyone nailing or stapling things down into the top of joists in the attic here so I don't know what code says about that.

author: ebastler
author_rank: Super Contributor
timestamp: January 26, 2020, 07:03:32 pm
content: Quote from: Zero999 on January 26, 2020, 06:31:54 pmWell, the big difference in my mind is that if something should go wrong with the DVD player, I can pull its plug without having to step inside its metal case.Obviously everything is fine as long as the installation is in good shape, cable isolation intact etc.. But I can think of various situations where something goes wrong, which make me feel queasy: Insulation gets damaged; someone does a sloppy job, installs a live wire and drops it onto the metal floor; an earth or neutral wire touches the floor and grounds your feet really well when you unfortunately touch some live wire, etc.Yes, all these scenarios are not very likely to occur. But since it is so easy to avoid, why put a conductive layer on the floor of your installation cabinet to make the potential consequences so much worse?

author: paulca
author_rank: Super Contributor
timestamp: January 27, 2020, 10:21:10 am
content: Quote from: ebastler on January 26, 2020, 07:03:32 pmYou know that a lot of office buildings have metal panel flooring right? The hung ceiling buildings usually have a gap under the floor and above the ceiling tiles for running cables. The ceilings are fibre board squares and the floors are metal plates set into a framework. Usually plug sockets and network end points are presented in special boxes placed in such metal plates.It allows floors to be completely stripped back and completely rewired and rebuilt without having to do any actual building work.Anyway, as a test I took a piece of this flooring and put my meter on it. OL. So I punctured the metal foil layer with the probes and got... OL. I tested the meter, it works. So while the extremely thin layer of metalisation forming the vapour barrier might be conductive it seems really difficult to actually make a connection to it as the plastic layer lines the puncture.Even if I wanted to Earth the flooring I don't know how I'm meant to make a connection to it.EDIT: I suppose a real test would be puncturing it with mains voltage, instead of the meesly little voltage my meter produces on Ohms... but I'm not prepared to do that. Might be one for ElectroBoom on YT.

author: Marck
author_rank: Regular Contributor
timestamp: January 27, 2020, 11:50:32 am
content: My bench is covered with a metallic looking vinyl that I can strip off and recover when ever it gets a bit ratty. I had similar thoughts about conductivity and it carries a much higher risk than a floor in a cupboard with a cable or 2 above it.So I borrowed an insulation tester and put 1000 volts across it. No sign of conductivity and testing at 4X mains voltage gave reassuranceIn this case I would leave the material you have put down and use a good quality tape to seal the edges mostly as a moisture barrier and then get a bit of carpet cut it to shape and lay that over the top for a barrier to protect that insulation and as another layer of insulation.But I do agree that the electrocution risk in this instance is not to bad and I wouldn’t loose any sleep over it. But I would sell a kidney to stop a freezing draft so finding a way to stop that would be on the top of my list.M

author: ebastler
author_rank: Super Contributor
timestamp: January 27, 2020, 12:00:48 pm
content: Quote from: paulca on January 27, 2020, 10:21:10 amHung ceilings are pretty much standard in office buildings here. But I don't think I have come across any raised floors except in a few special-purpose rooms (server/computer rooms). And where raised flooring is installed, I would typically expect the actual tiles to be made of, or at least covered with, a material that is non-conducting or maybe static-dissipating, not plain metal.

author: paulca
author_rank: Super Contributor
timestamp: January 27, 2020, 01:04:25 pm
content: Quote from: ebastler on January 27, 2020, 12:00:48 pmThe buildings I have worked in with this type of floor are IT office buildings. The metal plates are covered with anti-static carpet, but it comes loose sometimes which is why I know the panels are metal underneath.

author: BradC
author_rank: Super Contributor
timestamp: January 27, 2020, 01:07:05 pm
content: Quote from: GlennSprigg on January 26, 2020, 12:34:04 pmDunno which side of Aus you are on, but over in the West it's overhead straight from the pole (16mm x 4 on this place) to the point of attachment where it connects to a 10mm x 4 TPS to the switch board which then terminates in the 32A service fuses. Yes, that whole run is subject to the transformer fault current if it goes bang. There are no individual pole mounted fuses, just the drop-outs per segment.There are different configurations for the underground stuff, but we are still predominantly overhead.I've actually seen a set of drop-outs respond to a catastrophic fault current and there was no noticeable delay (tree branch shorted 2 phases). I was straight over the road from the pole at the time, looking up at the configuration as we'd lost a phase. Needed to go home and change my undies.

author: Jeroen3
author_rank: Super Contributor
timestamp: January 27, 2020, 02:15:38 pm
content: I have a thin reflective insulating foil under my floor. The hatch to get to it is covered in flammability warnings.It is also conductive. So you've made a large arc flash accelerator, cool...

author: jmelson
author_rank: Super Contributor
timestamp: January 27, 2020, 11:39:34 pm
content: YIKES!!! In the US, all the power entry cables are in metal conduit, or buried and armored. Only the lower current cable (we call it "Romex") is allowed to be exposed. So, there's a breaker on the transformer, then buried cable to the meter, then a service entry breaker right after the meter, then into the main panel with another main breaker there. Up to this point it is all encased insome kind of steel protection.Jon

author: james_s
author_rank: Super Contributor
timestamp: January 28, 2020, 12:30:45 am
content: PVC is allowed, at least by the NEC, at least it was the last time I did a panel replacement. There may be some localities that require steel conduit though.

author: TerraHertz
author_rank: Super Contributor
timestamp: January 28, 2020, 03:41:42 am
content: Quote from: Ed.Kloonk on January 26, 2020, 10:43:02 amSorry, imprecise. I meant 'took the blame' as in he got sacked because of it. I wasn't paying attention at the time and don't recall if he ever commented that he could have done better, or 'not my fault'. Perhaps I should have said "took the fall."Quote from: james_s on January 26, 2020, 06:45:13 pmEven in my new house built in 2000, mains wiring in the roof space is just run randomly via shortest path possible. Rarely if ever fastened down, and just lies across the tops of the ceiling beams. Which is fine, unless you place something opaque and electrically conductive over it all, then start punching staples down through that.I recall at the time of that scandal, thinking I bet Peter Garret never got up in a roof space and did any work in there.

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: January 28, 2020, 06:51:37 am
content: Quote from: TerraHertz on January 28, 2020, 03:41:42 amAll good mate. It's that higher-than-thou prick PG that I love to hate.Wires in the roof are supposed to be clipped. My understanding is the gyprocker should be able to come though after the rough-in and not have to deal with any cables to wrench on or pinch or whatever. You can get a blister if an inspector decides to check in the roof.

author: aargee
author_rank: Frequent Contributor
timestamp: January 28, 2020, 08:58:32 am
content: Not that I’m a friend of politicians but the reality was that the whole insulation debacle was rogue operators that did not adhere to standards for insulation, they should have been the ones that were pursued for the problems they created.

author: GlennSprigg
author_rank: Super Contributor
timestamp: January 28, 2020, 02:50:14 pm
content: Quote from: SeanB on January 26, 2020, 05:01:35 pmThank you for your reply!!!However, I can assure you that there were NO supply fuses on the pole. (Their fuses are at the main board).There may have been say 3-phase 4-core 10 or 16 mm cables through the roof, that are unratingly protected.