Electricians' Guide: Cable Rating Factors

Рет қаралды 19,514

Күн бұрын

There's all sorts of things that threaten our cables but the main one is heat. This is ironic as the cable will generate heat as current flows through it. However there are external factors that will affect how this heat is dissipated, this in turn will affect the size of cable you need to install.
Detailed explanations of what can affect your cable in this way, how intense that impact will be and how it will affect your cable selection are covered in this in-depth but simple explanation.
Take a dive with Joe into the exciting world of electrical design in this series of videos that will help you if you're just starting out in this area at college or work. Even if you've been an electrician for years, there's something for everyone in this series of videos.
If you want to take the full course this video is part of then click the link below to access our completely free training package you can take at a time convenient for yourself. Free, flexible, fully certified CPD: 👉 training.efixx.co.uk/course/i...
Made with support from the @lucecogroup see their full offering of electrical installation equipment here: 👉 www.lucecoplc.com/
Check out the other CPD content we've created with the Luceco Group here: 👉training.efixx.co.uk/#/home
For more information on the @ElectricHeatingCo electric boiler featured in the video click the link here: 👉 www.electric-heatingcompany.c...
🕐 Chapters 🕕
==========================================
00:00 What are rating factors for an electrical circuit?
00:06 Free Electrical Design Training: 👉 training.efixx.co.uk/course/i...
00:23 Previous video, Protective Device: 👉 • Electricians' Guide: C...
00:42 Do we need overload protection?
01:20 How much current does the cable need to carry?
01:47 Things that could reduce how much current the cable needs to carry
02:08 Rating Factor v Correction Factor
02:34 A scary formula explained
02:52 What is tabulated current carrying capacity?
03:10 Ambient Temperature
04:10 How a rating factor affects cable size
06:11 Grouping Factor
07:13 Installation Reference Methods
08:27 Combining Rating Factors
10:08 Thermal Insulation Factor
11:30 Protective Device Factor
12:32 Next video in the series, Selecting the right size cable: 👉 • Electricians' Guide: C...
12:35 Free CPD: 👉 training.efixx.co.uk/course/i...
==========================================
📍SUBSCRIBE TO THE CHANNEL eFIXX helps electricians, electrical contractors, building services engineers, and electrical apprentices. Watching our videos, you'll discover new products, explore new applications and find answers to your technical questions. So if you've been on the tools for years or just starting your electrical journey, we'll help you stay up to date with the latest regulations and developments in the electrical industry.
hub.efixx.co.uk/youtube-subscr...
================================
📺 NEW TO THE EFIXX CHANNEL Watch our essential videos playlist hub.efixx.co.uk/essentials
📺 CATCH UP ON THE LATEST VIDEOS
hub.efixx.co.uk/latest
📺 ELECTRICIANS' TOOL REVIEW
hub.efixx.co.uk/tools
================================
🔴 eFIXX LIVE Join us for our youtube livestream twice a month - features product sneak peeks, challenges, giveaways and live electrical banter.
NEXT STREAM HERE👉hub.efixx.co.uk/next-live-stream
Catch up on previous episodes👉hub.efixx.co.uk/livestream
================================
🆕 FREE CPD Learn about new applications, regulations and best practice with our FREE CPD modules. - New modules released every month covering everything from surge protection to lighting hub.efixx.co.uk/CPD
================================
📝 APPRENTICE HUB If you're an electrical apprentice, retraining as an electrician or looking to refresh your knowledge, then please check out our apprentice hub. It contains thousands of multiple-choice questions to help prepare for electrical installation exams. hub.efixx.co.uk/apprentice
================================
📩 eFIXX NEWSLETTER Sign up to find out about live events, competitions & product giveaways.
www.efixx.co.uk/sign-up
================================
FOLLOW US on your favourite social networks for behind the scenes action, breaking news and competitions.
🟠 INSTAGRAM hub.efixx.co.uk/Instagram
🔵 LINKEDIN hub.efixx.co.uk/linkedin
🟣 FACEBOOK hub.efixx.co.uk/facebook
🟡TWITTER hub.efixx.co.uk/twitter
==================================
❌ This content on this channel is for electrical professionals.❌ ==================================
📹 Presented by
Joe Robinson - Technical Editor
===================================
#electricaldesign #electricians #electricalinstallation

Пікірлер: 31

@Mark-xr4zt 5 ай бұрын

This is such an important subject, as I don't think a lot of sparks appreciate or fully understand the issues around cable temperature. This was evident when I did the design course and the lack of appreciation in the room around how to use correction factors or what they are trying to do, which is to manage the thermal load on a circuit with the intention of keeping it below its design temperature (normally 70C). The other misconception seemed to be that you needed to apply all the correction factors that could be applied along a cable's entire route rather than just the ones that applied in the worst combination on the route. A good example of this going wrong that I have come across is the good old electric shower (another example of a device that doesn't really need overload protection). In one case I encountered the MCB had been dropped to 32A from the original 40A to try and address the undersized 6mm2 cable which had shown signs of thermal damage at the pull cord. However, dropping the breaker did nothing to improve the safety of the circuit as it had no impact on the current being drawn and how hot the cable was getting. As a 32A breaker will sit not trip with this level of current draw all day long and certainly past the point that the cable and accessories will be subject to excessive thermal loads that will damage them. In this case, when I put the circuit in its current state through design software it came out with a cable temperature of 96C and low and behold when the circuit was running and I used a thermal camera to look at the cable's temperature it was in the high 90's (well above the cables 70C rating). The interesting thing though was that when I looked at the temperature at the switch and at the consumer unit the cable was running just as hot as it did at the worst point. Whilst this is not unsurprising it illustrates why when a circuit hasn't been properly designed or installed it can so easily lead to fires or thermal damage to accessories such as switches, MCBs etc. that will cause them to fail prematurely or not operate under fault conditions.

@007floppyboy 5 ай бұрын

it depends on the rating of the shower, say its 8.5kw, so around 35Amps, we all know that an MCB or fuse wont trip at that current, all day long. Good for 40 amps minimum (manufactures data says 47Amps in ideal conditions, add in some factors like insulation (method 101) and we have 27Amps, but, there is no way on earth folk get in and leave the shower on all day. So add some diversity (5-10 mins in use), now brings it back up to capable. Having said all that, yep 10mm would be what I fitted. But this is why 2.5mm for unfused spurs should be outlawed. backed up from a 32Amp mcb and capable of 17 Amps in insulation. Its a joke.

@jasongower9396 5 ай бұрын

Where did you get 27amps from for insulation?

@007floppyboy 5 ай бұрын

@@jasongower9396 Installation reference method 101, above a plasterboard ceiling covered by thermal insulation exceeding 100mm, clipped to wood beam. (6mm = 27Amps)

@Mrs-NWA Күн бұрын

So what happens when a government backed insulation crook comes along and dumps a load of insulation in a loft over all the cables that may already be underneath a layer of insulation already... Nobody seems to raising the concern of such home insulation schemes having an impact on the electrical installation...

@andysims4906 5 ай бұрын

I don’t always rely on calculations . Depending on the circumstances you don’t know what’s going to happen in the future. Example extra insulation, or extra load . Hence I often run a slightly larger cable than needed. A good example I can remember the SEB would wire showers in 4mm cable . At the time most showers were 6KW . They would put a sticker on the fuse box saying CLOSE CIRCUIT PROTECTED. Cartridge fuses must not be replaced with rewirable. . We always used to wire them in 6mm . When showers were upgraded to 7KW or even 8.5KW .9 out or 10 times the 6mm was adequate. Where the 4mm cable the SEB installed had to be replaced.

@picobyte 4 ай бұрын

Solar company advised us to go 16mm² for our 60m cable between PV and main distribution. The 6mm² does fine and due to some voltage buildup at peak production our amps stay well below specifications. Overall our 27Wp array here in the Netherlands performs as expected as crappy as stats show from when the first PV-stats for our 52N region became available. The cost of cable doesn't add up for the few losses during peak production!!

@CharlesDAlessandro 4 ай бұрын

Bundling cables has not been permitted in the USA for some time. We use stackers for multiple runs that maintain and equal space between conductor cables. Romex and metal clad cables have there own stacking systems.

@TheEulerID 5 ай бұрын

A lot of bungalows have their power cables running through the loft space. Now the recommendation is to install at least 270mm of the stuff, often added as extra layers. I wonder what effect that will have had as I can pretty well guarantee nobody considers that when topping up their loft insulation. Not likely to be an issue on lighting circuits though, at least in domestic properties as 1.5 mm^2, or even 1 mm^2 cable was already over-specced for a 6A circuit. It looks like the 6A under 270mm of loft insulation would be equivalent to around 12A, so 1mm^2 cable is under-sized (as that's 10A), whilst 1.5mm^2 cable, which I guess is more common is 16A, which ought to be OK. Of course, real world demand is likely to be a lot lower these days with low power LEDs taking over. But those power cables, whether for a cooker, ring or maybe 2.5mm radial stand a good chance of being underated if they are no buried under the government sanctioned 270mm of loft insulation (I have never once seen any warning from official sources to householders about this. I suppose loose-laid wiring could be placed on top of any new insulation, but that could make it much trickier to lay.

@adventuresofanathan 5 ай бұрын

I've come to a house that was rewired in 2017, and it looks like they are using previous joist holes to feed twin and earth and 3 core and earth cable in 2.5mm and 1.5mm - some joists have 6 cables in what looks very small how do I determine if what they have done is correct and should all cables be in there OWN joist hole or can they be shared? Does this makes sense? Can't find anything in the regs to say cables shouldn't or should be in their own joists

@Dr.Stacker 6 ай бұрын

@10:41 I wonder how the rating factors were determined for thermal insulation. Surely the calculation is more complex than just the thickness of insulation considering the thermal performance will vary with the material used. I.e. The R Value (m2K/W) may be twice as high for a 100mm PIR insulation board compared to say a 100mm slab of rockwool/ loft roll.

@efixx 5 ай бұрын

It's an interesting point, I guess there'd quickly come a point where it didn't make much difference. 🤔

@travoltasbiplane1551 5 ай бұрын

Rating factors only apply to rockwool. It states the u value in bs7671. Celotex we have no factors form you'd have to do some complex calculations based on the value of that. Basically keep cables away from it.

@Geordie_Peter 5 ай бұрын

Unless I missed it you didn't mention long runs and the permissible voltage drop.

@webbax90 5 ай бұрын

As a non UK person it sounds really interesting! As its not common in the UK loose wires in plastic conduits, how does that affect the thermal insulation from for example building insulation (i.e. rockwoll)?

@christophergallagher3845 5 ай бұрын

The cable rating factors for grouping cables in conduit and teu king can be found in tables in the regs book .

@tonywatson1412 5 ай бұрын

I have run cable to a shower....clipped to the rafters which are at 400mm. centres...in the loft....Well above the 300mm. thick insulation...it's quite cool up high because of the insulation...in fact it's ventilated via soffits. .the insulation is pulled away from the cable as it enters the switch...

@billysmart24830732 5 ай бұрын

If you were running cable clipped direct to an internal foundation i.e. large concrete thermal mass but then butted insulation right up to it, would you be of the opinion that as it was touching the concrete that all heat would easily be dissipated or would you derate according to how much insulation was covering it?

@thomasdadswell858 5 ай бұрын

You would de-rate it according to the insulation, There are to many unknown variables to account for in your scenario. There is no way of quantifying within the guidelines the regs how well the clips and what type of clips etc are conducting heat away from the cable into the wall size and thickness of the wall and so on.

@intercity125 5 ай бұрын

@@thomasdadswell858 The reference methods account for being in contact on one side with the thermally conductive wall... it's not the clips doing the conducting!!

@thomasdadswell858 5 ай бұрын

Yeah I know, I was trying convey that the insulation matters more than the thermal conductivity of the wall, and that for example armoured cable clips space the cable off the wall and t&e clips don't @@intercity125

@travoltasbiplane1551 5 ай бұрын

Unfortunately it would be celotex or equivalent... That's way more insulative than the stuff these rating factors allowed for.

@ItsAllJustBollox 5 ай бұрын

One factor that is not considered is when the government funded insulation grants are rolled out the insulation in home changes the effect it has on existing wiring in homes.

@effervescence5664 4 ай бұрын

I had to do this for a customer the other day as he didn't believe that 7 meters of 6mm t&e wasn't good enough for his 9.5kw shower. Suffice to say it's not good enough and the shower which was fitted didn't even have a local isolator which is required by manufacturers instructions - a DP RCD or RCBO in the board doesn't count.

@Mladjasmilic 5 ай бұрын

My simple calculations: For open air wires: 10A per mm² For open air cable: 8A per mm² For cable inside the wall: 6A per mm²

@maidsandmuses 5 ай бұрын

What baffles me is the apparently allowed practice to sell 3kW appliances like kettles and heaters with a 3 x 1mm2 cable as long as the cable is below a certain length. Combine that with the allowed practice of selling 13A fused thermoplastic-overmolded plugs, and you have both a hot running plug and hot running cable at the plug end in no time at all.

@retrozmachine1189 5 ай бұрын

Quite hot yes, but not over temperature. The kettle is a special one too as the kettle wouldn't likely be running continuously. It'll only be on for a few minutes while it brings at worst a full load of water to the boil.

@Byron88 5 ай бұрын

bizarre method of derating cables by dividing and making it seem like a larger number, in North America we multiply by the factor so say your wire is good for 50A and ambient temperature derating factor is .87 you 50X.87 = 43.5 aka now that same cable only has a current carrying capacity of 43.5A which is a lot more straight forward than the number going up when your derating them....

@buckshot5896 4 ай бұрын

99% of electricians are basically installers, they do everything according to the print. Also there’s not much thought that goes into residential wiring. If it was complicated they wouldn’t allow homeowner to do it. I do automation, plc’s and motor controls(vfd’s and starters)

@sam.p12345 5 ай бұрын

There’s a lot of nonsense going on in this video. You’re definitely overthinking it. If you’re really wanting to complicate things unnecessarily you should consider how most high-consumer electrical loads, which typically heat, will be doing less heating and so drawing lower current as ambient temperature increases. Which’ll put you back to square one. You could have summarised this whole video as just overrate the cable by 10% and you’ll be fine. The manufacturing tolerances on the cable are probably more significant than variations in ambient temperature.