Good to clear this subject Joe. Many people start bonding the metal, trays and baskets as precautionary measure thinking they have made the tray, basket safer, when potentially by bonding they have now created a potential path. Good video hope people watch and try understanding the concept of bonding. 👍👍👍
Great video; I gotta say though, I’ve always bonded it just for my own peace of mind. Earth potential or not, I’ve been “stung” with mechanically damaged insulation before and will forever continue to bond the metalwork.
Hi Joe, I prefer a cable tray/basket with good earth bonding. I have experienced a live cable touching the metalwork in a very long cable tray, that didn't trip the breaker(C16AMP without RCD) because it was not making good contact with earth. Me and a collegue were pulling a data cable for the security system and that collegue had a nice shock from it. Luckely he was standing in a platform lift aswell so some isolation from the earth.
Hi - sorry to hear about the shock. My take is all conductors must be insulated and sheathed and all junctions made in boxes etc for the metalwork to not be an exposed conductive part.
@@davidw460 Hi, even when you deliver the most perfect installation without making a good low impedance connection to earth. When an incident happens that a cable gets damaged and the line conductor makes contact with the cable tray. This cable tray will become live. So only two options remain, additional protection by rcd or earth bonding. When no additional protection is available the impedance to earth must be low enough to trip the breaker. 5-10 times In for C type characteristic.
I'm a domestic electrician so never do any tray work, but I had this dilemma in my own property where I installed tray in my garage supplying my consumer unit. All cables are double insulated and the tray has no contact to earth so I concluded it did not need bonding. however, due to doubting myself I stuck a 10mm bond on anyway 🤣🤣. At least I know categorically now it is not needed 👍
Great work as always Joe. Part of the confusion is that the regulations are attempting to describe, in words, quite complex things that could be explained clearly and simply by diagrams or illustration. We add to the confusion by using imprecise language when using the words "bonding" and "earthing" to describe the same thing. In my opinion the heart of the matter is whether the cable tray is an integral part of the electrical installation or just another piece of isolated building fabrication metalwork. For example: If a length of cable tray is installed to get cables from point A to point B but is not bolted or fastened to any other device in the system (switchgear, transformer etc.) then the cable tray is just a piece of isolated metal. If, however, it is bolted or fastened to any other electrical device then it becomes part of the electrical system and should be earthed. Just my view.
In my opinion, theres always the off-chance that a cable (or particularly a single insulated conductor in enclosed duct or similar) may fray and short out against the metal work. I've also found dead mice in duct who met thier demise chewing a line conductor. I personally think it is absolutely essential that the metalic parts are bonded with supplementary bonding at each joint to ensure continuity. Its similar to the classic case of a class 1 light fitting on a circuit lacking a cpc. The line comes loose or frays, comes into contact with the unearthed metal body and then its a timebomb waiting for someone to change the bulb. As we all know - people have lost thier lives to this. Granted this is less likely to happen with tray or basket as the cables are double insulated but they are not infallible. I've certainly seen damaged cables where both layers of insulation have been compromised.
If the cable has an earthed metal layer, I agree there is no reason to earth the supports. But if the cable is something like T&E or flex then all it takes is one sharp edge to cut through both layers of insulation. I'm not at all convinced that such scenarios are unlikely enough to rule out the need for earthing.
So what i take from that is that if the cable tray is installed correctly, fit for purpose, and not making contact with earth, then it dosnt need bonding... im sure ive got a lovely photo somewhere of my level 2 cable tray that you made me bond....
Sometimes cable tray / basket is fixed to the frame of steel frame buildings in which case it’s already bonded as the building frame would be connected to earth. I noticed in bs7671 that the metal frame of a building can be used even a CPC in certain criteria. . If the building was non conducive I would tend to bond it as good practice and piece of my own mind. Very interesting vlog .
When I worked in areas containing a potentially flammable atmosphere we bonded everything that was exposed and conductive, to ensure there were no inductive loops in addition to the normal reasons mentioned in the video. Long runs of pipework, cable tray etc could offer a lower resistance than an earth path, and therefore an alternative path for earth currents, if they were at earth potential at several separated locations.
Good to discuss this topic , we have another issue where I work , Lightning conductors on roof level poorly terminated , causing an earth path between metal building structures .The Electrical contractor did not Bond certain tray runs , however the LPS contractor indirectly bonded trays through metal structure . A Electrical inspection found various resistances between the tray work , which could cause touch voltages . We are looking at substantial bonding work to reduce these touch voltage potentials .
At numerous continuing electrical education classes ( need 8 hours a year to renew license ) they always stated that the USA NEC book states that anything likely to become energized must be grounded. Some inspectors think that all metal duct work and metal sinks feed with plastic water supply & plastic drain must be grounded. Better safe then dead.
What about ceiling grids? I used to do quite a bit of LV control cabling and remember once I popped my head into a ceiling and my ear touched the grid and I got a little buzz from it. Probed the grid with a multimeter and there was 50v ac between the grid and earth/CPC.
Ignoring all other "gotchas" for a moment, look at HOW the tray is actually mounted physically and then consider the "introduction of an earth potential" again. To illustrate the point I'm about to make, think about the old & deprecated "mains tester screwdriver". Testing a known live contact with one of these "should" light the neon. Whilst doing this, touch a masonry wall, particularly an external one at around 6-7feet high. Result? Hopefully everyone on this forum will know that the neon lights FAR more brightly, showing a much higher (but still safe) level of current flow. Now, obviously part of that is due to a much lower resistance through a bare hand c.f. a connection through much higher resistance footwear (including socks!) BUT it illustrates that masonry fabric of a building IS at ground potential for most considerations. Now the key point: Metal tray work bolted to a masonry wall IS therefore effectively at ground potential! So this is DIFFERENT to the situation shown in your video where the tray is mounted to a bare OSB wall. This is another aspect that needs consideration in the decision of "To bond or not to bond? That is the question." To paraphrase our most famous bard.
I guess it’s one of them questions, personally I don’t see any harm in bonding tray and I would see it as good practice but that’s my view I don’t deal very much with tray work
Great video again Joe - massive hate of mine is how many sparks don’t fully understand basic principles and differences between earthing & bonding. If more spent as much time educating themselves on the basics (cable calcs being another) instead of flexing on Instagram then they can adapt their skills to any installation that’s in front of them and there arguably wouldn’t be as many issues out there. RU-vid needs more of this type of content helping sparks brush up on knowledge and encourage meaningful debate. I’ve took a break from my channel to realise this but will coming back with similar content to help, educate and to create conversations around the industry . Keep up the good work guys 👍👍
Wouldn’t we class metal tray as an exposed conductive part as standard, given it forms part of the installation, and may become live under a fault condition due to cable damage???
But how likely is the cable to be damaged? If installed appropriately then cable should normally be unlikely to get damaged, if there's a high risk of damage then you need to consider what measures should be used to minimise those risks.
@@farmersteve129 I’d say it’s very unlikely for a cable to short down to the tray, but not an impossibly. A cable is more likely to become damaged nowadays due to these metal cable ties, being overnighted. I’m my book I’d call steel trunking, trays and baskets an exposed conductive part, and always install a bond 🤷♂️
A little tip. Although not related to cable tray. Suspended ceiling grids are not classed as extraneous. Beware however when removing older fluorescent fittings with new LED fittings. Older fluorescents are earthed, which in turn earths the ceiling grid. LED fittings are wired in 2 core cable (no earth) with an LED driver. Internal SMPSUs induce voltage up to 100 volts on the ceiling grid. Requires earth bonding to reduce touch voltage. With no bonding if you touch the grid and a metal earthed appliance at the same time - OUCH.
I am not an electrician and have no idea why this turned up on my recommendations, it was strangely compelling and suddenly I have a huge respect for electricians. Did I understand the middle bit correctly, an electrical fault somewhere else could send power back along the earth cable to an earthed item rather than going down to the planet and tripping a circuit breaker ?
It's possible if there wasn't a good incoming earth that in the event of a fault all metal could become live and stay live . This includes metal cased appliances, pipework, radiators etc . I had one years ago , woman complaining about getting a shock from the kitchen sink . Turned out the main earth connection at the supply intake wasn't connected so a faulty central heating pump was putting everything metal at mains voltage . Doesn't happen often but it's possible. This being a modern installation had incoming gas and water pipes made of plastic so no physical contact with the ground.
If the tray is holding armoured cable with earthed armouring id c3. Twin and earth C2 ive seen this type of cable snagged on basket and tray. Id always earth the tray or basket no different from armoured cable carrying a potential fault current. Lets have some Regulations that say do and not leave up to the individual spark as im sick of people interpretation of the Regs..
As someone who has requested trays to be installed I take a different view - I request that the trays are bonded and proven to be bonded - so any work in the future can not by accident cause a situation where the tray is connected to a voltage. So the bonding is there to protect the integrity of the installation, rather people who may come in contact with the trays.
All good but if you have a PEN fault then could get intreasting... Hard one really... I tend to wright up each traywork and enviroment as to bond or not bond
So a tray on a rubber roof, lifted by rubber feet would be a request to be bonded??? I think you still don't get bonding Vs earthing. You could test that my scenario wouldn't require bonding
this should be a public announcement on national tv, the amount of numpties that bond things they dont need to is crazy, but then again theres a lot that dont know why we bond anything, they just know it has to be done so do it, well sometimes.
Interesting subject. As an Aussie using AS/NZS 3000 if conductors are double insulated then no. But what if that insulation is mechanicaly damaged. Good practice is to equipotentualy bond it.
AS/NZS Requirements for metal cable enclosures are that they need not be earthed if cables are insulated and sheathed, affording double insulation their entire run inside the metallic enclosure. Metallic cable tray shall be earthed and must be electrically and mechanically continuous throughout the entire run. Clauses 3.10.3.3, 5.5.3.2, 5.5.4.2
So, if your tray or basket,is not , i. An exposed conductive part ii. An extraneous conductive, iii. Forms part of circuit and/or a CPC, It may just be a piece of Metal 🤓
@@efixx I’ve got an even better comment,, If wago technology meets the needs and classification of MF “maintenance Free” and are constructed not much larger than the smallest piece of Lego, Would it be optimal if manufacturers of MCBs, and RCBOs to incorporate this technology at the point of termination ? This would then negate the issue of over and under tightening at the terminals and mitigate the human error side of things which potentially causes fires?? I would patent the idea but I don’t understand the paper work involved..
Wago and Hager could collaborate and infuse the masterful technology each manufacturer is accredited for,,, And to save on branding consultancy fees I offer this suggestion to,, They could Brand it as a Wager , or a , Hago ,, Or Wylex and wago could be a Wygo,,? Sorry for not involving you guys at BG, but my vocabulary is limited,,
@Defectiveresistor well, I guess that solves it then,, you should share this epiphany with the wider world as it may be the solution to a lot of errors created by humanity
@Defectiveresistor Mr D, I totally agree,, I’ve personally experienced all those situations,, Take driving ,,even if we all followed the Highway Code to the letter, I would still want to wear my seatbelt and have my car fitted with an airbag.. nice chatting with you mr.d but this England rugby team are shocking so I must go and shout at the telly 👍🏻
As per Australian Standard - we bond. We provide an equipotential bond to the tray work - because a situation could occur whereby the tray becomes vulnerable to induced or other touch voltages. Having a path to earth is sensible.
I totally agree , I don't blame the tutors I blame the curriculum, plus a lot of new sparks don't understand how electricity works or seem to be interested .. i had 1 so called gold carded spark fitting neon switches and stuck all the neutrals in a wago .. go figure haha
when i was in college it was taught very well, it went a bit crazy in the early 90`s with people wanting to bond metal windows and the like, but as a rule most dont know your right.
So, here I am walking around on a concrete brick patio outside of the house and I notice a tube of conduit poking out of the house and onto the top of the brick concrete patio. But, not through the patio into the Earth, just to the surface of the patio. I bond it. But then, I'm walking around inside the house, and I notice a length of conduit attached to the concrete and brick wall inside the house, but not external to it. The wall essentially is attached to the Earth just like the concrete patio is attached to the Earth. I don't bond it. But both brick and concrete structures are in contact with the actual Earth, one gets bonded, the other doesn't. Anyone know why?
Joe, what’s your opinion on basket containment that is supported by unistrut and steel rods which is clamped to the structural steel, which is an extraneous part. Should the basket then be bonded?
Good question, I suppose it depends on a couple of things. Is it introducing earth potential into the installation, it may be that it is via the connection to the structural steel, however if the structural steel is bonded and the basket is making a good electrical connection via the strut and rods then maybe its already bonded via the structural steel?
When hauling cables and even after installation there is a chance for a live conductor to contact the tray and not to be detected by testing (fault might occur later due to earlier damage). I think it is better to have the tray bonded. The whole point of bonding is to remove a touch potential, so why would bonding the tray introduce one????
In Portugal it was a requirement back in 2007 at least, all lengths must be bonded to assure continuity, even in a café for example all stainless steel tables had to be bonded.. in other view, if there’s a wire connected to it and if an earth fault occurs, that metal can become electrified but if there was no wire connected to it, it wouldn’t. At the same time, I’d expect to have continuity just by the fact that it’s all bolted together and provided that there’s no severe rusting on them.. so I’d probably still catch a buzz 🤷♂️
The reason to provide bonding does not always as simple as reasons offered by 7671, this does not cover other standards requirements that are dependent on the use of the installed system. Where 7671 identifies no requirement, other installations do. Such as EMI protection to communications services covered within numerous communications standards, also not withstanding any owner requirements to cover the lifecycle of the installation as this will change, no one has a crystal ball. Everyone needs to get away from a "me" view to "we" with being a shared service provision, where multiple runs on the same hangers are provided, then distributed in different areas, the common route must take precedence to the need, not any text seen within 7671 as that is seen as a singular position written with the sole reference to electrical services. Other issues also appear between 7671 and other standards, as 7671 does not understand the requirements of those standards, it should we referenced that where another standard has additional requirements that these are taken into account i.e. 7671 is the starting point however, the high requirement take precedence.
We've run a containment of tray in a commercial building with twin and earth's on it. All above false ceilings. In my opinion earthing isn't necessary but what are everyone else's thoughts. Thanks
Putting the interference aside because I don’t really know. I’d say it’s not an exposed conductive as it’s not likely to become live under fault conditions and if it was to then the cable or containment is not suitable. And It’s not extraneous from the looks of it. So I’d say no. GN8 has a section saying doing so in situations can distribute touch voltage to areas it wouldn’t necessarily be if a fault was to occur elsewhere.
I got pulled up for not putting an earth strap across bolts on a trunking run ,my answer was there 8 screws joining the trunking what's the bond going to do ! Sidenote a year later the same person said oh no need for bond links ,ahhhh can't win!
Ok, so i'm installing basket tray in a factory. A forkLift truck has caught it's mast on a girder and ripped out some cables from the lighting circuit. They are swinging in free air, but come to rest on my Basket Tray. If it had been earthed it would have disconnected the circuit through the MCB, but with it not being earthed will it. Should i have earthed my basket tray?
forklifts and tray work in my book are high risk for damage regardless of type of cable so high-level would maybe be worth earthing it back to MET? thoughts
For me, if there's 30ma RCD protection on non metallic protected cables then it'll be safe. As you pointed out it's more important to select the correct wiring system to start with.
Nice thought, although you’d have to also consider what we know of RCDs these days. If the RCD is a type AC and it is serving any other load other than a purely resistive load the RCD could be blinded and make the additional protection useless. Earthing and bonding is the cornerstone of preventing potential difference. Although it really does depend on what kind of cable your running on the said cable tray. SWA for example would render bonding the tray pretty useless since the armour should be earthed, however if it where T&E or FP there is a real chance that the tray could become live if the cable is damaged. Like he said there is no simple answer and there are many factors which have to be taken into account.
Many thanks to Mark Coates (IET Regs 16th ed. contributor) who explained this same subject in a contractual dispute regarding bonding of raised flooring in 2003.
I'd bond it in any case. Rather then doing the bare minimum thinking if a DNO can use multiple earths why not. And say there was arcing within a cable and the tray is conductive in nature
To be sure PE connection should be installed. Because I think any normal cable (double installed, no SWA) can fail and create a short to the cable tray
What the regs state & the installation practices on site are miles apart. If installed near other metallic items, structures, the issue is more akin to zones where you need to look at the possibility/probability of a person touching 2 sides simultaneously or whether a metal ladder, pole or alike, is likely to ever be used at the given location… which in those environments is often yes. Providing cover for these faults can be provided by RCD protection unless in a critical environment (hospitals, etc.), & the regs (especially onsite guide) should give more definition & protection to all circuits that won’t endanger life if operated.
I'm doing tray on a flat roof for armoured cable sat on rubber feet on flag stones and I I'm told to earth strap every joint the start and finish ends of the tray are open and not connected to anything do I need to earth or not or just do as I'm told
I've had these same thoughts many times with tray and ladder rack, bonded all the way through the run but the ends open. I just do as I'm told by someone who gets paid more than me.
Used to do this in areas where bird damage was highly likely as the potential across the containment could differ if they pecked through live one end and cpc or neutral the other (the idea being if you came to do a maintenance check at any point it would save electric shock. In the end we just put ducting over the top for mechanical protection or swapped to swa so we didn't have to bother. I know on most high rise buildings AC contractors will use hi tuff and put up bird screening to avoid the problem and keep costs lower.
Just based on this I'd suggest it wouldn't need doing unless maybe there's some lightning protection issue. But if it's been designed by someone else and that's their decision then just crack on!
I would bond tray work as I see it could a cable that is not powered on could be damaged by chewing from a rodent could then make the tray work live when switched on. Bonding earthing and CPC I see bonding as pipe work earthing as metal work of equipment such as washing machine or oven any metal work that could be touched. That if there is a electrical fault may bring body work to live potential. Then could be touched. So the CPC brings the earthing bonding to metallic body of any equipment. But also as gas and water pipes are grounded if metallic coming out the ground we still attach to the incoming earthing. With a TN-C-S were there is one conductor and the earth comes in with the neutral we are told if there is a brake down on the pointing to ground along the line we lose are neutral leaving every think live. So what is CPC when attached to the bodywork of appliances. As then it is grounding and if has a water pipe forms part of the bonding.
Bear in mind that unnecessary bonding can actually increase risks. For example the increased likelihood of a dangerous touch voltage being distributed around the building as noted by GN8 and the video.
What wasn’t talked about - How do you prove the containment is or isn’t extraneous? It’s great to hear what the regs say, but I feel that communication was also needed about this so that people could understand how to go about doing the test needed to prove either way.
tray that carries cables that could be damaged by vehicles eg forklifts is a good starting bench mark in my book to weigh things up for equipotential bonding back to MET
Never underestimate the appetite of rodents for cable insulation. Especially when working on agriculture or food industry installations. But you are right there are a lot of unnecessary connections to earth, which might even introduce a risk.
yes tncs could make exposed metal work dangerous if there was an earth fault that then could introduce 😉 😜 touch voltages above 50v ac. think its good to bond any tray that goes outside 😌 and inside weight up the risks of damage to swa or other types of cables as to bond or not bond and class as exposed conductor. I personally would look to bond if could be damaged by forklift etc
Ahhh, the age old argument of how different people interpret the regs! I for one am more inclined to bond tray, I know my work is sound but can't guarantee the work of some of the morons who may carry out farther installations in the future.
Sorry thats not why pipes are bonded! Pipes are bonded incase they become conductive not as an earth! For example if a lightning strike hits a house roof it could strike the hot water cylinder vent or any pipes within the roof, that then travels through the entire plumbing system making taps and sinks live and without bonding it has no where to go. It has happened and will continue to happen.
