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"It Just Is"
Will we be allowed to use plastic as I'm not sure the metal ones would be suitable for the environment?
TT and metal CU's
- Thread starter davetheglitz
- Start date
Help Support Talk Electrician Forum:
- All Metal CU's to be locked and bolted through the wall and certified to be proof against small arms fire
- All existing plastic CU's will also now need three 1 litre plastic bottles of water to be stood on top to improve their self extinguishing properties
Most installs have the tails coming in from the bottom and bent back into the Main Switch, so there is not much chance of them falling out.
However, Reg 526.1 requires "every connection........ shall provide durable electrical continuity and adequate MECHANICAL STRENGTH and protection!"
Table 102 in BSEN61439-3 recommends Torque settings of terminals to achieve MECHANICAL STRENGTH, without the aid of any supplementary clamps.
So, provided the screws are torqued properly, they should theoretically achieve both electrical continuity and mechanical strength.
I reproduce the table here, which just happens to be on my Torque Screwdriver Price List
SBS Dave
However, Reg 526.1 requires "every connection........ shall provide durable electrical continuity and adequate MECHANICAL STRENGTH and protection!"
Table 102 in BSEN61439-3 recommends Torque settings of terminals to achieve MECHANICAL STRENGTH, without the aid of any supplementary clamps.
So, provided the screws are torqued properly, they should theoretically achieve both electrical continuity and mechanical strength.
I reproduce the table here, which just happens to be on my Torque Screwdriver Price List
SBS Dave
As Essex said though, if the cables were properly supported then the problem would be more or less sorted, but how many times to you see tails clipped back to the board... Guess my tails will not be pulling out!!View attachment 2581
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Austenitic stainless, so no, i do not have to have all the cables going through the same hole!! [An austenitic material not being ferromagnetic]
[well spotted though!!]
john..
[well spotted though!!]
john..
E54 would have been proud of you RoB. Aluminium gland plates can carry circulating currents but not magnetic. Hence our many arguments about transformer LV gland plates. E54 wanted paxolin, I wanted steel with epoxy filled slots to comply with M&Q. A case of never the twain shall meet.
On a basis of a 1/1 CT 100A flowing in the conductor will result in 100A flowing in an metal non magnetic gland plate. Where it gets complicated is when the circulating currents overlap/interact and cancel each other out to a limited extent. But there will be an underlying circulating current, for low current supplies not anything I would worry about.
On a basis of a 1/1 CT 100A flowing in the conductor will result in 100A flowing in an metal non magnetic gland plate. Where it gets complicated is when the circulating currents overlap/interact and cancel each other out to a limited extent. But there will be an underlying circulating current, for low current supplies not anything I would worry about.
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BS 7671 specifically disallows "ferromagnetic materials" they do not disallow "metal" Therefore, austenitic stainless is good enough for me.
john..
john..
Almost none of my work fell under BS7671, probably the same for RoB.
The same laws of physics apply to all branches of our trade. At low currents the amounts of circulating current in non ferrous material is negligible to the point of irrelevance, but they are there. Hence saying “I wouldn’t be worried about it”.
Get to 1000's of amps and you do have to think about it.
The same laws of physics apply to all branches of our trade. At low currents the amounts of circulating current in non ferrous material is negligible to the point of irrelevance, but they are there. Hence saying “I wouldn’t be worried about it”.
Get to 1000's of amps and you do have to think about it.
Hi Tony, i am not disagreeing!! fact of the matter is that austenitic stainless IS ferromagnetic, but only very slightly, so slight that in my application it is safe to state that it is a non ferromagnetic material.
But, if it was an application more like you are used to, thousands of amps, then yes, there might be a problem, however for my application i think it is safe to say that it "complies" as it were!!
john..
But, if it was an application more like you are used to, thousands of amps, then yes, there might be a problem, however for my application i think it is safe to say that it "complies" as it were!!
john..
I’ll say now, I like the way you have dressed and cleated the intake singles. That is far neater than I would have done.
[Script]
The boy replies with a laconic 1930’s upper class ascent, “I’ll comply”.
[/Script]
(Ealing comedies)
There was no dig at you intentional or intended, but if you get on to a large supply intake you need to keep things in mind.
At this point BS7671 has been chucked out the window. 200A and up to the maximum of a non dedicated supply which as far as I know is 630A (and that would be the DNO really pushing their luck). The DNO’s have their own rule book
Hi Tony, I never thought you were having a dig at all!! I am always interested to hear what you have to say. You are more skilled at this sort of thing than i could ever even aspire to be.
I tried to make things look neat!! I like things to be in orderly fashion, that is just the way i am!! I knew that i was not supposed to install anything in the DNO box, but i thought at least if it looks nice they are less likely to moan about it!!
john..
I tried to make things look neat!! I like things to be in orderly fashion, that is just the way i am!! I knew that i was not supposed to install anything in the DNO box, but i thought at least if it looks nice they are less likely to moan about it!!
john..
Don't they separate non ferrous metals (like copper and aluminium) from rubbish using induced magnetic fields????
We used that at the foundry, the lettuced that was taken with the ferrous to the charging system was unbelievable.
An old motor is in the main cast iron with high silicon steel laminations, both will be absorbed in the melt. If the copper windings got carried in it really screwed up the iron analysis. 70T of unusable iron to blend out with good stuff in the holding furnace at 2MVA/Hr.
Wasn't having a dig mate, just looks a good solution.
I can't quite make out, but the panel looks to be Eldon? I've not seen them with plates like that so I knew it was a custom job.
You wouldn't beleve how many installs I've seen, especially with transformer tails (singles) installed incorrectly. Ever seen steel lock rings melt, yep it makes a mess!
Hi Rob. I do believe it is an Eldon one yes. There is an MCCB in there, and, as the whole lot is outside, and the DNO plastic boxes might as well not even have a door on them [judging by the way the rain gets in] i wanted to make sure the damp did not get in, hence the tails go in through glands and the outgoing singles go out through glands as well.
I know that in theory, the CPC should also go through the same hole as it were, but space was severely limited so i skipped that bit. I have a proper earth terminal block thing with the link so that you can disconnect the earth for testing, but have not installed that either yet.
The outgoing cables are only temporary ones, so once i finish the shed i will make a proper plate gizmo to terminate some SWA and then run the cores through the glands and make a cover for them all so there is not unsheathed cable cores visible/touchable.
I am not an electrician at all, only a welder, so i just tried to do the best i could so at least it did not all look "homemade" or installed by someone from "down the pub" !!
When you see things like lock rings melt, is that the result of eddy currents caused by the normal output of the transformer, or as a result of fault currents??
john..
I know that in theory, the CPC should also go through the same hole as it were, but space was severely limited so i skipped that bit. I have a proper earth terminal block thing with the link so that you can disconnect the earth for testing, but have not installed that either yet.
The outgoing cables are only temporary ones, so once i finish the shed i will make a proper plate gizmo to terminate some SWA and then run the cores through the glands and make a cover for them all so there is not unsheathed cable cores visible/touchable.
I am not an electrician at all, only a welder, so i just tried to do the best i could so at least it did not all look "homemade" or installed by someone from "down the pub" !!
When you see things like lock rings melt, is that the result of eddy currents caused by the normal output of the transformer, or as a result of fault currents??
john..
The ones I've seen have been due to the normal operating currents.
If I'm honest I've only ever seen effects once the current gets over a couple of hundred amps. Nothing to worry about in a domestic environment, so it's purely good practice. The lock rings I saw melt were from the output of a 2MVA TX.
Don't think I've seen any eddy current damage resulting purely from a fault. Although I have seen the aftermath where copper earth bars that were undersized vaporize.
If I'm honest I've only ever seen effects once the current gets over a couple of hundred amps. Nothing to worry about in a domestic environment, so it's purely good practice. The lock rings I saw melt were from the output of a 2MVA TX.
Don't think I've seen any eddy current damage resulting purely from a fault. Although I have seen the aftermath where copper earth bars that were undersized vaporize.
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I've had them custom make cabinets before in st/st. Used to find it easier to take a small bench drill in the back of the van. 5mm st/st plate = plenty of Trefolex:
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