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Other Vintage Household Electrical or Electromechanical Items For discussions about other vintage (over 25 years old) electrical and electromechanical household items. See the sticky thread for details. |
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26th Apr 2022, 7:35 pm | #1 |
Dekatron
Join Date: Sep 2011
Location: Rugeley, Staffordshire, UK.
Posts: 8,830
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Mains filtering
As we all know, interference from SMPS and many other sources greatly affects, and can totally ruin attempts to receive AM transmissions in a domestic situation. I'm constantly dabbling with solutions and I recently fitted clip on ferrite rings to every device's mains lead (computer, printer, USB hub, monitor etc) in an area where I also have a couple of vintage radios nearby - they had ferrite rings fitted too. The result? no better. So I really got down to tracing the source using a modern portable transistor radio. To cut a long story short, the interference peaked whenever the radio was placed near to any mains cable on the ring main - the interference is 'everywhere'. BTW, I have a long wire external aerial that provides (in theory!) for a good signal to noise ratio, so I'm not just hanging a bit of wire out of the back of my radios.
It got me thinking about a 'global' mains filter unit and how effective it may be. I did some googling and found this as used by a radio ham and seems just the job: https://www.m0nwk.co.uk/mains-electr...ise-reduction/ Has anyone tried this kind of global filtering?
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26th Apr 2022, 10:41 pm | #2 |
Heptode
Join Date: Feb 2021
Location: Edinburgh, Scotland, UK.
Posts: 528
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Re: Mains filtering
Maybe I'm missing something but I thought you were only allowed one double socket on a spur unless it was protected by a 13A fuse.
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27th Apr 2022, 12:49 am | #3 |
Rest in Peace
Join Date: Apr 2008
Location: London, UK.
Posts: 2,508
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Re: Mains filtering
That is correct, a spur being specifically a branch from a ring final circuit that would be protected at 32A in the distribution board. But any number of points may be connected to a radial circuit wired in 2.5 sqmm protected at 20A. I don't see anything in the link that states the supply is a spur off a ring final.
The reason for the limitation on spurs is that regardless of the cable rating used for the spur itself, too many points connected to it would tend to concentrate too much of the ring final's total 32A in one place, increasing the probability of one leg of the RFC being overloaded. This in turn is because the RFC is a special case that violates the principle Ib <= In <= Iz (Design load does not exceed OCPD rating, OCPD rating does not exceed derated CCC of cable). It is an empirical solution that relies on a distributed load being somewhat shared between the two legs. There are situations in which multiple points on a spur would be perfectly safe but they do not fall within the specifically defined configuration of an RFC. |
27th Apr 2022, 7:59 am | #4 |
Heptode
Join Date: Feb 2007
Location: West London, UK.
Posts: 867
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Re: Mains filtering
I made up a filter for my shack by winding L N and E individually over 3 ferrite rods. It is not connected to a spur, just goes to a 4-way multi connector which has my ham gear connected to it.
Not sure if it reduces noise much but every little helps. You can buy ready made filters. John |
27th Apr 2022, 3:18 pm | #5 |
Dekatron
Join Date: Sep 2011
Location: Rugeley, Staffordshire, UK.
Posts: 8,830
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Re: Mains filtering
I've now added ferrite rings to my incoming mains supply (house), Still no better.
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27th Apr 2022, 3:50 pm | #6 |
Heptode
Join Date: Feb 2022
Location: Leicestershire, UK.
Posts: 690
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Re: Mains filtering
On the presumption that a battery powered radio is used, has anyone tried switching off the whole house mains supply off at the consumer unit to see if the interference then disappears ? This would prove or disprove re radiation via mains supply into the ring circuit or any other house wiring for that matter.
Roger |
27th Apr 2022, 4:14 pm | #7 |
Dekatron
Join Date: Sep 2011
Location: Rugeley, Staffordshire, UK.
Posts: 8,830
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Re: Mains filtering
Good point Roger.
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27th Apr 2022, 6:12 pm | #8 | |
Heptode
Join Date: Feb 2021
Location: Edinburgh, Scotland, UK.
Posts: 528
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Re: Mains filtering
Quote:
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27th Apr 2022, 7:12 pm | #9 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,996
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Re: Mains filtering
Pragmatically, to understand what supply-filltering will work for you. you need to understand the supply-schema used by your DNO.
Viddy here, my Droogs, as Alex would say in "Clockwork Orange" - https://www.lsp-international.com/power-supply-system/ If you're working with an old "Protective multiple earth" [PME] system then then at the incomer the customer 'earth' will be strapped to the neutral- whixh means that opening the customer 'main switch' still leaves the customer-side 'earth' connected to the DNO Neutral - so any RF noise on the Neutral still gets coupled into the building's cabling. [I don't know precisely what the capacitance between the earth-conductor and the L/N conductors of typical premises-wiring cable is, but I would hazard a guess that at HF/MF frequencies it will be sufficient that in a typical domestic-install where there aew hundreds ofv Metres of such cable the inter-wire capacitance is sufficient that you can assume that L/N/E are at the same RF potential] So "switching-off' the mains-switch as a diagnostic-technique, without knowing the DNO topology could ne a fool's errand. Same goes for fitting chokes on the L/N incomer cables... noise-on-the-neutral could be getting a free-pass round your efforts via the earth-conductor into your entire domestic wiring infrastructure, where it will happily re-radiate to the detriment of your MF/HF reception.
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27th Apr 2022, 7:58 pm | #10 |
Dekatron
Join Date: Sep 2011
Location: Rugeley, Staffordshire, UK.
Posts: 8,830
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Re: Mains filtering
In that case, any suggestions then?
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27th Apr 2022, 8:13 pm | #11 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,996
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Re: Mains filtering
First, consult your DNO and identify what supply-schema you have to your property.
Without knowing this, adding 'filters' could be futile - and potentially dangerous!
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28th Apr 2022, 8:57 am | #12 |
Nonode
Join Date: Mar 2010
Location: Dukinfield, Cheshire, UK.
Posts: 2,037
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Re: Mains filtering
I have exactly the same problem. It seems to be at its worst at the fusebox, indicating it may be coming in on the cable from outside. It's so strong I get modulation hum on strong signals when using a portable around the house. Luckily, my Wellbrook loop mounted at gutter height at the back of the house gets rid of most of it on my Amateur Radio/SWL stuff.
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28th Apr 2022, 9:01 am | #13 |
Dekatron
Join Date: Sep 2011
Location: Rugeley, Staffordshire, UK.
Posts: 8,830
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Re: Mains filtering
So, exactly what is the question that I ask of Western Power, as sure as eggs are eggs they'll throw a curved ball back at me?!
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28th Apr 2022, 9:08 am | #14 |
Moderator
Join Date: Dec 2010
Location: Exeter, Devon and Poole, Dorset UK.
Posts: 6,864
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Re: Mains filtering
Have a look here
https://en.wikipedia.org/wiki/Earthing_system Ask them what kind of earth your property has (if you cannot work it out for yourself) and when the come back with say TN-S or TN-C-S when you can see exactly what that means. Cheers Mike T
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28th Apr 2022, 9:33 am | #15 |
Dekatron
Join Date: Sep 2011
Location: Rugeley, Staffordshire, UK.
Posts: 8,830
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Re: Mains filtering
My earth is of my own making. I drove a long copper earth bar into the ground and brought a wire from it up to the electrical distribution box. What's that called?
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28th Apr 2022, 9:49 am | #16 |
Dekatron
Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 4,311
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Re: Mains filtering
It could be called "a pretty impressive ground loop" if it's competing with your electricity provider's earthing system. Under some circumstances I believe* it may also be hazardous, particularly in the event of certain types of faults elsewhere in your neighbourhood. As always, whether it's a problem and/or a hazard will depend on the details of your provider's earthing scheme.
Cheers, GJ *I wouldn't class myself as competent to advise authoritatively on this - if you're in any doubt then you should consult someone who is.
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28th Apr 2022, 9:55 am | #17 |
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Location: Ipswich, Suffolk, IP4, UK.
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Re: Mains filtering
That's similar to my own installation. The "company" never provided an earth terminal even when the supply was converted from overhead to underground.
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28th Apr 2022, 9:58 am | #18 |
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Location: Exeter, Devon and Poole, Dorset UK.
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Re: Mains filtering
If no earth is provided by the DNO then it will be TT
You will need to be using RCD at the very least as the ELI will be quite high. Cheers Mike T
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28th Apr 2022, 10:03 am | #19 |
Dekatron
Join Date: Sep 2011
Location: Rugeley, Staffordshire, UK.
Posts: 8,830
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Re: Mains filtering
What is TT? ELI? My distribution unit does use RCDs.
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28th Apr 2022, 10:08 am | #20 |
Moderator
Join Date: Dec 2010
Location: Exeter, Devon and Poole, Dorset UK.
Posts: 6,864
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Re: Mains filtering
Follow the Link in post #14
ELI is Earth Loop Impedance. TT is Terre Terre ie a local earth usually provided by a spike or a mat. If you want to improve the ELI you can use Marconite concrete which is what we use. Cheers Mike T
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