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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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19th Jul 2020, 4:45 pm | #1 |
Nonode
Join Date: Jan 2016
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Warning about high leakage current, and earthing. Farnell AP60/50.
I hope this is the right section, pretty sure it's getting on for 30 years old and a previous thread https://www.vintage-radio.net/forum/...d.php?t=129864 was in this section.
So my question is about a warning on the back of the PSU, that there is a high leakage current and earthing is vital. I was preparing to run mine from a petrol generator (to quickly charge a car battery where the car has been stood since Feb). Now a standalone genny has no 'real' earth, the earth connection on the socket is connected to generator's frame, but no actual ground to terra firma. My concern is the mentioned leakage is effectivley the class Y caps which I know this PSU has because I replaced the Rifas (as in the linked thread). So the question is, am I risking a belt (or worse) running an AP60/50 from a standalone generator? So far as I can ascertain, there's no local mains supply I can use, and no sensible way of driving an earth terminal into the actual ground (it's a block paved car parking area). |
19th Jul 2020, 5:05 pm | #2 |
Dekatron
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Re: Warning about high leakage current, and earthing. Farnell AP60/50.
When considering earthing problems you must consider the circuit and ask how a "belt" could occur. It is all about looking for potential differences.
Also, be aware that generators have different earthing schemes depending on their expected use. One scheme is to have the earth effectively half way between L and N, then be careful with domestic equipment because it wasn't designed for that. A properly floating system cannot give out a shock to an earthed person because there is no circuit route back to the power source in that case. If equipment cases are bonded together then there can be no potential difference there. But be careful with a power supply because its connections could change things, and check that the unusual configuration will not stress a part that does not normally expect to see much voltage e.g. because it assumes that N and E are the same, near enough. |
19th Jul 2020, 5:17 pm | #3 |
Nonode
Join Date: Jan 2010
Location: North Somerset, UK.
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Re: Warning about high leakage current, and earthing. Farnell AP60/50.
I believe that what you propose is safe since the generator output is "floating" without any connection to true earth.
If considered carefully, drawing a diagram if need be, under what circumstances could a shock to earth be received ? You could get a dangerous shock if touching BOTH sides of the generator output at the same time, but that is so unlikely as to be acceptable. In the case of a large or complex installation connected to a generator, then there are greater risks, but for one appliance connected to a generator via a short lead, I would not worry. |
19th Jul 2020, 5:18 pm | #4 | |
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Re: Warning about high leakage current, and earthing. Farnell AP60/50.
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19th Jul 2020, 5:22 pm | #5 | ||
Nonode
Join Date: Jan 2010
Location: North Somerset, UK.
Posts: 2,129
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Re: Warning about high leakage current, and earthing. Farnell AP60/50.
Quote:
A car battery left uncharged for many months may be scrap, especially if in doubtful condition beforehand but it is worth trying to save it. |
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19th Jul 2020, 5:42 pm | #6 |
Nonode
Join Date: Jan 2016
Location: Stafford, Staffs. UK.
Posts: 2,531
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Re: Warning about high leakage current, and earthing. Farnell AP60/50.
Thanks for the input so far. The battery isn't flat but low. I used my 20A charger a couple of weeks ago and it took charge well, so it's not yet scrap. When I started it was already above 11.2v and recovered to 11.9v within 1/2 an hour (while still supplying some current to the car). Trouble is I can't sit there for hours (the other residents might start getting stroppy about the noise of the genny). The cars alternator must be capable of delivering over 100A so I'm not concerned about the battery and charging, just whether I should stress about offset earth voltages and it biting.
I reckon you are right, it's about relative to real earth. The generator's frame is isolated from real ground by the engine / alternator's rubber mounting to the casing, and the casing's rubber feet to the ground. I'd expect that my 20A charger has Y class caps in it too and have been using that without incident for many years at car events I take part in. I just wondered if I was missing something. |
20th Jul 2020, 8:48 am | #7 |
Dekatron
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Re: Warning about high leakage current, and earthing. Farnell AP60/50.
most portable generators have the earth and neutral connected together at the outlet socket don't they, so the leakage should have somewhere to go. You could always meter it out for peace of mind. A mate of mine once got a nasty shock off a burger van fed by a portable generator, so something had gone wrong there!
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20th Jul 2020, 9:24 am | #8 | |
Dekatron
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Re: Warning about high leakage current, and earthing. Farnell AP60/50.
Quote:
All three common possibilities are likely to be found, i.e. E not connected to LN at all; E connected to N; E connected to (L+N)/2 If is has domestic UK sockets then I would hope for E to N and if it has the Blue 15A connectors or US connectors then more likely (L+N)/2. But you must always check, whatever you might think or even see documented. This also applies the other way round, i.e. if you have site power output (yellow 110V connectors) then you might expect centre-earthed but I have found examples where it wasn't like that. ALWAYS CHECK! |
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20th Jul 2020, 11:20 am | #9 |
Rest in Peace
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Re: Warning about high leakage current, and earthing. Farnell AP60/50.
I agree, there is no standard for portable generator output earthing schemes.
Anything with a 230V output for the UK/EU market might have either a floating or N-E linked output. Most small units are floating, and are intended to operate in IT (insulated from earth) configuration. IT is single-fault tolerant but provides no automatic disconnection in the event of that fault and an RCD will not function. Dual faults can be hazardous since they may occur indiscriminately to either pole, hence IT supplies are not generally suitable for connecting a larger number of devices or extensive wiring where the probability of more than one fault escalates. On units where the N & E are linked, or if you provide a link yourself, the CPC can be earthed by a rod to allow an RCD to function to protect against shock paths to true earth (if the Ra is sufficiently low). Without the rod, the RCD will still protect against abnormal leakage from line or neutral to the case of Class I appliances. What a 230V-outlet-equipped generator should NOT have in the UK is an earthed centre-tap, as this makes both legs of the circuit 'line' conductors, i.e not near earth potential, and defeats single-pole switching and protection. This is however the standard 120/240V configuration in the USA, where DP switchgear is standard for 240V. Regarding the leakage from the PSU, that should return along the green/yellow stripy wire a.k.a protective conductor to the generator neutral if the two are linked, and go nowhere if they are not. In either case it does not matter whether there is an earth rod installed i.e. whether the neutral and protective conductor are actually earthed. The presence of a rod would would only have an influence on the path taken by leakage current (to the supply terminals of the PSU) if the protective conductor were open-circuit. Last edited by Lucien Nunes; 20th Jul 2020 at 11:26 am. |
20th Jul 2020, 4:34 pm | #10 |
Nonode
Join Date: Jan 2010
Location: North Somerset, UK.
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Re: Warning about high leakage current, and earthing. Farnell AP60/50.
Whilst a centre earthed 230 volt supply is not ideal for the reasons given, it does not much matter with a small generator feeding a single appliance.
Various parts of Europe used mains supplies with both poles live. A few such systems remain in use. Standard domestic appliances are used on such supplies, even if such appliances incorporate single pole switches and fuses. The fixed premises wiring hopefully has fuses in both poles, but single pole switches are common. |
20th Jul 2020, 8:36 pm | #11 |
Nonode
Join Date: Jan 2016
Location: Stafford, Staffs. UK.
Posts: 2,531
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Re: Warning about high leakage current, and earthing. Farnell AP60/50.
Once again, thanks for the input. I've looked at circuit diagrams for the PSU, and the generator. Regarding the PSU, the housing is connected to the CPC, with L and N connected to the same via capacitors. Previously Rifa but now replaced. I can see that if connected to a normal UK supply, with the CPC missing, the class Y caps connected L-E and N-E would effectively put the housing at half mains voltage, albeit current limited. Potentially ouch.
Regarding the generator, which incidentally is more vintage than the PSU (Honda EX1000 from the 70's) the manual says that the CPC is connected only to the frame and engine / alternator. L and N are isolated allegedly with a resistance of 10Mohms. Tomorrows task is to double check that. It is a specifically UK market model. If that's correct, then essentially both L and N will be half mains voltage above the housings, but then I don't have access to either L or N. Also of interest perhaps, going back to the PSU, it's ex MOD. A label on it says 'Only for use with 8920c radio test set' which I find is a test rack for Clansman radios with a Marconi 2955. |
20th Jul 2020, 11:39 pm | #12 | |
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Re: Warning about high leakage current, and earthing. Farnell AP60/50.
Quote:
A rackful of test equipment was powered from a distribution strip of about a dozen IEC C14 outlets. So there were about ten Y capacitor pairs in play. The strip was connected to a 13A plug via a C14 connector and cable. Total power consumption was fine for the connector ratings. The C14 female connector has a design flaw. THe earth pin is longer than the others, so that the earth makes first and disconnects last which is good thinking. BUT the longer pin takes the lion's share of the weight and wiggling of the cable and so the tines of the female earth contact work harden and lose springiness and pressure. Ground goes open circuit through wear and tear. The rack was a receiver system with an N-type connector and 100m of heliax cable to an antenna bolted to the building steelwork on the roof. I was the guy who disconnected the antenna cable for a quick check on something else. I got a hand to hand shock frpm the cable end versus the metalwork and connectors. The current was limited by the Y capacitors and it was half mains voltage, but there were several sets of Y capacitors in parallel. I was unhurt, but I used up all the special words in my vocabulaty, even the very special ones. So I'm a bit touchy about taking care. David
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21st Jul 2020, 12:30 am | #13 |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
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Re: Warning about high leakage current, and earthing. Farnell AP60/50.
Similar story David, I got a belt trouble shooting a 10BASE2 network.
I separated two BNC's from the T piece, one in each hand. A downstream PC was plugged into a power circuit sans earth! (apart from via the other PCs and me of course). It must have been a common occurrence. Thinking about it, in an industrial setting the network could easily be bridging two mains phases. Shocking.
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21st Jul 2020, 8:36 am | #14 | |
Dekatron
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Re: Warning about high leakage current, and earthing. Farnell AP60/50.
Quote:
A single one is not dangerous, but multiples will add up - usually in the situation of having lots of devices plugged in. And worse is where a centre-earthed supply powers equipment not expecting it, where the much larger X class capacitors now get to join in too. |
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21st Jul 2020, 6:22 pm | #15 |
Nonode
Join Date: Jan 2016
Location: Stafford, Staffs. UK.
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Re: Warning about high leakage current, and earthing. Farnell AP60/50.
Just to keep up to date. Have checked and the generator is wired as the manual says: the earth terminal is connected to the generator frame, and not to either L or N. I didn't use an insulation tester (500v) but there was no sign of any resistance to the frame from L or N with my Fluke. That's also what the manuals for all my gennies say (don't ask) but I haven't checked the others. That said, apart from 2, they are all also Hondas, and the two that aren't have Honda engines with Italian alternators (one 1970s, one 2000s).
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22nd Jul 2020, 10:59 am | #16 | |
Rest in Peace
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Re: Warning about high leakage current, and earthing. Farnell AP60/50.
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22nd Jul 2020, 4:32 pm | #17 |
Dekatron
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Re: Warning about high leakage current, and earthing. Farnell AP60/50.
Not sure if it's been already mentioned as I've not read all the posts in detail, but a couple of points;
1) Most portable generators have a 12 volt output for battery charging. 2) Professional lab type regulated power supplies shouldn't really be used for charging batteries due to the battery back feeding them when connecting or switching off and blowing them up. |
22nd Jul 2020, 5:03 pm | #18 | |
Nonode
Join Date: Jan 2016
Location: Stafford, Staffs. UK.
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Re: Warning about high leakage current, and earthing. Farnell AP60/50.
Quote:
1. Yes but only 10A on this one. And my 20A max charger was taking too long hence wanting to use something more capable. I got up to 27A with this, making sure I limited charging voltage at the battery terminals to 14.4v. I reckon I got it to 20-30% SoC before rain stopped play. It was interesting to watch the battery 'wake up' and start drawing more current with the supply swicthing between CV and CI modes for quite a while. 2. Yes, I've contributed to a thread about this. Even worse if for some reason the OVP trips and crowbars the car battery (seen someone do it, had to fix the mess). But I have a nice inline dual schottky in an Isotop package with a big heatsink. NO current was going that way! Actually the operating situation changed. These AP 60/50s monitor the incoming mains and won't switch on the output if they don't like it. And it wouldn't when on the genny! Didn't have time to mess about checking the voltage and frequency so I don't know what it was fussing about. So I was about to give up when I was told that actually mains was available in a room just by where the car was parked! Typical! |
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23rd Jul 2020, 11:56 am | #19 | |
Dekatron
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Re: Warning about high leakage current, and earthing. Farnell AP60/50.
Quote:
Would the average electrician know how to deal with it? 3.5mA seems so tiny compared to the fault currents relating to the normal Ze & Zs tests. and the CPC contact area on a BS 1363 plug and socket is larger than the phase & neutral.
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