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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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Old 11th Jul 2022, 9:49 am   #21
McMurdo
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Default Re: Antique Belarusian Samovar

Anecdotally, if an accident occurs due to an appliance and there was suspicion of neglect on the part of a professional, (whether the manufacturer or the repairer) the item would be sent to an independent test & inspection house who would pull the thing apart and see what caused the problem. Their opinion is the one likely to make it to count in court if it went that way. I've read many court cases regarding electrical accidents and safety whether at work or home and it is always a third party, (in the case of an installation for example tthe NICEIC are usually called to investigate) whose findings are used as evidence.
I dont think a retrospectively earthed samovar is going to rattle an inspector's feathers (so long as its earthed continuously to all conductive parts) whereas letting an unearthed but non-double insulated part get passed by a repairer as fit for purpose and then killing someone due to an element fault for example, may well indict them with negligence.
(I'm no lawyer btw !!!)
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Old 11th Jul 2022, 10:05 am   #22
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Default Re: Antique Belarusian Samovar

That's reassuringly sensible, Kevin.
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Old 11th Jul 2022, 8:04 pm   #23
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Default Re: Antique Belarusian Samovar

As someone with zero professional training in this, can someone explain in words of one syllable why it's problematic to earth the samovar?

I guess the thing is large, metal and the 'electrics' are simply a heating element, perhaps with a bimetallic switch. If earthed with new flex, a fault that causes the thing to become live and a possible danger is then mitigated by tripping the RCD or blowing the fuse. Wouldn't the reasonable-person-test then say that the repairer has made the object safer than before?

The automotive analogy makes sense to me - my car is 50 years old and repairable. I take the responsibility of not having driver aids, and have to be a better driver, which is good enough for insurers and the government. The samovar's owner can be forgiven for not having the same attitudes to electrical use as when it was made (perhaps they were more cautious, or just got injured more often), so in this case why is earthing the object a problem, as to my conception that brings it more in line with modern domestic wiring?
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Old 11th Jul 2022, 8:07 pm   #24
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Default Re: Antique Belarusian Samovar

What you say makes perfect sense, but lawyers are likely to argue otherwise.
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Old 11th Jul 2022, 9:21 pm   #25
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Default Re: Antique Belarusian Samovar

I think the problem is that a modification must meet the current standards. Even if it makes the item safer than it was before, if it doesn't meet those standards it's not acceptable. If unmodified, the standards are not applied retrospectively. Yes, it's probably nonsense, but that's the world we live in.
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Old 11th Jul 2022, 9:27 pm   #26
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Default Re: Antique Belarusian Samovar

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Originally Posted by Station X View Post
What you say makes perfect sense, but lawyers are likely to argue otherwise.
That just about sums up dentistry in 2022 too, sadly.
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Old 11th Jul 2022, 9:34 pm   #27
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Default Re: Antique Belarusian Samovar

If an electrical product with exposed metalwork were to pass through my hands and I failed to earth the metalwork, and if that failure were then to result in a dangerous shock to the subsequent user, I would feel a responsibility. That would apply whether it was a samovar or a (mains isolated) record player.

The ‘regulations’ - Class 1, Class 2 etc address only current products made to current specifications and not the vintage products that we forum members are usually handling. I believe that the decision-making committees have avoided the issue of ‘classic’ products - the topic has gone into the committee’s too difficult’ tray, but it can’t be ignored by those of us who restore and subsequently put on the market classic products. We do need guidance.

In this forum, I believe that we have a role to help members use their technical common sense to ‘use all reasonable endeavours’ to restore products so that they are electrically safe in today’s user environment. Hopefully, the combined expertise being applied here to this difficult issue might sometime be cited in a standards committee or in extremis in some court of law which ponders the implications of the ‘all reasonable endeavours’ legal phrase.

There’s a certain poetry in the fact that our technical dialogue on this seminal issue relates to an historic samovar!

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Old 12th Jul 2022, 2:06 am   #28
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Default Re: Antique Belarusian Samovar

I would not worry about your Samovar.
There are plenty of white appliances on sale with so called safety components that are a danger in themselves.
Some of the worst ones get hot and are mounted so close to non flame retardant components that there is no point in them being flame retardant themselves.

Make up a kit to convert it to earthed with instructions and before shipping fit the old lead back on so that the end user fits the new safer cable themselves.
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Old 12th Jul 2022, 5:33 pm   #29
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Default Re: Antique Belarusian Samovar

This is a bit of thread drift, so perhaps should go elsewhere, but prompted by this discussion.

I struggle to understand the objection to the earth pole of the OP socket on an isolation transformer being connected to the incoming earth. The transformer output is floating, such that you could safely connect yourself between either side and earth (not that you should do so deliberately, but if you do so accidentally you should be safe). That is useful if, for example, you're testing something with chassis connected to one side of the supply, or wanting to connect a scope to somewhere in the mains part. If the equipment that you're powering is intended to have an earth connection, how does maintaining that connection become unsafe if the supply is floating?
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Old 13th Jul 2022, 9:58 am   #30
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Default Re: Antique Belarusian Samovar

The problem arises if the plug on the device under test (DUT) has its mains plug incorrectly wired, with the earth wire swapped with one of the supply wires. You can then get the transformer secondary connected between mains earth (through the DUT) and the - supposably earthed - metalwork of the DUT.

Hence you would get the very dangerous situation of having 240V between the DUT metalwork and any the metalwork of any other equipment.

So you have a slight risk (the wrongly wired plug) of a very dangerous situation (240V between adjacent boxes). You can argue that you should check the plug before doing anything else, every single time without fail, even with non-standard flex colours etc, but a more foolproof solution is to remove the earth connection at the isolation transformer output socket, and use a flying lead to connect the DUT chassis directly to mains earth when necessary.

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Old 13th Jul 2022, 10:52 am   #31
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Default Re: Antique Belarusian Samovar

There is another issue in that the electrical separation of the secondary circuit is then reliant on the insulation of the device under test and is only as good as the worst of that. One might have a nice reliable isolating transformer to BS5733 with the protection it offers defeated by anything from a leaky transformer to a solder splash on the back of the power switch in the DUT. If you need to earth part of the live circuit then you will be aware that the other pole will be elevated wrt. earth, but the point of the isolating transformer is that it this will only occur by deliberate action, not by a fault.
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Old 13th Jul 2022, 11:17 am   #32
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Default Re: Antique Belarusian Samovar

Quote:
Originally Posted by Lucien Nunes View Post
There is another issue in that the electrical separation of the secondary circuit is then reliant on the insulation of the device under test and is only as good as the worst of that. One might have a nice reliable isolating transformer to BS5733 with the protection it offers defeated by anything from a leaky transformer to a solder splash on the back of the power switch in the DUT. If you need to earth part of the live circuit then you will be aware that the other pole will be elevated wrt. earth, but the point of the isolating transformer is that it this will only occur by deliberate action, not by a fault.
Yes but ... how is that worse with the DUT having an intact earth connection?
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Old 15th Jul 2022, 6:24 pm   #33
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Default Re: Antique Belarusian Samovar

Quote:
The problem arises if the plug on the device under test (DUT) has its mains plug incorrectly wired, with the earth wire swapped with one of the supply wires
You could say that about even the most modern class-1 appliance such as a washing machine or fridge
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Old 15th Jul 2022, 10:24 pm   #34
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Default Re: Antique Belarusian Samovar

Never heard of a Samovar. Just looked it up - Russian tea urn?

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Old 16th Jul 2022, 11:50 am   #35
Lucien Nunes
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Default Re: Antique Belarusian Samovar

Quote:
Yes but ... how is that worse with the DUT having an intact earth connection?
If a DUT is powered from an isolating transformer and has no earth connection, an earthed person can touch its L, N or chassis individually without harm. If an earth connection is provided to the chassis and an internal leakage exists between L (or N) and chassis, then an earthed person will be shocked by touching N (or L) in the DUT.

Had the DUT been plugged into RCD-protected raw (TN) mains, either the leakage or the shock current would be likely to have tripped the RCD. However an electrically separated (IT) source cannot benefit from RCD protection as there can never be a differential current at the source terminals.

Therefore although two possible methods of protection exist against shock-to-earth, combining a separated supply with an earthed DUT defeats both of them when a single fault exists within the DUT.
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Old 16th Jul 2022, 6:49 pm   #36
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Default Re: Antique Belarusian Samovar

When I was involved with offshore oil installations, it was sometimes the practice to use an isolation transformer to produce 120-0-120, earth the centre tap and use an rcd on the output. Also, in some installations the centre tap would be earthed via a device which continually monitored the insulation resistance of the live conductors (checking for water leaks etc). I guess none of this protected from getting across the two live conductors though.
Incidentally, there was sometimes a problem with the energy stored in the load(say rotating machinery) so the fault detection kit included a massive crowbar circuit to dump the energy. Wish I’d taken more notice.
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