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Old 12th Sep 2023, 2:34 pm   #1
JH_7188
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Default Synchronous clock safety

I have a number of old synchronous clocks of various makes including Smiths, Metamec, Gent and Synchronome, most of which I believe date from the 1960s - they all appear to work fine (based on being plugged in and allowed to run for a few hours) and most are almost completely silent with the others emitting a gentle hum - the movement cases warm up slightly when they've been running but certainly don't feel at all hot. I'd quite like to use at least some of these live but there is clearly a need for caution when it comes to older electrical equipment...

I'm trying to establish whether PAT testing is actually sufficient to determine whether an old clock is safe to use - some of the clocks appear to have newer cables whereas others have cables which I suspect may be original and therefore 50+ years old. The older cables will clearly need to be changed and I'm trying to establish whether doing so and then having PAT tests carried out is sufficient or whether there should be more to it than this - a bit of online reading suggests that there's an argument for rewinding the coil to run at a lower voltage but a number of other resources suggest that this isn't necessary. In case it's significant, all the cables are 2-core.

In theory I could replace the existing movements with new battery-powered ones but I believe doing so effectively ruins the clock so I don't intend to do this.

Any thoughts on the above much appreciated!
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Old 12th Sep 2023, 2:41 pm   #2
paulsherwin
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Default Re: Synchronous clock safety

PAT testing isn't really relevant.

Opinions do differ over the safety of mains powered synchronous clocks. They were designed and built to lower safety standards than would be applied today, but the majority view is that they are sufficiently safe to be used by responsible adults. I'm certainly unaware of anyone being fatally electrocuted using one.

Obviously any damaged or rotted cabling should be replaced.

The position is different if you intend to sell these clocks as working, as there will be liability issues. A PAT test doesn't get you off the hook.
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Old 12th Sep 2023, 4:17 pm   #3
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Default Re: Synchronous clock safety

Yes, common sense and a good visual inspection are mandatory.

As is a 1A fuse in the plug, and an RCD (there's usually one in the consumer unit unless your wiring is old).

And it goes without saying that all houses should have a working smoke alarm on each floor, as a bare minimum.
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Old 12th Sep 2023, 8:30 pm   #4
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Default Re: Synchronous clock safety

As stated above.
I have run many synchronous clocks for many years, and would never consider them an ‘issue’.
Glad you are not going to ruin them with a quartz movement.
Enjoy them
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Old 12th Sep 2023, 9:35 pm   #5
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Default Re: Synchronous clock safety

I have an ancient specimen which graces my workshop. The only mod. I considered desirable was connection using 3-core, so the metalwork was earthed, just in case of a motor to mech. leakage.
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Old 12th Sep 2023, 10:08 pm   #6
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Default Re: Synchronous clock safety

i have no concerns about the bedroom Metamec. I replaced the fraying mains flex, and improvised some additional strain relief.

Like Nick's it's got a 1A fuse in the plug, although that's probably an order of magnitude too large.
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Old 13th Sep 2023, 3:53 pm   #7
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Default Re: Synchronous clock safety

A 1 amp fuse is consistent with what was done years ago clock connectors had a 1 amp fuse in them even if the connector was wired from a 5 amp light or plug circuit so it seems sensible to have one now. Not sure how much power a clock pulls but can't be more than a few watts either way it's very sensible to put a low rated fuse in

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Old 13th Sep 2023, 5:58 pm   #8
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Default Re: Synchronous clock safety

Remember that the fuse in the plug is there to protect the flex not the appliance.

In times past I have fitted a 20mm cartridge fuse holder with a 60mA fuse internal to some VFD clocks to provide protection of the actual working bits.
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Old 13th Sep 2023, 6:12 pm   #9
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Default Re: Synchronous clock safety

Yes, a 50mA fuse internally would be nice, as would a thermal fuse. But don’t botch a 25x5mm into the plug as I’ve seen advocated, as it would not comply with the relevant British Standards in the way a ceramic, sand-filled BS1362 one does.
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Old 13th Sep 2023, 6:27 pm   #10
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Default Re: Synchronous clock safety

This is a bit OTT though. It's not completely impossible that a synchronous clock will develop live metalwork or burst into flames, but it's very, very unlikely. Most of them run for half a century or more with little or no maintenance and no drama. The few that develop electrical faults just get open circuit motors, which simply stops them working.

Using an RCD is a good belt and braces protection measure though, especially if there are children around. As said, modern consumer units provide this as standard, but older installations can just use a plug in adaptor.
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Old 13th Sep 2023, 6:51 pm   #11
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Default Re: Synchronous clock safety

The windings in a typical electric clock are so fine (try rewinding one!) that they will soon fuse open if there's any overcurrent event.
Let's not get hysterical about it! The danger's far more likely from a frayed or perished flex than the state of the clock itself.
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Old 15th Sep 2023, 1:47 am   #12
Oldmadham
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Default Re: Synchronous clock safety

Quote:
Originally Posted by JH_7188 View Post
I have a number of old synchronous clocks of various makes including Smiths, Metamec, Gent and Synchronome, most of which I believe date from the 1960s - they all appear to work fine (based on being plugged in and allowed to run for a few hours) and most are almost completely silent with the others emitting a gentle hum - the movement cases warm up slightly when they've been running but certainly don't feel at all hot. I'd quite like to use at least some of these live but there is clearly a need for caution when it comes to older electrical equipment...

I'm trying to establish whether PAT testing is actually sufficient to determine whether an old clock is safe to use - some of the clocks appear to have newer cables whereas others have cables which I suspect may be original and therefore 50+ years old. The older cables will clearly need to be changed and I'm trying to establish whether doing so and then having PAT tests carried out is sufficient or whether there should be more to it than this - a bit of online reading suggests that there's an argument for rewinding the coil to run at a lower voltage but a number of other resources suggest that this isn't necessary. In case it's significant, all the cables are 2-core.

In theory I could replace the existing movements with new battery-powered ones but I believe doing so effectively ruins the clock so I don't intend to do this.

Any thoughts on the above much appreciated!
Coming from an Australian perspective,"50 + years old" in 2023 doesn't imply perished rubber & frayed fabric cables like such an age would have meant in, say, 1980.

The 1960s were, (again in Oz, so your experience in the UK may have differed) the time when much the same style of power cables came into (mandated) use that are normally used now.

These had PVC insulated conductors and outer sheaths, or for cords requiring extreme flexibility and/or heat resistance like toasters, electric kettles, clothes irons, etc., PVC insulated conductors and a patterned fabric outer. The PVC conductor insulation was equally tough in either case.

The most serious safety concern may be that of some enthusiastic handyman in the interim years replacing a perfectly adequate 1960's lead with salvaged 1930's/1940's cable "to get a longer cord".

The motor itself is probably a simple device like the old record player motors, with one winding, insulated to transformer standards.

Such small synchronous motors are still made and differ little from 70-year-old ones!
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Old 29th Jan 2024, 8:16 pm   #13
JH_7188
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Default Re: Synchronous clock safety

Thanks for all the advice - much appreciated. Clearly there are a few considerations, but one thing I don't intend to do is to convert any of the clocks to quartz - I'd rather keep them as authentic as possible!
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Old 29th Jan 2024, 9:43 pm   #14
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Default Re: Synchronous clock safety

Agree all these comments.

Specifically, PAT is a sketchy and non-invasive snapshot of the status quo at a fleeting moment in time.

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