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Old 16th Feb 2021, 3:02 pm   #1
chriswood1900
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Default Correct wiring of Plessey Mains Connector?

I have several of the Plessey 3 pin mains connectors used on EX military test equipment including a CT160. On an original one it is wired as per the EMERs instructions with each conductor with rubber sleeves a plastic liner in the metal body and a screening braid in the mains lead which screens the lead and also earths the Plessey connector back to the mains plug.
However, I have others which concern me such as the one on the attached photo with 3 conductors just soldered to the pins no sleeving or cover. The main concern is should the live wire come loose it could touch the metal body and become live for example when plugging or unplugging it.
So should I tie the connectors body back to the earth pin or just sleeve the conductors as per the EMERs instructions and rely on the earthing once it is plugged in?
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Old 16th Feb 2021, 6:11 pm   #2
Leon Crampin
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Default Re: Correct wiring of Plessey Mains Connector?

These connectors are just not safe. Apart from the possibility of loose wires arising from a poor cable grip, there remains the obvious shortcoming of the earth pin being the same length as the others. In any mains connector, the earth must always mate first and unmate last.

If originality is important, I screw them up with a wrench and tape up the outer barrel of the connector - the consumer then has a fixed mains lead. Horrible connectors (should have been nominated in a recent thread....).

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Old 16th Feb 2021, 7:07 pm   #3
McMurdo
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Default Re: Correct wiring of Plessey Mains Connector?

Not fair to blame the connector, maybe its usage. They're still in use, one local company fits them to military radar. The spec is impressive and they have pressure-bulkhead and fire-bulkhead ratings, (I assume for flight) and creepage for high DC ratings.

In the 80's I saw them as mains inlet connectors on a type of infra-red camera used to monitor moisture in clay on a conveyor belt. The manufacturer had a small earth wire joined and sleeved with the main earth and then brought out of the gland and fitted with a solder tag to one of the strain relief clamp screws. But as Leon says the earth ought to connect first otherwise fitted within a place where they're not accessible to mate/unmate live.

Manufacture is now by Weald and distributed by FC Lane.
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Old 17th Feb 2021, 9:56 am   #4
chriswood1900
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Default Re: Correct wiring of Plessey Mains Connector?

Kevin - That is interesting I was wondering about taking a wire from the earth lead to the body and your example would seem to indicate that was an acceptable practice.
In use I try to make sure that the cables are attached before I use the equipment but we all know its easy to forget when busy.
Leon - I take your point but I want to maintain originality, I suppose on the original usage where there was an earthed screen to the body that made contact first even before the conductors so there is lower risk compared with the example I now have.
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Old 17th Feb 2021, 1:27 pm   #5
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Default Re: Correct wiring of Plessey Mains Connector?

I have got a 110V device that uses a 2 pin one like the B40 comms receiver does.
The case is the only earth.
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Old 17th Feb 2021, 3:43 pm   #6
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Default Re: Correct wiring of Plessey Mains Connector?

I've seen the 'additional earth wire to one of the grip-screws' thing too.

Still seems to me to be a major bit of kludgery. While Plessey-plugs may have been 'acceptable' for mains in decades-past, these days they're definitely not, and something like an IEC309 kettle-lead - or maybe one of the smaller 'cloverleaf' connectors as generally found on laptop PSUs - is much to be preferred.

[Same goes for the 3-pin Bulgins and - as I came across recently - a 6-pin Cinch-Jones connector being used - with wiring different depending on whether it was a 240VAC input or a 12VDC one.]

There's one version of the Cloverleaf that fits through the same-sized chassis hole as a Plessey, meaning you only need to drill two small screw-mounting holes - and these are close enough to the big hole that if you were to want to you could refit the Plessey and not see the holes.
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Old 17th Feb 2021, 6:09 pm   #7
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Default Re: Correct wiring of Plessey Mains Connector?

I have never seen any equipment with a Plessey chassis connector that is not heavy enough to allow to connect a Plessey connector to it without it sliding on the shelf/bench.
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Old 17th Feb 2021, 6:42 pm   #8
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Default Re: Correct wiring of Plessey Mains Connector?

Quote:
Originally Posted by G6Tanuki View Post
... a 6-pin Cinch-Jones connector being used - with wiring different depending on whether it was a 240VAC input or a 12VDC one.
Ah yes, standard practice on older Yaesu Transceivers
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Old 18th Feb 2021, 12:58 pm   #9
chriswood1900
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Default Re: Correct wiring of Plessey Mains Connector?

For the sake of originality, I want to keep the Plessey connector, so I took it apart, sleeved each of the conductors with a Hellerman Sleeve and ran an earth wire back out to attach to the screws on the grip. The inside of the body was insulated with a plastic sleeve so that should a wire come loose it cannot easily touch the body. The earth wire was continuous from the cable to the tag so if the solder joint fractured earth continuity to the body of the connector was maintained.
That was the best I could come up with, thankyou to those that provided me with some information, hopefully this thread will be useful to others.
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Old 18th Feb 2021, 4:17 pm   #10
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Default Re: Correct wiring of Plessey Mains Connector?

I think that is the best solution, and not to disconnect it live (well not with both hands!).
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Old 24th Feb 2021, 8:35 am   #11
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Default Re: Correct wiring of Plessey Mains Connector?

Yes, there's quite a few connectors that whilst rated for mains-voltage use, are not touch-proof enough for modern standards, so should only be used within equipment / not connected / disconnected when powered.

The PowerCON ((Mains etc. rated version of SpeakCON) connectors are apparently still used on stage equipment, but wouldn't be allowed on domestic equipment for consumers as not touch-proof enough to be connected / disconnected whilst still live.
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Old 24th Feb 2021, 9:10 am   #12
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Default Re: Correct wiring of Plessey Mains Connector?

I disagree regarding Powercon. Earth mates first and demates last. The body is insulating. They have seriously generous receptacles and screws. They are guaranteed for >1000 mate/demate cycles. They have a collet type strain relief, and are provided with two collets to suit different cable diameter. You would need to be seriously determined to get something into the contacts - more so than with a kettle lead.

They are VDE, UL, cUL and JET approved.

And they are locking, and so do not work loose in the same way the kettle leads do.

And yes - I use Powercons on my three amplifer stack that powers my active LX521 loudspeakers.

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