size of flex required

[SillyOldDufferModerator @sillyoldduffer]

Posted by Robert Atkinson 2 on 04/08/2020 22:24:47:

Posted by Len Morris 2 on 04/08/2020 17:59:39:

… I think no volt relays are omitted from no end of home machines. They are mandatory in industry.

…

Only switch the live feed NEVER both the live and neutral (or just neutral) with an E-Stop. If the neutral contact fails the machine will stop but the entire wiring will including the neutrla up to the switch, will still be live, waiting to electrocute someone faultfinding a "dead" machine.

Robert G8RPI.

Always cast a suspicious eye on the electrics of older machines. In yesteryear amateurs often fitted their own motors. Installation quality is pot-luck, ranging from gormless to professional. And NVR was common on industrial machines long before home equipment, so mechanically impressive classic machines might well be below standard electrically. (New machines are more likely to meet modern standards.) Dangerous when an old machine's rubber insulation is perished, or damaged, or the motor is damp, or the operator catches his sleeve in the chuck!

Old electrical books and standards can be dodgy too. Older wiring diagrams often show both Live and Neutral being switched and/or fused. Only later was it realised it's safer to fuse and switch only the Live feed. I believe 'both sides' was official best practice well into the 1930s, and I've seen examples in much later books. (Presumably because no-one noticed an old circuit needed updating.)

On the plus side, home-metalwork machines powered by domestic electricity don't often cause more than minor injuries. I guess it's due to relatively low voltages, relatively low power motors, working precisely, and a certain awareness of risk. Woodwork, DIY and gardening all have worse reputations! And as for motorbikes…

Dave

[Len Morris 2Participant @lenmorris2]

A no volt release relay triggered by an E-Stop stops the machine after a power failure. The machine will not restart when power is restored. It is not intended as an isolation relay. A fuse protects the supply circuit not the appliance.

I think some people are becoming scared of their own shadow!

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