Electrical safety mats in workshops

An RCD will provide protection and they don't really care about the impedance. If its too high for it to trip then its too high for it to be dangerous or for the machine to work.

The over current breaker is a different matter but it won't protect you in the same way as an RCD. Its there to protect the wiring and prevent fires.

RCB's work by detecting slight current imbalance between the line and neutral legs, so I would have thought that would not be affected by high loop impendence.

When I was working on live chassis TV sets the workshops were fitted with individual bench isolating transformers, rubber floormats, and a central voltage operated ELCB.

Garden?

If you were using an isolation transformer then your TV chassis shouldn't be live in the first place, surely? And what's an ELCB?

very fancy

NT

Sorry I should have said it's a bare, concrete-floored workshop in this instance.

That's why you used the isolation transformer. One side of a live chassis design is connected directly to the mains. Hopefully, the neutral.

Earth leakage circuit breaker.

That's my point, a belt & braces approach.

Earth Leakage Circuit Breaker, it was much the same as an RCD but worked differently.

Earth Leakage Circuit Breaker.

They were all the rage at one time, and worked on measuring earth leakage rather than L-N current imbalance.

Live chassis TV means the chassis is directly connected to one of the mains conductors (live or neutral). This is because it uses a crude power supply which doesn't provide any mains isolation, i.e no mains transformer. Most valve sets worked this way (and had no earth connection).

Protection from electric shock was by the wooden case, pressed hardboard back cover, plastic shafts on knobs, and capacitive isolation of the aerial socket.

Most chassis I came across had the chassis at neutral potential, so in reality it was quite safe if wired correctly.

I do recall one design that had the chassis at "mid potential", where it used a bridge rectifier, with chassis connected to -ve rail.

The most dangerous situation I came across was an old radio, where the plug wires were of the US persuasion. That was probably the most dangerous shock I ever had where substantial current must have passed across my chest due to the confusion of what coloured wire was connected to chassis.

I have an old nylon hearthrug. It keeps my feet warm as well as insulating me.

Bill

Except that the term RCD wasn't adopted until some time after the introduction of devices that were triggered by the current imbalance so for a number of years both forms were referred to as ELCB's, sometimes preceded by the words "current operated" or "voltage operated" to distinguish between the two. I have an old 1979 MK catalogue which shows

That's what was intended, but in that era you often found 5 or 15 amp round-pin sockets that had reversed polarity so you could never assume.

Often called "floating chassis" at the time, although that term has a different meaning now.

Very common on colour sets of 1980s vintage, not used on ant monochrome set I have seen.

I thought for a moment you were going to relate an anecdote about "Line Chord" on an imported 110v valve radios. If you've never come across any, just be thankful.

As I endlessly tell my wife at breakfast time, you shouldn't operate electrical stuff with bare feet.

You mean the resistive mains cable! I think the offending radio had one of those, not sure.

Whilst in the UK we have polarised sockets, most other places don't, so half the sets would be chassis on live, other half on neutral. The mains flex was often not polarised in any case.

Very common for early radios and TVs to have 2 pin plugs. Before working on them you touched the chassis with 1 finger to feel if it was live. Some used capacitive droppers, 80mA per uF was the rule of thumb for these.