are three phase machines any safer than single phase?

[misterroy]

at a frieinds work the single phase machines have to go because of Health and Safety rules. Are 3 Phase Machines safer than Single? There is only single phase in the shed he works in. Thanks

[alan_m]

Because they are single phase or possibly because they failed a test, the safety guard is missing etc. etc.

[misterroy]

reason given is only "single phase"

[TimW]

They are often the same machine sold with either single or three phase motors. Single phase always smallish of course, there's a limit to how much power you can get out of the domestic supply.

TW

[Tim Lamb]

Maybe H+S think they should have DC injection braking?

[Fredxxx]

My limited experience of a comparison, is that for the same output power, 3-phase are smaller?

[Nightjar]

I would have thought that if anything, working at higher voltage, three phase machines should be considered the more dangerous. However, you do get some odd things wrongly claimed in the name of health and safety.

[Cursitor Doom]

Yes, physically smaller motors using thinner gauge windings.

[Fredxxx]

That was my thought as indeed not so long ago there were rules on how close single phase outlets could be which were supplied from different phases.

I don't understand the argument and can only believe there must be another reason, or the friend has misunderstood the claim.

[Davey]

Who gave this as a reason? They surely have to be able to explain the reasoning.

[TimW]

Yes, I meant smallish capacity machines, not the physical size of the motor. TW

[bert]

That was around in the 60s before elfin was born. ISTR it had to be greater than arms apart length

[Fredxxx]

It was in the 14th edition, superseded by 15th in 1981.

[John Rumm]

They may have better speed control, reversing and braking... but I can't see a strong argument.

[damduck-egg]

Hasn't the rule been relaxed over the years? I've seen commercial kitchens where adjacent outlets have small stickers by them warning that they were on different phases, quick google ------------ Just like this one.

G.Harman

[harry]

That is total drivel. Three phase motors are generally smaller than the equivalent single phase and are self starting hence more reliable. Also easier to reverse. Motors larger than a a couple of Kw are usually three phase for technical reasons.

There is no difference in the safety.

[charles]

Who ever inspected these machines had probably only ever seen 3 phase ones in the past. therefore these were unknown - therefore unsafe. An appeal should be launched.

[Brian Gaff]

I don't see any issues with single phase. The main issue is that you need to load all phases of the supply equally to keep the supply happy and good. If you have a lot of machines then 3 phase makes sense especially if they are powerful when they have to start up the current is of course greater. I've yet to see how safety comes into it. Brian

[Brian Gaff]

Yeah, but they load one phase of the supply which is not good, not because of safety. Brian

[Nightjar]

I suspect an over-zealous interpretation of the rules. I once had a young factory inspector tell me that a 2 ton three phase lathe should have a PAT sticker on the basis that it was connected through a 3P+N plug and socket and was, therefore, a portable appliance.