Commercial appliance through home socket

[Taylortwocities]

Aah, so effectively a fuse in the neutral then..I'm just being impish.

 

[JohnW2]

Aah, so effectively a fuse in the neutral then..I'm just being impish.

I suppose so. However, as I said, it doesn't seem conceptually all that different from a 3-phase situation - if protected by fuses (rather than some sort of breaker, which would have 3 linked poles), one (or two) of those fuses can operate, still leaving a potential relative to earth on two (or one) of the conductors ... which has much the same implications as a neutral fuse operating in a 2-wire situation, doesn't it?

Kind Regards, John

 

[westie101]

Think of a UK 110V site transformer with a centre tapped earth. Though it has a "neutral" it is not earthed as a 230V UK supply would be.

Another way of looking at it is as 2 phases at 180deg

 

[JohnW2]

Another way of looking at it is as 2 phases at 180deg

Quite so - but call it a '2-phase supply' for that reason and you'll probably end up (yet again!) with a few pages of argument - even though that's what BS7671 calls it!

Kind Regards, John

 

[ericmark]

Just as when we use USA single phase 110 volt stuff on our split phase 110 we need to add a fuse to the neutral connection and make it a second phase so using USA split phase we need to remove one fuse and make it into a neutral.

But the problem is the 60Hz it may run on 50Hz but it may not and motors could overheat.

 

[bernardgreen]

It quite simple if one accepts that a wire can be Neutral at one end and Phase at the other end,

Or more precisely

Neutral ( Appliance UK 230 volt ) can be connected to a Phase ( Supply USA 110 volt )

Live ( Appliance UK 230 volt ) can be connected to another Phase ( Supply USA 110 volt )

 

[ericmark]

We consider neutral as a live and it is unlikely that the insulation designed for 110 volt would not be enough for 230 volt. We are not allowed to fuse a neutral or switch a neutral without also cutting the line supply but it is unlikely this would be a problem.

The main problem with this Canadian machine is the frequency. An inverter to convert from 50 to 60 Hz for this power would be expensive.

 

[ban-all-sheds]

the guy I bought it off said it would be just plug and play with a converter.

Do you have any proof of that?

Was this a private purchase or a business one?

 

[JohnW2]

It quite simple if one accepts that a wire can be Neutral at one end and Phase at the other end, Or more precisely
Neutral ( Appliance UK 230 volt ) can be connected to a Phase ( Supply USA 110 volt )
Live ( Appliance UK 230 volt ) can be connected to another Phase ( Supply USA 110 volt )

In what sense is one of the connections to the Appliance a "Neutral"? I thought that (not unreasonably, IMO) the definition of neutral required that it be connected to earth somewhere - usually (always?) at the source (and sometimes also other places, as in PME).

The danger of thinking of things as you have suggested is that, as has been discuss, it would/could result in a switch/isolator not interupting a conductor which was at a substantial potential above earth.

Kind Regards, John

 

[bernardgreen]

In what sense is one of the connections to the Appliance a "Neutral"?

In the sense that the manufacturer labels it as Neutral because in the UK almost every appliance requires a Neutral and a Phase ( Live ) in order to have a 230 volt supply.

I thought that (not unreasonably, IMO) the definition of neutral required that it be connected to earth somewhere - usually (always?) at the source (and sometimes also other places, as in PME).

My understanding is that Neutral is the mid point of a multi-phase distribution system where if a multi-phase load(s) is evenly balanced across the phases then no current flows along the Neutral.

There is no requirement for the Neutral to be earth for the system to work as a supply system. The Neutral is connected to earth to enable safety devices to operate when there is a fault.

If the network Neutral was not connected to ground then the risk of electric shock would be reduced as there would be no return path. There is some "resemblance" to the opinion that bonding sinks and baths to earth ground increases the risk of electric shock.

 

[JohnW2]

I thought that (not unreasonably, IMO) the definition of neutral required that it be connected to earth somewhere - usually (always?) at the source (and sometimes also other places, as in PME).

My understanding is that Neutral is the mid point of a multi-phase distribution system where if a multi-phase load(s) is evenly balanced across the phases then no current flows along the Neutral. There is no requirement for the Neutral to be earth for the system to work as a supply system.

We need a referee, then - maybe my 'understanding' is incorrect. I agree that the neutral of a multi-phase supply will be as you describe, but I thought it had to be earthed. Are you suggesting that a true single-phase supply cannot have a 'neutral', even if one side of the supply is earthed at source? BS7671 certainly acknowledges the concept of a single-phase 2-wire distribution system with conductors labelled as L & N - if there was not a requirement for the N to be earthed, how would one distinguish between L&N?

Any referees out there?.

Kind Regards, John

 

[JohnW2]

There is no requirement for the Neutral to be earth for the system to work as a supply system. The Neutral is connected to earth to enable safety devices to operate when there is a fault. ... If the network Neutral was not connected to ground then the risk of electric shock would be reduced as there would be no return path.

I should perhaps also have commented on this. It seems to be a bit of a vicious circle - as you imply above, if the supply were not earth-referenced at all (i.e. totally floating wrt earth), there would not really be any need for any safety devices to operate in response to a single fault (between one phase and exposed-conductive parts). The argument for earthing could be in relation to the (very low) risk of two independent faults (both phases having faults to different, simultaneously touchable, exposed parts), particularly given that, in the absence of protective devices, the first fault would probably go unnoticed, and hence would persist. It may also be impractical to ensure that a supply is, and will always remain, floating relative to earth.

Kind Regards, John

 

[ban-all-sheds]

Hence the problems and restrictions around IT systems.

 

[JohnW2]

Hence the problems and restrictions around IT systems.

Indeed, although the hypothetical system to which I was implicitly comparing would, I suppose, be "II".

Do you have a view as to whether a "neutral" has to be earthed (somewhere) in order to be a neutral?

Kind Regards, John

 

[ban-all-sheds]

Given it's name I would say yes.

The appliance (probably¹) doesn't care though - as long as it gets 230V between its two poles it will work.

In theory, subject to arcing inside the machine to earthed components, and to any suppression circuitry, and operator safety, it would work if the terminals were connected to 2 lines at 1000V & 1230V wrt earth.


¹ I wouldn't like to predict what would happen to or with any filters with a path to earth which is expected to be at approximately 0V.