3phase electric query

[Karl]

If I have a 5 pin 440v supply (ie 3 live, 1 neutral, 1 earth), can I use it to supply a 230v maching using just one of the lives, the neutral and the earth?

Or am I barking up the wrong tree??

Cheers

Karl

 

[Sawdust Sam]

Yes you can

 

[mbartlett99]

In short yes; that is how the electricity board do it and how I'm about to hotwire a temp supply for the welders coming to my boat this afternoon. If this is a permanent installation you really, really should install a properly sized 240v breaker/RCCB. If its a temp lash up use common sense. It doesn't matter which phase you use.

 

[NazNomad]

As you say, one phase, neutral and earth would give you a 240v supply.

 

[Karl]

Thought so. Cheers guys.

 

[CHJ]

Just be aware that if you do this with more than one piece of equipment you should avoid them being on different phases if they are in close proximity to each other.
It's seems the obvious thing to do to balance the load but it means under earth or neutral fault conditions two adjacent pieces of equipment could have 440 volt between them even if it's only via suppressor capacitors.

We had on incident some years ago when neighbours had an accident because they had run an extension lead from another neighbours property for extra supplies into their garden for a barbeque party. A grill and lights were on different phases and earthing/neutrals were at different potentials.

 

[deema]

If it's wired correctly you cannot have an earth loop or neutral loop to create different potentials. Earth and neutral must always be at the same potential.

It's a long number of years ago I did the IEEE regs, but I was taught that you always balance the load, and for two pieces of equipment to have a 415, potential four faults must occur! Both pieces must develop a live fault, both pieces must have had a failure of the detection / earthing for it to remain at this state. Therefore not something I believe that needs to be considered when deciding whether or not to balance the loads.

 

[MikeK]

If it's wired correctly you cannot have an earth loop or neutral loop to create different potentials. Earth and neutral must always be at the same potential.

This is easy to say, but difficult to achieve if not done correctly (or not possible at all). Three-phase loads, if working properly, should have no current on the neutral conductor, if the conductor is even used. All of the 3-phase motors in my shop equipment are Delta wound and do not use the neutral conductor. However, taking a three-phase 400V distribution, and making three single-phase 230V circuits will require using the neutral conductor and will require the neutral conductor to carry current. The resistance of the wire will create a voltage drop on the neutral conductor.

One of the rooms in my basement was built and wired for a sauna. The builder installed a 5-wire cable, but the original home owner never started the sauna installation. Since this was the only utility circuit in that room, I am using one phase for the low-power equipment. The total load with all equipment in operation is 5.6A, and this current is also on the neutral conductor, as verified with my clamp-on ammeter.

 

[CHJ]

If it's wired correctly you cannot have an earth loop or neutral loop to create different potentials. Earth and neutral must always be at the same potential.

.

Most DIY equipment will be on flex leads, if the earth fails for whatever reason there could be suppressor capacitors between the frame and the live, it does not need a live wire short to cause a current path.

I've had an instance at Pershore Airfield where a whole Aircraft became live in relation to another Ground Power transformer parked alongside powering test gear, it was because the two 3phase supplies on each side of the hangar had different earthing busses and they were not common after many years of corrosion etc. on earth spikes and structure. Fortunately the operative that caught the problem only had a mild tingling sensation.

 

[CHJ]

If it's wired correctly you cannot have an earth loop or neutral loop to create different potentials. Earth and neutral must always be at the same potential.
..

You don't live in our village, every household has its own earthing arrangements, the supply does not provide one tied to supply transformer neutral, some properties do not have RCD's only fuses and earth leakage trips earthed by a 7x. 029 cable to local *spike.
I can't safely fit a modern Fire resistant Metal clad Distribution unit or Metal Clad RCD in the supply chain because there is no guarantied earth loop back to the local transformer so nothing to guarantee the casings won't become live under short conditions.
Despite my property being the only one in the village to have underground shielded feed since it was built in the 60's the incoming supply provides no earth path. (it terminates at the top of distribution Pole with no Earth only a Neutral.)

Some years ago a house almost opposite in our lane had an intermittent boiler fault, if it rained hard in the winter it was not unknown for it to trip their 30ma earth leakage, the local distributor in their wisdom replace the Earth trip with an 80ma unit, it was only after other folks nearby started having their trips go for no apparent reason was it pinned down to the original property.
No one could explain exactly what path or how reverse current feeds were taking place (local water saturation in thin soil on top of rock, suppressor capacitors ?) but sorting the boiler out removed the problem.


* fat lot of use that is when you connect an immersion heater or a boiler/pump system up to house mains earth ring when it's in parallel with the local water supplies.

 

[Karl]

Most of my stuff is 440v. I moved my thicknesser (230v), and whilst there is a 16a supply for it, it would mean moving cabling etc. In its new position there is a 5pin 440v supply about a metre away, hence the question.

Cheers

Karl

 

[n0legs]

Karl if the move is permanent/semi permanent and the existing 3ph is a dedicated radial. You may be better changing the outlet to a 1ph and ditching the two extra phases at the distribution board. Correctly protected by the right size single phase breaker.
Just an idea mate.

 

[RogerS]

....Earth and neutral must always be at the same potential.

.....

In theory, yes. In practice, usually no. Just try connecting earth to neutral on a ring main and see the RCD trip.