single phase vs. 3 phase

[Morgans]

Normally, Three phase is not even in the neighborhood, so it is not an option, no matter the cost. I suppose they would string new lines, if you asked them, with a big checkbook!

[Bob Davis]

Unless you already have 3 phase feeding your shop and pay for it, I think you will find that the power company will charge a premium to supply it to you. It requires more equipment on their part to supply it to you and they in return expect higher useage to justify it. Check with your utility company to see what your costs to get 3 phase would be, before you even entertain which is better for a saw.

Bob

[Gfretwell]

We use single phase 120/240 with the 240 feeding large loads. It is derived from a single phase center tapped transformer. In fact you don't see 3 phase transformers until you get to very large industrial pad mounted units. The norm here (US) is a smaller single phase transformer hanging on the pole and serving 2-3 homes. If the 3 phases are available on the pole, usually only if you live on a main power route, it is possible to add one more transformer and provide "open vee" 3p delta with a centertap. That uses the existing service and adds the extra transformer to get the 3d phase. That arrangement isn't perfect 3 phase and can get some strange phase shifts with unbalanced loads between phase ab and bc but it does work, particularly if you are just feeding motor loads that balance out fairly well. For a bit more money they will add the 3d transformer and give you true 240v delta or, more common 208v wye with 3 120v to ground legs.

[Andy Dingley]

American electrics terrify me (a lot of your working practices are seen as screaming nightmares in our standards documents). And you do it in timber framed buildings too !

But I really don't understand how you can operate a system with such a mixture of 240 / 208 and 110 / 120 V systems. It must keep the motor-swap shops in business.

Here in Europe we just have single phase and three phase. Then barring the half-a-dozen different socket outlet styles, I can move any appliance around between _any_ two European countries and have it work, straight off. Standard voltage, right across the continent. Even dodgy old places like Spain and Greece are now getting their acts together (15 years ago I installed VFDs in a Spanish factory where we barely had a working phoneline)

-- Die Gotterspammerung - Junkmail of the Gods

[Morgans]

It is not a hard concept. You only make a mistake once!

Really, the 110 plug will not fit in the 220, and also the other way around. If you don't understand it, don't play with it. A few do get it wrong, but not many.

It is nice to run 220 a greater distance, with lighter wires, and less voltage loss. You can't claim that as a disadvantage for us.

[Gfretwell]

It is what happens when you invent something and never abandon any idea each inventor came up with. You folks were helped a lot by a war that destroyed enough of your infrastructure that you had to build it all back at one time, with uniform standards. We still have major utilities that date back to Thomas Edison. I have always said, the best thing we could have done was bomb all of our infrastructure to the ground in 1945 and build new stuff so we would be on equal footing with the rest of the world. In the long run we would have saved money.

Most commercial grade motors can be tapped for any of those voltages by swapping a couple wires in the bell.

[Bay Area Dave]

I was about to say that. :)

dave

Scott Lurndal wrote:

industrial

[Greg O]

handles tied together then you gave 220v single phase. If there

doubt you have 3-phase power.

Might not help. Some main breakers are a one molded-one piece affair. Not easy to tell the difference by just looking at it. On the other hand there should be some printing on the breaker that will tell the difference. Greg

[Lazarus Long]

What? This isn't common? It's that way on all the houses I can see around here. Nobody's place is going up in flames, at least not because of anything the power companies doing.

How's it done in Europe?

[Blair]

[Silvan]

Don't give Al Qaeda any ideas...

[admin]

The easy way is to _count_the_wires_ tied to the master breaker. this works *regardless* of whether it's a "molded one-piece affair", or not.

[Andy Dingley]

We do bind our earths (grounds) to our neutrals, but we only do it at our substations, not at each premises (actually there are earthing systems where this is done, but it's not the usual way). So it's accepted that neutral may well be at some considerable potential w.r. to earth (depending on soil conditions) and thus should be insulated.

We generally regard electricity supply as a "3 wire" deal, where the electricity company feed offers live, neutral and earth as a package, and they're all treated separately inside the premises.

-- Die Gotterspammerung - Junkmail of the Gods

[Jim Wilson]

...

...

You missed out.

You could have used one of the three-phase motors as an "idler motor" to generate the third phase. Then, by adding capacitance to balance the inter-phase voltages and power factor for your typical loads, you could have used this "rotary converter" to power your three-phase equipment at full capacity.

Jim

[Jim Wilson]

Careful! Let's not get neutral and ground wires confused.

Jim

[Gfretwell]

In the US, on the utility side, neutral is ground. They don't have to conform to NEC rules. They are regulated by the NESC

[Larry Jaques]

On Sat, 25 Oct 2003 12:06:26 +0100, Andy Dingley brought forth from the murky depths:

Crikey, it sounds like yet another Lucas scheme to badly ground the world. I'll bet you can see 50v floating grounds in that system.

So measuring each wire to earth, you get 220v on the live and zero on the neutral? Here, we measure 120v from each of the lives to ground, and 240v across them.

Here, we have two lives and a ground. Neutrals appear in the house as feedbacks to ground. The two lives are carried through the house singularly as 120v lives and the neutrals run back to the service panel (you might call that the mains box or something similar) and are tied to the same bar as ground. Grounding rods are at the telephone poles (old style) and at each house (newer).

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[Andy Dingley]

We have a similar system to that for on-site work.

50V is "safe". It must be safe, because that's what the telephone system runs on, which is owned by the post office, so it would cost The Man a bunch of money to insulate. So 50V is regarded as the borderline between "compleely safe" and "instantly lethal".

On-site, we use 240V -> 110V isolation transformers, centre-tapped and earthed. So there's never any more than 55V earth difference on either leg, thus the tool is safe for on-site work.

-- Die Gotterspammerung - Junkmail of the Gods

[Kevin Craig]

That system makes sense. In household mains, is it a two-wire system, with the normal potential 240V to earth (ground)?

Do you have a safety (fault) ground (earth)?

Kevin

[Larry Jaques]

On Sun, 26 Oct 2003 01:40:10 +0100, Andy Dingley brought forth from the murky depths:

Sure, if you like being nibbled by the 'lectricity.

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