3 phase dimmers on 1 phase service??

[mstaylor]

Tim, your explanation left out some qualifiers. I understand what you are doing but without double cam locations on either the dimmers or distro, what you are saying doesn't make sense. You have to jump the third leg off one of the others and that is what the second row of cams are for, in this case. Also, I don't see how it will balance the load any. No matter the order, you will always be pulling two legs from one other. That means you have to stay under that leg's limit with the two combined, plus the nuetral needs to be oversized.
I'm not saying you are wrong, just it may be unclear to someone with less experience than yourself.

 

[JD]

Easiest way to tell Single Phase from two legs of Three Phase is to look at the hot-to-hot voltage:

Single Phase ~ 240 volts

Not Single Phase ~ 208 volts

 

[TimMiller]

Easiest way to tell Single Phase from two legs of Three Phase is to look at the hot-to-hot voltage:

Single Phase ~ 240 volts

Not Single Phase ~ 208 volts

Definitely not always true. When you are using 3 phase 120/208 wye it is but there are buildings that have 3 phase delta. In delta you will have 120 on two legs and measure 240 between them but you will have a single hot or "wild" leg of 208. Never tap directly onto this leg unless the equipment is specifically designed for it and it IS NOT COMPATIBLE WITH MOVERS THAT STATE 208V OPERATION. Always meter all three legs of 3 phase power and between all 3 so you know exactly what you are working with.

 

[David Ashton]

The joys of US power systems

 

[STEVETERRY]

The joys of US power systems

Err....how about we move on to the joys of grounding systems in the rest of the world?

http://en.wikipedia.org/wiki/Earthing_system

After we get done with that, US power systems look pretty simple!


ST

 

[Chris15]

Err....how about we move on to the joys of grounding systems in the rest of the world?

Earthing system - Wikipedia, the free encyclopedia

ST, I'm curious which particular bits of international Earthing practice you might be referring to...

 

[JD]

Definitely not always true. When you are using 3 phase 120/208 wye it is but there are buildings that have 3 phase delta. In delta you will have 120 on two legs and measure 240 between them but you will have a single hot or "wild" leg of 208. Never tap directly onto this leg unless the equipment is specifically designed for it and it IS NOT COMPATIBLE WITH MOVERS THAT STATE 208V OPERATION. Always meter all three legs of 3 phase power and between all 3 so you know exactly what you are working with.

If you are using two legs of Delta to power a lighting system then you are working off of the one center tapped leg, which is single phase. (120-0-120, 240v) We are talking in this thread about a feed that appears single phase. In this case, the rule in my post above would apply.

 

[STEVETERRY]

ST, I'm curious which particular bits of international Earthing practice you might be referring to...

Anything but TN-C-S.

ST

 

[David Ashton]

I find it really difficult to conceptualize how dimmers can work on a delta trnsformer, I would have thought that the chopped waveform would play havoc with a "closed" system like delta, can you elucidate?

 

[JD]

I find it really difficult to conceptualize how dimmers can work on a delta trnsformer, I would have thought that the chopped waveform would play havoc with a "closed" system like delta, can you elucidate?

(In the USA)

A floating Delta cannot be used for lighting. (Unless you are only splitting it up to run a bunch of movers that run on 240 volts!) Each hot-to-hot measures 240 volts, and there is no hard connection to (what would be) the neutral. There are often bleeder resistors, or other drains (like MOVs) that may give you fictitious readings with reference to neutral or ground. No load can be placed there.

More common, or at least the one we would see used for lighting, is that one of the three windings is center-tapped. So, you have three windings connected end to end, giving you A, B, and C. We will say the winding between A and B is the center tapped one. As such, we are actually running a single phase system. The "center tap" is your neutral, and you therefore have 120-0-120 from your H-N-H. The third phase leg is where the other two windings come together, and is often called the "wild leg" as it is 208 to neutral. For practical purposes, this would not be used. (Or, at least, I would not want it mixed in with my feed!)

This type of Delta was common in buildings with mixed usage. All the heavy air conditioning would be run off the Delta 240-240-240, yet you would also have some 120 circuits for offices and such. Where I am in PA it has fallen out of favor. Almost everything is Wye, where you have three legs of 120v and 208 between the hots to run AC and heavy equipment.

The heavy chopping (caused by dimmers) in this circuit will occur across the tapped winding, but you are right in that the Delta is a balanced closed loop, so any sag caused by the chop is going to partially be felt on the other two windings. I am sure someone out there has done the math, but the loading to fill the sage would be fractional on the other two legs. On the bright side, since it is basically a single phase (0 / 180) circuit, there would be no neutral over current.

Picture credit: Random graphic found on internet

 

[lightingguy1]

Hey guys,

Thanks for the over my head Information!

Now, I do have one of those, What would happen electrical questions.....

In theory, If someone had regular 150 amp home Service, and had 3 circuits from a regular panel, connected to, say an ETC Smartpack Dimmer. Each circuit rep.-ing a phase, with the three nuetrals for the Nuetral connection, What would happen when you went fire this puppy up?

 

[mstaylor]

I'm not sure what you are asking. Are you saying you are pluging into three wall outlets in an attempt to power three phases? A household panel is 99% probably to be single phase. Now try refining your question.

 

[David Ashton]

Should work fine

 

[lightingguy1]

Mstaylor,


No, thats not what I meant, but I guess thats rather the same concept.

If you installed three breakers, each rated for 40 Amps, and had the wires coming from there (Hot x 3, Neutral x 3, and ground x3 ) going over to the Dimmer Pack in this fashion:

Example,

Hot 1 = Phase 1 // Hot 2 = Phase 2 // Hot 3 = Phase 3

Neutral 1,2,3 = Neutral

Ground 1,2,3 = Ground


Make sense?

 

[mstaylor]

Sure, it would work except most residential electric is single phase, two legs of power at 110v per leg. If you look at your panel you will see four wires coming in, two hot, one neutral and a ground.
Another problem is you have to have connected breaker, a double pole breaker, to be compliant. At that point you are back to faking a leg.

 

[David Ashton]

Are the 2 hot wires the same size as the neutral?

 

[epimetheus]

Are the 2 hot wires the same size as the neutral?

Generally speaking, yes.

Sent from my Xoom using Tapatalk

 

[mstaylor]

In most cases yes.

 

[JD]

Are the 2 hot wires the same size as the neutral?

If you are faking three phase by running three hots off a single phase source, then two of those hots are coming off the same phase leg. Therefore, your neutral would have to be upgraded to the equivalent of twice the size of your hot lines if you are using a common neutral. H-H-H-2N-G

If you are running a simple single phase (H-H-N-G) then they would be the same gauge as long as your two hots are off opposing legs. ( 0/180 p)

 

[David Ashton]

and what power system produces 2 phase with 180 degree phase difference? any 2 phases off a standard supply are going to be 120.