Single phase/Three phase?

[DirtyLunka]

If I'm working in a building with three phase and come across a machine that needs a 240v single phase plug to power it, can I come out of a 3phase panel with a 2pole breaker? And if so how is 2 poles out of this panel 240, but three poles 208. Hope fully someone can help.

 

[Dennis Alwon]

If I'm working in a building with three phase and come across a machine that needs a 240v single phase plug to power it, can I come out of a 3phase panel with a 2pole breaker? And if so how is 2 poles out of this panel 240, but three poles 208. Hope fully someone can help.

I believe you will get 208 out of the 3 phase panel on 2 legs. If you do indeed need 240 volts then you will need a tranformer to step up from 208 to 240

 

[steelersman]

you should be able to operate the 240 volt appliance or whatever it is with the 208. Shouldn't be a problem at all.

 

[steelersman]

If I'm working in a building with three phase and come across a machine that needs a 240v single phase plug to power it, can I come out of a 3phase panel with a 2pole breaker? And if so how is 2 poles out of this panel 240, but three poles 208.

coming out of this 3 phase panel with a 2 pole breaker will give your machine 208volts. And this should be fine to power your 240Volt rated machine. Hope this helps.

 

[Dennis Alwon]

coming out of this 3 phase panel with a 2 pole breaker will give your machine 208volts. And this should be fine to power your 240Volt rated machine. Hope this helps.

That is not necessarily true. It depends on the equipment being used.

 

[DirtyLunka]

Without getting to confusing on this subject, how do you get 208 between two leads on your wiggy's, but 208 calls for three legs? Sorry to be a pain on this but I am use to single phase where 1 leg is 120 and add another and you have 240.

 

[steelersman]

Without getting to confusing on this subject, how do you get 208 between two leads on your wiggy's, but 208 calls for three legs?

you get 208 between any 2 of the 3 legs and 120 between any 1 leg and ground. Some loads require 3 phase or 3 legs such as motors but still they are 208 but only between any of the 2 legs while some loads only require 2 legs.

 

[charlie b]

. . . I am use to single phase where 1 leg is 120 and add another and you have 240.

One thing you need to learn, and it is not self-evident, is that whenever you deal with three phase systems, the number "square root of three" is going to come into the equation, one way or another. For example, take 120 volts, and multiply it by the square root of three (about 1.732), and tell me what you get.

I don't have time to explain right now. But in simple terms, when voltage is reaching its peak on Phase A of a three phase system, neither Phase B nor Phase C will be reaching its peak. They are not timed together, so you can't simply add 120 to 120 and get 240. By contrast, on a single phase 120/240 volt system, when the voltage on Phase A is reaching the top (positive peak) of its value, the voltage on Phase B is reaching the bottom (negative peak) of its value. The are timed together, although exactly opposite. That is why you can add 120 to 120 and get 240.

There is much more to learn on this topic. Stay tuned.

 

[DirtyLunka]

Thanks for the responses guys this site has been most helpful.

 

[hardworkingstiff]

If you do a search for three-phase and single-phase, you will have lots of reading material and if you finish the threads, quite a bit of knowledge.

 

[wasasparky]

...They are timed together, although exactly opposite. That is why you can add 120 to 120 and get 240...

You mean like two phases???:-?:grin:

 

[charlie b]

You mean like two phases???

No. I mean single phase. There exists a "two phase system," but it is weird, and is seldom used, and I have never seen it myself.

 

[76nemo]

Here we go again,........

 

[wasasparky]

No. I mean single phase. There exists a "two phase system," but it is weird, and is seldom used, and I have never seen it myself.

Just havin fun, nemo knew where I was going...:grin::grin:

 

[quogueelectric]

I will not throw gasoline on that fire however sometimes 208 doesnt cut it for 240 volt equipment and you will need a single phase step up xformer to bring the correct voltage to the equipment. 208 to 240 single phase step up. SOMETIMES it will work but this is the wrong way to look at every installation. 240 works great for 240 and 208 works great for 208 anything other than this is hack especially if electronics and or motors are involved. Electric heater elements arent affected much other than the lower amperage must be adjusted for.

 

[frenchelectrican]

quogueelectric.,

Pretty much sum it up However.,, I always check the manufacter nameplate for info if have dual voltage rating like 208-240 V then it will be no grand deal with it.

Few sistuation yeah get B-B to get it right voltage as you need to run properly.

Merci,Marc

 

[MadeInUSA2007]

jigga what? "Does not compute" made easy

jigga what? "Does not compute" made easy

Why do you get 208 between two legs? It's caused by the transformer. A different transformer (maybe it's PG&E's transformer) could get you 240 volts.

Likewise a 277/480 volt system can give you 277 volts per leg, but 480 phase to phase.

Yes, a 2-pole breaker is just fine in a 3-phase panel, or use a 3-pole breaker but choose only two of the legs.

FYI some 3-phase panels have a "stinger" or wild leg, giving 208 volts on one leg only. If you hook up a single plug circuit, don't use that leg. But if you need a two pole breaker, any combination of legs can be used, and the device will still work. except for the exceptions.
hope I was helpful. ta ta for now. and that's the way the cookie crumbles.