# Question from a student



## Dyer (Mar 8, 2011)

I am not a professional yet, but I need to ask professionals. 

The job I'm asking about is not actually being built, but I have to design it. My instructor believes I should find out how to do this on my own as much as possible, so here I am on the internet.

We are designing a booster pump station and require 480V 3phase power for motors and 120/240V 1phase for everything else. I am told that our power from the utility will be 220V or 240V (would this be 1phase or 2phase?), so I have to use a phase converter and transformer.

I am struggling with a diagram of how to distribute the power and what equipment to get. If anyone could at least take a look at the diagram and the link to the safety switch I've selected, and tell me whether or not it will work, I would really appreciate it. It is just a basic sketch right now because I am trying to get the concept of what I'm doing clear in my head. I don't fully understand how to do this yet.

Here is the safety switch I found. It is to be used to distribute the incoming power out to the 2 breaker panels.
http://www.grainger.com/Grainger/SQUARE-D-Safety-Switch-2JYL1?Pid=search

I've also attached the very basic diagram of what I'm trying to do. Its in pdf form.

I'm open to any advice you can give me.


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## MDShunk (Jan 7, 2007)

Deja vu? I swear to God that we had this exact same question a few months ago. Almost word for word.


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## MDShunk (Jan 7, 2007)

In your diagram, the transfer switch must be marked "suitable for use as service equipment". I didn't look up the catalog number of the one you spec'd, so you'll have to check that on your own. You can forgo the safety switch, since your manual transfer switch will serve that purpose. You need overload and short circuit protection for the phase converter, so you'll need to feed that from a breaker of some sort; likely from your single phase panel. Sizing the equipment will be interesting, because you haven't given enough information to do that yet. Sizing the phase converter can be tricky if you want to undersize it and stagger-start the motors.


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## erics37 (May 7, 2009)

Dyer said:


> We are designing a booster pump station and require 480V 3phase power for motors and 120/240V 1phase for everything else. I am told that our power from the utility will be 220V or 240V (would this be 1phase or 2phase?), so I have to use a phase converter and transformer.


240V is available from a few different standard utility configurations. It sounds like you're not totally clear on what your service voltage and phase configuration will be. If you have a 240V single-phase service then yes, to get 480V 3-phase you would need a transformer and a phase converter. More likely, though, for a booster pump station, would be a 240V 3-phase Delta service. If that was the case, then all you would need for the 480V motors is a transformer.

A 2-phase service is very uncommon and I think you may have some terms mixed up. A 240V circuit is typically single-phase or three-phase... by "single-phase 240V" we mean two hot wires. This is sometimes a confusing concept; there are two phases present, yeah... but we just call it "single-phase."

Two-phase electric power



> I am struggling with a diagram of how to distribute the power and what equipment to get. If anyone could at least take a look at the diagram and the link to the safety switch I've selected, and tell me whether or not it will work, I would really appreciate it. It is just a basic sketch right now because I am trying to get the concept of what I'm doing clear in my head. I don't fully understand how to do this yet.
> 
> I've also attached the very basic diagram of what I'm trying to do. Its in pdf form.
> 
> I'm open to any advice you can give me.


Generally your electrical service will be required to have a service disconnecting means usually before most everything else in the electrical system. A transfer switch can be used as a service disconnect sometimes, but it has to be rated as suitable for service equipment.

Here's one way to do it if your service is in fact single-phase 240V:

Meter ---> Service Disconnecting Means ---> Transfer Switch ---> 240/120 Panel ---> All the other crap.

Your safety switch doesn't look like it's designed to serve a couple separate loads. It's basically just a really heavy-duty light switch with fuseholders. Your lighting, plugs, etc. plus your transformer and (depending on what your service voltage is) phase converter could all be fed from a properly sized distribution panel of some sort.


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## 480sparky (Sep 20, 2007)

erics37 said:


> .............. by "single-phase 240V" we mean two hot wires. This is sometimes a confusing concept; there are two phases present, yeah... but we just call it "single-phase."
> 
> Two-phase electric power
> 
> ...........


Sorry. Single phase does NOT have two phases. Single phase has just ONE phase... it's just carried by two ungrounded conductors.


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## madmaxx (Nov 12, 2010)

try looking over this for some ideas.

http://artikel-software.com/file/mechanial%20and%20electrical%20design%20of%20pumping%20stations.pdf


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## Big John (May 23, 2010)

480sparky said:


> Sorry. Single phase does NOT have two phases. Single phase has just ONE phase... it's just carried by two ungrounded conductors.


 How do you figure? If I have something that needs 480 "single phase," and I grab phases A and B to feed it, how is that one phase on two conductors?

-John


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## backstay (Feb 3, 2011)

Single phase 120/240 volt as in a res service is a center tapped transformer. If you have an A phase and B phase then you don't have single phase.


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## Big John (May 23, 2010)

backstay said:


> ...If you have an A phase and B phase then you don't have single phase....


 That's what Eric was pointing out: It is not technically single phase, but it is _called_ single phase. Maybe because it could be derived from a single transformer, even though it usually isn't? I don't know why. :confused1:

-John


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## erics37 (May 7, 2009)

480sparky said:


> Sorry. Single phase does NOT have two phases. Single phase has just ONE phase... it's just carried by two ungrounded conductors.












So if I wanted a single-phase 208V circuit from that transformer, I'd connect a wire to Phase A and I'd connect a wire to Phase B and then hook those wires up to the load. How is that not using two phases for our nominal single-phase circuit?


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## crosport (Apr 4, 2010)

erics37 said:


> So if I wanted a single-phase 208V circuit from that transformer, I'd connect a wire to Phase A and I'd connect a wire to Phase B and then hook those wires up to the load. How is that not using two phases for our nominal single-phase circuit?


Yeah but 208 is derived from a 3 phase system.240/120 isn't.You're only using 2 phases of three.A center tap transformer for 120/240 you're saying has both an A and B phase then?


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## kaboler (Dec 1, 2010)

It's a single phase, with 2 legs. You take the SINGLE phase the power company is sending you, and you run the hot in the middle and the legs on opposite sides. It's single phase, with opposite LEGS. But it's still single phase.

The challenge would be to go out in the country where there's only 1 conductor and figure out how they send more than 1 phase down it. (visible in the country)


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## ScooterMcGavin (Jan 24, 2011)

A three phase system has three legs each 120 degrees apart from each other. Inside a motor this creates a rototating magentic field which allows the motor to start rotating without out any external help, ie: a 3 phase induction motor. Even if you take two hot legs of a three phase system you don't have a rotating magentic field which can turn a motor. The two legs alternate amplitudes similar to police headlights. 

In order for a single phase motor to start it needs a phase shift to get it "kicked started". Once rotating the rotation of the motor itself will cause a great enough phase shift for the motor to continue running. The starting phase shift can be accoplished using capacitors, start windings, shaded poles etc. In the early days 2 phase service which is 90 degrees out from each other uses two seperate circuits on four wires to create this required phase shift to get motors going.

So although your single phase 208V motor is using 2 phases of a three phase system as for as the motor is concerned it is only a single phase source.

This is also the reason that if you single phase a three phase motor it won't turn and it will burn up if not protected properly.

Think of it this way: Take two dots on a paper which represent two legs of your three phase power. You can only draw one line in between them. Now if you add just one more dot you can draw a triangle which means you have three individual lines ie: three phases. Two phase power is just a pair of two dots giving you two individual lines.


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## I_get_shocked (Apr 6, 2009)

kaboler said:


> It's a single phase, with 2 legs. You take the SINGLE phase the power company is sending you, and you run the hot in the middle and the legs on opposite sides. It's single phase, with opposite LEGS. But it's still single phase.
> 
> The challenge would be to go out in the country where there's only 1 conductor and figure out how they send more than 1 phase down it. (visible in the country)


Hot in the middle, huh? Here I thought single phase was just one secondary winding consisting of two ungrounded conductors and a center tapped neutral. I guess my textbooks were wrong too.


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## Englishsparky (Nov 6, 2010)

I love reading kabolers posts, he does make me chuckle, and this is before he has got to college...


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## nitro71 (Sep 17, 2009)

Do I look like your teacher? Make him earn his damn pay! Ask him.. You're probably someone that doesn't know **** trying to have us build you're project.


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## nitro71 (Sep 17, 2009)

Englishsparky said:


> I love reading kabolers posts, he does make me chuckle, and this is before he has got to college...


Kaboler is either ******** or a troll.. I dunno..


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## screwball (May 22, 2011)

when i feel like im getting somewhere someone mashes the brakes and smashes my face back into the winshield. i love electricty


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## HARRY304E (Sep 15, 2010)

screwball said:


> when i feel like im getting somewhere someone mashes the brakes and smashes my face back into the winshield. i love electricty


:blink::laughing::laughing:


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## sureline (Jun 11, 2011)

kaboler said:


> It's a single phase, with 2 legs. You take the SINGLE phase the power company is sending you, and you run the hot in the middle and the legs on opposite sides. It's single phase, with opposite LEGS. But it's still single phase.
> 
> The challenge would be to go out in the country where there's only 1 conductor and figure out how they send more than 1 phase down it. (visible in the country)


TOO MUCH COUGH SYRUP TODAY? :no:


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