The Electrical Contractor Network

ECN Electrical Forum
Discussion Forums for Electricians, Inspectors and Related Professionals

Books, Tools and Test Equipment for Electrical and Construction Trades

Register Now!

Register Now!

We want your input!

Featured:
   

2017 NEC and Related
2017 NEC
Now Available!

   
Recent Posts
Industrail Control Panel bonding per 409.108
by HotLine1
52 minutes 53 seconds ago
Calling all Non-US members!! (Non-US only)
by aussie240
12/07/16 02:39 AM
Photo Upload Tutorial
by DanK
12/06/16 11:35 PM
Sprinklered equipment 26-008
by bigpapa
12/02/16 04:24 PM
On Delay Relay with Auto Reset
by Potseal
12/01/16 09:59 AM
New in the Gallery:
12.5A through 0.75mm˛ flex (just out of curiosity)
Shout Box

Top Posters (30 Days)
gfretwell 13
HotLine1 10
sparkyinak 8
Texas_Ranger 8
Potseal 6
Who's Online
0 registered (), 215 Guests and 4 Spiders online.
Key: Admin, Global Mod, Mod
Topic Options
Rate This Topic
#5366 - 11/17/01 02:45 PM two phases
Mike Shn Offline
Member

Registered: 06/13/01
Posts: 26
Loc: New York
Hello
I'm helper in electric company. We use 2 phases for boiler and blower but we don't use neutral for it. Why is that? How that works? For outlet we need phase and NEUTRAL.

Thanks

Top
Work Gear for Electricians and the Trades

Work Gear for Electricians and the Trades
Work Gear for Electricians and the Trades
Arc Flash Clothing, Gloves, KneePads, Tool Belts, Pouches, Tool Carriers, etc. etc....

#5367 - 11/17/01 02:54 PM Re: two phases
sparky Offline
Member

Registered: 10/18/00
Posts: 5545
Hi Mike,
Would I be correct to assume your Q eludes to how the 'juice' returns. We had quite a thread going on this a while back, some very indepth posts by Scott T, and others in the 'theory' section i believe. Bill, has this passed into the great cybervoid???

Top
#5368 - 11/17/01 05:38 PM Re: two phases
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Hello Mike,

Well, explaining 3-phase power in a concise way is quite a task.

Basically, you have three "hot" wires supplying power. Are you familiar with the sinewave pattern of AC? Each hot wire is 120 degrees out of phase with the others, which in simple terms means that the peaks and nulls of the sinewaves on each phase don't coincide. That means that as well as there being voltage between any phase and neutral, there is also a voltage between phases. Thus you can obtain power by connecting either phase-to-neutral or phase-to-phase.

You can always work out the relationship between the voltages by multiplying or dividing by the square root of 3.
So a common 3-phase system specified as 120/208 volts will have 120V from any phase to neutral, but if you measure between any two phases you will get 208V. So a heater, blower motor, or whatever connected between two phases must be designed for the higher voltage.

The same relationship holds true for other 3-phase systems, such as your 277/480V system in America or the 240/415V we use here in England.

Perhaps a little easier to understand is the residential 3-wire system which has a neutral and two "hot" lines.

Technically, this is single-phase, but the lines are 180 degrees out of phase with each other, so when one is at its positive peak the other is at its negative peak. Thus you can get 120V from either line to neutral for normal lights & outlets, but 240V by connecting between the two hot lines. Hence the 120/240V specification for residential services.

That's all pretty simplified, but I hope it helps.

[This message has been edited by pauluk (edited 11-17-2001).]

Top
#5369 - 11/18/01 08:11 AM Re: two phases
Bill Addiss Offline
Member

Registered: 10/07/00
Posts: 4196
Loc: NY, USA
Sparky,

Everything should still be there. When you go to that Forum check that the dropdown menu (Top Right) says "Show all Topics" rather than "last 100 days" or whatever.

If not, you can always do a search.

Personally, I think that a picture of a center-tapped coil showing 120v to center (Neutral) on each side and 240v between the 2 "ends" would be easier to get the point across.


Bill

Top
#5370 - 11/18/01 01:04 PM Re: two phases
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Bill:

For newcomers I've also found it helpful to start by explaining a 3-wire DC system, as this seems to be more easily grasped by many people. Once that concept is understood, it's then easier to explain a 3-W AC setup.

Top



ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals