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#55261 - 08/23/05 02:50 PM 240Volt Loads without neutral
Clydesdale Offline
Member
Registered: 11/25/04
Posts: 138
How come some 240V single phase loads don't require a neutral; just 2 hot legs and a ground?
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#55262 - 08/23/05 02:58 PM Re: 240Volt Loads without neutral
Sandro Offline
Member
Registered: 12/30/01
Posts: 444
Loc: Stoney Creek, ON, Canada
Load is Balanced. No neutral req.
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#55263 - 08/23/05 04:40 PM Re: 240Volt Loads without neutral
Clydesdale Offline
Member
Registered: 11/25/04
Posts: 138
So in a 240 V oven the load isn't balanced?
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#55264 - 08/23/05 05:18 PM Re: 240Volt Loads without neutral
Attic Rat Offline
Member
Registered: 12/14/03
Posts: 524
Loc: Bergen Co.,N.J. USA
... Clydesdale,it's not that the load is unbalanced in an electric oven,..but that the timer,clock and light requires 120 volts,..ergo the much needed neutral..
Russ
_________________________
.."if it ain't fixed,don't break it...call a Licensed Electrician"
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#55265 - 08/23/05 06:30 PM Re: 240Volt Loads without neutral
renosteinke Offline
Cat Servant
Member
Registered: 01/22/05
Posts: 5316
Loc: Blue Collar Country
Clyde, let me try to give a VERY simple explanation.

You have two "hot" wires. They are "hot" with AC. Measure either to ground, and you have 120 volts; together, and you have 240.

This is because the 120 originates at opposite ends of the same transformer. Since they come from the same transformer, they are exactly opposite in timing of the "60 hz."

In a manner of speaking, the first wire is at +120 at the exact same instant as the other is at -120. So they can be considered to "cancel each other out;" were there a neutral wire, it would have no current flowing on it.
Another way to look at it is that one wire is "hot" while the other is "off." In this model, you imagine each wire using the other as a neutral, in turn.
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#55266 - 08/23/05 06:32 PM Re: 240Volt Loads without neutral
gfretwell Offline


Member
Registered: 07/20/04
Posts: 9039
Loc: Estero,Fl,usa
I still wonder why the appliance folks didn't just use 240v bulbs, motors and timers in dryers and ranges.
They sell millions every year so there is plenty of volume. These parts are just used in the specific appliance anyway.
There may have been a big cutover but that is nothing compared to the change in a quarter billion dryer and range receptacles and a mixed cord standard.
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Greg Fretwell
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#55267 - 08/23/05 07:20 PM Re: 240Volt Loads without neutral
sierra electrician Offline
Member
Registered: 02/12/05
Posts: 219
Loc: North Fork, CA USA
Let me see if I understand this theory correctly. Since I don't have an oven I'll just hold the 2 hot legs together to simulate the element, Timmy are you ready?.........Will they still "cancel each other out" or will see a really huge flash, oh well here it goes.

Ah Oh, I think we need a new Timmy!
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#55268 - 08/23/05 08:39 PM Re: 240Volt Loads without neutral
Clydesdale Offline
Member
Registered: 11/25/04
Posts: 138
ok. so, the clock/timer in the 240V appliance is only using one hot leg(120V), therefore my resoning tells me that there is unbalanced current.
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#55269 - 08/25/05 10:52 AM Re: 240Volt Loads without neutral
Larry Fine Offline
Member
Registered: 02/18/05
Posts: 693
Loc: Richmond, VA
Correct - the current is unbalanced by an amp or two, which is why this type of appliance (dryer, range, etc.) now requires a neutral.

A dryer, for example, uses 240 only for the heating element, which is why they function fine on 208v with slightly less heating power.
_________________________
Larry Fine
Fine Electric Co.
fineelectricco.com
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#55270 - 08/26/05 04:33 PM Re: 240Volt Loads without neutral
foestauf Offline
Member
Registered: 08/01/05
Posts: 49
Loc: Florida
Like said they balance the load between eachother, and there will always be an amp or two differance, just the way the phase works.

Then you get into 3-phase wich has an even less amount of time between pulses. In 240 you only have 2 pulses per cycle, at 3phase you get 3 pulses, so less amount of time that a device's voltage is lowering.
Wich is why 3-phase is more efficient.

Now all new range/dryers require a nuetral, but still not on air handlers, A/C's, water heaters etc...
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