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240Volt Loads without neutral #55261
08/23/05 04:50 PM
08/23/05 04:50 PM
C
Clydesdale  Offline OP
Member
Joined: Nov 2004
Posts: 138
How come some 240V single phase loads don't require a neutral; just 2 hot legs and a ground?

Work Gear for Electricians and the Trades
Re: 240Volt Loads without neutral #55262
08/23/05 04:58 PM
08/23/05 04:58 PM
S
Sandro  Offline
Member
Joined: Dec 2001
Posts: 444
Stoney Creek, ON, Canada
Load is Balanced. No neutral req.

Re: 240Volt Loads without neutral #55263
08/23/05 06:40 PM
08/23/05 06:40 PM
C
Clydesdale  Offline OP
Member
Joined: Nov 2004
Posts: 138
So in a 240 V oven the load isn't balanced?

Re: 240Volt Loads without neutral #55264
08/23/05 07:18 PM
08/23/05 07:18 PM
Attic Rat  Offline
Member
Joined: Dec 2003
Posts: 524
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.. [Linked Image] [Linked Image]
Russ


.."if it ain't fixed,don't break it...call a Licensed Electrician"
Re: 240Volt Loads without neutral #55265
08/23/05 08:30 PM
08/23/05 08:30 PM
renosteinke  Offline
Cat Servant
Member
Joined: Jan 2005
Posts: 5,316
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.

Re: 240Volt Loads without neutral #55266
08/23/05 08:32 PM
08/23/05 08:32 PM
G
gfretwell  Offline

Member
Joined: Jul 2004
Posts: 9,166
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.


Greg Fretwell
Re: 240Volt Loads without neutral #55267
08/23/05 09:20 PM
08/23/05 09:20 PM
S
sierra electrician  Offline
Member
Joined: Feb 2005
Posts: 219
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!

Re: 240Volt Loads without neutral #55268
08/23/05 10:39 PM
08/23/05 10:39 PM
C
Clydesdale  Offline OP
Member
Joined: Nov 2004
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.

Re: 240Volt Loads without neutral #55269
08/25/05 12:52 PM
08/25/05 12:52 PM
L
Larry Fine  Offline
Member
Joined: Feb 2005
Posts: 693
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
Re: 240Volt Loads without neutral #55270
08/26/05 06:33 PM
08/26/05 06:33 PM
F
foestauf  Offline
Member
Joined: Aug 2005
Posts: 49
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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