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Electrical Wiring FAQ (Part 1 of 2)
Section - A word on voltages: 110/115/117/120/125/220/240

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	One thing where things might get a bit confusing is the
	different numbers people bandy about for the voltage of
	a circuit.  One person might talk about 110V, another 117V
	or another 120V.  These are all, in fact, exactly the same
	thing...  In North America the utility companies are required
	to supply a split-phase 240 volt (+-5%) feed to your house.
	This works out as two 120V +- 5% legs.  Additionally, since there
	are resistive voltage drops in the house wiring, it's not
	unreasonable to find 120V has dropped to 110V or 240V has dropped
	to 220V by the time the power reaches a wall outlet.  Especially
	at the end of an extension cord or long circuit run.  For a number
	of reasons, some historical, some simple personal orneryness,
	different people choose to call them by slightly different numbers.
	This FAQ has chosen to be consistent with calling them "110V" and
	"220V", except when actually saying what the measured voltage will
	be.  Confusing?  A bit.  Just ignore it.

	One thing that might make this a little more understandable
	is that the nameplates on equipment ofen show the lower (ie: 110V
	instead of 120V) value.  What this implies is that the device
	is designed to operate properly when the voltage drops that
	low.

	208V is *not* the same as 240V.  208V is the voltage between
	phases of a 3-phase "Y" circuit that is 120V from neutral to any
	hot.   480V is the voltage between phases of a 3-phase "Y"
	circuit that's 277V from hot to neutral.

	In keeping with 110V versus 120V strangeness, motors intended
	to run on 480V three phase are often labelled as 440V...

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Top Document: Electrical Wiring FAQ (Part 1 of 2)
Previous Document: My house doesn't meet some of these rules and regulations. Do I have to upgrade?
Next Document: What does an electrical service look like?

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Send corrections/additions to the FAQ Maintainer:
clewis@ferret.ocunix.on.ca (Chris Lewis)





Last Update March 27 2014 @ 02:11 PM