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Message |
ball
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Electrical Wiring
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Oct 4 01:52 UTC 2006 |
Are residential electrical outlets in the U.S. wired as a
ring, or as a straight line from a supply to an end-point?
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| 19 responses total. |
keesan
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response 1 of 19:
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Oct 4 04:06 UTC 2006 |
There are several separate circuits, separately fused or with separate circuit
breakers. I know that the wiring goes from the fuse box or breaker panel to
the first outlet, from there to the second, etc. So I think 'ring' is the
answer.
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gull
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response 2 of 19:
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Oct 4 04:42 UTC 2006 |
There are a few different configurations possible, but one common one
seems to be to daisy-chain from one outlet box to the next. (Calling
it a "ring" would be a misnomer because the last outlet doesn't need a
wire going back to the electrical panel.) That's within a circuit, of
course. Each circuit branches off from the main electrical panel,
star-style. There are rules about how many outlets you're allowed to
have on one circuit, how many wires can be spliced inside a box of a
particular size, etc.
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keesan
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response 3 of 19:
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Oct 4 15:07 UTC 2006 |
Since an electrical cord has two or three wires in it (one is a ground) the
electricity actually runs along one of the hot wires to the last outlet or
appliance in the circuit and then back along the other hot wire, which is more
of a loop than a straight line.
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rcurl
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response 4 of 19:
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Oct 4 17:03 UTC 2006 |
Actually (!), since its AC, the electricity just jiggles back and forth in
both wires.
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ball
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response 5 of 19:
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Oct 4 22:56 UTC 2006 |
Re #1: It would only qualify as a ring if there were an
additional pair of conductors from the power supply (fuse
box) to the last outlet in the chain. That is the norm in
Britain.
Re #4: I love that description :-)
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rcurl
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response 6 of 19:
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Oct 4 23:21 UTC 2006 |
They must use lighter wire in home wiring in Britain. There is no need for
completing a circle otherwise. Or perhaps they don't install as many separate
circuits? There are something like 6 separate outlet cicuits in my house,
plus additional applience outlet circuits to the kitchen and separate circuits
for the stove, dishwasher, washer and drier, furnace, and AC.
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gull
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response 7 of 19:
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Oct 5 17:58 UTC 2006 |
A ring configuration *would* reduce the problem of voltage drop at the
later outlets in the string. I had a big problem with that in my old
apartment. (In the one I'm in now, the voltage is just plain low
everywhere. And some of the outlets aren't grounded. The trials of
living in an old complex.)
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rcurl
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response 8 of 19:
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Oct 5 18:19 UTC 2006 |
The problem of voltage drop is caused by using an improper wire gauge (or
overloading the circuit). Britain uses 220 volt circuits so current demand
is halved for the same power, so they can use finer wire - but perhaps they
overdo that.
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ball
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response 9 of 19:
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Oct 5 22:24 UTC 2006 |
240V AC, 50 Hz, usual ring main is 30A and (I'm told) uses
2.5mm^2 conductors.
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gull
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response 10 of 19:
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Oct 5 23:54 UTC 2006 |
That *is* thinner than U.S. practice. In the U.S. we'd use 10 gauge
for that current level, which is 5.26 mm^2. But I suppose using a ring
structure means you're effectively splitting the load across two
conductors, allowing each individual conductor to be thinner. Very
interesting.
It's worth noting that in most U.S. homes there are two types of
circuits. Most general-purpose outlets are 120V, 15A. High-power
appliances such as electric clothes dryers, stoves, and water heaters
are powered by 240V, 30A circuits. Power is delivered to the house on
three wires -- two "hot" and one neutral. Going from either hot wire
to neutral gives 120V, going across the two hot wires gives 240V. This
is called a "3-wire split-phase" system.
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ball
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response 11 of 19:
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Oct 6 01:25 UTC 2006 |
Sounds like a centre-tapped winding on the transformer. Some
notes that I found suggest that you can use 2.5mm^2 on a
ring main where you would have to use 4mm^2 for a point-to-
point or bus arrangement. If I bought a new house (unlikely)
should I expect NEMA 14-30 sockets for things like stove and
dryer hookups?
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