I know this is a stupid question, but is there any reason why switches
for outlets can't have neutral wires? I'm currently building a house,
and I requested a neutral wire at all the switches. The light switches
do have neutrals, but the switched outlets don't. Most of those are in a
box with a light switch, so there is neutral in the box, but a few
aren't. Does each switch in a multiswitch box need a neutral coming in?
Any help for this newbie would be appreciated. Thanks!
ANY switch can have a neutral but most don't need them as wired (for no
As long as you are paying for the work, you can insist on them so that you
will have them available for future automation uses.
The preferred method of wiring is to bring power (hot and neutral) into the
switch box, interrupt the hot leg with a switch, then carry the power (hot
and neutral) on to the load, be it switch or outlet.
Sometimes, though, it's quicker, easier, and saves a lot of Romex to run
power to the load, then use a piece of romex to extend the hot into the
switch box. The white wire then becomes a switched hot, and is marked with
black tape or marker. This results in no neutral.
If they wired a box without a neutral even after you asked them to, it is
their responsiblity to fix it. You need to get your GC on your side in terms
of cost: the electricians almost certainly WILL try to bill you for their
I have a somewhat related question:
In my home, there is a 3-way circuit which controls a group of outlets and a
group of lights. In the process of stripping the outlets out of the
circuit, I discovered that the circuit hot comes from the breaker, but the
neutral comes from another (unswitched) circuit of outlets.
By my thinking -- the neutrals are all common at the breaker anyway, so it
shouldn't make a difference. Is there any reason for me to be concerned
Yes, I second this notion. Best to bring the hot/neutral/ground to the wall
plate and then run a four-wire (hot/neutral/switched/ground) to the ceiling
or other switched fixture. That way if at some point in the future you
install a fixture that needs it's own power you'll have it there already.
Things like ceiling fans operated by remote often their own power full time,
in addition to that controlled by a wall switch. Outside motion sensors
also. But basically it's your house, get it the way you want it. Wire is
cheap and the labor to do this is no different than any other method.
Granted, it will require having 3 conductor romex in addition to the regular
2 conductor but that's a negligble difference.
Just specify to the electrician that you want a neutral at each switch and
he can do it. I did that in my home and even if it wasn't used for anything
else, I have a neutral tail available at every switch.
Close, but one problem...
The white wire in these "switch leg" or "switch loop" circuits is the
always hot wire and the white wire is the switched hot wire. This makes
identification of a unknown white wire easier since it is always hot not
just hot when the switch is on.
This is covered in 200-7(c) of the National Electrical Code where the
"conductor with white or natural gray insulation or a marking of three
continuous whit stripes is used to supply the switch." The requirement
to remark the white wire with black came in the 1999 NEC.
Yes. There are a few cases where this is legal but it is a bad practice
even then and can pose a safety risk.
The theory about them all being equal because they are connected at the
breaker is only valid if there is no resistance in the wire or connections
and all connections are 100% reliable.
If the neutral is connected to a 2nd circuit and ANYTHING is on (including
night lights, or AV equipment that has a remote) they are putting a voltage
on the neutral for that circuit.
Depending on where your branch of the neutral is connected to the circuit,
the voltage on it will vary but will not be 0.
I can't speak for the US regs, but that's not allowed in UK regs.
Only the earth/ground wire is allowed to be cross-connected
between different circuits. Cross-connecting a neutral like this
could result in circuit which has been isolated for work to be
carried out on it actually being live due to the cross-connect.
Yes, you should be concerned, at least from my UK perspective. Here it's
normal to disconnect one circuit to work on it, leaving the rest of the
circuits live. If you disconnect one live and one neutral, your safety
depends on that neutral *not* being connected to any other live though
an appliance. So it's not permitted to mix the neutrals.
You said "the neutrals are all common anyway" and that is true normally,
but not always.
Can you try that again? You've confused me, now. :)
My way of thinking (in the US) is that an unknown white wire is going to be
assumed neutral. An unknown black wire is going to be assumed hot. If I'm
wrong, I'm wrong.. but I've always seen white with a black mark as the
switched leg, black as the always hot leg.
Went to dinner, came back, re-read, and understood. Though I do believe you
meant "black is switched." That way, there's no way to assume the white is
neutral... it's always hot. If it were switched, and off, you might think it
Got it. Thanks!
"E. Lee Dickinson" wrote in
Answer: It depends.
I believe that this is permitted in the U.S.A. as long as:
1) The two circuits are on opposite phases of a split phase service.
2) The two circuit breakers have equal limits and are mechanically tied
together so that tripping or turning off one breaker shuts off both.
Rule 1 is important because two circuits sharing a neutral on the same
phase could potentially double the current in the wire. Being on opposite
phases, the current is the difference between what the two circuits are
using (leaving out reactive loads).
Rule 2 is important because it prevents shocks during servicing.
Otherwise, with one circuit shut off, the other circuit can make the
neutral hot through any lights or appliances that are left on. I have been
shocked (*) by such a circuit that did not have tied breakers because it
was wired before this rule was made part of the NEC.
(*) I was shaken and greatly surprised but learned a valuable lesson: Use
a meter to verify prior to touching!
In the cases that I have seen, the wiring from the circuit breaker panel to
the loads used Romex with four wires in this case: Ground (bare), Neutral
(white), Line 1 (black), Line 2 (red).
Other countries may be different. Particular locations within the U.S.A.
may be different. Older wiring may be different. Mistakes can cause
While all the above is true, my experience with piped (conduit) wiring in
residential new construction is that shared neutrals are the norm for 15 and
20 amp circuits, not the exception. Each pipe leaving the service panel
will have several hot wires and at most two neutral wires, unless the
associated breakers are ground or arc faults. In these cases the neutral
wires are dedicated and usually slate/gray rather than white.