Ungrounded Conductor

This was posted on Mike Holt’s news letter;

210.4 Multiwire Branch Circuits.
(B) Disconnecting Means. Each multiwire branch circuit must have a means to simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates.


Can someone explain to me why this is called ungrounded conductors when the grounds and neutrals are hooked up?

Confused Confusious. ;):slight_smile:

That is two 120 V circuits pictured Marcel. Two Hots that are ungrounded with a shared Neutral(grounded conductor).

As Michael mentioned the MWBC contains two ungrounded and one grounded conductor (neutral) which is a shared between the two ungrounded conductors. A MWBC can be either 2 or 3 ungrounded with one grounded conductor. The 3 ungrounded/1 grounded MWBC would be from a 3Ø system. It’s ungrounded because it’s not intentionally connected to ground and has a voltage potential to ground.

The ungrounded conductor is the “hot” conductor, which is “waiting” for a return path or ground to complete the circuit.

Thanks Robert;

I am familiar with the schematics of this using a 12/3 with ground. Seen it in the field and wired some of my own like this.

I am confused with the terminology. They are 2 20 amp circuits, I understand that.
The first one is grounded, correct?

The second one is sharing the neutral, but is ungrounded?
Why? Are we talking about the bare ground or the neutral ground?

Sorry for all the questions. I am just trying to understand this ungrounded term. :slight_smile:

We were posting at the same time. See post 4.

Marcel, The neutral is the grounded conductor and both outlets use the same neutral circuit.

Thanks Mike and Jeff.

So the second outlet, since it is using the shared neutral, that hot leg is deemed ungrounded? This correct Jeff.?

The red and the black are ungrounded.

Yes. A standard 120 volt circuit will consist of one ungrounded conductor (hot), one grounded conductor (neutral) and one equipment grounding conductor (ground). A MWBC will contain one additional ungrounded conductor (hot).

A standard 240 volt circuit will contain two ungrounded conductors (hots) and an equipment grounding conductor (ground). Depending on the type of circuit and the code in effect, the 240V circuit may also contain one grounded conductor (neutral).

So is a T-bar required on double pole breakers?

Just kidding of course ;-)!

Yes it is. Not kidding. :wink:

Thanks Mike and Jeff, got it.
Well after my Carpenter friend Jim McKee called to explain in a Carpenters way. :mrgreen:

Ungrounded was thowing me off in the understanding, because I was thinking of the bare ground and neutral.

Thanks guys. :slight_smile:

This might help.

Think of the bare wire as “Earth” the way they do in Europe.

Yep, and never crossed my mind that a hot wire was an ungrounded conductor. I always looked at it a a hot wire period.
Glad I was a builder and not an electrician. :):wink:

Side question…In this configuration, wouldn’t the neutral/grounded conductor get overloaded serving as the return circuit for both 120 circuits instead of the common 220 configuration?

Boy, I am glad I got Mike Holt and a bunch of friends on this network so I can help someone else. :mrgreen:

*Caution: If the ungrounded conductors of a multiwire circuit aren’t terminated to different phases or lines, the currents on the neutral conductor won’t cancel, but will add, which can cause an overload on the neutral conductor. *


I also found this one on his site:

Also check out EC&M - tons of great information on electrical.

mwbc schematic.jpg

What I thought…I figured with it in mike’s illustration I was wrong somehow.

Electrician around here also refer to them as “Edison” circuits.