Can I use four-wire cable from the panel to create a two-circuit duplex outlet?

Question

I am planning on adding a server to one of the closets in my house. In order to do that I need to run electrical to the location of the server. For severs they recommend having 2 independent lines of power, for redundancy, that way if one breaker trips the server won't go down. The server has 2 power supplies with independent cords. I am wondering if I can do a single 240v run from my breaker box to the location of the server and then separate the 240 to 120 and into 2 outlets, also can I run it into 2 outlet with 2 plugs, and would there be any code violations?

This is what I'm thinking, except this is all a 4-wire cable instead of 4 separate wires.

Answer 1

Cannot do it. Nosirree.

Cannot use a MWBC

As you have stated it in your question, you are describing a multi-wire branch circuit (MWBC).

Singular.

That is not 2 independent circuits. It is a multi-wire branch circuit.

Further, it has a serious defect in that it is taking power from unrelated points on the panel. Code absolutely requires that MWBCs be both opposite-phased, and handle-tied for common shutoff (which in the real world means common trip most of the time). This defeats your purpose.

Even worse, if you simply put the breakers "wherever" on the panel, then over the years as you rearrange circuits in the panel, you may accidentally wind up with both MWBC legs on the same phase. That means instead of carrying only differential current, neutral would carry the sum of currents causing an overload of the neutral. Neutrals don't have breakers. On almost every panel type, handle-ties force the breakers onto opposite poles, so use of handle ties averts this danger. (Usually; looking at you GE).

So your MWBC absolutely requires either a 2-pole or handle-tied breakers. 2-poles definitely have common trip, and handle-tied breakers usually have common trip (not guaranteed but very likely from handle motion).

For the circuits to be independent, they need to each have their own neutral wires. But wait.

Cannot put 2 independent circuits on the same yoke

That receptacle there, with 2 sockets, is on what's called a "Yoke". That means a single device of any kind - switch, pilot light, GFCI, whatever, that mounts through the usual mounting screws.

So, suppose you run a second neutral. Now you're splitting the receptacle and having 2 circuits each with its own neutral, one powering each socket. You can't do that either. Or to be more precise, the circuits cannot be independent if you do.

210.7 Multiple Branch Circuits. Where two or more branch circuits supply devices or equipment on the same yoke, a means to simultaneously disconnect the ungrounded conductors supplying those devices shall be provided at the point at which the branch circuits originate.

When 2 separate circuits serve the same yoke, again they must be handle tied, and again this defeats your purpose.

There's a very good reason for the handle-tie requirement. Someone servicing the wiring will typically plug a radio into one of the sockets, and trip off breakers until the radio goes silent. Then turn everything else back on, and go to work on the wiring. Think about it. That procedure will leave one of the sockets "hot", unbeknownst to the maintainer. So again those 2 circuits must be handle-tied.

Why would anyone ever put 2 independent circuits on the same yoke, when the MWBC approach does that better? AFCI/GFCI. They don't make 2-pole AFCIs and 2-pole GFCIs are expensive. Often the only way to provision GFCI/AFCI to such a split recep is to have separate neutrals.

Socket size must exactly match breaker size if there is 1 socket

As manassehkatz noticed, you are speccing a 20A breaker that is feeding exactly one 15A socket. Nope. Breaker size and socket size must exactly match, NEC 210.21(B), so you must use a 20A socket or a 15A breaker.

"But people use 15A sockets on 20A breakers all the time!" Because there is an exception for 15A sockets when 2 or more sockets exist on a circuit, which is the usual situation.

You have no option that will allow you to split a yoke.

and maintain independent trip (in practice). Further, you wouldn't want to anyway, because anyone looking at your setup would think you made a mistake by putting both power supplies on the same yoke. (and they'd be right if you followed Code).

Your only option is to fit a 2-gang junction box so you will have 2 yokes, and run 2 independent circuits with either dual /2 cable or /2/2 cable. (can't use /4 cable since you can't re-mark blue to be neutral). At that point you'll have 2 sockets per circuit and 15A duplex receps are fine. If you really want 1 socket per circuit you can get 20A simplex receps, but their rarity means cost.

Answer 2

As described in some other answers, a Multi Wire Branch Circuit (MWBC), can do exactly what you want, with one exception.

• An MWBC lets you get 2 x 120V on 3 wires instead of 4, because the two 120V circuits share neutral.
• Assuming this duplex receptacle is the only thing on the circuit, it must be a 20A receptacle as each 120V section will only have one receptacle. There is an exception for an ordinary 120V circuit where both receptacles are on the same (single) 20A breaker. Once you split it, each receptacle (unless you have more daisy-chained) is the only receptacle on the circuit, so it has to be a 20A receptacle to match the 20A breaker. But a 20A duplex receptacle basically costs the same as a 15A duplex receptacle - just get the right item.
• While an MWBC does not need common trip, it does need handle tie for common maintenance shutoff. But the usual way to get common maintenance shutoff is a double breaker == common trip, since MWBCs are required to be on breakers next to each other. So if you really want to make sure that an overload of one does not affect the other, you need two totally separate circuits.

The exception is: What are you trying to protect against? Power supply failure/replacement or overload?

If the main concern is a passive non-breaker-trip failure of the power supply, then an MWBC will do just fine. This is also the case if you want to put in two UPSes, one in line on each power supply. With an MWBC (or any other method of providing 2 120V power sources), this will allow replacement of a UPS (e.g., battery degraded and needs replacement) while letting the other circuit continue powering the server.

On the other hand, if you are concerned about catastrophic power supply failure (blaze of glory/magic smoke), then a momentary overload often comes with the failure, resulting in a breaker trip that, on an MWBC, may trip the power going to the other side as well.

Answer 3

If you split the neutral jumper on the receptacle and hot receptacle so you feed the receptacles like you want each having a hot , neutral and pigtailed ground they are 2 separate circuits and not required to be handle tied . You can have multiple circuits as long as the hot and neutral are separate 210.4 requiring a handle tie is because of the common grounded or neutral conductor. This is more common in server rooms Where each receptacle is utilized at its limit note this requires a 20 amp receptacle on a duplex outlet because there is only 1 receptacle.

Edit I just remembered the receptacle was required to be labeled fed from more than 1 source.