Wires crossing in a 3 phase disconnect

[infinity]

I was confused by saying "switched before". The way I see the disconnects, the line goes in the top side and load at the bottom. With the line at the top, when the knife switch is open, the fuse holders are disconnected from power. Is that correct?

Yes what you don't want to do is this, transformer feeding the disconnect:

 

[Fred B]

Yes what you don't want to do is this, transformer feeding the disconnect:
View attachment 2554079

Just a thought or question if you will. I dont have experience with 3ph but don't they have switches that (top feed or bottom feed) depending on need like I get for residential? That would avoid either having live fuse (no disco) or a Sw that is "off" in up position, (flipping panel over, *** not suggesting it be done***)
I definitely wouldn't want to be the one to change those fuses in that disco. Depending on voltages couldn't that pose a HUGE Arc hazard?

 

[infinity]

Just a thought or question if you will. I dont have experience with 3ph but don't they have switches that (top feed or bottom feed) depending on need like I get for residential? That would avoid either having live fuse (no disco) or a Sw that is "off" in up position, (flipping panel over, *** not suggesting it be done***)
I definitely wouldn't want to be the one to change those fuses in that disco. Depending on voltages couldn't that pose a HUGE Arc hazard?

I've seen some custom switchboards that are designed and built for bottom feed or some circuit breakers enclosures but never seen a standard off the shelf a fused disconnect built that way.

 

[Carultch]

Hello all,
I would like to know if it is code compliant to physically cross wires from the Line side of the disconnect switch and the Load side of the disconnect switch. I am involved in elevator applications and I have always seen it done where these wires never cross within the 3-phase disconnect switch. The line side would be on one side of the switch and the load side would use the other. If the code section can be referenced if this is true please mention it and thank you for your effort on my behalf.

The top terminals of the disconnect are meant for the line-side terminals, and the bottom terminals are meant for the load-side terminals. That is the industry norm for how these devices are built. The circuit that remains energized after the disconnect is opened, is what is supposed to be connected on top. That way, the blades, fuses, and unshielded terminals get de-energized when the disconnect is switched to the off/open position. The intent is that as much of the disconnect is de-energized as possible, when opened.

If the geometry of how you are routing your circuits makes it more convenient to connect the line-side raceway to the bottom, and the load-side raceway to the top, it is perfectly acceptable for both circuits to cross over one another in the wiring space, so they can both U-turn to their correct terminals. Even if the line-side conductors classify as service conductors. It is in a raceway or other wiring method, where you are not allowed to mix service conductors and load-side feeder conductors, in order to mitigate the risk of faults. The 1 to 2 feet of shared wiring space in a disconnect is considered negligible enough for this not to be an issue.

 

[Little Bill]

I know on an open delta 240/120, the high leg (orange) would be on "C" phase in the meter and on "B" phase in the panel. Would it matter if the high leg landed on "C" phase in the disconnect and then moved to "B" phase at the panel? Or do you have to have the disconnect match the panel?

 

[Carultch]

I know on an open delta 240/120, the high leg (orange) would be on "C" phase in the meter and on "B" phase in the panel. Would it matter if the high leg landed on "C" phase in the disconnect and then moved to "B" phase at the panel? Or do you have to have the disconnect match the panel?

That is a high-leg delta system where this matters. I.e. where the transformer windings are connected phase-to-phase, with one of the windings center-tapped to derive the neutral. I don't know what the rule is for an open-delta system.

Panelboards require the high leg on the B-phase, as of NEC1975. Disconnects or single circuit breaker enclosures don't require it on any particular phase, but to keep it simple, it should be consistent with what you do for the panelboard. In any case, it requires orange identification unless local codes require otherwise.

The ANSI standard for utility meters require it on the C-phase, and this standard did not get changed when the NEC set the standard for it to be on the B-phase. As of 2008, the NEC allows a C-phase high leg, if necessary to work with service metering that is an integral part of the panelboard or switchboard. A separately-installed panelboard requires it on the B-phase.

For modern electronic/digital meters, typically those made in the current century, the meter doesn't really "care" where you put the high leg. Such a meter will correctly measure power and energy the same either way. It is on old-fashioned 1800's and 1900's mechanical meters where it mattered, because the meter would do something different when measuring the high leg, than it would do with the other two phases. And it was critical to wire the high leg to the correct phase in the socket.

 

[paulengr]

Just a thought or question if you will. I dont have experience with 3ph but don't they have switches that (top feed or bottom feed) depending on need like I get for residential? That would avoid either having live fuse (no disco) or a Sw that is "off" in up position, (flipping panel over, *** not suggesting it be done***)
I definitely wouldn't want to be the one to change those fuses in that disco. Depending on voltages couldn't that pose a HUGE Arc hazard?

If it was wired the normal way (top to bottom), no. The whole bottom of the switch is dead. The switch itself is covered. The only thing exposed is the lugs at the top and even those are guarded by design and about a foot away from the fuse jacks. 480 v restricted approach boundary is 1 foot, and fuses will fall to the bottom away from live gear.

In industrial systems MOST panels are this way. When you open the disconnect or breaker, the top is still hot but it is guarded thus not a shock or arc flash hazard unless you go poking around past the guard. The other shock hazard is that quite often aux contacts wired to an external source (dry contacts) are also energized with control power, 120 VAC.

In switchgear, pulling MCC buckets, and over 1,000 VAC there will be a shutter mechanism. Over 1000 AC controls are in an isolated compartment, and the door interlock is generally not defeatable without taking it completely apart.

Arc flash is really only a hazard in two situations. The first is working on equipment that is suspect/defective. The second is when doing a task where the safety of the task is 100% relying on the person(s) doing the job. For instance racking buckets back onto energized bus especially MCC but it’s design specific, attempting to fish cable blindly into energized spaces, working above or on exposed energized equipment with tools that can short it if they fall into it, or attempting to remove or land cable while energized. All of these often end badly.

So the only people that can’t safely work on it are untrained safety inspectors that were transferred to the position because they were too dangerous to be allowed in the field.

 

[rnatalie]

 

[Fred B]

So the way this is pictured those fuses will be hot with no way to de-energize prior to changing out a fuse? Is that beyond a safety hazard, a code violation?

 

[rnatalie]

I can be that that disconnects instructions/markings say that the hot side needs to run to the switch side. That would make it obligatory under the code.

 

[infinity]

So the way this is pictured those fuses will be hot with no way to de-energize prior to changing out a fuse? Is that beyond a safety hazard, a code violation?

Yes that's the issue. The installer wired the switch by swapping the line and load side connections. The 480 volt disconnect could be opened to change the fuses but that still doesn't make it code complaint.

 

[Hv&Lv]

For modern electronic/digital meters, typically those made in the current century, the meter doesn't really "care" where you put the high leg. Such a meter will correctly measure power and energy the same either way. It is on old-fashioned 1800's and 1900's mechanical meters where it mattered, because the meter would do something different when measuring the high leg, than it would do with the other two phases. And it was critical to wire the high leg to the correct phase in the socket.

The old form15 meters only had two CT internally.
The CT on the left measured the current through A & B phase and divided it in half. The CT on the right side metered the high leg only, so the high leg HAD to go on the right to meter correctly.
With SOME of today’s meters, like you stated, the meter works no matter where the High Leg is at as long as it’s Blondel compliant.
About everyone I talk to uses either form 9 or form 16 meter..

a HUGE reason the POCOs won’t let up on this requirement now is storms or accidents.
say the overhead three phase service is torn down, we fix it that night. If the wire is torn in half, getting it right can be a nightmare. If we KNOW the high leg is on the right we can check the voltage and leave once the repair is complete. With the rotation marked on many transformer rated metering, we can get the rotation correct also.
If not, we aren’t sending 208 to the120V loads, but the possibility it there to have reverse rotation..

 

[kwired]

So the way this is pictured those fuses will be hot with no way to de-energize prior to changing out a fuse? Is that beyond a safety hazard, a code violation?

See 240.40.

In the picture mentioned the supply conductors need to go to the top side of the switch so that opening the switch will leave the fuseholders not energized when changing or other servicing of the fuses.

Also in picture one can possibly argue you can always disconnect the primary side of the transformer - and maybe with some justification. But probably still not a great idea, most people will expect fuses to be dead if the switch is "off".

However good safety procedures still dictate you test before touching.

 

[paulengr]

So the way this is pictured those fuses will be hot with no way to de-energize prior to changing out a fuse? Is that beyond a safety hazard, a code violation?

No Code issue.

You can use the plastic fuse removers to get them out or use an insulated screw driver and pop them back in with rubber gloves. It’s just far easier and safer not to go that route.

 

[TheElevatorGuy]

I was confused by saying "switched before". The way I see the disconnects, the line goes in the top side and load at the bottom. With the line at the top, when the knife switch is open, the fuse holders are disconnected from power. Is that correct?

Yes. The fuses and everything below the line side termination points are dead. Thank you.

 

[TheElevatorGuy]

Kind of my question as well, what exactly is meant by "crossing".

Having line and load conductors pass near each other within the enclosure is fine, any other meaning of "crossing" needs more detail before we can answer.

I meant it exactly how you said it. Line and load conductors running up the same side of the switch or being close to each other based on the entry points.

 

[TheElevatorGuy]

Reading the OP carefully, it sounds like they're talking about the line conductors entering the bottom of a disconnect and running up the side to the line terminals, also the load conductors enter at the top and running down the side to the load terminals. I see nothing wrong with that.

This is the kind of thing where a pic or sketch would be clearer than the words.

You are correct about what I meant and I will send a diagram next time. Thanks for your help.

 

[TheElevatorGuy]

The top terminals of the disconnect are meant for the line-side terminals, and the bottom terminals are meant for the load-side terminals. That is the industry norm for how these devices are built. The circuit that remains energized after the disconnect is opened, is what is supposed to be connected on top. That way, the blades, fuses, and unshielded terminals get de-energized when the disconnect is switched to the off/open position. The intent is that as much of the disconnect is de-energized as possible, when opened.

If the geometry of how you are routing your circuits makes it more convenient to connect the line-side raceway to the bottom, and the load-side raceway to the top, it is perfectly acceptable for both circuits to cross over one another in the wiring space, so they can both U-turn to their correct terminals. Even if the line-side conductors classify as service conductors. It is in a raceway or other wiring method, where you are not allowed to mix service conductors and load-side feeder conductors, in order to mitigate the risk of faults. The 1 to 2 feet of shared wiring space in a disconnect is considered negligible enough for this not to be an issue.

Thanks very much for your response.

 

[kwired]

I meant it exactly how you said it. Line and load conductors running up the same side of the switch or being close to each other based on the entry points.

Thank you, just wanted to clarify it was that and not something else, those kind of misunderstandings do happen occasionally and we end up chasing down something that isn't even happening.

 

[ICPete]

I'd like to piggy-back on this thread with a very similar question.
How does this line-load top-bottom convention apply to non-fusible safety switches?
In particular I'm going to be installing three Eaton DG224URK single-phase 200A disconnects in a photovoltaic application.
I'm working out the raceway routing and box locations, and while it's good to understand that the wires can enter the box at the end OPPOSITE to where they will terminate at the switch terminals, I'm wondering whether, for this sort of double-break switch design, is it still intended that line goes to the top terminals and load to the bottom terminals? Again this is non-fusible.