Are there any drafting standards for single-line drawings? Specifically, I have seen drawings produced both by SKM and by drafters in AutoCad that have the main bus in panels, MCCs, switch gear, etc that on either end the bus just hangs out there beyond the first and last branch or feeder that drops down from the bus. Who or what dictates this? I have a customer that said he didn't want those lines hanging out there so we had to go through the entirety of the one-line drawings and crop those lines away. I always assumed (I know, I know.... assume) that with the line extended beyond any branch circuits or feeders that this implied there was still space available for additional circuits, but have absolutely nothing to base this on. Any thoughts?

With regard to SLD (single line diagram) one aspect is to show the future or unused termination point in the MCC etc. to indicate there is room for expansion. The typical SLD is to show only the active devices/apparatus which are in service and either energized or capable of becoming energized via switching etc.

I'm not aware of a standard for SLD.

You have no basis for that assumption. Having the line "hanging" means only one thing, that the line is hanging.
If you actually look you will find VERY little in the way of actual standards regarding onelines, or drawings at all.

As far as the hanging line bit goes, I prefer do do that in my drawings. I always leave the end of the bus line hanging one step beyond the first and last feedsers in SKM.
This is largely for practical reasons, but also prefer the look. If I need to extend the bus (and add components) then it is easiter to grab its handle that way.

For that matter it is not even possible in SKM to have a (non-node)Bus with one feeder, NOT hang at one end or the other.

This is not meant to flame any company, but, don't you find that SKM and ETAPP both have a crude drawing output? I have reviewed multiple studies that were done by both and they not plotted in a true one-line format??

The answer is as simple as complex - For every design engineers there is at least two opinions and both are right!

The One-line from any power system analysis software may not give the same detail as a drafted (AutoCAD) drawing. I have never spent the time in any of the system softwares to develop an accurate one-line with ALL the infomation - it is simply not worth my time.
Not only that I have less control on how it looks!

All that being said - an SKM one-line is better than nothing

I almost forgot to answer your question - There are not standards that I am aware of but a lot of "industry standards". One-lines for a commercial site (store/school) and an industrial site and a sub-station all look very different but are close within their own industry

I would say the line extensions are an industry standard. While not formally written, it is the method used in the IEEE color book series, and is therefore an IEEE standard, even though it is undefined. Trimming the lines would be non-standard.

I use IEEE std 315 symbols and other than designing per NEC plus State Code and verifying with IEEE color books, I do not see any standard requirement for one-line diagram. Of course one-line diagram is very important because it represents our design that manufacturers will build or if it is an existing equipment, it represents the existing equipment configuration in the field. In most design that I have seen for LV system, the utility transformer feeds customer's switchgear. The switchgear feeds switchboards, which feed MCC & Panelboards. If there is any spare requirement for instance like breakers we show it on the one-line diagram. But the bus hanging like you mentioned might be used for short circuit calculation and arc flash. For instance, if you know the breaker & cable information that is going to feed a contractor's temporary equipment during construction, then a bus hanging at the end of the cable may give a good information about available short circuit current and Ei at that cable terminal where it feeds the contractor's equipment. And I think most importantly, it is not up to the customer whether they like the hanging bus or not because if the plant was designed in a way that during risk assessment, you feel there is a need to show the information at the terminals (line/load sides), populating customized data on the bus and a little explanation can be helpful.

I wouldn't worry much about the appearance of single line diagram as long as it is complete and calculated short circuit fault current values are accurate, namely the analysis is based on the comprehensive method for short circuit analysis, factors in both active and reactive parts of equipment impedance and takes into account contributions from multiple sources including motors and generators. Below is a copy of sample single line diagram created using Short Circuit Analytic software program meeting the above criteria:

In terms of symbols there is the defunct JIC standard that is very close to a "North American" standard for controls. NFPA has taken up maintaining it under NFPA 79. There are about 3 IEC standards that mostly resemble IEEE 315 but with either one most Americans consider it almost unreadable since for instance a breaker is expected to look like a parathensis and a breaker and a switch look identical in the IEEE/IEC symbols. Outside of these there are few standards. I guess if you use AutoCAD Electrical, it is a "standard". SKM/ETAP are not great examples of single lines but their purpose is functional, not diagrammatic.

But all that being said, there are multiple variations on single lines. A true " relay" diagram has only circles with relay numbers so for instance a breaker is a 52. Relay diagrams drive me nuts though because like an instrument diagram they leave a lot of implementation details out and the companies that use them exclusively (e.g. Powell) use it as a shorthand kind of like an HVAC diagram that leaves almost all details out, making it hard to use unless you are used to one and only one way of wiring functions. As I'm not tied to just one vendor, this doesn't work for me.

SKM and ETAP output is fine if all you have is radial distribution with a solid ground and 50/51 relays but throw in ground fault, 87, or distance relaying and its useless. I prefer a hybrid that is essentially one step above a three line diagram.

One thing to remember is that SKM, EasyPower, etc. only use the one line to model the system. It is not a drafting program although the one line can be exported to AutoCad and used as the base for a more detailed, aesthetically pleasing one line. For places that do not have a real one line, the software model one lines do help.

Going back to a old text on electrical safety; the posted single line diagram should be simplified and show only the necessary information needed to shut off and de-energize the system for work. I usually try to fit it on a 11" X17" paper. It should be posted under glass near the entrance to each equipment room, and inside the room. Each major switch, equipment and circuit breaker should have a unique identifier. This should be placed on the diagram. Old mills use to identify all the equipment throughout the plant with unique identifiers, Four or five-character alpha-numerical designers van identify a lot of equipment uniquely.

If no ANSI standard exists, look at how one-lines are depicted in IEEE books and journals. If you match an IEEE publication, no one can legitimately say you are wrong.

I have always taken the position that the oneline diagram serves two purposes, which purposes dictate the content requirements depicted on the diagram. The first is functional, and the second relates to Code compliance.

1) Functional: the oneline diagram provides a simplified depiction of how power flows from the source to the end loads. It shows key operating components such as breakers, disconnect switches, system interlocks, CTs, switchboards, MCCs, bus-tie breakers, transformers, VFDs, back-up power sources, etc., from the utility service entrance on down to the loads supplied. This provides operators and maintenance staff all the high-level information needed to safely route power to system loads, or to isolate power from areas of the system for maintenance and other purposes. Device labels are key to this aspect, as all equipment labels on the oneline must precisely match the corresponding component labels in the field to ensure, for example, that the correct isolation point is operated to deenergize a particular load. This includes cable and conduit numbers.

2) Compliance: a good oneline diagram should provide all of the information needed to verify NEC compliance. By providing conduit and cable sizes and types, numbers of current carrying and grounding conductors in the run, protective device ratings, load sizes, transformer ratings, etc. An engineer should be able to verify all key Code compliance issues including proper circuit ampacity, conduit fill, protective device ratings, etc. This same information should also be sufficient to perform a short-circuit analysis and arc flash study.

Even if you do not match IEEE books and journals....who can legitimately say you are wrong?

As I stated earlier, there is an IEEE standard and an NFPA standard (which is close to an old JIC standard) and an IEC standard. There is no "ANSI" or "NIST" standard. Besides that, ASTM and ANSI these days are really just collections. The individual standards, similar to IEC, are maintained by other organizations and the ANSI and IEC standards are more or less just lending their name to the standard. For example the ANSI Cxx standards are mostly maintained by NEMA.