17.) The mixing of emergency (Article 700) system wiring with legally required (Article 701) and optional (Article 702) system wiring.
This problem most often occurs when emergency systems receive their supply from a generator as opposed to unit equipment. Before you can understand the problem you must be able to understand the difference between types of emergency systems. One major difference is that Articles 700 and 701 cover those systems legally required and classed as emergency by municipal, state, federal, or other codes, or by any governmental agency having jurisdiction and Article 702 covers strictly optional systems.
Article 700 covers emergency systems that are legally required and intended to automatically supply illumination or power, or both, to designated areas and equipment in the event of failure of the normal supply or in the event of accident to elements of a system intended to supply, distribute, and control power and illumination essential for safety to human life. The most common example of this would be the means of egress lighting in a public building. Section 700-9 (b) requires, unless it is permitted in subsections one through four, that the wiring from an emergency source or emergency source distribution overcurrent protection to emergency loads be kept entirely independent of all other wiring and equipment and it shall not enter the same raceway, cable, box, or cabinet with other wiring.
Article 701 covers those systems that are legally required and intended to automatically supply power to selected loads (other than those classed as emergency systems) in the event of failure of the normal source. Note that these systems are legally required and not those that are classified as "emergency systems". However, unlike Article 700, Section 701-10 permits legally required system wiring to be contained in the same raceways, cables, boxes, and cabinets as other general wiring.
Article 702 applies to optional systems that are intended to supply on-site generated power to selected loads, either automatically or manually, for public or private facilities where life safety does not depend on the performance of the system. A very common example of this would be a single family dwelling which has a generator that supplies selected loads during a power outage.
Example: A large hotel is located in an area that has frequent power outages. They have decided to install a generator capable of carrying all the load of the building in order to allow the building to function normally during a power outage. The emergency lighting (means of egress lighting) is supplied by selected normal light fixtures which have been supplied with both normal and emergency power. The emergency lighting in this case would be an Article 700 application and therefor the system wiring would have to be kept separate from all other wiring. Also, you would have to have two transfer switches one to supply the emergency system loads and one to supply the legally required and optional loads. If this hotel had elected to use unit equipment (battery packs) to light the means of egress then the life safety system would not be dependent on the generator and one transfer switch could be used to supply the legally required and optional loads.
This language should not be confused with the languagein Section 517-30 (b) (4) which allows for essential systems in health care facilities, of l50 KVA or less, to be served by one transfer switch.
When you consider whether a system is legally required or optional it seems that knowing what is the intended use is imperative. If the hotel mentioned above is intending to remain fully operational during a power outage then there are several systems that may be legally required. For example; if the hotel provides meals that are prepared on site there may be an exhaust fan that must remain running during use of certain cooking equipment or if the hotel had sewerage ejector pumps they would have to remain operational while the hotel is occupied. These systems would be legally required by a health or "other code". Also refrigeration, heating, communication systems, or ventilation systems could be either legally required or optional depending on the intent. Note that Section 702-9 allows the system wiring for optional loads to occupy the raceways, etc. with other general wiring methods.