Electrical systems: Designing electrical rooms—your questions answered

In addition to the questions answered in the webcast event, the presenters answered several questions about designing electrical rooms.


Question: What is the code clearance requirement if the room has switchboard, generator, and battery chargers all in the same room?

Mr. Rener: Each piece of equipment will require the working specified in the NFPA 70: National Electrical Code (NEC). For example, if the generator disconnect faces the switchboard, then the distance would fall under condition 3 in the code.

Question: Do you see conflicts between the lighting foot-candle requirements discussed and those stated by energy efficiency standards (ASHRAE)? If so, how do you resolve?

Mr. Rener: The requirements for lighting energy can take several forms, but at 30 foot-candles, it would be unlikely that you could not fall below the W/sq ft requirements for an electrical room, particular considering the use of T5 lamps or even LED fixtures. The space would be exempt from automatic lighting control requirements of ASHRAE due to NEC.

Question: You mentioned that battery rooms should be maintained at a temperature near 77 F. Is there a code or guideline that this number comes from?

Mr. Rener: This is not a code requirement, but manufacturer guidelines. As mentioned you can run the room hotter but the battery life will be drastically reduced.

Question: If the manufacturer's medium-voltage switchgear can be installed with the rear against the wall, are we required to provide the minimum rear clearance of 30 in.?

Mr. Rener: If there is no requirement for rear servicing or maintenance, then you should be able to locate against a wall per NEC.

Question: Why is there a 6-ft space requirement above panels?

Mr. Rener: This is to provide space for the exit and entrance of conduits, bus, or any other support required by the electrical equipment. The point is to make sure there is enough space around the electrical equipment and that it doesn’t get taken up by other nonelectrical services such as ductwork.

Question: Would working space required for measuring the voltage at a receptacle?

Mr. Rener: Receptacles would not normally require live maintenance or testing.

Question: The automatic lighting controls statement: Is that code, engineers choice, OSHA, etc.?

Mr. Martin: This is a requirement of the NEC, specifically Article 110.26(D). Note that you can have automatic controls; the lighting is just prohibited from being controlled automatically only.

Question: What space-saving solutions are available to consider in electrical room design?

Mr. Rener: You can consider specifying different types of equipment—for example switchboard will generally require less space than switchgear. Panel boards require less space than motor control centers (MCCs). Were multiple large pieces of equipment are planned, geometries and alternative placements of equipment should be examined.

Question: What are the key factors to determine if power factor correction is required?

Mr. Martin: This topic was not covered in our presentation. I recommend that you read the following Consulting-Specifying Engineer article: The economics of improving power factor.

Question: With more and more LED lighting being installed, is lighting control still required?

Mr. Rener: Manual means should be provided; even the use of LED lighting would not justify continuous “always on” operations.

Question: The 86 F, the recommended ambient in electrical room: Where did this value come from?

Mr. Martin: This is a general recommendation, but it is based on a few key points.

  • The allowable ampacity tables of many common conductors is based on 86 F ambient. Refer to Table 310.15(B)(16) and Table 310.15(B)(2)(a). Keeping the ambient of the electrical room below 86 F avoids de-rating conductors in the electrical room.

  • Most electrical equipment is rated to 104 F; 86 F for the room generally keeps electrical equipment from exceeding this temperature.

Question: Small buildings (5,000 sq ft or less) where the electric room commonly is also the phone room, IT/data room, security equipment room, camera recorder room, tenant computer stuff. It seems 77 F cooling is adequate plus add in equipment heat loads.

Mr. Martin: In general I agree.

Question: Are there code requirements for minimum safety clothing and face gear for electricians servicing electrical equipment?

Mr. Martin: There is not a one-size-fits-all answer to this question. I recommend that you research what is referred to as the OSHA general duty clause and the recommended personal protective equipment (PPE) requirements spelled out in NFPA 70E. Here is a link to a collection of many articles from Consulting-Specifying Engineer that may help: http://www.csemag.com/media-library/eguide-arc-flash-safety.html.

Question: My jurisdiction is still under the 2008 NEC. Sprinklers are not permitted in the dedicated electrical equipment space. What code edition does this change to be allowable per the slide presented?

Mr. Martin: The 2014 NEC allows sprinkler protection for the dedicated space, not specifically that the piping can run in the dedicated space. Please refer to our example diagram in the presentation. The NEC states that the sprinkler protection must comply with the other portions of 110.26(E). This provision is in the 2008 NEC as well.

Question: What is the difference between a switchboard and switchgear?

Mr. Martin: Switchboards are built to UL 891 standards and switchgear is built to ANSI C37 standards. Generally switchgear uses using drawout construction (low-voltage power circuit breakers), requires rear access, is 30-cycle rated, and will require more space. Switchboards may contain a variety of different class of breakers, are typically front-access only, and are typically 3-cycle rated. These are general guidelines, however switchboard construction in particular has been changing rapidly.

Question: I heard that transformers do not have room requirement. I believe section 450.21(B) requires a transformer room for dry type transformer, unless the transformer meets either exception 1 or 2. And in the case of other than dry type there are numerous space requirements as specified is Part II of Article 450.

Mr. Martin: You are correct and this was touched on during our presentation. A good way to think about it is not that electrical rooms do not have a requirement, but rather that they do not necessarily have a requirement. However, transformers that meet exception 1 and 2 are off-the-shelf items and easy to procure.

Question: In an electrical room with a switchboard rated above 1200 amps, if the switchboard is front access only and is over 6 ft wide. If there is unobstructed egress from the working space is it acceptable to have one door?

Mr. Martin: Per the 2014 NEC, yes this is acceptable. This example is in the NEC 2014 Handbook as exhibit 110.21.

Question: What is the definition of exposed live parts for electrical equipment clearances? Is it from the outer face of the cabinet or to the first internal live component? For small spaces this could be a critical issue.

Mr. Martin: The NEC 110.26(A)(1) states, “Distances shall be measured from the exposed live parts or from the enclosure or opening if the live parts are enclosed.” It sounds like your live parts are enclosed, so the working space would be measured from the opening.

Question: Are listed panic hardware required on all doors between electrical room and outside?

Mr. Martin: As in all rooms you must pass through between the electrical room and exterior. NEC 110.26(C)(3) states, “…there is a personnel door(s) intended for entrance to and egress from the working space less than 25 ft from the nearest edge of the working space, the door(s) shall open in the direction of egress and be equipped with listed panic hardware.”

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