Outdoor Utility Transformers
To: Customers &Code Enforcement Staff
From: Joe Weathers, Electrical Code Administrator
Re: Outdoor Utility Transformers Policy
Date: September 1, 2009
Oil-insulated transformers that are placed too close to other equipment or buildings can pose a significant public safety hazard if they explode.
Although Mecklenburg County Code Enforcement does not have authority to regulate the location of utility-owned oil-insulated transformers, the department was instructed by the North Carolina Department of Insurance (DOI) that there must "be protection for the buildings or structures and equipment, both inside and out, from such installations," as stated in Article 450.27 of the NEC.
The standard to be used to enforce the DOI mandate to provide protection from the resulting hazards of utility-owned oil-insulated transformers is as follows:
"While the section (NEC 450.27) does not prescribe a specific distance, it requires the code official to identify what a safe distance would be based on the circumstances. Article 450.27 is structured to allow the code official to facilitate a safe distance between combustible construction and a transformer. Since there are many types of transformers, voltages, etc., the specific distance is left to the approval of the inspector. ...Have the inspector draw from their experience in this area."
At the industry's request, Mecklenburg County Code Enforcement, Duke Energy's Engineering Standards and Applications Team, the County Manager's Office and local engineers have collaborated to provide written guidance that can be used as an alternate method to DOI's mandate. This effort resulted in developing a document of protection guidelines called the Duke Energy Standard. Code Enforcement intends to accept this standard as an alternate method for dealing with utility-owned oil-insulated transformers in compliance with Article 450.27 of the NEC.
The NEC does not offer precise clearance guidelines for this issue. Therefore, Code Enforcement has also allowed other alternate methods such as Factory Mutual Global recommendations, IEEE 979, and other nationally recognized standards to be used on a case-by-case basis while working with Duke Energy and others to determine the best method of protection.
Other Important Information
Examples of Imminent Danger
Utility Transformer FAQs
Alternate methods and means is a process where registered design professionals submit a detailed substitute for the code requirement that will assure equivalent protection or performance, when the code standard can not be practicably applied. The FM Global Data sheet shows a 3' clearance allowed with FR3 fluid filled transformers.
The Utility company needs to be contacted for a concise answer. In our brown bag meeting one Utility stated the raw costs increase is about 15%.
Existing transformers that are replaced by the Utility without any owner improvements will not be evaluated by Code Enforcement, but may need to adjust per Utility requirements. If changes are made to the owner's system the current Code Enforcement policy will need to be complied with. Additionally new transformers may affect adjacent buildings and their installation will need to comply with the policy.
No, the protection is for the building as well as the occupants.
These terms are defined in the NC State Building Code and by compliance with recognized standards. Chapters 6 & 7 are applied to obtain the ratings.
Doors are addressed in the Duke Standard. All "wall openings", fire escapes, fire exits, windows, doors, and vents are addressed with dedicated clearances. Per 450.27 of the NEC; Combustible material, combustible buildings, and parts of buildings, fire escapes, and door and window openings shall be safeguarded from fires originating in oil-insulated transformers installed on roofs, attached to or adjacent to a building or combustible material.
Currently the Duke Standard has been agreed to by four of the five area Utilities and as an acceptable method of compliance per Code Enforcement. Hopefully the remaining Utility will agree as well in the near future. The Duke Standard is currently in play for all new installations since January 1st this year. Code Enforcement will evaluate all on a case by case basis per our direction from the NC Department of Insurance and the NEC.
Both are addressed by NEC and the Duke Standard. Each installation will be considered individually as the installations are not all the same.
Utilities differ in structure and regulation. Please call your utility provider for precise information.
The permitted projects prior to January 1st will be evaluated on a case by case basis. Only those that pose imminent danger will need to be addressed.
All required egress means are to be protected per the Duke Standard and the NEC.
The process arose from our questions of how the utilities were addressing building and occupant protections from the hazards that may arise from placement of oil filled transformers inside and outside of buildings. The NEC and the NC State Electrical Code in Article 450.27 lists methods by which protections can be achieved. Code Enforcement began seeing several installations that appeared to be questionable with regards to safety of potential electrical arc faults, explosion and fires. The utilities seemed to have somewhat differing guidelines and the National Electrical Safety Code addresses the issue in Section 15, 152. A. 2 much the same as the NC State Electrical Code. We were aware that the General Statutes excluded us from authority over the utility equipment. We contacted NCDOI/OSFM for clarification of how we needed to address our concerns. We were informed that while we indeed had no authority over the utility equipment we still had to protect the buildings and occupants from the imposed dangers.
We are to enforce the code as adopted by the State of NC and as stated above the NCDOI/OSFM directed us to protect the buildings and occupants. By NC Statute they are responsible for our general supervision.
The Codes apply where ever they are adopted and in NC they are to be enforced statewide. Additionally utilities have standards that they enforce.
Said another way, what exactly are we trying to accomplish with the added distances (<12' from a combustible structure (measured from the overhang) 20' from doors, 10' from windows) that is not currently adequate? It sounds like there is a lot of dialogue on alternative methods to meet the ruling, and the hope is that they are cost neutral.
Answer: The goal is to protect the buildings and occupants with reasonable and practical engineering practice and recognized industry standards, in recognition of the imposed hazards.
The enforcement policy resulted from existing codes and standards, and as previously stated was an effort to conform to reasonable compliance with them. Not being a new code change the cost study associated with NC State Code changes was not done.
While not intended as a negative force, the reality of safety standards inevitably will contribute to costs factors. We are trying as much as possible to inform all parties of the situation and dangers, and to have everyone understand that it is a total industry concern that must be addressed in partnership with all involved. At this time we are informed that a standard will be presented for adoption to the NC State Code, in an effort to harmonize standards and enforcement.