OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at https://www.osha.gov.

September 12, 1991

Mr. Kenneth T. James
Chairman, Hospital Signaling Group
National Electrical Manufacturers Association (NEMA)
Suite 300
2101 L Street, N.W.
Washington, D.C. 20210

Dear Mr. James:

Thank you for your inquiries of June 26, and August 14, pertaining to electrical interface units used to connect nurse call systems with pocket page transmitters and other ancillary equipment. We apologize for the delay in responding.

In your letter you asked us to reconsider a statement from our April 23 response to you, as follows: "Because it is not clear that an approved interface would eliminate errant current potentially introduced by pocket page transmitters connected to the interface, OSHA cannot accept such a hookup, unless the entire system is approved through testing under UL 1069 or its equivalent". At the time of our April 23 letter, we did not have definitive input from the Underwriter Laboratories advising that the UL 1069 approval of the interfaces included evaluation for the safe handling of errant electrical current by the interfaces. The letter of June 17 from Mr. P. E. Patty and Mr. I. I. Papier of Underwriters Laboratories Inc. (UL) to this office (copy enclosed) has provided the necessary input for us to answer your concern. The last paragraph on page one and the first paragraph on page two of that letter cover the issue. They are quoted as follows:

The interface serves to isolate and safeguard the functionality of the nurse call system. Under the new requirements, which become effective on March 1, 1992, the interface function requirements will be expanded to include leakage current affecting the patient which is a magnitude significantly smaller than the safety levels for hospital workers.

We are in the process of conducting a file review on all presently listed products to determine their compliance with a revised UL 1069 which goes into effect March 31, 1992. The revised Standard addresses your concern about leakage currents that may enter a nurse call system through an interface as a result of the operation of ancillary type equipment. Specifically, Par.4.2 of UL 1069 states:

isolation shall be provided between any equipment, such as CRTs, printers, pocket page, telephone and the like, and circuits extending into the patient care area stations so that, in the event of breakdown between primary and secondary windings, the high voltage does not appear on the patient circuits and the sum of the leakage currents from the nurse call system and ancillary equipment does not exceed the limits of the Leakage Current Test as described in this Standard.

In light of the above communication, interface units determined by Underwriters Laboratories to be in compliance with the new UL 1069 requirements which will go into effect on March 1, 1992, will be acceptable under 29 CFR 1910.303(a). Pocket page transmitters and other ancillary equipment connected to acceptable interface units must also have been determined to be safe, independently or in combination with the interface unit, by a nationally recognized testing laboratory.

If we can provide further assistance, please do not hesitate to contact us again.


Patricia K. Clark, Director
Directorate of Compliance Programs