The plaintiffs, a group of individuals, corporations, and trade unions involved in'the business of installing, maintaining, and servicing burglar and fire alarm systems within the Commonwealth, brought an action in the Superior Court as a direct judicial challenge (see G. L. c. 30A, and G. L. c. 231A) to Rule 2.2 of the Rules and Regulations of the Board of State Examiners of Electricians of the Commonwealth of Massachusetts (1974) (board). See now 237 Code Mass. Regs. 4.02(3) (1981). That rule requires that only licensed electricians “engag[e] in or work[ ] at the business of installing wires, conduits, apparatus, fixtures or other appliances for carrying or using electricity for light, heat, or power purposes, fire alarm and all signal work requiring the use of wire for transmission.”
The plaintiffs contend: (1) that they are outside the scope of the licensing requirements set forth in G. L. c. 141, § 1, because their systems are not for “light, heat or power purposes” and such requirements cannot be enlarged by the board through use of its rulemaking authority; and (2) that because alarm systems convey information, installation of such systems is exempt from the board’s regulation by reason of G. L. c. 141, § 7, a section providing that c. 141, § 1, is inapplicable to the “work of companies incorporated for the transmission of intelligence by electricity.”
The trial judge concluded that § 1 was not applicable to the plaintiffs and that, even if it were, the plaintiffs would be exempt from its coverage by § 7. A judgment entered declaring that the regulation “is invalid in its application to each of the plaintiffs” and permanently enjoining the board from enforcing, civilly or criminally (see G. L. c. 141, § 5), the regulation against any of the plaintiffs.
We conclude that the regulation is valid, that it is consistent with the purpose of § 1, and that the plaintiffs are not within the scope of the exemption claimed under § 7. We do not, however, determine the applicability of the regulation to the individual plaintiffs because the record is inadequate for such purpose.
*19I. Facts.
A stipulation of agreed facts was filed by the parties and incorporated by the trial judge in his findings of fact. The parties also presented three witnesses, but the trial judge made no additional findings based upon their testimony.
General Laws c. 141, § 1, as amended by St. 1943, c. 308, provides, in pertinent part:
“No person, firm or corporation shall enter into, engage in, or work at the business of installing wires, conduits, apparatus, fixtures or other appliances for carrying or using electricity for light, heat or power purposes, unless such person, firm or corporation shall have received a license and a certificate therefor, issued by the state examiners of electricians and in accordance with the provisions hereinafter set forth.”
Pursuant to its rule making authority under § 2 of the statute,2 the board promulgated the disputed regulation, which substantially tracks the language of § 1, with the major exception of the emphasized additional phrase:
“All persons, firms and corporations entering into, engaging in or working at the business of installing wires, conduits, apparatus, fixtures or other appliances for carrying or using electricity for light, heat, or power purposes, fire alarm and all signal work requiring the use of wire for transmission, within the Commonwealth of Massachusetts shall be governed by the applicable provisions, now or hereafter in force, of all general and special laws; all rules and regulations made and promulgated pursuant to the provisions of any such law; and in respect to all matters not therein expressly provided shall be governed by the standards set forth in the 1981 Massachusetts *20Electrical Code, 527 CMR; 12.00 and as may be from time to time amended, for Electrical Wiring and Apparatus as Rules and Requirements for Electrical Wiring in Massachusetts as adopted by this Board on June 22, 1981.”
With these provisions in mind, we turn to the facts set out in the parties’ stipulation. “All modem burglar alarm systems and approximately fifty percent of all fire alarm systems are connected to a power supply by means of a plug-in transformer. The remaining systems are hard wired to a power supply but, when hard wiring is necessary, it is done by a licensed electrician” (emphasis supplied).
There are attached to the stipulation excerpts, including a diagram, from Hahn, Modem Electronic Security Systems (1976), which the stipulation states “fairly describe the essential elements and functions of a typical burglar alarm system.” A second attachment to the stipulation is a hand drawn diagram (of unidentified origin) labelled “Typical Fire Alarm System,” which the parties stipulate “fairly represents the essential elements and functions of a typical fire alarm system.”3 There are also, according to the undisputed testimony in the record, *21more sophisticated fire alarm systems which can perform various mechanical functions, such as automatically operating elevators or reversing ventilation systems to expel smoke from a building.
Collectively, the plaintiffs install all of the described systems . Their argument is that they do not fall within the licensing requirements of G. L. c. 141, § 1, because their alarm systems do not use electricity for purposes of the end products of light, heat, or power. Although the alarm systems, according to the parties’ stipulation, draw upon electricity to supply power to the systems, the plaintiffs contend that they are outside the scope of G. L. c. 141, § 1, because: “Burglar, fire and smoke alarms do not have heat or light as a purpose. . . . Nor is power an end product, as the signals given out by alarm equipment are not power.” They contend that to bring their activities within the control of the board is to enlarge the scope of § 1, which must be done by legislative, rather than rule making, authority.
The board argues that the statutory phrase “light, heat or power” is inclusive and general and does not refer to “end-products.” It contends that the alarm systems utilize electricity for power purposes and that, therefore, the systems must be installed by licensed electricians.4 II. The Statute.
The board’s interpretation of c. 141, § 1, as giving it the authority to require licensed electricians to install burglar and fire alarms is entitled to “respect.” White Dove, Inc. v. Director of the Div. of Marine Fisheries, 380 Mass. 471, 477 (1980). “Although the usefulness of regulations should not be overrated, their importance is never greater than where, as here, an agency must interpret a legislative policy which is only broadly set out in the governing statute.” School Comm. of Springfield v. Board of Educ., 362 Mass. 417, 442 (1972). See *22also Consolidated Cigar Corp. v. Department of Pub. Health, 372 Mass. 844, 850 (1977); Massachusetts Organization of State Engineers & Scientists v. Labor Relations Commn., 389 Mass. 920, 924 (1983).
Since the meaning of the term “power” is not immediately apparent, we must construe the phrase “light, heat or power purposes,” in light of the history of the statute, which dates from St. 1915, c. 296, and its relation to other statutes touching upon the same subject matter. See generally Commonwealth v. Welosky, 276 Mass. 398, 403 (1931); McCarthy v. Rogers, 295 Mass. 245, 249 (1936); Nichols v. Commissioner of Corps. & Taxn., 314 Mass. 285, 291 (1943). The obvious intent of the Legislature in enacting what is now c. 141, § 1, has been, since 1915, to require that electrical work be performed by licensed electricians. See Maria v. State Examiners of Electricians, 365 Mass. 551, 554 (1974).
We do not think it consistent with that intent to read “light, heat or power purposes” as words of limitation. Rather, we view them as a shorthand expression for the most common uses of electricity at the time of the statute’s enactment. Interpretations of the words, “light, heat or power” as used in 1915 support this conclusion. The term “power” was construed broadly in Commissioner of Corps. & Taxn. v. Springfield, 321 Mass. 31 (1947). In that case the court made clear, at least for purposes of construing a 1916 corporate franchise tax statute, that the distribution of electricity for purposes of power included furnishing electricity “for such purposes as operating a radio, a toaster, a refrigerator or some other household article.” Id. at 37.5 A 1913 legislative report issued pursuant to a *23resolution to revise the laws of the Commonwealth pertaining to the manufacture and transmission of gas and electricity again shows a broad use of the term “power” and that the words “light,” “heat” and “power” were used interchangeably with the term “electricity.” The report pointed out that some statutes referred to sale of gas and electricity for “light and heat,” some for “light, heat or power,” some spoke of sale of “electric light,” others of “electricity.” 1913 House Doc. No. 1925, at 13. After citing the “lack of uniformity” in the array of statutes, the report explained that “electric light and electric power” companies were not defined, that both classes of companies sold electricity, and stated, “‘Light,’ ‘heat,’ and ‘power’” as used in the statutes “are but varied manifestations of the same thing. Its identity is not affected by the use which the purchaser may perhaps make of it.” Id. at 14.* ****6
We thus conclude from these contemporaneous interpretations of the words “light, heat, or power,” that although they are arguably redundant when viewed with the hindsight of tech*24nological advancement,7 they were just different ways of phrasing the common uses of electricity.
The fact that the board did not promulgate the present regulation until 1974 does not, in our view, minimize the weight to be given the board’s interpretation of § 1. See Federal Trade Commn. v. Bunte Bros., 312 U.S. 349, 352 (1941). We think it inappropriate to infer that the board’s nonaction between 1915 and 1974 was the result of a deliberate interpretation of § 1 in a manner contrary to that taken in 1974. It is equally plausible that the 1974 regulation was a “carefully considered interpretation,” issued in response to the circumstances supported in the record, namely that alarm systems have become more and more sophisticated. See 2A Sands, Sutherland Statutory Construction § 49.05, at 239 (4th ed. 1973). The board “may decline to exercise its full potential jurisdiction.” Brooks v. Architectural Barriers Bd., 14 Mass. App. Ct. 584, 589 (1982). The broad grant of power conferred upon the board by reason ofc. 141, §§ 1 and 2, permits it to consider changing conditions and “necessarily implies a range of authority for establishing priorities for enforcement of the general legislative policy.” 14 Mass. App. Ct. at 588.
We are also influenced by the fact that another agency, the Board of Fire Prevention Regulations, has interpreted language identical to c. 141, § 1, to permit regulation of burglar and fire alarms by that agency. General Laws c. 143, § 3L, as amended through St. 1977, c. 64, § 1, provides that the board shall “make . . . regulations relative to the installation, repair and maintenance of electrical wiring and electrical fixtures used for light, heat and power purposes.” The Board of Fire Prevention Regulations has regulated “outside wiring for fire alarm and burglar alarms,” 527 Code Mass. Regs. 12.00, art. 800-1 (1981) since 1951, just one year after its enabling statute *25was enacted. See St. 1950, c. 617. Thus, there is a consistent, long-standing administrative interpretation of the phrase in question by another agency dealing with the same or almost the same subject matter. See Cleary v. Cardullo’s, Inc., 347 Mass. 337, 343 (1964); School Comm. of Springfield v. Board of Educ., 362 Mass. 417, 441 n.22 (1972); Devlin v. Commissioner of Correction, 364 Mass. 435, 439 (1973). We note that there is no justification in the statutory language for the distinction made by the dissent between high and low voltage wiring. We also note that were we to adopt the plaintiffs’ construction of the phrase “light, heat or power purposes,” i.e., distinct, limited end products of electricity, we would render meaningless the exemption set out in G. L. c. 141, § 7, for telephone and telegraph companies. (See part IV of this opinion, infra.)
In view of all these considerations, we reject the plaintiffs’ contentions as to the construction of the statute.
III. The Regulation.
In their brief the plaintiffs correctly concede that “the purpose of the enabling legislation was to protect the health and safety of the public.” Thus, by well established law, “we must apply all rational presumptions in favor of the validity of the administrative action and not declare it void unless its provisions cannot by any reasonable construction be interpreted in harmony with the legislative mandate.” Consolidated Cigar Corp. v. Department of Pub. Health, 372 Mass. at 855. Quite simply, the question is whether the regulation is “reasonably related to the purposes of the enabling legislation.” Mourning v. Family Pub. Serv., Inc., 411 U.S. 356, 369 (1973). See Consolidated Cigar Corp. v. Department of Pub. Health, 372 Mass. at 855; Levy v. Board of Registration & Discipline in Medicine, 378 Mass. 519, 524 (1979); Coonamesset Inn v. Chief of the Falmouth Fire Dept., 16 Mass. App. Ct. 632, 635 (1983).
As in Coonamesset, at 636, it is here also “readily apparent that [c. 141, § 1] does not address comprehensively all of the matters that may come within its scope.” However, there was testimony on a point we think obvious: that the improper installation of wire conduits could cause fire and electrical shock. We *26need go no further to conclude that the regulation is reasonably related to the enabling statute.
By their complaint the plaintiffs sought and obtained a determination that the regulation “is invalid in its application to each of’ them. “In a challenge under G. L. c. 30A, § 7, to a regulation, the plaintiff must prove its case in the judicial proceeding [citations omitted].” Grocery Manufacturers of America, Inc. v. Department of Pub. Health, 379 Mass. 70, 81 (1979). The parties’ stipulation does not satisfy the heavy burden that the plaintiffs must meet to entitle them to a declaration that the regulation is invalid in its application to them.
Both at trial and on appeal, the thrust of the plaintiffs’ argument has been that the regulation is inapplicable to them because their systems produce signals rather than light, heat, or power.8 They have not prevailed with that argument in this court. That the regulation might be applied to alarm systems not reasonably within the comprehension of c. 141, § 1, is a question which must await a more focused attack and better record. All that has been shown here is that collectively the plaintiffs install all the previously described alarm systems. We will not ignore the plaintiffs’ burden of proof or the need for the board’s expertise concerning any given system in order to declare which system installed might not “require the use of wires for transmission,” as that regulation is construed in harmony with c. 141, § 1. We determine only that the regulation is not invalid on its face and that the plaintiffs are not entitled to a declaration of the invalidity of the regulation as applied to them. Our holding does not preclude any further litigation by these plaintiffs on the issue of the applicability of the regulation to any particular system claimed to be outside the scope of the statute and regulation.
*27IV. The Exemption.
The plaintiffs also claim (and the trial judge agreed and concluded) that even if § 1 and the regulation were applicable to them, they are exempt therefrom by reason of § 7.
General Laws c. 141, § 7, provides in pertinent part: “[Chapter 141] shall not apply ... to the work of companies incorporated for the transmission of intelligence by electricity in installing, maintaining, or repairing wires, apparatus, fixtures or other appliances used by such companies and necessary for or incident to their business, whether or not such wires, conduits, apparatus, fixtures or other appliances are on its own premises.” Section 7 has remained unchanged since its adoption by St. 1915, c. 296, § 7.
The plaintiffs claim the benefits of § 7 on the basis that “[t]he fundamental purpose of all [alarm] systems is to transmit or communicate, by means of the wires and other devices installed, the fact that an intruder is on the premises or that there is a fire, or smoke, on the premises .... [T]he purpose is to convey specific intelligence to persons in the vicinity or who are specifically monitoring the system.” The plaintiffs read the exemption as applying to all information transmitted by electricity.
The board, on the other hand, argues that the words “transmission of intelligence by electricity” refer to the telephone and telegraph (see Commonwealth v. Boston, 97 Mass. 555, 559 [1867]; Pierce v. Drew, 136 Mass. 75, 76 [1883]; New England Tel. & Tel. Co. v. Boston Terminal Co., 182 Mass. 397, 398 [1903]) and that the exemption applies only to telephone and telegraph companies.
In construing the statutory exemption contained in § 7, we note that the telephone and telegraph have been described as modes of transmitting intelligence. See Pierce v. Drew, 136 Mass. at 81; Mentzer v. New England Tel. & Tel. Co., 276 Mass. 478, 483 (1931). While the phrase “transmission of intelligence” has come to embrace other modes of communicating information, the term still is generally used within the telecommunications industry. See, e.g., First Data Corp. v. State Tax Commn., 371 Mass. 444, 445, 448 (1976); Westinghouse *28Bdcst. Co. v. Commissioner of Rev., 382 Mass. 354, 357-358 (1981). See also e.g., KAOK-CATV, Inc. v. Louisiana Cable T.V., Inc., 195 So.2d 297, 300 (La. App. 1967); Waterville v. Bartell Tel. TV Syss., 233 A.2d 711, 717 (Me. 1967); White v. Ann Arbor, 406 Mich. 554 (1979). Cf. Owl Protective Co. v. Feinberg, 3 App. Div. 2d 340, 344-345 (N.Y. 1957), where the Supreme Court stated that “[b]ecause a burglar may involuntarily telegraph his unlawful entrance over a leased wire, it does not follow that either the owner of the protected establishment, or the burglar alarm company, is engaged in the telegraph business.”
Even assuming that c. 141 is penal in nature by reason of § 5, see Maria v. State Examiners of Electricians, 365 Mass. at 554, and that the exemption § 7 must, therefore, be broadly construed, cf. Wood v. Commissioner of Correction, 363 Mass. 79, 81 (1973), we cannot interpret § 7 so that it is “stretched by enlargement of signification to comprehend matters not within the principle and purview on which they were founded when originally framed and their words chosen.” Commonwealth v. Welosky, 276 Mass. at 401-402. We conclude that the exemption applies to the transmission of intelligence by telephone, telegraph, and similar or analogous instrumentalities. The plaintiffs’ burglar, fire, and smoke alarm systems may well transmit informative signals, noise, light, or any combination thereof, but they do not convey that type of intelligence comprehended by the exemption set out in § 7.
V. Conclusion.
The judgment in its present form is vacated, and the matter is remanded to the Superior Court for the entry of a new judgment declaring that the regulation is valid and that the plaintiffs are not exempt from the operation of G. L. c. 141, § 1, by reason of c. 141, § 7.
So ordered.
General Laws c. 141, § 2, provides in pertinent part that “[t]he state examiners of electricians, in this chapter called the examiners, may make necessary rules for the proper performance of their duties.”
It appears from these attachments to the stipulation that a “typical burglar alarm system” consists of the following: a control unit connected to a power supply and standby power supply, the former connected to a 120 volt (AC) “Input”; “space detectors,” “perimeter detectors,” and “remote key switch stations,” having the capability of transmitting signals over wire into the “security control” unit; a “local alarm bell” or “local alarm siren” which can be activated by signals over wire from the “security control” unit; and a “reversing telephone relay,” “automatic telephone dialer,” or “McCulloh Circuit,” having the capability of placing a telephone call to an answering service or control security station when activated by signals over wire from the “security control unit.”
A “typical fire alarm system” appears to function in a substantially similar manner. A control unit connects to a power source (115 Volts AC or “Plug In Transformer output twelve volts”); various smoke detectors, thermostats, and “manual pull stations,” having the capability of transmitting signals over wire into a “Fire Alarm Control” unit; and horns or sirens which can be activated by signals over wire from the control unit. The control unit also has the capacity to transmit an alarm signal over wire to a central alarm station, city fire department, or “master box.”
The board has been joined in its position by the Electrical Contractors Association of Greater Boston (association). A single justice of this court granted the association leave to file a brief as an amicus curiae. Mass.R. A.P. 17, 365 Mass. 864 (1974).
In rejecting an argument by the Commissioner of Corporations and Taxation that two companies “incorporated for the purpose of furnishing light and power by electricity and heat” were power and not electric light companies within the meaning of the relevant statute, the court pointed out that nothing appeared in the report accompanying the original statute or in the 1916 statute itself, “indicating that an electric light company which sold electricity for power was not to be regarded as an electric light company. It was a matter of common knowledge that electric light companies were furnishing electricity for power; and although the amounts furnished for this purpose have greatly increased, especially with reference to ordinary *23household equipment, so that it is highly improbable that there is a single electric light company furnishing electricity for illumination which does not also furnish electricity for such purposes as operating a radio, a toaster, a refrigerator or some other household article, and although [the statute] has been amended, ... the phrase ‘electric light. . . companies’ has remained unchanged, and this must be taken to mean that the Legislature was satisfied that this phrase included a company that was distributing electric energy not only for the purpose of illumination but also for power.” Commissioner of Corps. & Taxn. v. Springfield, 321 Mass. at 37 (emphasis supplied).
We are not unmindful that G. L. c. 166, § 30, first adopted in 1890 (see St. 1890, c. 404, § 1), speaks in terms of wires designed to carry “light and power current” (later to include heat, see St. 1899, c. 337, § 1) and wires not so designed. The nature of any distinction existing in c. 166, § 30, and its historical predecessors, however, becomes apparent, in our view, in R. L. c. 122, §§ 1 through 30 (1902), and it is not based upon wires carrying light, heat and power and wires carrying “other” electrical products. Rather, the distinction rests on whether the wires were installed by electrical companies or telephone and telegraph companies. See also G. L. c. 166, §§ 21, 22A, and 25. Nor is there anything in G. L. c. 143 which detracts from our analysis. As we read that chapter, although telephone and telegraph company employees need not be licensed electricians under G. L. c. 141, § 1, by reason of § 7 of that chapter, we see nothing in G. L. c. 143 which exempts such company employees from compliance with the electrical code promulgated under G. L. c. 143, § 3L.
Because, as previously noted, we view § 1 as a “legislative policy which is only broadly set out,” School Comm. of Springfield v. Board of Educ., 362 Mass. at 442, thereby requiring that the board’s interpretation be given deference and great weight, it is not enough for the plaintiffs to show that § 1 might arguably lend itself to the construction which they urge. See Consolidated Cigar Corp. v. Department of Pub. Health, 372 Mass. at 855.
From our examination of the record, which includes the transcript of trial and lobby conferences, we think that the judgment entered by the trial judge rests upon his agreement with the plaintiffs’ argument in general and not upon any particular determinations as to the methods of installation and operation of the various individual alarm systems.