There is shown in FIG. 1 an example of a watthour meter 1 according to the prior art. Although such meters come in various styles, they are generally comprised of a meter body 32 which mates with a socket 29 which may be attached to a conventional meter box (not shown). The meter body 32 has a base portion 2 to which a cover 41 is attached using lugs 40, shown in FIG. 2. The cover encloses a metering element for sensing the power consumed in a load circuit. Traditionally, the metering element was a mechanical register having a number of dials for indicating the power consumed. More recently, electronic meters have been developed in which the metering element is an electronic register 34 which, using techniques well known in the art, electronically performs the watthour accumulating function of a traditional mechanical register, as well as other specialized function, such time of day use and peak demand.
As shown in FIG. 1, the socket 29 is connected to ground via conductor 33. In addition, the socket 29 has two openings 31 through which the incoming and outgoing conductors of a three phase load circuit (not shown) are fed. Each phase of the load circuit is connected to one of three pairs of jaws 30 formed in the socket 29. A additional jaw 30 is connected to the ground wire of the load circuit. The meter body 32 has three pairs of blades 3 extending from the outboard side 38 of the meter base 2, each of which connects with one of the jaws 30 in the socket 29. Referring to FIG. 2, in this example, blade pairs 3.sup.1, 3.sup.2, and 3.sup.3 are connected via the jaws 30 to the first, second and third phases of the load circuit. Blade 3.sup.4 is connected via a jaw 30 to the ground wire of the load circuit.
As shown in FIG. 1, a conductor 43 connects each blade 3 to the other blade in the pair so that the circuit is not interrupted, thereby allowing the current flowing in the load circuit to pass through the meter 1. A current transducer 35 and a voltage transducer 42 are provided for each of the blade pairs 3.sup.1, 3.sup.2 and 3.sup.3 shown in FIG. 2. The current and voltage transducers 35 and 42, respectively, are connected to the metering element and step down the current and voltage in the load circuit to values suitable for metering. As shown in FIG. 2, a vent 12 is formed in the meter base.
In order to protect the meter from transient surges in either the utility service or user circuits connected to the meter, surge protectors, sometimes referred to as "lightening arrestors," are conventionally provided. As shown in FIGS. 2-4, according to the prior art, a three phase meter such as that shown in FIG. 1 is provided with three surge protectors, one for each phase. Each surge protector is comprised of an electrode 6, conductor 5, resistive block 8, ground strap 7 and spark gap 14. The electrodes 6 are connected by conductors 5 to one of the voltage input blades 3 in each blade pair in this example. A post 9 protruding from the meter base 2 secures each electrode 6 to the inboard side 36--that is, the side enclosed by the cover 41--of the meter base. As shown in FIG. 4, each resistive block 8 is disposed in a hole 15 formed in the meter base. A dimple 13 formed in the end of the electrode 6 presses the electrode against the resistive block 8. A hole 10 extends from the bottom of hole 15 and a ground strap 7 lies over the hole 10. Posts 9 secure the ground straps 7 to the outboard side 38 of the meter base 2. The end 44 of the ground strap 7 extends from the outboard side 38 so that it is spring loaded against the socket 29 when the meter body 32 is attached thereto. A dimple 13 formed in the ground strap 7 forms a spark gap 14 between it and the resistive block 8.
A voltage potential is created across the spark gap 14. During normal operation this potential is too small to cause arcing. However, a transient surge in any phase will increase the voltage developed across the spark gap 14 of the surge protector connected to that phase. If the voltage potential becomes great enough, the air within the spark gap 14 will ionize, thereby creating an arc across the gap which diverts the surge to ground via the ground strap 7, socket 29 and conductor 33. Since ionization creates gases in the spark gap 14 which are highly conductive, the resistive block 8 is placed in series between the electrode 6 and ground strap 7 to prevent the arcing from causing excessive current to flow and to ensure that this current flow extinguishes at the zero crossing of that current.
Although the surge protector arrangement according to the prior art, as described above, works well for its intended purpose, it requires a large number of components for a three phase meter. Specifically, the resistive blocks 8 and ground straps 7 must be duplicated for each phase. Moreover, since the paint on the socket 29 must be manually scrapped away in the vicinity of the ground strap 7 to ensure good electrical contact, the labor required to install a meter employing prior art surge protectors is significantly increased. In addition, since the resistive block 8 is mounted on the inboard side 36 of the meter base 2, the meter cover 41 must be removed to replace the resistive block. This increases the labor associated with maintaining the meter.
Accordingly, it would be desirable to provide a surge protector arrangement for a multi-phase watthour meter which did not require the multiplicity of components necessary under the prior art approach and which allowed the resistive block to be replaced without removing the meter cover.