Meter Enclosures & the Grounded Conductor

[erickench]

I see here a possible misinterpretation of the NEC on the part of manufacturers in regards to connecting the grounded conductor to meter enclosures. NEC 250.24(C) contains specific wording in that it state's:

Where an ac system operating at less than 1000 volts is grounded at any point, the grounded conductor(s) shall be run to each service disconnecting means and shall be connected to each disconnect means grounded conductor(s) terminal or bus. A main bonding jumper shall connect the grounded conductor(s) to each service disconnecting means enclosure.

However, I do not see any similar wording for meter enclosures. NEC 250.92(B) give's rules for bonding service enclosures together which would seem to make it a violation to use PVC nipples or even to bond just one end of the connecting metal raceway between the service enclosures. NEC 250.174 would give rules for earth grounding meter cases in systems that are 300 volts or more to ground which can be accomplished via connection to the equipment grounding conductor.

I know we had a similar discussion on another thread on this topic but I would like to hear more.:slaphead:

 

[iwire]

The grounded conductor must be bonded to the meter enclosure, it is often the only effective means of grounding it.

250.110 requires the enclosure to be grounded, 250.142 gives us permission to used the grounded conductor to do so.

250.142 Use of Grounded Circuit Conductor for
Grounding Equipment.

(A) Supply-Side Equipment. A grounded circuit conductor
shall be permitted to ground non?current-carrying metal
parts of equipment, raceways, and other enclosures at any
of the following locations:

(1) On the supply side or within the enclosure of the ac
service-disconnecting means

(2) On the supply side or within the enclosure of the main
disconnecting means for separate buildings as provided
in 250.32(B)

(3) On the supply side or within the enclosure of the main
disconnecting means or overcurrent devices of a separately
derived system where permitted by 250.30(A)(1)

(B) Load-Side Equipment. Except as permitted in
250.30(A)(1) and 250.32(B) Exception, a grounded circuit
conductor shall not be used for grounding non?
current-carrying metal parts of equipment on the load
side of the service disconnecting means or on the load
side of a separately derived system disconnecting means
or the overcurrent devices for a separately derived system
not having a main disconnecting means.

Exception No. 1: The frames of ranges, wall-mounted ovens,
counter-mounted cooking units, and clothes dryers under
the conditions permitted for existing installations by
250.140 shall be permitted to be connected to the grounded
circuit conductor.

Exception No. 2: It shall be permissible to ground meter
enclosures by connection to the grounded circuit conductor
on the load side of the service disconnect where all of the
following conditions apply:

(1) No service ground-fault protection is installed.

(2) All meter enclosures are located immediately adjacent
to the service disconnecting means.

(3) The size of the grounded circuit conductor is not
smaller than the size specified in Table 250.122 for
equipment grounding conductors.

Exception No. 3: Direct-current systems shall be permitted
to be grounded on the load side of the disconnecting means
or overcurrent device in accordance with 250.164.
Exception No. 4: Electrode-type boilers operating at over
600 volts shall be grounded as required in 490.72(E)(1)
and 490.74.

 

[erickench]

NEC 250.110 gives rules for connecting to the EGC but not the grounded circuit conductor. NEC 250.142(B) permits but does not require grounded conductor connection to the meter enclosure but only if the meter(s) are on the load side of the service disconnecting means. It's the old story where objectionable current is caused by the manufacturer's specifications.

 

[don_resqcapt19]

The code does not require the separation of the grounded and grounding conductors on the line side of the service disconnect. The grounded conductor serves both purposes on the line side of the service disconnect. The section Bob cited is the section that permits this.

250..142. (A) Supply-Side Equipment. A grounded circuit conductor shall be permitted to ground non?current-carrying metal parts of equipment, raceways, and other enclosures at any of the following locations: ...