individually mounted metering

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opes at askronald

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I have a situation with a local building department who is mandating a rule I believe to be incorrect and borders on a code violation, in my opinion.

Individually mounted electric service metering has a short circuit rating as given by the manufacturer based on their testing criteria and is usually 10,000amperes. UL has not provided to the manufacturer a testing method to determine the withstand rating of metering as with cricuit breakers and other power distribution equipment.

Seimens places a label on their meter that says in part; "when used in conjunction with clas J and T fuses may be connected on a system with a fault current in excess of 10,000amps. THe word in question is "conjunction". The building department is interpreting that to mean any where in the circuit. load side or line side. Since the utility does not allow the fuses on the line side the building department is demanding we put class J and T fuses on the load side in accordance with the metering label.

My argument is this.

Service metering now falls under NEC rules. Under NEC rules any unit of equipment installed in the distribution system must be able to withstand or interrupt the available fault current safely. To protect the equipment and personnel, the current limiter or circuit protective must be up stream or on the line side of the equipment being protected. The building department is mandating that we place a fused switch with class J and T fuses down stream of the meter to satisfy the label were it reads "in conjunction with". Has any one thought about this or had similar problems? We have a single 400A service with 86,000amps available at the utility transformer and about 36,000amps at the meter. The utility company will not allow a fuse between the meter and utility connection. How would you properly protect the meter against excessive fault currents under NEC rules? Thank you
 
Cable limiters in the line side lugs? Just guessing off the cuff. I think it's safe to say that the J's or K's on the load side won't do a blessed thing.
 
Now, this is interesting, from the UL White Book:

CIRCUIT BREAKER CURRENT LIMITERS
(DIRW)
Circuit breaker current limiters are designed to be used in conjunction
with specific circuit breakers and to be directly connected to the load terminals
of the circuit breakers. They contain fusible elements which function
only to increase the fault current interrupting ability of the combination
which is intended for use in the same manner as circuit breakers when
installed at the service and as branch circuit protection. The limiters are
rated 600 v or less.
The fusible elements in circuit breaker current limiters are so coordinated
that they function at currents below those specified in short circuit test
requirements for circuit breakers. Except for this feature of short circuit
operation, combinations of circuit breakers and circuit breaker current limiters
meet all requirements applicable to branch circuit and service circuit
breakers and, in addition, are required to clear circuits up to and including
25 times their amp rating, and circuits of 1000 amps or less regardless of
amp rating, without causing operation of the fusible elements in the current
limiter. For additional information see Circuit Breakers.
Circuit breaker current limiters are marked to indicate the breakers with
which they are intended to be used.
Circuit breaker current limiters which are marked ‘‘Current Interrupting
Rating(s), MAXIMUM RMS SYM. AMPERES VOLTS
’’ have been investigated in conjunction with the circuit breaker
and found suitable for the marked interrupting rating.
An interrupting rating on a circuit breaker current limiter included in a
piece of equipment does not automatically qualify the equipment in which
the combination is installed for use on circuits with higher available currents
than the rating of the equipment itself.
The combination of circuit breaker and circuit breaker current limiter is
intended to be mounted in listed enclosures.
Equipment (such as panelboards, service equipment, and dead front
switchboards) which has been investigated and found suitable for use with
the combination of circuit breaker current limiter and circuit breaker is
marked to indicate that both may be used.
Circuit breaker current limiters as listed herein are for use with copper
conductors unless marked to indicate which terminals are suitable for use
with aluminum conductors. Such markings shall be independent of any
marking on terminal connectors and shall be readily visible.
Unless the circuit breaker current limiters is marked to indicate otherwise,
the wiring space and current-carrying capacity are based on the use of 60 C
wire in circuits rated 100 amp or less, and the use of 75 C wire for higher
amp rated circuits.
For additional information, see Electrical Equipment for Use in Ordinary
Locations (AALZ).
The basic standard used to investigate products in this category is UL
489, ‘‘Molded-Case Circuit Breakers, Molded-Case Switches and Circuit
Breaker Enclosures’’ .
The Listing Mark of Underwriters Laboratories Inc. on the product is the
only method provided by UL to identify products manufactured under its
Listing and Follow-Up Service. The Listing Mark for these products
includes the name and/or symbol of Underwriters Laboratories Inc. (as
illustrated in the Introduction of this Directory) together with the word
‘‘LISTED’’, a control number, and the following product name: ‘‘Circuit
Breaker Current Limiter’’ .

I do not understand.
 
Circuit breaker limiters are different animals than cable limiters. I have never seen documentation on the correct use of cable limiters to protect equipment other than cables.

The meter socket withstand rating presents an interesting issue - does the NEC apply if the socket is installed on the line side of the service disconnect?
NEC 110.9 addresses the short circuit rating of devices that interrupt current. Clearly a meter socket is not intended to break current although it is commonly used as a disconnect.
NEC 230.82(3) requires meter disconnects, but not sockets, to have a short circuit rating equal to the availble short circuit current.
NEC 312 only deals with the construction, not the ratings, of meter sockets.
 
Individually Mounted Metering

Individually Mounted Metering

Meter bases are not typically considered a load break device but do have a built in by-pass switch for meter replacement. I understand the deference between series rated and fully ratred equipment and how current limiting devices work. Current limiting devices is not the question and seems to cuase even the meter base manufacturers to scratch their heads. Me and emails are not the best. Here is the situation. I have a project that is connected to a 500KVA 208/120v 3phase 4wire utility transformer with 1.6%Z. THis equates to about 86KAIC on the transformer secondary with unlimited primary source. With twos sets of 350KCM as my service feeders there is about 36KAIC at the meter base. The meter base is only rated for 10KAIC. Since the utility co. will not allow a fuse or circuit breaker between the individually mounted meter and their transformer we have no way to protect the meter against excessive fault current. Lake County Florida's mandating a class T or J fuse on the load side of the meter base so if the building goes into a fault condition at least the meter will not blow off the wall. This is the response I received from the plans examiner.

My problem is now is that installation of the meter base falls under NEC rules and is being treated as part of the building installation by the AHJ, at least in Lake County. As the engineer of record I am hard pressed to sign and seal a drawing knowing there is equipment not protected for the AIC available. Yet the AHJ continues to reject plans unless we specifically call out a fused service entrance disconnect with class J or T fuse on the load of the meter base or multimeter installation. The fuses do nothing to protect the meter base and only adds to the burden of having to get non standard disconnects and fuses not normally used in commercial applications.

Any suggestion???
 
I'm curious what the reasoning is that the POCO won't allow a fused disconnect on the line side of the meter base. Up in this neck of the woods, the POCO and the AHJ won't accept anything (at least commercial wise) that doesn't have a fused disconnect (or main breaker) on the line side of the meter.

Vern
 
opes at askronald said:
Meter bases are not typically considered a load break device but do have a built in by-pass switch for meter replacement. I understand the deference between series rated and fully ratred equipment and how current limiting devices work. Current limiting devices is not the question and seems to cuase even the meter base manufacturers to scratch their heads. Me and emails are not the best. Here is the situation. I have a project that is connected to a 500KVA 208/120v 3phase 4wire utility transformer with 1.6%Z. THis equates to about 86KAIC on the transformer secondary with unlimited primary source. With twos sets of 350KCM as my service feeders there is about 36KAIC at the meter base. The meter base is only rated for 10KAIC. Since the utility co. will not allow a fuse or circuit breaker between the individually mounted meter and their transformer we have no way to protect the meter against excessive fault current. Lake County Florida's mandating a class T or J fuse on the load side of the meter base so if the building goes into a fault condition at least the meter will not blow off the wall. This is the response I received from the plans examiner.

My problem is now is that installation of the meter base falls under NEC rules and is being treated as part of the building installation by the AHJ, at least in Lake County. As the engineer of record I am hard pressed to sign and seal a drawing knowing there is equipment not protected for the AIC available. Yet the AHJ continues to reject plans unless we specifically call out a fused service entrance disconnect with class J or T fuse on the load of the meter base or multimeter installation. The fuses do nothing to protect the meter base and only adds to the burden of having to get non standard disconnects and fuses not normally used in commercial applications.

Any suggestion???
Click to expand...


I happen to agree with you on this issue. That transformer has a pretty low impedance value.

I would contact the manufacturer to see if they can help. This cannot be the first time they have seen this issue.
I am willing to bet all of Mike Holts money (;) ) that the manufacturer is going to tell you to purchase a different meter that has an AIR rating for the amount of fault current available at it's lugs.
 
Vern,

Sorry its taken me so long to respond to your message. All I can say is that I am in Florida!! There never is a good reason why the AHJ or utility does what they do here. As an example on a recent project, the AHJ approved our plans with CT metering and then later called the owner to tell him not to install per the approved signed and sealed plan but if he follows the AHJ verbal mandate his service will pass. He is forcing the owner to ignore our plans and install class T or J fuses on the load side of the meter. Not too smart on the building inspectors part. If he does there will be a letter sent for sure.

Regards
 
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