disconnect on line side of utility meter

Status
Not open for further replies.
M

mjmike

Senior Member
I have recently ran into a situation where the power company is requiring a non-fused disconnect switch on the LINE side of the utility meter on a 480V 3-phase system. I am wondering how common this is and if the NEC addresses this at all.

Thanks
 
Re: disconnect on line side of utility meter

The NEC does not address the utility side of the meter. I have no information to offer on how common this situation might be. Our resident utility power engineer (The "Other Charlie") is out of the area for a while, and might not be able to chime in. Any other utility people out there?
 
Re: disconnect on line side of utility meter

230.82(3) discusses meter disconnects on the line side of the meter. The Handbook has additional commentary. I practice in New Mexico, and in the eastern part of the State, XCEL Energy requires meter disconnects on 277/480 volt services.

Jim T
 
Re: disconnect on line side of utility meter

Do you also have a fused disconect? I work in the utility industry but in power generation. It seems weird to me that you would need 2 disconnects. Another question is does the transformer only serve you or are there multiple facilities on the same transformer?
 
Re: disconnect on line side of utility meter

Jim T.

Interesting reference. I'm in Xcel's area up here in MN. The 2004 "Blue Book" from Xcel says the following:
COLD SEQUENCE METERING

The use of line-side disconnects may be required by the Company or the local Public Authority. Line-side disconnectsshall be installed on the same wall directly ahead of and within 24" of the meter.

The cold sequence disconnect(s) shall contain provisions for a Company wire seal for the cover and a Company padlock in the operating handle lock-off position. Wire seals will be used by the Company to secure the enclosure from unauthorized entry and will allow the customer emergency access to reset breakers or to replace fuses. A Company padlock will only be used to lock disconnects in the off position for services that are shut off.

The amp rating of the cold sequence disconnect shall not exceed the amp rating of the meter socket and shall be installed in accordance with 2002 NEC? Article 230, or as may be amended.

The cold-sequence disconnect on a 3-phase, 3-wire, corner -grounded delta service shall be a 2-pole device and the grounded phase shall not be switched. The grounded phase shall not be fused in accordance with 2002 NEC? Article 230.90(B), or as may be amended.

The cold sequence disconnect(s) shall be furnished, owned, and maintained by the customer.

Cold-sequence metering will only be required on commercial and industrial self-contained meter installations for 480 volt services, for both single -phase and three-phase. In addition, no current-limiting fuses will be required for any services, inclusive of 480 volt and below. With regard to 480 volt services, the cold-sequence disconnect may be a circuit breaker, molded case circuit switch, T-type Pullout, or a non-fusible load-break safety switch. The disconnect shall be rated load-make/load-break and shall be capable of being operated and maintained without opening the enclosure. All affected services shall have the disconnect operating handle accessible to the customer without opening the enclosure cover. Multiple tenant meter sockets are permitted to have a single currentlimiting main disconnect ahead of the common bus. Local Public Authorities may not allow overcurrent protection devices ahead of the electric meter. Please check with your local Public Authority to determine requirements relevant to overcurrent protection.
Click to expand...
 
Re: disconnect on line side of utility meter

If the service is not CT metered, the POCO will not want to install or remove the electric meter with the meter socket energized. Electric meters sometimes blow up and this is the POCOs way to minimise injuries to employees. Also, meter sockets are not rated for load-breaking. At 480V, you can get quite a fire ball interrupting load by removing the meter. Just a safety issue for the POCO.
 
Re: disconnect on line side of utility meter

The POCO has the right to lock any equipment before the meter. It needs to be non-fused because they do not want to be in the fuse changing business. Our POCO has required a disconnect in front of 208 meters if the bank serves multiple customers
 
Re: disconnect on line side of utility meter

I'm also in Minnesota, and deal with Xcel Energy on a regular basis. As mentioned above, they require a disconnect on the line side of the meter on 480vac three phase services with inline meters, which essentially means it only applies to 100 or 200 amp services (400 amp services and larger use CT cabinets.) The curious thing is that they aren't necessarily consistent about it...I've had some projects where the Xcel rep told me the line side disconnect wasn't required.

Another recent change around here is that one of the other local electric utilities is prohibiting inline meters on all three phase services - CT cabinets are required, no matter what ampacity is used.
 
Re: disconnect on line side of utility meter

This new (2005) allowance in the NEC to allow a disconnect ahead of the meter, not a service disconnect, is located in 230.82 (C). The problem is the requirement for the switch to have a short-circuit rating equal to or greater than available short-circuit current. All non-fused disconnects only have a short circuit rating when protected by upstream OCD. No meter manufacturer makes a meter disconnect/meter combination yet that has a short circuit rating without protection. Most utilities do not want fusing in that disconnect as they want to keep it locked and under their control. If there is no upstream protection, such as a service, then using a nonfused disconnect is illegal and probably dangerous.

Fred
 
Re: disconnect on line side of utility meter

Originally posted by derf48:
The problem is the requirement for the switch to have a short-circuit rating equal to or greater than available short-circuit current.
Click to expand...
Fred I disagree, this unfused switch is not required to have a short-circuit rating equal to or greater than available short-circuit current.

110.9 Interrupting Rating.
Equipment intended to interrupt current at fault levels shall have an interrupting rating sufficient for the nominal circuit voltage and the current that is available at the line terminals of the equipment.

Equipment intended to interrupt current at other than fault levels shall have an interrupting rating at nominal circuit voltage sufficient for the current that must be interrupted.
Click to expand...
This meter disconnect is not intended to interrupt current at fault levels.

The meter disconnect fits the second paragraph of 110.9 and as such needs only to be rated for the load served.
 
Re: disconnect on line side of utility meter

Bob,
The short circuit current rating is from 230.82 and is a withstand rating, not an interrupt rating.

Fred
 
Status
Not open for further replies.
Top