Cold-Sequence Switch & AIC Ratings

[kcunningham59]

I am curious what others are doing in this situation since I have stumbled across it on a few jobs. As you know the standard AIC rating of a disconnect without fusing is 10,000A. The available utility fault current is generally higher than this. When POCOS require a cold-sequence switch how do you handle? If you fuse the switch it can't be the SE point because POCO usually won't allow ground wires through the CT cabinet. If you don't fuse it, it is not sized to handle the available fault current. Current limiters are one option. Another is to fuse it and label it as the meter disconnect switch as stated in the NEC and then the first disconnecting means after the CT would be the service point. Thoughts? I don't really see any issues with the latter as long as it is labeled as such as the NEC suggests.

 

[tom baker]

We have had the requirement for a switch ahead of the meter since 1980 on 480 services 200 A and under
If there available fault current is over 200A we use a fused disconnect and put our lock on it. Took a few years for POCO to accept disco with customer lock ahead of meter
And this disco is not the service point. The service point is inside the building

 

[augie47]

Our POCOs won't accept fused disconnects and so far the inspectors have looked at it as "utility equipment not under NEC" and ignored the 10k rating,.

 

[kcunningham59]

Our POCOs won't accept fused disconnects and so far the inspectors have looked at it as "utility equipment not under NEC" and ignored the 10k rating,.

Show the local inspector 230.82 which talks about meter disconnects. "Meter disconnect switches nominally rated not in excess of 1000 volts that have a short-circuit current rating equal to or greater than the available fault current, if all metal housings and service enclosures are grounded in accordance with Part VII and bonded in accordance with Part V of Article 250. A meter disconnect switch shall be capable of interrupting the load served. A meter disconnect shall be legibly field marked on its exterior in a manner suitable for the environment as follows:"

 

[roger]

Show the local inspector 230.82 which talks about meter disconnects.

He didn't say "local inspectors" he said "POCO's". He said "local inspectors" were leaving it to the POCO

 

[don_resqcapt19]

Easiest fix is to have the utility specify the service point is on the load side of the meter disconnect.

 

[electrofelon]

If you fuse the switch it can't be the SE point because POCO usually won't allow ground wires through the CT cabinet.

One option is to fuse it and not call it the service disconnect. I do not see any restriction in the NEC for the meter disconnect to have fuses.

Another option, if for some reason your POCO is not allowing 'ground wires" through the meter, is to use 250.142(B) exception #2

 

[augie47]

Our POCOs lock the cold sequence switches to prevent access to wiring prior to the meter. They do not want these switches to be fusible as they would have to respond in the event a fuse was blown

 

[tom baker]

What this comes down to is agreement between the POCO and AHJ. One of the 480 services with unfused disconnect I did in about 1990 I took a picture and sent it to Mike Holt, it’s in several of his books