Cold-Sequence Switch & AIC Ratings

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kcunningham59

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Location
Audubon, NJ
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.
 
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
 
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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,.
 
augie47 said:
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,.
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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:"
 
Easiest fix is to have the utility specify the service point is on the load side of the meter disconnect.
 
kcunningham59 said:
If you fuse the switch it can't be the SE point because POCO usually won't allow ground wires through the CT cabinet.
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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
 
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
 
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
 
kcunningham59 said:
yeah but then still you either have a fused disconnect switch on the line slide that some POCO's would prefer not be fused. When it isn't fused, AIC issues conflicting with the NEC
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See if you can have a conversation with the head of the metering department and inform them of your concerns.

Here, when the issue was brought to the utilities attention, they updated the standard to allow for fused switches.
My method was to use a Molded Case Switch (MCS), this will open under a fault but not an overload scenario. The local utility signed off on this in advance.
Your worst case going this path is in a fault, which device opens first. The MCS or your main CBer or fuse?
The MCS requires an AIC rating above what the AFC is at its location.

Your concerns are valid. I looked at it if I was telling an EC to install a piece of equipment it needed to be NEC compliant...regardless of a utility company telling you to do something that may not be. Not much of an argument if the NFD fails.
 
kcunningham59 said:
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.
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Just curious what size service are you taking about? You mention CT cabinet. Are your utilities requiring or disconnect switch ahead of a CT cabinet? I have never come across that requirement and only find the disconnect required for a self-contained meter socket. If it's 200 amp, it's quite unlikely you will exceed the 10K sccr of an NF Disco. For a class 320 it is much more plausible, however I find most utilities do not allow self-contained class 320 480v services, and require a CT for anything over 200 for non-residential. So at least for me and the utilities I work for it's kind of a non-issue.
 
MyCleveland said:
See if you can have a conversation with the head of the metering department and inform them of your concerns.

Here, when the issue was brought to the utilities attention, they updated the standard to allow for fused switches.
My method was to use a Molded Case Switch (MCS), this will open under a fault but not an overload scenario. The local utility signed off on this in advance.
Your worst case going this path is in a fault, which device opens first. The MCS or your main CBer or fuse?
The MCS requires an AIC rating above what the AFC is at its location.

Your concerns are valid. I looked at it if I was telling an EC to install a piece of equipment it needed to be NEC compliant...regardless of a utility company telling you to do something that may not be. Not much of an argument if the NFD fails.
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Great feedback! Thank you
 
electrofelon said:
Just curious what size service are you taking about? You mention CT cabinet. Are your utilities requiring or disconnect switch ahead of a CT cabinet? I have never come across that requirement and only find the disconnect required for a self-contained meter socket. If it's 200 amp, it's quite unlikely you will exceed the 10K sccr of an NF Disco. For a class 320 it is much more plausible, however I find most utilities do not allow self-contained class 320 480v services, and require a CT for anything over 200 for non-residential. So at least for me and the utilities I work for it's kind of a non-issue.
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Many of my local POCO's require cold sequence for all 480V services. some require for larger service sizes only (>2,000 amps). All the jobs in questions would be on with a CT Cabinet and Meter with a disconnect upstream of the setup
 
Does the utility require a cold sequence disconnect for the entire service or just for the meter? With a CT setup, can you disconnect the meter and short the CTs without disconnecting the service?
 
kcunningham59 said:
Many of my local POCO's require cold sequence for all 480V services. some require for larger service sizes only (>2,000 amps). All the jobs in questions would be on with a CT Cabinet and Meter with a disconnect upstream of the setup
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Oh wow. So sort of following up with Winnies question, bit of you have say a 1000A CT service you are needed a 1000A disco before the CT cab?
 
kcunningham59 said:
Many of my local POCO's require cold sequence for all 480V services. some require for larger service sizes only (>2,000 amps). All the jobs in questions would be on with a CT Cabinet and Meter with a disconnect upstream of the setup
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Forgive me…my comments were based on the thread title…I missed entirely the reference to CT cabinets. My comments were based on services with feed through meter bases at 480V.
Here, NO disconnect is required ahead of the CT cabinet unless something has changed recently.

Have you actually seen this in your utilities guidelines from the company website?
If yes, please call out the website, I would like to see this.

I have had multiple ECs call when they come across what you are describing, but in each case the utility designer had misunderstood the company rules and was corrected after pointing out the error.
Is a 1600A or greater non fused switch even offered by any manufacturer?
 
MyCleveland said:
Forgive me…my comments were based on the thread title…I missed entirely the reference to CT cabinets. My comments were based on services with feed through meter bases at 480V.
Here, NO disconnect is required ahead of the CT cabinet unless something has changed recently.

Have you actually seen this in your utilities guidelines from the company website?
If yes, please call out the website, I would like to see this.

I have had multiple ECs call when they come across what you are describing, but in each case the utility designer had misunderstood the company rules and was corrected after pointing out the error.
Is a 1600A or greater non fused switch even offered by any manufacturer?
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Just uploaded some pictures at bottom of thread
 
kcunningham59 said:
Just uploaded some pictures at bottom of thread
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I found your diagram at....
Page 198, Did not try to find the text you show starting with (5.).

Document is dated March-2024.

I am stumped on why they are demanding this. Spoke with a few local EE's here to see if this has migrated outside your area and it has not...yet.
I did look at PSE&G Long Island handbook, and it does not contain this requirement.

My guess is the metering department is behind this so they can work inside the cabinet without calling for the primary to be opened.

Is this your first time having to deal with this?
Have you spoke with other EC's to see how they have dealt with the issue?
 
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