New Section 230.91B

Josh111

Senior Member
Location
USA
The proposed 2023 code has a rule requiring an overcurrent device in a separate enclosure for the service disconnect for services over 1600 amps. Does anyone else think this as written may require more than is needed for safety? For instance, 2 sections that have thick sheet metal in between them and with insulators around the bus to seal it would likely achieve the safety objective proposed here. But it seems the text requiring a separate "enclosure" may needlessly create difficulty. Wouldn't it be better if they said something like "the service disconnect shall be in its own section that is independently capable of sustaining all fault current likely to be imposed."

I might submit a comment but wanted to see if there was any insight here on this.

Secondly BTW: It would be nice if they would synchronize the threshold for some of these rules about large equipment. One size main for large equipment rules in 110.26, a different one for when to mark the clearing time in 110.16, one more for when to use arc energy reduction, one for when to use ground fault protection of equipment, and yet another now for when to use a separate enclosure. Many of these are rules where, having it at all levels may benefit but may be infeasible. So it's not like they can't settle on a common value for all these extra requirements.
 

romex jockey

Senior Member
Location
Vermont
The proposed 2023 code has a rule requiring an overcurrent device in a separate enclosure for the service disconnect for services over 1600 amps. Does anyone else think this as written may require more than is needed for safety? For instance, 2 sections that have thick sheet metal in between them and with insulators around the bus to seal it would likely achieve the safety objective proposed here. But it seems the text requiring a separate "enclosure" may needlessly create difficulty. Wouldn't it be better if they said something like "the service disconnect shall be in its own section that is independently capable of sustaining all fault current likely to be imposed."

I might submit a comment but wanted to see if there was any insight here on this.

Secondly BTW: It would be nice if they would synchronize the threshold for some of these rules about large equipment. One size main for large equipment rules in 110.26, a different one for when to mark the clearing time in 110.16, one more for when to use arc energy reduction, one for when to use ground fault protection of equipment, and yet another now for when to use a separate enclosure. Many of these are rules where, having it at all levels may benefit but may be infeasible. So it's not like they can't settle on a common value for all these extra requirements.
my spidey sense sez the manufacturers are making good on their previous failed 408.3 (A) (2) attempt some few cycles ago

~RJ~
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
You may be thinking of my proposals to require a separate compartment for the service disconnect, and those were opposed by the manufactures.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
The proposed 2023 code has a rule requiring an overcurrent device in a separate enclosure for the service disconnect for services over 1600 amps. Does anyone else think this as written may require more than is needed for safety? For instance, 2 sections that have thick sheet metal in between them and with insulators around the bus to seal it would likely achieve the safety objective proposed here. But it seems the text requiring a separate "enclosure" may needlessly create difficulty. Wouldn't it be better if they said something like "the service disconnect shall be in its own section that is independently capable of sustaining all fault current likely to be imposed."

I might submit a comment but wanted to see if there was any insight here on this.

Secondly BTW: It would be nice if they would synchronize the threshold for some of these rules about large equipment. One size main for large equipment rules in 110.26, a different one for when to mark the clearing time in 110.16, one more for when to use arc energy reduction, one for when to use ground fault protection of equipment, and yet another now for when to use a separate enclosure. Many of these are rules where, having it at all levels may benefit but may be infeasible. So it's not like they can't settle on a common value for all these extra requirements.
Is there a product standard that would apply so the manufacturer's have some guidance to built to? Also not sure you could have a "fit-all" design, as there are areas that have a line side available fault current above 200,000 amps.
 

Josh111

Senior Member
Location
USA
Is there a product standard that would apply so the manufacturer's have some guidance to built to? Also not sure you could have a "fit-all" design, as there are areas that have a line side available fault current above 200,000 amps.
As for whether there is a product standard that one would apply I don’t know if there is one. However, we have rules requiring that equipment be capable of sustaining fault current likely to be imposed. This normally means that if all of the covers are bolted onto the gear and there is a fault in the gear, that the cover should not fly off and injure someone. If they say that a separate enclosure is required to protect someone in another section of switchgear from being injured in an arc flash, then how can they say that their gear can sustain the fault current likely to be imposed? It would seem to me that the same level of safety that would be had at the two or three exposed sides of a multi section pad mounted switchboard could be achieved on the fourth side simply by having thicker metal instead of requiring it to be in a separate enclosure.

On whether there could be a fit all design, I don’t think there could be. But just like mentioned we deal with fault current capability of enclosures all the time and it would seem that a thicker wall on the side of the enclosure that faces another section would bring that side to be just as strong as the other sides, which have already been required to be able to contain the fault current likely to be imposed.

Quite frequently the NEC makes rules and then UL comes up with the standard for what is considered to meet the rules.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
As far as I know, unless you have blast resistant switchgear, there is no expectation that the blast will be contained within the equipment. Take a look at the metal thickness, number and size of the bolts, and number, size, and type of cover latches, in blast resistant switchgear compared to conventional gear.
 

Josh111

Senior Member
Location
USA
I thought all switchgear was supposed to be able to withstand the fault current likely to be imposed. Meaning it should be capable of containing it. I think even Mike Holt’s program I took years back mentioned such was a requirement of I believe it was 110.10. I thought that’s why you don’t have to suit up in an electrical room unless you are actually switching or removing the covers.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
I thought all switchgear was supposed to be able to withstand the fault current likely to be imposed. Meaning it should be capable of containing it. I think even Mike Holt’s program I took years back mentioned such was a requirement of I believe it was 110.10. I thought that’s why you don’t have to suit up in an electrical room unless you are actually switching or removing the covers.
Being able to handle a fault is not the same as containing it.

NFPA70E does not consider just being in a room near electrical gear as requiring PPE. Some companies may require it, but it is not common.
 

Josh111

Senior Member
Location
USA
Being able to handle a fault is not the same as containing it.
Perhaps so. But even the 70 E training offered directly by the NFPA had slides and audio giving an example of a case where the entirety of the interior of a piece of switchgear was destroyed by an arc flash but the equipment contained the fault and it said that this was an example of a complaint installation because when the covers were on it didn’t damage anything outside of the equipment.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
... when the covers were on it didn’t damage anything outside of the equipment.
The covers should stay on, however they may deform allowing the products of the arcing event to escape from the enclosure.
 

pv_n00b

Senior Member
Location
CA, USA
According to PI 4261, the purpose of this is to protect workers working on energized equipment in sections adjacent to the section with the main disconnect from arc flash energy on the line side of the main disconnect. This is a valid concern in switchboards since there is no arc flash energy protection between sections. Arc fault incident energy is usually much higher on the line side of the main disconnect, particularly on service entrances, than on the load side. The partitions between sections and around the line side of the main disconnect are there only for protection from contact with energized conductors and generally don't stop arc flash migration between sections. Switchgear has much greater protection between sections and I feel should be excluded from this requirement. I agree that this change will significantly improve safety when working on energized switchboards but the downside is a big problem with the additional room needed for isolated sections. And preparing for energized work that may never be allowed seems to be excessive.
 

pv_n00b

Senior Member
Location
CA, USA
I want to add to the above that while LV switchgear generally has better isolation between sections it's not tested to prevent arc fault propagation. So unless it's specifically arc fault rated it should be treated like a switchboard.
 

Josh111

Senior Member
Location
USA
My thinking is just that if they had a thicker metal barrier and some reinforcement between the sections it likely would be sufficient. Currently they might use, say 1/8” thick steel around the outside of a switchboard, and a 1/32” or thinner sheet metal barier between the sections. If the sections were 1 wall per section and the same thickness as the outside facing walls (meaning a double thick barrier between service disconnect and feeder sections) this may be a major improvement that might resolve the concern that prompted the PI but in an easier manner.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
I am pretty sure the equipment manufacturers have been trying to developed an arc flash solution for the past decade. I don't think any legal department is going to let them say they have something, until there is an industry accepted testing standard.
 
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