2017 240.67 arc energy reduction

[iceworm]

Good morning all. It has been a while. However I can't think of many I could ask this.

So, anybody looking at 240.67.B.2. It's not effective until 2020. But, I'm not seeing any way to implement This being, "a maintenance switch that reduces the available energy from a set of fuses.

It came up is a code class. The answer I got was, "Well that is why the code gives the manufacturers until 2020 to come up with a method". Perhaps someone is on the code panel that understands how this could be done.

If anyone has any ideas, I would appreciated knowing. I'm at a loss.

 

[charlie b]

I can envision a switch that puts a different set of fuses into the circuit, or one that inserts an impedance element. I don't like either idea though.

 

[ron]

I don't have a 2017 yet, but 2014 (240.87(B)) allows you to pick one of the five choices, where the maintenance switch is only one of them, and you would only pick that one if you have a breaker.

Is the language in 2017 different?

 

[packersparky]

I don't have a 2017 yet, but 2014 (240.87(B)) allows you to pick one of the five choices, where the maintenance switch is only one of them, and you would only pick that one if you have a breaker.

Is the language in 2017 different?

Yes. 240.87(B) now gives us seven choices

(B) Method to Reduce Clearing Time. One of the following
means shall be provided:
(1) Zone-selective interlocking
(2) Differential relaying
(3) Energy-reducing maintenance switching with local status
indicator
(4) Energy-reducing active arc flash mitigation system
(5) An instantaneous trip setting that is less than the available
arcing current
(6) An instantaneous override that is less than the available
arcing current
(7) An approved equivalent means

and 240.67(B) gives us four

(B) Method to Reduce Clearing Time. A fuse shall have a
clearing time of 0.07 seconds or less at the available arcing
current, or one of the following shall be provided:
(1) Differential relaying
(2) Energy-reducing maintenance switching with local status
indicator
(3) Energy-reducing active arc flash mitigation system
(4) An approved equivalent means

 

[iceworm]

I can envision a switch that puts a different set of fuses into the circuit, or one that inserts an impedance element. I don't like either idea though.

Yeah - I thought of two disconnects with motor operators. One with fast acting non-coordinated fuses

Didn't think of switching in an impedance. Still, as you said, I don't like either one much either.

Additionally, as for 240.67, I don't understand the concept of differential relaying as it could possibly apply to fuses.

Still, I am hoping someone has a direct connect to the code panel and can give me some clues.
----------------------------------

When 240.87 first came in, I wondered if the code panel was doing an end run at being a design document and telling us to use fuses.

Considering the changes to 240.87 and the addition of 240.67, now I'm wondering if they have changed their mind and now want us to use CBs with a maintenance switch that reduces the Short-Time to "no intentional delay".

 

[ron]

Considering the changes to 240.87 and the addition of 240.67, now I'm wondering if they have changed their mind and now want us to use CBs with a maintenance switch that reduces the Short-Time to "no intentional delay".

Both 240.87 and 240.67 are in the 2017 code? The conditions must be different?

BTW, it wouldn't be the first time the CMP had a bias toward fuses or breakers. The selectivity requirements in 700.28 and 701.27 and the definition of selective coordination being the full range were initially lobbied into the code by Bussman. Now that the breaker manufacturers have tested combinations, it is working ok for CBs too, but I was annoyed for a while at the situation, because I have been in too many critical situations where an old fuse blew and there was no spare to be found ....

 

[don_resqcapt19]

Both 240.87 and 240.67 are in the 2017 code? The conditions must be different?

BTW, it wouldn't be the first time the CMP had a bias toward fuses or breakers. The selectivity requirements in 700.28 and 701.27 and the definition of selective coordination being the full range were initially lobbied into the code by Bussman. Now that the breaker manufacturers have tested combinations, it is working ok for CBs too, but I was annoyed for a while at the situation, because I have been in too many critical situations where an old fuse blew and there was no spare to be found ....

Unlike the selective coordination that was submitted by Bussmann, the arc energy reduction for fuses was not submitted by a manufacturer. It was a submission from an IBEW safety guy.

 

[iceworm]

Don -
Do you have a link to the submission? Maybe that would have some clues.

 

[petersonra]

maybe you could put in reactors that are normally shorted out by a switch or a contactor. To reduce the arc energy you could open the switch or contactor.

 

[iceworm]

Yeah one could BUT:
1200A reactors sized to double the impedance (not saying that has to be - just for example). Definitely bigger than a breadbox, smaller than a Volkswagen. Cost maybe half of the 500KVA xfm feeding the 208V system. And the voltage regulation just went into the toilet for the duration of the maintenance.

More and more I'm leaning toward the point is to force designs toward CBs with electronic trips. Consider an electronic trip with a maintenance setting costs the same and takes the same space as a CB without a maintenance setting.

Ah ... New thought:
Maybe the Fuse MFGs will bring out an 1199A disconnect and fuses, similar to 601A fuses. Probably would only last for one code cycle:roll:

Ah .. ANT:
Perhaps the point is push fuse mfgs to come up with a trip curve that trips in .06s at 3X - 10X. This one is kind of serious. Consider the twisted fuse TCC that are available for transformer energization, motor starting, and high current semiconductors. Fuse MFG are tricky - they could do this. Maybe that is the answer.

ice

 

[don_resqcapt19]

Don -
Do you have a link to the submission? Maybe that would have some clues.

Go to nfpa.org/70, scroll down to "first draft report" under "archived revision information". (This new process they are using for code changes is not near as easy to use as the old ROP/ROC process.) Once you get to the section in the first draft report, you can click on the "FR-xxxx" in the upper right, and that takes you to the panel action, and on that page there is a link you can click on to see the original PI.

 

[iceworm]

Don - Thanks. I looked it up. Couldn't exactly follow your directions, but I think I got close enough to see the proposal. Even read the one dissenting comment.

Sigh - still don't understand the physics behind how one would either get a maintenance switch without essentially duplicating the install. And, completely at a loss about how one could do differential relaying with fuses.

Maybe they used a shotgun to a board of random electrical phrases, knowing they have three years to change the words so they meet the equipment available and of course, meet known physics.

Depressing

Thanks guys for looking in.

iceworm

 

[mbrooke]

Yeah one could BUT:
1200A reactors sized to double the impedance (not saying that has to be - just for example). Definitely bigger than a breadbox, smaller than a Volkswagen. Cost maybe half of the 500KVA xfm feeding the 208V system. And the voltage regulation just went into the toilet for the duration of the maintenance.

More and more I'm leaning toward the point is to force designs toward CBs with electronic trips. Consider an electronic trip with a maintenance setting costs the same and takes the same space as a CB without a maintenance setting.

Ah ... New thought:
Maybe the Fuse MFGs will bring out an 1199A disconnect and fuses, similar to 601A fuses. Probably would only last for one code cycle:roll:

Ah .. ANT:
Perhaps the point is push fuse mfgs to come up with a trip curve that trips in .06s at 3X - 10X. This one is kind of serious. Consider the twisted fuse TCC that are available for transformer energization, motor starting, and high current semiconductors. Fuse MFG are tricky - they could do this. Maybe that is the answer.

ice

I guess to basically force a "hot line" tag at the 600 volt and under level :happyno:

 

[mbrooke]

Sigh - still don't understand the physics behind how one would either get a maintenance switch without essentially duplicating the install. And, completely at a loss about how one could do differential relaying with fuses.


iceworm

A ton of CTs and a shunt trip main breaker. At least thats my best guess. But who knows, at this point we have the most bureaucratic code on earth.

 

[petersonra]

Yeah one could BUT:
1200A reactors sized to double the impedance (not saying that has to be - just for example). Definitely bigger than a breadbox, smaller than a Volkswagen. Cost maybe half of the 500KVA xfm feeding the 208V system. And the voltage regulation just went into the toilet for the duration of the maintenance.
ice

could do the same thing with a set of fuses. just jump them out of the circuit when you don't want them to operate.

 

[don_resqcapt19]

Don - Thanks. I looked it up. Couldn't exactly follow your directions, but I think I got close enough to see the proposal. Even read the one dissenting comment.

Sigh - still don't understand the physics behind how one would either get a maintenance switch without essentially duplicating the install. And, completely at a loss about how one could do differential relaying with fuses.

Maybe they used a shotgun to a board of random electrical phrases, knowing they have three years to change the words so they meet the equipment available and of course, meet known physics.

Depressing

Thanks guys for looking in.

iceworm

There are fused overcurrent protection systems with switching devices so they can comply with 230.95. Additional relaying for that type of setup would be able to accomplish the arc energy reduction.

 

[iceworm]

There are fused overcurrent protection systems with switching devices so they can comply with 230.95. Additional relaying for that type of setup would be able to accomplish the arc energy reduction.

Truly, I have never seen one of these. However, could be. I looked up High Pressure Contact switches (HPC). They are pretty fast, GE spec says .03 seconds. Rated to interrupt 12X current , 3 times. So a 1200A switch would be rated to interrupt 14,400A.

I think you got something here. Possibly even handle a differential relaying scheme.

Good thinking.

ice