fuses vs CB's for selectivity

[mshields]

I'm having a devil of a time achieving 0.01 sec selectivity on an Emergency branch of a 100kW 208Y/120V generator. Would like to consider using fuses but am wondering if I'll have to use fuses all the way down to the 20A, 120V Emergency lighting circuits. Do they even make 42 pole, fusible switch branch circuit panelboards. If so, who makes em. Am open to suggestion.

Thanks,

Mike

 

[don_resqcapt19]

I'm having a devil of a time achieving 0.01 sec selectivity on an Emergency branch of a 100kW 208Y/120V generator. Would like to consider using fuses but am wondering if I'll have to use fuses all the way down to the 20A, 120V Emergency lighting circuits. Do they even make 42 pole, fusible switch branch circuit panelboards. If so, who makes em. Am open to suggestion.

Thanks,

Mike

Not sure if they still make it, but right after Bussmann put the rule in the NEC, they had a panelboard with both fuses and breakers connected in series. They said it provided the required selective coordination.

Also if you are using the 2014 code, the common reading of the new definition of selective coordination is that it has to go to time "zero"

 

[mshields]

time zero

time zero

How does the "selective coordination having to go to time zero" effectively change the requirement for 0.01 seconds on the Emergency branch. Isn't that just another way of saying it has to coordinate in all area's of the respective time current characteristic curves for the breakers involved?

 

[mbrooke]

Unless you can engineer every single trip curve on your breakers than fuses would be right for you.


This is one company:


http://www.cooperindustries.com/con...l/products/quik_spec_fusible_panelboards.html

 

[mbrooke]

Another one, but its more for data centers:

http://www.tnbpowersolutions.com/cyberex_hpp

 

[don_resqcapt19]

How does the "selective coordination having to go to time zero" effectively change the requirement for 0.01 seconds on the Emergency branch. Isn't that just another way of saying it has to coordinate in all area's of the respective time current characteristic curves for the breakers involved?

If you are talking about an Article 517 application the definition of selective coordination as found in Article 100 does not apply. There is another defintion in Article 517 that only applies to that article.

If you are talking about selective coordination as required in Articles 700 and 701, the new definition in Article 100 applies.

 

[GoldDigger]

If you are talking about an Article 517 application the definition of selective coordination as found in Article 100 does not apply. There is another defintion in Article 517 that only applies to that article.

If you are talking about selective coordination as required in Articles 700 and 701, the new definition in Article 100 applies.

In [2011] I do not find a definition of selective coordination in 517. Only use use of "selective" specifically with respect to ground fault detection.

 

[jim dungar]

We regularly are able to coordinate breakers all the way down to 'time zero'. We pay attention to the available fault currents and we use the selectivity tools available from breaker manufacturers. We also rarely try to coordinate more than 3 devices in series.

This is an on-line version from Schneider Electric, but every major vendor has an equivalent.
http://www.schneider-electric.us/sites/us/en/customers/consulting-engineer/nema-selector.page

It is extremely unlikely that you would be able to have 'branch breakers' coordinate with fuses.