mstrlucky74
Senior Member
- Location
- NJ
Which fuses are more common in a fused safety switch. Timedelay or fast acting? Thanks.
Which fuses are more common in a fused safety switch. Timedelay or fast acting? Thanks.
I didn't mean this the way it sounds to me now. Molded Case Breakers operate without an intentional time delay once they enter their Inst range.After all, circuit breakers are time delay.
It depends but I would have to say time delay as most safety switches are used for some motor or a/c units. If the equipment is not a motor of any kind then you will see non time delay. At least that has been my experience. We hardly ever see fuses anymore.
If proper overcurrent protection is already provided upstream - it is not necessary to provide it again at a local disconnecting means whether the disconnect is required or not.Most switches you install nowadays are non fused?
Agreed, but in my experience the vast majority of stock disconnects are gonna be fused.If proper overcurrent protection is already provided upstream - it is not necessary to provide it again at a local disconnecting means whether the disconnect is required or not.
Agreed, but in my experience the vast majority of stock disconnects are gonna be fused.
When I did plant maintenance I spec'd non-fused because it was one less part to troubleshoot, and they were often special-order.
And especially if you are in a competitive situation you are going to use the $12 - $15 pull out type unfused disconnect that is popular on AC units.That is probably true in commercial work but we never see a heat pump or an a/c unit in residential that demands a fuse. I can't remember the last time we used a fused disconnect.
When I did plant maintenance I spec'd non-fused because it was one less part to troubleshoot, and they were often special-order.
That is probably true in commercial work but we never see a heat pump or an a/c unit in residential that demands a fuse.
And especially if you are in a competitive situation you are going to use the $12 - $15 pull out type unfused disconnect that is popular on AC units.
No problem if in an application where 60c NM cable is being used anyway.A lot of those are only rated 60c so that cost savings has the potential to require a larger conductor.
If proper over current protection is already provided upstream - it is not necessary to provide it again at a local disconnecting means whether the disconnect is required or not.
You sure on that? Some of the literature on the Siemens switches I used to use says 100,000 ASCCR. Not sure if they have an interrupt rating as they are not OCPDs.Keep in mind regardless of the units requirements non fused switches are limited to 10,000 amps fault current...
In general, there is almost no need to use non-time delay fuses in the <600A range....When I do arc flash studies, a common recommendation is to get rid of the inexpensive fuses.
I would bet the fine print says when used with upstream protection using a specific fuse or breaker.You sure on that? Some of the literature on the Siemens switches I used to use says 100,000 ASCCR. Not sure if they have an interrupt rating as they are not OCPDs.
A lot of those are only rated 60c so that cost savings has the potential to require a larger conductor.
No problem if in an application where 60c NM cable is being used anyway.
Why?Both hold true in our facility, instantaneous are rarely used; and since arc flash studies have been done, any RK5 fuses are to be replaced with the RK1 class whenever the opportunity arises.