# What Purpose?



## GEORGE D (Apr 2, 2009)

Any idea why these fuses have been incorporated into this lighting control cabinet considering all circuits are fed from 20 amp breakers? The lights are just 6 lamp T5 highbays. Ever so often I have to come change a fuse. (Not complaining just curious)


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## Wirenuting (Sep 12, 2010)

Better to pop a low fuse then to let a bad light cycle on and off until its destroyed. 
We have done that here because the re-lamping isn't done until a large number of lights burn out. 

That's my guess on the fuse.


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## Dennis Alwon (May 9, 2009)

What size fuses are they? Fuses do trip faster than breakers


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## GEORGE D (Apr 2, 2009)

Dennis Alwon said:


> What size fuses are they? Fuses do trip faster than breakers


20 amp fuses, still doesn't make sense to me for lights to need fast-acting ocpd.


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## EBFD6 (Aug 17, 2008)

GEORGE D said:


> 20 amp fuses, still doesn't make sense to me for lights to need fast-acting ocpd.


They aren't for fast acting over current protection. 

The are fast acting short circuit and ground fault protection.


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## GEORGE D (Apr 2, 2009)

EBFD6 said:


> They aren't for fast acting over current protection.
> 
> The are fast acting short circuit and ground fault protection.


Doesn't a breaker react fast enough for SC GF protection? Still makes no sense to me.


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## Dennis Alwon (May 9, 2009)

GEORGE D said:


> Doesn't a breaker react fast enough for SC GF protection? Still makes no sense to me.



Yes but a fuse is even quicker which can protect the equipment from damage. You see it on some a/c units. Why it is necessary for lights I don't know.

Do you have to do anything else when you change the fuse? I don't know enough about it but it would seem if the fuse blows then something is causing that problem.


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## GEORGE D (Apr 2, 2009)

Dennis Alwon said:


> Yes but a fuse is even quicker which can protect the equipment from damage. You see it on some a/c units. Why it is necessary for lights I don't know.
> 
> Do you have to do anything else when you change the fuse? I don't know enough about it but it would seem if the fuse blows then something is causing that problem.


this happens about once every other month. Next time i'm there I will get on phone with EMS company and have them cycle lights on and off to get an amp measurement on lighting strartup. The electrical room is remote from building, in its own modular type building, and the distance may be the problem (#12's possibly 300-500' @277 volt). I didn't have time today to even attempt that but will eventually. On the other hand that's a guaranteed service call ever so often!


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## frenchelectrican (Mar 15, 2007)

Sometime when you get the power surge the voltage and current do increase pretty fast which the convential circuit breaker is not reacting quick enough to prevent any damage to the electrionic loads which they will use the fast acting fuse.

I have done replaceing few fuse when it done the job as supposed to be even thru I know someone did install a very fast acting class A breaker some case it still not fast engough to inturpt the short circuit.

Merci,
Marc


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## Big John (May 23, 2010)

If it's a lighting panel, are the fuses in front of relays that control the lights? A short circuit can destroy a solid-state relay before a thermal breaker would ever trip, so the fast-acting fusing may be an attempt to protect the panel itself.


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## Dennis Alwon (May 9, 2009)

Big John said:


> If it's a lighting panel, are the fuses in front of relays that control the lights? A short circuit can destroy a solid-state relay before a thermal breaker would ever trip, so the fast-acting fusing may be an attempt to protect the panel itself.


That makes total sense.


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## GEORGE D (Apr 2, 2009)

Big John said:


> If it's a lighting panel, are the fuses in front of relays that control the lights? A short circuit can destroy a solid-state relay before a thermal breaker would ever trip, so the fast-acting fusing may be an attempt to protect the panel itself.


Okay that's probably the case considering it has all the components mentioned ,thanks


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