Protection of conductors????

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Rich1968

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I have a question with regards to protection of feeder conductors:

An installation was designed with 4 sets of #500 to feed an 800 amp distribution due to voltage drop. Question I have is the 4 sets are coming from a 2000amp switch which will have 800amp fuse reducers installed. is that considered a legal installation ? What prevents somone in the future from installing larger fuses say 2000 amp fuses and overloading the conductors..

i just dont think its good design practice / common sense ..

Please advise.
 
Nothing will prevent someone from installing larger fuses, this would be the same thing where you use a 200 amp fused disconnect with 125 amp fuses for a 125 amp feeder, anyone can put 200 amp fuses in at some time in the future

There will always be "what if's" and if you let them worry you, you will never sleep.

Roger
 
roger said:
Nothing will prevent someone from installing larger fuses, this would be the same thing where you use a 200 amp fused disconnect with 125 amp fuses for a 125 amp feeder, anyone can put 200 amp fuses in at some time in the future

There will always be "what if's" and if you let them worry you, you will never sleep.

Roger
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whatif.jpg

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Rich1968 said:
What prevents somone in the future from installing larger fuses say 2000 amp fuses and overloading the conductors?
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Well, for one thing, the fact that 4 sets of 500 MCM are not rated for 2000 amps. But in any event, the future design change is the responsibility of the future designer.
 
Overcurrent protection article 240.40

Overcurrent protection article 240.40

Guys doesnt article 240.4 protecting of Conductors cover what i was stating ???
 
Rich1968 said:
Guys doesnt article 240.4 protecting of Conductors cover what i was stating ???
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240.4 doesn't change the fact that it is possible that someone may change a perfectly legal installation into an illegal installation in the future and we have very little (if any) control over that.

Roger
 
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roger said:
240.4 doesn't change the fact that it is possible that someone may change a perfectly legal installation into an illegal installation in the future and we have very little (if any) control over that.

Roger
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Yes of course .. but my point in quoting article 240.4 is doesnt that force either adding two additional sets or reconfigure existing 2000 amp switch to 800 amps?

Rich1968
 
Rich1968 said:
Yes of course .. but my point in quoting article 240.4 is doesnt that force either adding two additional sets or reconfigure existing 2000 amp switch to 800 amps?

Rich1968
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No, it does not. 240.4 requires that conductors be protected against overcurrent in accordance with their ampacities specified in 310.15...(unless otherwise permitted or required in 240.4(A) thru (G).)

4 sets of 500mcm has an ampacity of 1520. That is clearly protected against overcurrent by an 800A OCPD. 240.4 doesn't require any change to that setup.
 
jumper said:
Wasn't there something about a 601 amp fuse size related to this?
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Until fairly recently, UL did not list fuses sized 600A and smaller in Class L construction nor did they allow fuse reducers, so 601A was the smallest amperage available if you were had an 800A or larger switch.
 
Cow said:
And someone could put a 100 amp breaker on those #10's feeding your dryer. What's the difference?
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Gentleman,

Thank you for the responses and clarifications. I still feel some limitations should be placed on conditions such as this one....

Enjoy the weekend......

Rich1968
 
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