225A fused disconnect

[hhsting]

???? Can you clarify what you have? Your numbers have changed a few times now. But either way... if the disconnect is rated for 225A but is furnished with 175A fuses, you don't have an issue.

Disconnect is rated for 200A with 175A fuse.

Upstream breaker is 225A trip

I dont follow

 

[jap]

???? Can you clarify what you have? Your numbers have changed a few times now. But either way... if the disconnect is rated for 225A but is furnished with 175A fuses, you don't have an issue.

The disconnect is not rated for 225 amps.

It's a 200 amp disconnect.

JAP>

 

[hhsting]

Have you ever seen a 200 amp tap made from a 400, 600... 1200 amp feeder?

A 200 amp fused switch or breaker would be at the end of the tap.

Same fused switch often could also be a service disconnecting means and for the most part can have no real OCPD ahead of it.

Ok well you cant apply tap application.

First its not a tap it has 4/0 awg copper.

Second the disconnect is next to RTU on roof and panelboard is probably at basement

 

[kwired]

Ok well you cant apply tap application.

First its not a tap it has 4/0 awg copper.

Second the disconnect is next to RTU on roof and panelboard is probably at basement

Tap rules are about OCPD on the tap conductors. All that means is if the feeder is too long for tap rules then you must have conductors sized per the upstream OCPD device. If your upstream device were a 200 amp OCPD, you wouldn't even need fuses in your disconnect.

 

[hhsting]

Tap rules are about OCPD on the tap conductors. All that means is if the feeder is too long for tap rules then you must have conductors sized per the upstream OCPD device. If your upstream device were a 200 amp OCPD, you wouldn't even need fuses in your disconnect.

I see the point but its not tap so Forget tap rules.

Where in code it says 175A internal fuse can protect 200A disconnect?

 

[kwired]

I see the point but its not tap so Forget tap rules.

Where in code it says 175A internal fuse can protect 200A disconnect?

What is the point of installing a fuse if you not lowering the protection level? These are intended to do just that.

 

[hhsting]

What is the point of installing a fuse if you not lowering the protection level? These are intended to do just that.

Yea of the downstream cable device not for device in which their is fuse. Does code say anywhere disconnect would be protected by internal fuse?

 

[Rock86]

Yea of the downstream cable device not for device in which their is fuse. Does code say anywhere disconnect would be protected by internal fuse?

Its a 200A rated disconnect. I could install 30A fuses if I wanted. If I install 225A fuses, now there is a problem. Read section 240.

 

[hhsting]

Its a 200A rated disconnect. I could install 30A fuses if I wanted. If I install 225A fuses, now there is a problem. Read section 240.

Nothing in that section says internal 175A fuse would protect the 200A disco while upstream breaker can be 225A trip?

 

[kwired]

Nothing in that section says internal 175A fuse would protect the 200A disco while upstream breaker can be 225A trip?

Find us any section that says you must have ocpd ahead of the switch.

You will find somewhere that you typically need a switch ahead of the fuses, this so that you can service the fuses while not energized.

 

[Rock86]

Nothing in that section says internal 175A fuse would protect the 200A disco while upstream breaker can be 225A trip?

The 175A is not protecting the disconnect switch... well it kind of is... but that is not their main purpose, they are protecting the equipment downstream. the 225A breaker is protecting the conductors feeding to the disconnect. Again... read 240

 

[hhsting]

Find us any section that says you must have ocpd ahead of the switch.

You will find somewhere that you typically need a switch ahead of the fuses, this so that you can service the fuses while not energized.

I dont disagree that breaker ahead of disco is needed.

I am just saying if the disco is rated at 200A then upstream breaker should be 200A size not 225A otherwise provide 225A disco.

Internal fuses in disco are for downstream feeder and device protection

 

[hhsting]

The 175A is not protecting the disconnect switch... well it kind of is... but that is not their main purpose, they are protecting the equipment downstream. the 225A breaker is protecting the conductors feeding to the disconnect. Again... read 240

So lets say I have 220A current the upstream breaker wont trip since its 225A

The disco enclosure is rated at 200A.

Wont the disco fry or at least burn?

 

[Rock86]

So lets say I have 220A current the upstream breaker wont trip since its 225A

The disco enclosure is rated at 200A.

Wont the disco fry or at least burn?

what caused the fault? The 175A fuses would go before the RTU could put a continuous draw of 220A upstream from the disconnect.

 

[Rock86]

I dont disagree that breaker ahead of disco is needed.

I am just saying if the disco is rated at 200A then upstream breaker should be 200A size not 225A otherwise provide 225A disco.

Internal fuses in disco are for downstream feeder and device protection

You are getting into design aspects with regards to this. There are reasons which may result in this reasoning which are not known to us.

 

[hhsting]

what caused the fault? The 175A fuses would go before the RTU could put a continuous draw of 220A upstream from the disconnect.

Anything caused it. What about if its 180A instead of 220A?

 

[hhsting]

You are getting into design aspects with regards to this. There are reasons which may result in this reasoning which are not known to us.

Is that reasoning in code anywhere?

 

[kwired]

I dont disagree that breaker ahead of disco is needed.

I am just saying if the disco is rated at 200A then upstream breaker should be 200A size not 225A otherwise provide 225A disco.

Internal fuses in disco are for downstream feeder and device protection

The entire fused switch assembly is considered to the the OCPD. Just like a circuit breaker is.

You probably wouldn't question the switch component in a breaker being protected or not in a similar situation.

How about the common practice of using 15 amp snap switches on 20 amp circuits. That is fine as well if the load is not over 15 amps.

 

[hhsting]

The entire fused switch assembly is considered to the the OCPD. Just like a circuit breaker is.

You probably wouldn't question the switch component in a breaker being protected or not in a similar situation.

How about the common practice of using 15 amp snap switches on 20 amp circuits. That is fine as well if the load is not over 15 amps.

So then would 100A feeder breaker upstream be ok with 60A fused disconnect with 60A fuse downstream?

 

[kwired]

So then would 100A feeder breaker upstream be ok with 60A fused disconnect with 60A fuse downstream?

yes.

If you had a switchboard with fused units instead of circuit breakers you might very well have exact same switch and fuseholder components that were used in the stand alone "safety switches" that were made at same time period and they are ultimately connected to say a 2000 amp protected bus in the switchboard.