wire protection

[Brandon Loyd]

If I find a 200 amp breaker with 100 amp wire installed, but follow the conduit 200 feet away to find that wire feeds a 100 amp disconnect, with 100 amp fuses installed, which serves a chiller, is the wire considered protected from source to load?

 

[socalelect]

If i read your post correctly , and the start of the run is the 200 amp CB i would say your wires are not protected , as your CB is 200 amp and your wire is only rated for 100 amps i believe for 100 amps you would most likely have #2 cu @75deg and for 100 amps you would probably need 3o or 4o cu @75deg for 200 amps . so basically IMO your conductors would be damaged before your cb trips if there was a fault between your CB and disco

 

[kwired]

What you have can be called a feeder tap but must meet provisions in 240.21(B).

With a length of 100 feet it pretty much has to be an outside feeder tap or in a high bay manufacturing facility as mentioned in 240.21(B)(4). All other feeder taps are limited to 25 feet or less.

 

[hurk27]

If i read your post correctly , and the start of the run is the 200 amp CB i would say your wires are not protected , as your CB is 200 amp and your wire is only rated for 100 amps i believe for 100 amps you would most likely have #2 cu @75deg and for 100 amps you would probably need 3o or 4o cu @75deg for 200 amps . so basically IMO your conductors would be damaged before your cb trips if there was a fault between your CB and disco

Fault current and overload current protection is two different animals, a bolted fault on a 100 amp feeder would most definitely open a 200 amp breaker, and overload protection is handled by the 100 amp breaker in the disconnect, but the 25' tap rule must be followed if inside.

This is the same reason we are allowed to run smaller conductors to a motor that has overload protection but fed by a higher amperage breaker.

 

[david]

This is the same reason we are allowed to run smaller conductors to a motor that has overload protection but fed by a higher amperage breaker.

So you need to go to 440.6 in regards to the wire size and oveercurrent protection as hurk pointed out there are additonal considerations when sizing wire to chillers.

 

[kwired]

Fault current and overload current protection is two different animals, a bolted fault on a 100 amp feeder would most definitely open a 200 amp breaker, and overload protection is handled by the 100 amp breaker in the disconnect, but the 25' tap rule must be followed if inside.

This is the same reason we are allowed to run smaller conductors to a motor that has overload protection but fed by a higher amperage breaker.

So you need to go to 440.6 in regards to the wire size and oveercurrent protection as hurk pointed out there are additonal considerations when sizing wire to chillers.

There is more to look into here before condemning the installation. The OP says there is 200 amp CB at the supply and 100 amp fuses at the load end of this feeder. If we had same type of overcurrent protection at each end this may be a little less complicated. The breaker may have needed to be increased because it had problems holding under starting conditions. That would be acceptable but is likely 125 or 150 would have been enough to hold during starting.

 

[Brandon Loyd]

I come across this a lot when inspecting facilities. I find what appears to be unprotected wire, but then on the other end of the room, the wire feeds a smaller breaker/fuses which are correctly sized for overcurrent. Or mabye the motor these wire serve have internal thermal protection. I origianlly thought these wires are still unprotected because what if someone tapped off the wires between the breaker and fuses, thus increasing the load, they may have issues. But if these wires were ran undergroung, this could never happen. So my thought now is these wires serve one purpose only (a motor), and because there is proper overcurrent protection at the motor, there is no way those wires will ever see more than 100 amps. I am trying to confirm my thinking on this is correct? Or does a 25 ft tap rule apply?

 

[kwired]

I come across this a lot when inspecting facilities. I find what appears to be unprotected wire, but then on the other end of the room, the wire feeds a smaller breaker/fuses which are correctly sized for overcurrent. Or mabye the motor these wire serve have internal thermal protection. I origianlly thought these wires are still unprotected because what if someone tapped off the wires between the breaker and fuses, thus increasing the load, they may have issues. But if these wires were ran undergroung, this could never happen. So my thought now is these wires serve one purpose only (a motor), and because there is proper overcurrent protection at the motor, there is no way those wires will ever see more than 100 amps. I am trying to confirm my thinking on this is correct? Or does a 25 ft tap rule apply?

If the minimum size circuit breaker required to be able to start the motor is what you have then it likely is alright, otherwise tap rules apply. If it is standard I/T 200 amp breaker and fuses are 100 amp time delay fuses I find it hard to believe 200 amp breaker is minimum size needed to be able to hold while starting. I might believe that a 150 amp breaker is needed, and would not question at all a 125 (assuming the 100 amp fuse is smallest fuse needed to hold for starting).

 

[DARUSA]

Short circuit protection inverse time breakers up to 250% ,instantaneus trip breakers up to 800% .
OL protection up to 40deegres C, 115% SF -115% in most cases.
The Installation appears to meet the requirements of the Article 430.

 

[kwired]

Back in OP it was said this was feeding a chiller. Very likely the chiller has a nameplate with maximum overcurrent protection on the nameplate. Even if it does not, the rules in 430 apply. (Nameplates almost always match what you would calculate using rules in 430 anyhow, they have just done the calculations for you.) T430.52 says 250% of full load current for inverse time breakers and 175% for time delay fuses. (These are most likely what we have in the OP, although it was not mentioned). If the 100 amp fuses are based on 175% of full load current then the full load current is near 60 amps. If full load current is 60 amps then the maximum I/T circuit breaker is 150 amps. If that will not allow the motor to start then you may go larger. So unless the 150 would not allow starting I say you can not use the 200 unless you also comply with feeder tap rules for the portion with the 200 amp breaker providing protection, or increase the feeder conductors to 200 amps. Also don't forget that 175 is a standard size and likely should be tried before the 200 if the 150 did not allow starting.

If I find a 200 amp breaker with 100 amp wire installed, but follow the conduit 200 feet away to find that wire feeds a 100 amp disconnect, with 100 amp fuses installed, which serves a chiller, is the wire considered protected from source to load?

 

[Brandon Loyd]

Another example

Another example

I found a 400 amp breaker in a distribution panel with 350 kcmil wire, feeding a 1200 amp main breaker for a few sections of MCC approx. 200 feet away. Granted the wire should be at least 600 kcmil if it is fed from a 400 amp breaker. Lets say it is 600 kcmil, would the wire be considered protected for overload protection?

 

[kwired]

I found a 400 amp breaker in a distribution panel with 350 kcmil wire, feeding a 1200 amp main breaker for a few sections of MCC approx. 200 feet away. Granted the wire should be at least 600 kcmil if it is fed from a 400 amp breaker. Lets say it is 600 kcmil, would the wire be considered protected for overload protection?

Same general rules as first example. If you have a 400 amp conductor (actually 351 or higher since 350 is a standard size) it must be protected with a minimum of 400 amp overcurrent device. The 1200 amp main at the load end of the circuit means nothing when it comes to overcurrent protection if there is a smaller protective device ahead of it.

The only way it can be over 400 amps is for certain loads that allow higher overcurrent protection like motors, capacitors, transformers, that typically need to allow for so called inrush current when first energized.

 

[Brandon Loyd]

Let imagine the 1200 amp breaker is a non-fused disconnect that is simply used as a disconnecting means at the MCC Section. If the wire was rated for 400 amps, in my eyes the wire would be protected by the 400 amp breaker at the start of the circuit. Couldn't you view the 1200 amp breaker as simply a disconnecting means, as is it obviously to large, and the 400 amp breaker as your protection?

 

[kwired]

Let imagine the 1200 amp breaker is a non-fused disconnect that is simply used as a disconnecting means at the MCC Section. If the wire was rated for 400 amps, in my eyes the wire would be protected by the 400 amp breaker at the start of the circuit. Couldn't you view the 1200 amp breaker as simply a disconnecting means, as is it obviously to large, and the 400 amp breaker as your protection?

Yes, and it is not too large, just larger than it needs to be. Like taking a 727 on a trip with one passenger when a single engine plane would do.