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Old 06-28-2016, 04:38 PM   #1
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Default Feeding a Fusable Disconnect

Hello, new member here. Bit of a lurker but I have a question that I cant find a good answer for.

Customer at a factory bought a new piece of equipment (30 A Rated) to replace his 60A rated piece of equipment..

currently it is fed from a 60A breaker to another room with a 60A non-fusable disconnect and then to the equipment, an air compressor.

My first thought was to replace the 60 non-fusable disconnect with a 30 amp FUSABLE disconnect and wire the machine accordingly.

the other electrician I work with says we need to change the 60A breaker to a 30A breaker... I don't believe this is necessary. but he thinks it is.


what are your opinions??

the breakers are several hundred dollars so I don't want to replace the breaker unnecessarily.

I attached a picture here to further illustrate what I want to do.

https://1drv.ms/i/s!As6O9tf6Tvo7knPl6hpL3KK87XJs

Thanks!
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Old 06-28-2016, 05:28 PM   #2
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In theory the C/B is to protect the field wiring.

Since you've not touched it, the wiring, then you're good to go.

From the point of the new disconnect// safety switch -- now 're- fused' to 30A -- you're free to downsize those conductors from that point towards the load.

I should think that the HVAC unit will be well labelled at the new disco, at the unit, and back at the panel so that servicing techs get onto the same page -- as the reduction might confuse them.
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Old 06-28-2016, 05:45 PM   #3
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First of all welcome aboard! What you describe is done all the time with newer more energy efficient equipment. The fuses in the disco are what is going to protect your equipment.
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Old 06-28-2016, 06:06 PM   #4
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Quote:
Originally Posted by zibz View Post
Hello, new member here. Bit of a lurker but I have a question that I cant find a good answer for.

Customer at a factory bought a new piece of equipment (30 A Rated) to replace his 60A rated piece of equipment..

currently it is fed from a 60A breaker to another room with a 60A non-fusable disconnect and then to the equipment, an air compressor.

My first thought was to replace the 60 non-fusable disconnect with a 30 amp FUSABLE disconnect and wire the machine accordingly.

the other electrician I work with says we need to change the 60A breaker to a 30A breaker... I don't believe this is necessary. but he thinks it is.


what are your opinions??

the breakers are several hundred dollars so I don't want to replace the breaker unnecessarily.

I attached a picture here to further illustrate what I want to do.

https://1drv.ms/i/s!As6O9tf6Tvo7knPl6hpL3KK87XJs

Thanks!

My first thought was to replace the 60 non-fusable disconnect with a 30 amp FUSABLE disconnect and wire the machine accordingly.

You are correct. This will work.
But, since you are looking at overall cost.
1; Total cost, material and labour for a fusible disconnect, fuses and labour to replace the disconnect.
2; leave the 60 amp disconnect and cost of breaker and labour to replace the breaker (taking into account the value of the panel being shut down, while changing the breaker) -lost production, overtime etc.

wiring from the field disconnect is the same cost, whether from the existing 60 or new 30 amp unit.
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Old 06-28-2016, 06:39 PM   #5
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One more vote for replacing the 60 non-fusable disconnect with a 30 amp
FUSABLE disconnect and wiring the machine accordingly.
The wire from the breaker to the disc is already protected.
Welcome to the forum,
P&L
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Old 06-28-2016, 07:06 PM   #6
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Replace the disco with a 30 amp fused.
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Old 06-28-2016, 07:56 PM   #7
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Interesting.

Have a look at Rule 14-012.

Borgi
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Old 06-28-2016, 09:03 PM   #8
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Interesting.

Have a look at Rule 14-012.

Borgi


doesn't this just say that the interrupting devices must withstand possible fault currents?

having a hard time interpreting the rule in this scenario. could you explain for my feeble mind I think it has to do with the AIC rating of the devices but not sure how it relates.
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Old 06-28-2016, 09:09 PM   #9
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Let me take another stab at it... so as long as the AIC of the devices are equal or the AIC of the Upstream device is HIGHER than the downstream device (the 30a fusible disconnect) the we are okay???

is this right
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Old 06-28-2016, 09:12 PM   #10
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Quote:
Originally Posted by zibz View Post
doesn't this just say that the interrupting devices must withstand possible fault currents?

having a hard time interpreting the rule in this scenario. could you explain for my feeble mind I think it has to do with the AIC rating of the devices but not sure how it relates.
Guess I'm feeble minded too. Sticking with my previous vote.
P&L
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Old 06-28-2016, 09:48 PM   #11
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Quote:
Originally Posted by PlugsAndLights View Post
Guess I'm feeble minded too. Sticking with my previous vote.
P&L
I agree, done this countless times and never had an issue from any inspector.
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Old 06-29-2016, 12:26 AM   #12
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I would be more inclined to replace the breaker at the distribution panel with a 30 amp, and be done.

Feeding a rated 30 amp disconnect, fused or not, from a 60 amp breaker does not meet code, or feel safe to me. In my interpretation. I can explain further later, but it's cold pop time, then bed.

Far too often I hear that the breaker protects the cable, which it should, but it should provide a little more protection than that.

For example, a 20 amp breaker feeds a rated 15 amp device, with #12 cable. I am not liking that one bit.

But, I am open for debate.

Borgi
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Old 06-29-2016, 02:00 AM   #13
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From appendix B in the code...( for some additional info ) Rule 14-012
It is the intent of this Rule to ensure that the overcurrent protective and control devices, the total impedance, and other characteristics of the circuit to be protected are selected and coordinated so that the circuit protective devices will clear a fault without extensively damaging the electrical components of the circuit.
Interrupting ratings of overcurrent devices (circuit breakers or fuses) are 5000 A symmetrical maximum for circuit breakers rated 100 A or less and 250 V or less, and 10 000 A symmetrical maximum for circuit breakers rated above 100 A or above 250 V unless otherwise marked. The interrupting rating of fuses is 10 000 A symmetrical
maximum unless otherwise marked.
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Old 06-29-2016, 02:02 AM   #14
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And from the handbook....Rule 14-012 requires that switches and overcurrent devices be able to interrupt the available fault current at their terminals, which can make distribution centres (e.g., panelboards) costly, depending on the available fault
current of the system. For more flexibility in designing installations, Rule 14-014 allows the use of a downstream circuit breaker with a lower interrupting rating than the available system fault level in combination with a fully rated upstream overcurrent device, provided that the upstream breaker opens before the downstream breaker
when this level of fault current is detected in order to protect the downstream breaker from blowing up.
So with that being said, im thinking it should be copasetic to do so. As always, its the inspectors opinion that matters.
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Old 06-29-2016, 02:12 AM   #15
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Quote:
Originally Posted by Judoka View Post
And from the handbook....Rule 14-012 requires that switches and overcurrent devices be able to interrupt the available fault current at their terminals, which can make distribution centres (e.g., panelboards) costly, depending on the available fault
current of the system. For more flexibility in designing installations, Rule 14-014 allows the use of a downstream circuit breaker with a lower interrupting rating than the available system fault level in combination with a fully rated upstream overcurrent device, provided that the upstream breaker opens before the downstream breaker
when this level of fault current is detected in order to protect the downstream breaker from blowing up.
So with that being said, im thinking it should be copasetic to do so. As always, its the inspectors opinion that matters.
I agree. Good points.

As already mentioned, not my method of installation.

Borgi

Last edited by 51360; 06-29-2016 at 02:52 AM. Reason: Correction
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Old 06-29-2016, 02:26 AM   #16
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My concern is that 60 amps is available at the terminals of the 30 amp disconnect. The disconnect is not approved for that!

I am open to other interpretation, but I would minimize the risk, and avoid the risk by replacing the 60 amp breaker at the distribution panel with a 30 amp.

Borgi
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Last edited by 51360; 06-29-2016 at 02:27 AM. Reason: Clarity
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Old 06-29-2016, 02:56 AM   #17
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Quote:
Originally Posted by Judoka View Post
And from the handbook....Rule 14-012 requires that switches and overcurrent devices be able to interrupt the available fault current at their terminals, which can make distribution centres (e.g., panelboards) costly, depending on the available fault
current of the system. For more flexibility in designing installations, Rule 14-014 allows the use of a downstream circuit breaker with a lower interrupting rating than the available system fault level in combination with a fully rated upstream overcurrent device, provided that the upstream breaker opens before the downstream breaker
when this level of fault current is detected in order to protect the downstream breaker from blowing up.
So with that being said, im thinking it should be copasetic to do so. As always, its the inspectors opinion that matters.
You left an important note from appendix B out. No matter, I don't agree with CSA on this.

Quote:
Rule 14-014 A series rated system is one in which either a circuit breaker or a fuse is in series with a downstream circuit breaker that has an interrupting rating less than the fault current available at the line terminals of the upstream overcurrent device. The upstream device always has an interrupting rating at least equal to the available fault current.This series combination is tested and approved at the higher rating in accordance with special requirements for series rated devices in the CSA Standards for the equipment involved (e.g., circuit breakers, panelboards, or metering equipment). The tests verify that the combination acts together to safely clear a fault up to the maximum rating of the line side overcurrent device. The downstream equipment is marked, as a part of its electrical rating, with its series rating and with the specific upstream overcurrent device required to achieve the series rating. Where motors are connected in the system between the series connected devices, any significant motor contribution to the fault current should be considered. It is generally agreed that the contribution of asynchronous motors to the short-circuit current may be neglected if the sum of the rated currents of motors connected directly to the point between the series connected devices is 1% or less of the interrupting rating of the downstream circuit breaker. (See IEC 60781.)
Borgi

Last edited by 51360; 06-29-2016 at 03:09 AM. Reason: Addition
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Old 06-29-2016, 05:33 AM   #18
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Like tesla says, the breaker is there to protect the conductor, not the equipment. Unless the equipment manufacturer specifies otherwise, you don't have to change a thing.
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Old 06-29-2016, 06:04 AM   #19
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Quote:
Originally Posted by Borgi View Post
I would be more inclined to replace the breaker at the distribution panel with a 30 amp, and be done.

Feeding a rated 30 amp disconnect, fused or not, from a 60 amp breaker does not meet code, or feel safe to me. In my interpretation. I can explain further later, but it's cold pop time, then bed.

Far too often I hear that the breaker protects the cable, which it should, but it should provide a little more protection than that.

For example, a 20 amp breaker feeds a rated 15 amp device, with #12 cable. I am not liking that one bit.

But, I am open for debate.

Borgi
60 amp disconnect with 30 amp fuses. That was easy.
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Last edited by 99cents; 06-29-2016 at 06:11 AM.
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Old 06-29-2016, 06:40 AM   #20
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Borgi, a 15 amp device is allowed to be on a 20 amp circuit for feed through, meaning there must be more than one device on the circuit. I agree, though, it's kinda sketchy.
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