1600A 480V Stand-Alone Fused Switch

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philly

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I have a customer that wishes to insert a fused switch on the secondary of a 480V transformer between the transformer and downstream MCC in order to reduce Arc Flash at downstream location.

Does anyone have experience with a stand-alone switch with this high of a current rating at 480V? From what I see available this would typically be something in a Switchboard type enclosure as opposed to a disconnect type structure? Is it more feasible/economical at this side to just go with an enclosed breaker?

This solution will likely be one that is close coupled to existing transformer secondary due to existing UG conduits.
 
It’s not quite that simple. They make a breaker that has a “maintenance” switch that changes the settings on the breaker to reduce arc flash potential while the load side is being exposed. And yes, whether it be fused, or breaker, it will most likely be in a switchboard type enclosure.
 
philly said:
I have a customer that wishes to insert a fused switch on the secondary of a 480V transformer between the transformer and downstream MCC in order to reduce Arc Flash at downstream location.

Does anyone have experience with a stand-alone switch with this high of a current rating at 480V? From what I see available this would typically be something in a Switchboard type enclosure as opposed to a disconnect type structure? Is it more feasible/economical at this side to just go with an enclosed breaker?

This solution will likely be one that is close coupled to existing transformer secondary due to existing UG conduits.
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Why do they think this will reduce arc flash downstream? has someone put the proposed system into the software and determined that it actually does what they want?
 
petersonra said:
Why do they think this will reduce arc flash downstream? has someone put the proposed system into the software and determined that it actually does what they want?
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Because the worst case for arc flash is at the enclosure that contains the first OCPD for the secondary of a transformer. It appears that now that OCPD is the main breaker in the MCC. Installing an OCPD between the transformer and the MCC puts that worst case at the new OCPD enclosure. You could easily go from level 4 PPE to level 2 or even 1 by doing this.
 
hillbilly1 said:
It’s not quite that simple. They make a breaker that has a “maintenance” switch that changes the settings on the breaker to reduce arc flash potential while the load side is being exposed. And yes, whether it be fused, or breaker, it will most likely be in a switchboard type enclosure.
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It really is just that simple where the first OCPD on the secondary side of the transformer is the MCC main breaker. In that case the incident energy is based on the settings and clearing time of the transformer primary OCPD. By installing an OCPD in its own enclosure between the transformer and the MCC, the incident energy at the MCC will be based on the settings and clearing time of the new OCPD that you have installed between the transformer and the MCC.
 
The concept that I mentioned in the two previous posts is explained in this Eaton Document. In the document they are talking about placing the secondary OCDP in the transformer itself as that is the product they are trying to sell, but any location that is not within the downstream MCC or panelboard will have the same results. Note that with the selection of the OCDP they used in the transformer, they went from an incident energy of over 40 cal, to 1.05.
 
don_resqcapt19 said:
Because the worst case for arc flash is at the enclosure that contains the first OCPD for the secondary of a transformer. It appears that now that OCPD is the main breaker in the MCC. Installing an OCPD between the transformer and the MCC puts that worst case at the new OCPD enclosure. You could easily go from level 4 PPE to level 2 or even 1 by doing this.
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This was first evaluated using software analysis to verify desirable results. And yes you are correct right now first OCPD is main breaker in MCC with extremely high IE on line side. Goal is to move the higher IE level to the new OCPD enclosure which will require much less frequent maintenance interaction than the MCC.
 
don_resqcapt19 said:
It really is just that simple where the first OCPD on the secondary side of the transformer is the MCC main breaker. In that case the incident energy is based on the settings and clearing time of the transformer primary OCPD. By installing an OCPD in its own enclosure between the transformer and the MCC, the incident energy at the MCC will be based on the settings and clearing time of the new OCPD that you have installed between the transformer and the MCC.
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That’s the part that’s not that simple, just throwing another main in without calculations may or may not reduce the incident energy.
 
jim dungar said:
And the physical separation from the location where work will be performed.
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That would remove the need for PPE while working in the MCC, yes, if the main is off.
don_resqcapt19 said:
It always does because of the trip trip time and rating of the primary OCPD.
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If the settings are higher than the secondary ocpd it wouldn’t. So you can’t say always.
 
hillbilly1 said:
That would remove the need for PPE while working in the MCC, yes, if the main is off.

If the settings are higher than the secondary ocpd it wouldn’t. So you can’t say always.
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Yes, it removes the power, but you still need the PPE to verify that the power is off. After you have verified the de-energized state, you can remove the PPE.

The worst case is always the line side of the OCPD, by putting the OCPD in its own enclosure, you have moved the worst case outside of the MCC.
 
electrofelon said:
Just for me own education, would a breaker a BPS be used for this? Is one generally more desirable than the other for this application?
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The latest NEC requires a maintenance reduction switch on devices 1200A and larger. This is very easy to implement with a breaker and all but impossible with a Bolted Pressure Switch. Even though a BPS may have shunt trip capability, like when supplied with GF protection, it needs to be able to sense and clear the arcing fault much faster. This has resulted in many hybrid breaker and fuse devices, similar to the old GE HPS.
 
jim dungar said:
The latest NEC requires a maintenance reduction switch on devices 1200A and larger. This is very easy to implement with a breaker and all but impossible with a Bolted Pressure Switch. Even though a BPS may have shunt trip capability, like when supplied with GF protection, it needs to be able to sense and clear the arcing fault much faster. This has resulted in many hybrid breaker and fuse devices, similar to the old GE HPS.
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This is interesting that you point out. What code section is this new requirement in?

So does this essentially mean that any protective device 1200A or larger needs to be a breaker with MM capability and thus eliminates the application for fuses over 1200A?

I would think that a current limiting fuse operating in current limiting region would have a faster clearing time (less than 1/2 cycle) than any breaker.
 
don_resqcapt19 said:
Yes, it removes the power, but you still need the PPE to verify that the power is off. After you have verified the de-energized state, you can remove the PPE.

The worst case is always the line side of the OCPD, by putting the OCPD in its own enclosure, you have moved the worst case outside of the MCC.
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I’ve stated that in other threads, but if the main is in the mcc, even with it off, you would still need PPE because of the exposure to the line side. Many conveyor installs are now requiring a disconnect outside the enclosure that totally removes voltage inside. The same would be with the OP’s situation.
 
philly said:
This is interesting that you point out. What code section is this new requirement in?

So does this essentially mean that any protective device 1200A or larger needs to be a breaker with MM capability and thus eliminates the application for fuses over 1200A?

I would think that a current limiting fuse operating in current limiting region would have a faster clearing time (less than 1/2 cycle) than any breaker.
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The issue has to do with fuses that are not operating within their current limiting range, as is often the case with arcing faults on large feeders.

240.87, for breakers, was added in the 2017 NEC and 240.67, for fuses, became effective in 2020.
 
jim dungar said:
The latest NEC requires a maintenance reduction switch on devices 1200A and larger. This is very easy to implement with a breaker and all but impossible with a Bolted Pressure Switch. Even though a BPS may have shunt trip capability, like when supplied with GF protection, it needs to be able to sense and clear the arcing fault much faster. This has resulted in many hybrid breaker and fuse devices, similar to the old GE HPS.
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New in 2020 or 2023?
 
jim dungar said:
See dates in post #18.
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#18 was the one where I asked the question. The post I was replying to said only "the latest NEC"; the 2023 is the latest published but the 2020 is the latest adopted by most AHJs.
 
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