Non-Fusible Disconnect Vs. Circuit Breaker as Disconnecting Means

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rc7288

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A 200A 480V circuit breaker in a MCC in an existing building is feeding a new building. Code says that the incoming service conductors must terminate at some type of service disconnecting means. I'm trying to decide which of the following would be better as a choice for the disconnecting means: a non-fusible disconnect switch or an enclosed circuit breaker. I believe the main difference is that the circuit breaker will trip when overloaded, whereas the non-fusible disconnect will only disconnect power to the new building when manually switched. The circuit breaker would prevent someone from having to walk to the existing building and flip the breaker back on if there's ever an overload, since the breaker in the new building will have already tripped. Therefore, I'm leaning more towards the enclosed circuit breaker. Am I missing something? Are there other benefits to having a non-fusible disconnect that I'm overlooking? The cost difference between the two isn't an issue, I'm just looking for what would be best. Below are a couple examples of the types of switches and circuit breakers I'm talking about. Thanks.

http://www.eaton.com/Eaton/ProductsServices/Electrical/ProductsandServices/ElectricalDistribution/SwitchesandDisconnects/SafetySwitches/HeavyDuty/Non-Fusible/index.htm
http://www.eaton.com/Eaton/Products...Breakers/100EnclosedCircuitBreakers/index.htm
 
you may not have a choice.

the SCCR of an unfused switch is typically 10kA. What is the available short circuit current at the point where you plan to install the disconnect?
 
Watch your wording. :)
If it comes from a breaker in an MCC in another building it is not a service, since there is an OCPD upstream.
The feeder to a building also requires a disconnect, but it does does not have to be fused.
A service disconnect MUST be (or must be closely associated with) an OCPD since there is no effective OCPD on the POCO side.
 
GoldDigger said:
Watch your wording. :)
If it comes from a breaker in an MCC in another building it is not a service, since there is an OCPD upstream.
The feeder to a building also requires a disconnect, but it does does not have to be fused.
A service disconnect MUST be (or must be closely associated with) an OCPD since there is no effective OCPD on the POCO side.
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Depends actually. I've had it interpreted, by an AHJ, that if it leaves an MCC/Switchgear as a feeder, but goes to another building, it IS the service entrance at that other building. Now mind you, I did not BID the job that way, in that the main Breaker in the second building was not SUSE labeled, but I had to pay to get it re-worked because the AHJ called it a new service entrance. It was a long time ago and I recall there was some sort of odd criteria about it that I thought was silly, as in the distance between the buildings or there was a paved surface between the buildings, something like that. I've never tried to parse that one out, because the job was about to go into LD so it was cheaper for me to comply than it was to fight it. (I don't havemuch recollection of all of the details now, but if anyone has an idea, it would be interesting to hear).

MiElectrician said:
I don't understand the advantage of a non fused disconnect. I have no experience here, just curious.
Click to expand...
Aside from being lower up front cost, sometimes you already have a breaker or a fuse feeding it so adding another one is not only unnecessary but also sets up a situation where you don't know WHICH one of the OCPDs cleared, which increases the troubleshooting time. Might only be a few more minutes to sort it out, but in some industrial plants you have huge $/minute in down time losses.
 
This is what I come up with for a quick summary regarding fused vs non-fused vs circuit breaker & enclosure. Feel free to add/correct:

1. As others have said, the non-fused has a relatively low SCCR, although they do series rate with fuses.
2 IIRC, fused with fuses is similar in price as circuit breaker & enclosure.
3. Fused can have much higher AIC than circuit breakers
4. In some situations, the equipment may specifically require fused protection, so the FD will get you there.
5. FD and circuit breakers would allow to utilize the tap rules which may be convenient.
6. FD and NFD may be required for "visible verification" that the circuit id disconnected, for example POCO's and solar systems.
7. NFD certainly the least expensive if you do not need overcurrent protection.
8. Circuit breaker will open all poles unlike a FD.
9. I think a circuit breaker w/ enclosure is typically smaller than a FD.

Any others?
 
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