Disconnect need to be fused ?

[Anode]

Lead electrician was not so much challenging the plans, as he was curious to why the disconnect could be unfused when entering the building after more than 15 feet ( I believe that is what he said ).

30 Year Electrician vs. Solar Designer/Project Engineer, I take anything he says with great weight, as he has been doing this far longer than I have.

He made mention of service conductors, and I said, well that is probably why, as the conductors entering the building I believe are considered as feeders, which maybe is why there is an exception.

Can anyone shed some light on this so I can make good on my promise to "ask a few friends". Code references and explanation would be great in this instance.

 

[electrofelon]

Lead electrician was not so much challenging the plans, as he was curious to why the disconnect could be unfused when entering the building after more than 15 feet ( I believe that is what he said ).

30 Year Electrician vs. Solar Designer/Project Engineer, I take anything he says with great weight, as he has been doing this far longer than I have.

He made mention of service conductors, and I said, well that is probably why, as the conductors entering the building I believe are considered as feeders, which maybe is why there is an exception.

Can anyone shed some light on this so I can make good on my promise to "ask a few friends". Code references and explanation would be great in this instance.

A few more details of the installation would be needed to give an answer. Is this a service? If so "The service overcurrent device shall be an integral part of the service disconnecting means or shall be located immediately adjacent thereto." IF this is a feeder supplying a building, you only need a disconnect.

 

[ggunn]

Lead electrician was not so much challenging the plans, as he was curious to why the disconnect could be unfused when entering the building after more than 15 feet ( I believe that is what he said ).

30 Year Electrician vs. Solar Designer/Project Engineer, I take anything he says with great weight, as he has been doing this far longer than I have.

He made mention of service conductors, and I said, well that is probably why, as the conductors entering the building I believe are considered as feeders, which maybe is why there is an exception.

Can anyone shed some light on this so I can make good on my promise to "ask a few friends". Code references and explanation would be great in this instance.

There's not a lot of detail in your question, but I can address this in general terms.

If the interconnection is via a backfed breaker, the only OCPD necessary on the conductors between the inverter and the service is the breaker. This is because any fault current in excess of the ampacity of the conductors can only come from the service. The inverter is a current limited device and in a properly designed system the conductors are sized such that their derated ampacity (both for conditions of use and for continuous use) exceeds the maximum output of the inverter, so no OCPD is necessary to protect the conductors from the inverter.

If the interconnection is a supply side one and there is a fused disco within ten feet of the interconnection (as there must be per code), that set of fuses is the only OCPD needed for the same reason as above.

 

[pv_n00b]

I have found that on supply side interconnections the disconnect has to be either fused or part of a series rated OCPD system so that it has the minimum short-circuit rating for the available fault current from the utility. I use a lot of Eaton disconnects and this is what they say about it:

The UL listed short-circuit ratings for Eaton non-fusible switches are based on the switches being properly protected by overcurrent protective devices. For applications that require a UL listed short-circuit rating of 10,000 rms symmetrical amperes or less, an Eaton non-fusible switch must be properly protected by any overcurrent protective device rated no greater than the ampere rating of the switch.

For applications that require a UL listed short-circuit rating of greater than 10,000 rms symmetrical amperes, an Eaton non-fusible switch must be properly protected by the appropriate class and size fusing noted. Otherwise, this non-fusible switch must be replaced with an Eaton fusible switch that uses the appropriate fusing required.​

This basically prevents someone from opening the disconnect during a fault when you may have say 20kA running through it if there is no OCPD, and having the thing explode.

 

[Anode]

Yes, backfed via breaker. Thank you for answering generally, with both scenarios. Understood already that supply side connections require fused disconnect.

There's not a lot of detail in your question, but I can address this in general terms.

If the interconnection is via a backfed breaker, the only OCPD necessary on the conductors between the inverter and the service is the breaker. This is because any fault current in excess of the ampacity of the conductors can only come from the service. The inverter is a current limited device and in a properly designed system the conductors are sized such that their derated ampacity (both for conditions of use and for continuous use) exceeds the maximum output of the inverter, so no OCPD is necessary to protect the conductors from the inverter.

This explanation is exactly what I was looking for. Thank you.

 

[pv_n00b]

If you have a breaker in there somewhere between the disconnect any the service, and the AIC rating is good then there is no reason to have any fuses in the disconnect that I am aware of. It might just be that people are used to seeing fuses in disconnects when the disconnect is used on a load.

 

[ggunn]

If you have a breaker in there somewhere between the disconnect any the service, and the AIC rating is good then there is no reason to have any fuses in the disconnect that I am aware of. It might just be that people are used to seeing fuses in disconnects when the disconnect is used on a load.

I am told that sometimes a fused disco is actually cheaper than an unfused one. In that case, go ahead and use fuses if you want; they won't hurt anything.

 

[SAP]

Pedestal Service

Pedestal Service

I have a pedestal MSP with only one 100 amp breaker.The plans call for 60 amp backfeed breaker I have no room, my plan is to tap into the #2 AWG wire on the load side of the ocpd then into a 60 amp fused disconnect, then to my AC combiner box, or would I be better off putting a 100 amp subpanel instead of disconnect

 

[SAP]

I have a pedestal MSP with only one 100 amp breaker.The plans call for 60 amp backfeed breaker I have no room, my plan is to tap into the #2 AWG wire on the load side of the ocpd then into a 60 amp fused disconnect, then to my AC combiner box, or would I be better off putting a 100 amp subpanel instead of disconnect

Can some on please move this this is my own question can you please move it to its own thread

 

[kwired]

Can some on please move this this is my own question can you please move it to its own thread

Send a PM to a moderator - they are the only ones that can do that, include a link to this thread or at least the title of this thread so they can find it easier. Otherwise they won't know unless they happen to read your post.