AC Disconnect- Fused or Unfused?

[rick.m650]

What are the factors in deciding if the AC Disconnect should have a fuse or not?

[sensij]

What are the factors in deciding if the AC Disconnect should have a fuse or not?

You need over current protection for the AC conductors somewhere in the circuit. If the AC circuit is after the main service panel, usually a breaker in that panel serves that purpose. For line side (supply side) taps between the pole and the main panel, fuses in the disconnect are more common.

[GVF]

I am applying for a permit to install a system on my barn with load-side connection and submitted a one-line diagram representing a knife blade fused type AC disconnect between the inverter and the subpanel. The inspector who reviewed my plan stated, "Since the barn is a detached structure, the disconnect is required to be a knife blade non-fused type disconnect installed on the outside of the barn and marked “PV disconnect”." Why must it be non-fused rather than fused? The relevant NEC reference would be most appreciated. Thank you!

[bob-n]

It makes sense that it has to be outside the barn and marked, so that emergency crews can deactivate it before entering or before fighting a fire. You already knew that.

I can't think of any reason why unnecessary fuses would be disallowed, ever.

Could it be that you and he are not understanding eachother? In other words, could it be that he's really trying to say that he doesn't care about fuses?

Is it possible to follow-up with a phone call? I know that's so old-fashioned, but it often clears up confusion.

[foo1bar]

Why must it be non-fused rather than fused? The relevant NEC reference would be most appreciated. Thank you!

It may not be NEC.
Utility also gets to impose requirements.
And they might require a disconnect that has a visible blade, and is lockable in the open position.

I think there are fused disconnects that would meet those requirements.

Maybe if you tell the plan reviewer "I was looking at your notes, and to address the issue you brought up about a disconnect, I was looking at XYZ product that has fuses AND knife-blade disconnect that can be locked open - here's is the information on it. Will that meet code and utility company requirements? "

But it may be easier/cheaper to have the OCPD (aka fuse / breaker) and the disconnect be separate boxes.

[solarix]

Non-fused disconnects are generally a utility requirement so that they have an OSHA approved means of lock-out, tag-out disconnecting for use by a lineman when they are working on the lines in your neighborhood. Its not done in most jurisdictions - check with your utility. Just one of the reasons why you kind of need a professional installer who knows the local deal. The whole requirement is pretty dumb imho as inverters just can't operate without a grid and there is zero risk of them shocking a lineman. But try to tell OSHA that. I've never seen a lineman use them either. Just a legacy requirement that serves to drive up the cost of solar - which the utilities could care less about... The non-fused type are so the utility can make them safe by locking the door closed and also not possible to change a fuse. Your branch breaker is your overcurrent protection anyway.

[GVF]

Thank you. Here was our conversation:

He stated: "Since the barn is a detached structure, the disconnect is required to be a knife blade non-fused type disconnect installed on the outside of the barn and marked “PV disconnect”."

I asked: "So the solar AC disconnect must be DU222RB (non-fusible 60A knife) rather than D222NRB (fusible 60A knife)?"

He replied: "Yes."

[bob-n]

Obviously, if he said do it, you have to do it. And it will save you $10!

But to me, they are both lockable. I can't understand why he required non-fusable.