PV utility non fuse disco

hhsting

Senior Member
Attached sketch shows non fuse PV utility disco that is required by utility sp says the plans. The AC disco upstream is fused. I have heard but not sure that non fuse short circuit rating is 10kA and their is no interrup rating. I was wondering do these utility non fuse disco for PV have to comply per NEC 2014 Articles 110.10?
 

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Hv&Lv

Senior Member
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Engineer/Technician
Yes they are 10k and have to comply. Note that they typically series rate with fuses.
Question...
that looks like a trough entrance and the meter is part of a CT meter installation. Just voltage and reduced current wiring.
With this now being part of the associated POCO metering assembly, would it have to comply?
 

pv_n00b

Senior Member
Location
CA, USA
Non-fused switches have no SCCR by themselves. Each switch manufacturer is going to have a series rating table that give an SCCR for the switch based on the upstream OCPD type. Eaton for instance gives a 10kA SCCR rating with any type of upstream OCPD as long as the OCPD rating is equal to or less than the switch rating. The switch has to comply with all applicable NEC requirments, it's not part of the utility system so no exemption there.
 
Non-fused switches have no SCCR by themselves.
This is odd. It was always my understanding that they had a SCCR of 10k by themselves with higher ratings available under series ratings. I did some digging, and came across some non-nonsensical statements by the manufacturers. These two are from square D, saying similar thing just different wording, I thought I would include them both:



Non-Fusible Heavy Duty Safety Switches do NOT provide any overcurrent protection, therefore the non-fusible heavy duty safety switches alone do NOT provide any SCCR, it MUST be protected upstream by the correct Fuse Class or a circuit breaker.
First, a Non-Fused Safety Switch by itself does NOT provide any short circuit current rating because it does not contain any overcurrent protection.
to me that is non sequitur and I do not follow the logic there. Then this one from Eaton:

The ULT 98 Standard (Enclosed and Deadfront Switches) allows non-fusible switches to have a maximum short-circuit interrupting rating of 10 kA. This is because as a stand-alone device without integral overcurrent protection, the system designer may not know the upstream overcurrent protection. UL permits higher series connected fault current ratings if specific products are tested together. UL Listed combination ratings must be printed on the safety switch pub on the door, and must specify which upstream devices may be used to protect at higher fault current levels. Additionally, UL does not permit series combination ratings with motor circuit protectors
I dont know what to make of the statement in red. A NF switch is interrupting anything. Lets put that aside and assume they mean SCCR and move on to to the blue. Newsflash I guess, if i cant verify the upstream equipment then I cant assume anything, ok got it :roll:, so that statement seems to imply they are rated 10k with no upstream equipment.

So is the common practice of using a NF disco as a meter disconnect switch not allowed, even if the available fault current is under 10k?
 
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pv_n00b

Senior Member
Location
CA, USA
It looks like the Eaton information in that document is not clearly written. It does not say that a switch has a 10k rating with no upstream OCPD, it says it has a maximum of a 10k rating when the system designer does not know what the upstream OCPD is. But they are assuming that there is some kind of upstream OCPD. In the catalog, they say the switch has a 10k rating with any upstream OCPD with a trip setting equal to or less than the switch rating.

Using an NF switch on the supply side of the main disconnect as a meter disconnect would not be NEC compliant since it would be unprotected. If it's in the utility-owned part of the system with a cold sequence meter service entrance then it might be fine based on utility standards. But using an NF switch on the supply side of a PV interconnection would not be allowed by the NEC.
 
It looks like the Eaton information in that document is not clearly written. It does not say that a switch has a 10k rating with no upstream OCPD, it says it has a maximum of a 10k rating when the system designer does not know what the upstream OCPD is. But they are assuming that there is some kind of upstream OCPD. In the catalog, they say the switch has a 10k rating with any upstream OCPD with a trip setting equal to or less than the switch rating.

Using an NF switch on the supply side of the main disconnect as a meter disconnect would not be NEC compliant since it would be unprotected. If it's in the utility-owned part of the system with a cold sequence meter service entrance then it might be fine based on utility standards. But using an NF switch on the supply side of a PV interconnection would not be allowed by the NEC.
So what do you make of those statements by Square D? It doesn't make any sense to me. First, something doesn't "provide" a SCCR, it HAS a SCCR.. Ok I am willing to let that go, but more importantly, what does the presence of an OCPD ahead of the switch have to do with anything (other than potentially give the switch a HIGHER SCCR due to series rating effects)? If the AFC is less than the switch rating then the switch will be fine. Only thing that I can think of is perhaps it is a "duration" concern? I don't know the parameters for testing SCCR.
 

pv_n00b

Senior Member
Location
CA, USA
Sounds like Square D is confused. But let's look at it this way, we want to protect the device and there is no internal OCPD. So we say it must be installed with an upstream OCPD with a setting equal to or less than the switch rating to prevent overloading and give some protection against fault current. That's pretty reasonable. Next, we look at the mechanical design and look at how much fault current the switch can take for how long without ripping apart inside. To do that we look at the current that different OCPD will let through before opening and we can base the available fault current at the device we will allow on the type of OCPD with a known trip time. If we know nothing about the OCPD we go low and allow 10kAIC and build the basic switch to withstand that for the time that the slowest OCPD might react. To get higher available fault currents we are going to specify specific OCPD that we know will have a given operation time that the switch can withstand.
 
Sounds like Square D is confused. But let's look at it this way, we want to protect the device and there is no internal OCPD. So we say it must be installed with an upstream OCPD with a setting equal to or less than the switch rating to prevent overloading and give some protection against fault current. That's pretty reasonable. Next, we look at the mechanical design and look at how much fault current the switch can take for how long without ripping apart inside. To do that we look at the current that different OCPD will let through before opening and we can base the available fault current at the device we will allow on the type of OCPD with a known trip time. If we know nothing about the OCPD we go low and allow 10kAIC and build the basic switch to withstand that for the time that the slowest OCPD might react. To get higher available fault currents we are going to specify specific OCPD that we know will have a given operation time that the switch can withstand.
Although it seems logical to protect a piece of equipment at it's rating, many things do not have such a requirement: meter sockets and MLO service panelboards for example. Switches also do not have such a requirement under the NEC, but there must be something in the product standards for NF safety switches (UL98, NEMA ks-1-2001). It all just doesnt make a lot of sense to me.
 

pv_n00b

Senior Member
Location
CA, USA
I agree it does not make sense. In the intersection between the NEC and the NESC, there are some weird things happening. So I just follow what's in the installation information. I try to understand why something is done a certain way, sometimes I can figure it out sometimes I can't. It would be easier it UL Standards were available for everyone and not $3,000.
 
I agree it does not make sense. In the intersection between the NEC and the NESC, there are some weird things happening. So I just follow what's in the installation information. I try to understand why something is done a certain way, sometimes I can figure it out sometimes I can't. It would be easier it UL Standards were available for everyone and not $3,000.
Yeah, it's crazy how expensive they are. :rant: Almost worth it if I knew I would end up willing an argument due to purchasing, but bummer to pay it and up up losing :p
 

hhsting

Senior Member
Although it seems logical to protect a piece of equipment at it's rating, many things do not have such a requirement: meter sockets and MLO service panelboards for example. Switches also do not have such a requirement under the NEC, but there must be something in the product standards for NF safety switches (UL98, NEMA ks-1-2001). It all just doesnt make a lot of sense to me.
Not true I think meter sockets and MLO panelboards have SSCR rating same deal line side certain overcurrent protection certain SSCR.
 

hhsting

Senior Member
So what do you make of those statements by Square D? It doesn't make any sense to me. First, something doesn't "provide" a SCCR, it HAS a SCCR.. Ok I am willing to let that go, but more importantly, what does the presence of an OCPD ahead of the switch have to do with anything (other than potentially give the switch a HIGHER SCCR due to series rating effects)? If the AFC is less than the switch rating then the switch will be fine. Only thing that I can think of is perhaps it is a "duration" concern? I don't know the parameters for testing SCCR.
Going back to non fuse meter disconnect supply side of service disconnect if their is no overcurrent protection ahead of non fuse meter disco then their is no SSCR and it cannot satisfy 230.82 SSCR greater than avaliable fault current.

Only way then to satisfy 230.82 is to place fuse in meter disco. 230.82 says meter disco is not service disco does not distguish between fuse or non fuse just SSCR greater than avalible fault current. Main service grounding electrode system, main bonding jumper would be downstream of fuse meter disco since it is not service disco. If utility is ok then where in code it say this is not okay?
 
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Going back to non fuse meter disconnect supply side of service disconnect if their is no over-current protection ahead of non fuse meter disco then their is no SSCR and it cannot satisfy 230.82 SSCR greater than available fault current.
That appears to be the case based on what the manufacturers and product standards say, although it is quite common. To me, it seems like based on the wording in 230.82(3) and how they apparently go out of their way to refer to the relatively low SCCR of NF switches, they are referring to the non fused type.

Only way then to satisfy 230.82 is to place fuse in meter disco. 230.82 says meter disco is not service disco does not distinguish between fuse or non fuse just SSCR greater than avalible fault current. Main service grounding electrode system, main bonding jumper would be downstream of fuse meter disco since it is not service disco. If utility is ok then where in code it say this is not okay?
I think it is ok. I Agree there is no specific mention that the meter disco must be NF to be a meter disco and if you add fuses it must be considered the service disco (although as mentioned above, i think it is sorta assumed it is NF. Might want to ask your AHJ).
 

hhsting

Senior Member
That appears to be the case based on what the manufacturers and product standards say, although it is quite common. To me, it seems like based on the wording in 230.82(3) and how they apparently go out of their way to refer to the relatively low SCCR of NF switches, they are referring to the non fused type.



I think it is ok. I Agree there is no specific mention that the meter disco must be NF to be a meter disco and if you add fuses it must be considered the service disco (although as mentioned above, i think it is sorta assumed it is NF. Might want to ask your AHJ).
Wording in 230.82(3) dont follow you on that?

Twist is I am contractor for AHJ review and if AHJ knew then I would post it. They are as confused about this and ofcourse designers ask challanging question such as where is it in NEC fuse meter disco is considered service disco and more so it says meter disco is not service disco no mention of fuse or non fuse. AHJ cannot make up and say fuse meter disco is service disco if not in local code or not in the NEC.

Just wanted everyones opinion or experience regarding only way then to satisfy 230.82 is to place fuse in meter disco. 230.82 says meter disco is not service disco does not mention fuse or non fuse so even if fuse it is still meter disco not service disconnect.

Also called the local utility company in charge PEPCO who says they dont have any rule as to meter disco should be fuse or non fuse.
 
Wording in 230.82(3) dont follow you on that?

Twist is I am contractor for AHJ review and if AHJ knew then I would post it. They are as confused about this and ofcourse designers ask challanging question such as where is it in NEC fuse meter disco is considered service disco and more so it says meter disco is not service disco no mention of fuse or non fuse. AHJ cannot make up and say fuse meter disco is service disco if not in local code or not in the NEC.

Just wanted everyones opinion or experience regarding only way then to satisfy 230.82 is to place fuse in meter disco. 230.82 says meter disco is not service disco does not mention fuse or non fuse so even if fuse it is still meter disco not service disconnect.

Also called the local utility company in charge PEPCO who says they dont have any rule as to meter disco should be fuse or non fuse.
There is no chief electrical inspector? Not sure how exactly it works where you are but someone has to be the decider. Maybe in your case you are the decider, if so make the call.

I am more on the side that there is nothing saying it cant be fused to me a meter disconnect, however OTOH, NF does have quite a low SCCR compared to other equipment and they seem to be acknowledging this in the wording of 230.82 by specifically mentioning that ASSC must be above SCCR of disconnect.
 

hhsting

Senior Member
There is no chief electrical inspector? Not sure how exactly it works where you are but someone has to be the decider. Maybe in your case you are the decider, if so make the call.

I am more on the side that there is nothing saying it cant be fused to me a meter disconnect, however OTOH, NF does have quite a low SCCR compared to other equipment and they seem to be acknowledging this in the wording of 230.82 by specifically mentioning that ASSC must be above SCCR of disconnect.
Electrofelon my buddy I wish it would say what you wrote but NEC 2014 Article 230.82(3) says SCCR must be equal to or greater than ASSC.

Can you increase SCCR by placing fuse in meter disco or upstream of meter disco?
 
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