65000 amp short circuit rating
- Thread starter MBLES
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petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
You need 65k, but 100k is OK as well.
its now required to install before meter can a non fused disconnect. Do they make NON fused disconnects 100k AIC or is just for Service Disconnect?
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Nonfused switches do not have an AIC rating. That only applies to OCPD. They would have a SCCR though. I don't know of any that are that high.
You face a dilemma that many of us have seen when it comes to "meter disconnect switches". Most POCOs want the switch to be unfused but as you have discovered there are few if any with a high enough SCCR rating. In most jurisdictions of which I am aware the AHJs consider that switch to be POCO's jurisdiction and as such not within their jurisdiction.. an easy 'cop out' for us 
.
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kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Look more carefully at documentation of the switch, it may be acceptable if certain overcurrent device (probably a fuse) is located upstream or downstream, but at 65kA that chance of finding one that works for you probably does go down.
Also if it is required by POCO and is ahead of the "service point" NEC may not necessarily apply there, this kind of makes it the POCO's problem should there ever be an issue with it, but it is typically only their technicians that will operate this switch anyway.
Also if it is required by POCO and is ahead of the "service point" NEC may not necessarily apply there, this kind of makes it the POCO's problem should there ever be an issue with it, but it is typically only their technicians that will operate this switch anyway.
To which we can surmise that POCO technicians are capable of withstanding arc faults or expendable
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Assuming you do have to deal with it:
UL98, which is what covers disconnect switches, only allows a maximum SCCR of 10kA for an unfused switch. But what kwired said is right; many manufacturers have submitted them for series ratings with either their own specific breakers or with fuses, and that fuse or breaker can be down stream. Depending on the size we are talking about, series combos with breakers don't usually go that high, so you will likely end up with fuses, and the series ratings will only be with SPECIFIC fuses. So bottom line you must chose a supplier that has a series rating, then follow their instructions exactly.
If your meter feeds a service panel with a main breaker, the NF switch would have to be the same mfr. to have a chance at all of having a series rating, but in looking at Eaton, that isn't going to happen at under a 200A 480V service. Their series ratings with CBs under 200AF top out at 25kA. I imagine most others will be the same.
kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
Based on 65,000AIC, you are saying you could have a 3.1MVA xfmr at 480V, with Z= 5.75%, FLA = 3740A.
A good size service.
Numbers like these need to be confirmed. Go out and look at the service transformer, get nameplate data, then call the utility and ask for the available line data and maximum planned short circuit. 3ph, and 1ph.
Then you can chart your plan of attack.
A good size service.
Numbers like these need to be confirmed. Go out and look at the service transformer, get nameplate data, then call the utility and ask for the available line data and maximum planned short circuit. 3ph, and 1ph.
Then you can chart your plan of attack.
Tony S
Senior Member
- Location
- Resting under the Major Oak UK
You need to talk to the POCO, 65KA sounds like an infinite source calculation. You need the system impedance.
Post the transformer details and any other information you can lay your hands on.
Post the transformer details and any other information you can lay your hands on.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
just how far downstream can it be?
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Well they do seem to be able to do some tasks that other electrical workers are not supposed to do, I guess the equipment knows who is operating it and responds accordingly:blink:To which we can surmise that POCO technicians are capable of withstanding arc faults or expendable
- Location
- Placerville, CA, USA
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- Retired PV System Designer
They carry a courtesy card from the Electron's Union.
- Location
- Illinois
- Occupation
- retired electrician
That makes the huge assumption that you can't have a fault between the disconnect and the downstream OCPD.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
I've never seen a specific distance mentioned, but I believe everyone understands it as being immediately adjacent because yes, the possibility of a fault between the disconnect and downstream OCPD is problematic at the very least, just like a fault between the service transformer and the SE device always is as well. The only time I have seen this issue brought up is in regard to a Meter socket -> NF disconnect -> SUSE panel with a main breaker, all connected with close nipples.
As I mentioned in the other related thread on this subject, I usually just tell people to use a fused disconnect and be done with it, trying to use an NF disconnect on anything with more than 10kA fault current available is too complicated if you ask me. I can't imagine the PoCo refusing to connect your service because you used a fused vs a non-fused disconnect.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
I can see POCO denying you access to the fuse compartment though (as a potential pre-meter connecting point), which could lead to interesting problems down the road.
An NF disconnect would not have that problem and POCO would not necessarily even want to lock the switch handle.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
The switch is after the meterI can see POCO denying you access to the fuse compartment though (as a potential pre-meter connecting point), which could lead to interesting problems down the road.
An NF disconnect would not have that problem and POCO would not necessarily even want to lock the switch handle.
This one is very typical of what I see. http://forums.mikeholt.com/showthread.php?t=171257&p=1667769#post1667769
- Location
- Massachusetts
That would be odd to have a non-fused switch after the meter. What would be the point of that?
Typically it would be supply to utility required non-fused meter disconnect to metering equipment to NEC required fused or breaker service disconnect.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Honestly, it puzzles me too, but I've seen it in project drawings and specs now 4 or 5 times in the last year, most recently this Monday. I don't know if this is coming from the utilities or from some class the consulting engineers are taking somewhere, it makes no sense. I get involved because this seems to be most prevalent in pump panel installations on things like sewage lift stations and booster pumps where this is the only thing on the service. I only see ones that involve VFDs, and VFDs have some picky requirements on up stream protection that a lot of consultants don't pay attention to either. The contractors are coming to me asking if they can just use a fused disconnect ahead of the VFDs instead of the NF version, because it kills two birds with one stone. I'm telling them to do it.
My theory is that maybe some packaged pump controller mfr has spit out some free drawings of their system to consultants, who don't think for themselves and just paste it into the project plans.
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