Service switch with a 10k interrupting fuse, is that cause for concern?

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Tainted

Tainted

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I went to an apartment building that has 60 residents living in there. There was a 400A service switch with 10kA interrupting rated 400A fuse in it feeding house loads . The service switch is close to the service end box which it's getting power from.

Does this make any sense to you or am I missing something? Now I don't know the utility available fault current but there is NO WAY to suspect the utility fault current is less than 10kA.

Is there any reason the 10kA rating is used? or is this just someone being incompetent in specing fuses?
 
Tainted said:
I went to an apartment building that has 60 residents living in there. There was a 400A service switch with 10kA interrupting rated 400A fuse in it feeding house loads . The service switch is close to the service end box which it's getting power from.

Does this make any sense to you or am I missing something? Now I don't know the utility available fault current but there is NO WAY to suspect the utility fault current is less than 10kA.

Is there any reason the 10kA rating is used? or is this just someone being incompetent in specing fuses?
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I mean 60 units, not 60 residents.
 
What kind of fuse has a 10K rating these days? My guess is it was put in back before anybody cared about such things. I have yet to hear of a legitimate case where an underrated piece of equipment failed catastrophically and harmed anybody because either the short-circuit current rating or the amps interrupting rating was lower than the available short circuit current.
 
Tainted said:
I went to an apartment building that has 60 residents living in there. There was a 400A service switch with 10kA interrupting rated 400A fuse in it feeding house loads . The service switch is close to the service end box which it's getting power from.

Does this make any sense to you or am I missing something? Now I don't know the utility available fault current but there is NO WAY to suspect the utility fault current is less than 10kA.

Is there any reason the 10kA rating is used? or is this just someone being incompetent in specing fuses?
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It could be fine, or it could be under dutied. How far away is the transformer? Just a couple days ago I did a calculation a 300 KVA Bank with very low 1.4 impedance, was down to 10K after 136 ft for a 200 amp feeder.
 
electrofelon said:
It could be fine, or it could be under dutied. How far away is the transformer? Just a couple days ago I did a calculation a 300 KVA Bank with very low 1.4 impedance, was down to 10K after 136 ft for a 200 amp feeder.
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Not sure how far, but I know a similar building with similar number of units and a 400A fuse for house loads, the utility said the fault current is 119500 at that building.
 
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petersonra said:
What kind of fuse has a 10K rating these days? My guess is it was put in back before anybody cared about such things. I have yet to hear of a legitimate case where an underrated piece of equipment failed catastrophically and harmed anybody because either the short-circuit current rating or the amps interrupting rating was lower than the available short circuit current.
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this is the fuses that's in the disc. switch:

31XRv0Sf14L._AC_.jpg
 
electrofelon said:
Is that at the end box? If that's what they say then that is what you have to go by, unless you can get the actual transformer data and calculate it yourself.
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I believe so but I could be wrong, their letter said:

"Install SB##### to existing POE 1-4-500 AC cable to establish total 2-4-500 service // short citcuit - ISC: 119500A | Z:300 +j1000 Micro ohms" etc...
 
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Tainted said:
this is the fuses that's in the disc. switch:

View attachment 2558729
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Cheapest fuses available, most places will not even allow them any longer. They're Class H, rated 50kA, but only up to 60A, after which they drop down to 10kA.

I'd say there is a good chance that the installation originally had proper Class K or L fuses but after they blew, the cheap landlord bought the cheapest fuses he could find. I'd be willing to bet it's not really a 400A service either, but the NON are not Time Delay fuses so they kept clearing when all the A/C units turned on at once after a power failure, so he put in larger fuses to keep them from blowing and costing him more money...
 
Not really that uncommon on old systems, fault current may have been under 10 k at time of installation. Poco’s have been doubling line voltages over the years to increase capacity, so what was sufficient years ago, is not now.
 
hillbilly1 said:
Not really that uncommon on old systems, fault current may have been under 10 k at time of installation. Poco’s have been doubling line voltages over the years to increase capacity, so what was sufficient years ago, is not now.
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Good luck even getting that info out of the POCO to make a realistic calculation for AIC rating. They don't like to give the info or will greatly exaggerate the figure to avoid any liability as they change out or up their capacity.
OP:
I would say replace like for like unless you have reason to suspect it is underrated and you had trouble with it failing. Also series rating can allow for lower AIC threshold down stream than might appear to be needed, again falls into "if it ain't broke don't fix it", and unless you have reason to suspect a failure due to undersized AIC on the fuse. Also the mention of conductor length has been made. That too can help to reduce the fault current available at any given point by the resistance of the wire, reducing the need for higher AIC.
Other question is what is the rating of the equipment? You indicate a 10Kaic service switch. If your fuse is over rated compared to the equipment, the equipment is now the weakest link and catastrophic failure would occur on the equipment rather than take out the fuse, so caution is required "if" you are looking at changing to a different AIC rated fuse or breaker. Example: installing a 22KAIC breaker on a 10KAIC panel, now the entire panel will fail rather than the individual breaker. I'm sure with supply shortages we are going go see alot more of this issue in the near future (whatever fits in without considering AIC).
So if the OP has reason to suspect fuse failure do to high AIC the entire system replaced or a series rating would need to be incorporated to correct.
But likely if it was a 10 rating replace with a 10 rating and be done as services switch is only 10K, and original was correct from perspective of the equipment installed.
 
I have replaced a 10 k rated service equipment due to a feeder ground fault. The transformer supplied an excess if 30 k. It blew right past all the poorly installed EMT ground with die cast fitting. Then it went bad from there. It was an old six handle rule fused handles MDP. It shorted during the fault and took out the gear. Smoked it up real good untill it cleared it self and took out the primary fuse when it went phase to phase. I'll see if I can dig up some pics. This even had illegal buss taps for a seventh handle. This tap is what set it in motion.
This was a 208/120 system with the trans right out side. Three sets 18' runs of 500 mcm copper.
If memory serves it was a 500 kva trans @ 3.5%

It was replaced with a 42 k set up MDP. The utility was also ask to change the transformer. Of course they said no. The facility received all new feeders and panles as well.
This the only time I have seen it.
 
Tainted said:
I went to an apartment building that has 60 residents living in there. There was a 400A service switch with 10kA interrupting rated 400A fuse in it feeding house loads . The service switch is close to the service end box which it's getting power from.

Does this make any sense to you or am I missing something? Now I don't know the utility available fault current but there is NO WAY to suspect the utility fault current is less than 10kA.

Is there any reason the 10kA rating is used? or is this just someone being incompetent in specing fuses?
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So are you tasked with fixing this or is it just something you noticed and were curious?
 
electrofelon said:
So are you tasked with fixing this or is it just something you noticed and were curious?
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I noticed it, and I'm writing a report so that we can persuade client to upgrade their entire infrastructure. I'll be doing the design to demolish and rebuild the entire system. I typically get involved in projects in buildings that are ancient, I've seen a lot of crazy stuff in the old NYC landmarked buildings. It's absolutely terrifying seeing electrical installations in old NYC buildings... Heck, I wouldn't even dare to live in a NYC apartment building unless their electrical infrastructure is upgraded. lol
 
Tainted said:
I noticed it, and I'm writing a report so that we can persuade client to upgrade their entire infrastructure. I'll be doing the design to demolish and rebuild the entire system. I typically get involved in projects in buildings that are ancient, I've seen a lot of crazy stuff in the old NYC landmarked buildings. It's absolutely terrifying seeing electrical installations in old NYC buildings... Heck, I wouldn't even dare to live in a NYC apartment building unless their electrical infrastructure is upgraded. lol
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That’s not unique to NYC. Sadly, 99% of renters are woefully ignorant of these kinds of issue when it comes to electrical infrastructure and are trusting their landlords to keep them safe. We get the other side of that picture and know how cheap they can be, even though some of their actions are risking the lives and safety of their tenants. This is why inspections matter. It’s not perfect, but it’s better than allowing them to do what they want.
 
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