High impedance wires

Tainted said:
not even sure if the terminals are rated 90 degree but good idea... would need 2 sets of 400s if this is the case.

We need main fuses to feed the meter bank
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I do not believe there is any Listed LV equipment connection, especially those on breakers and fusible switches, rated for use with 90°C ampacities, except for some power distribution blocks.
There are many devices that require 90° conductor insulation but still.only use the 75° ratings.
 
electrofelon said:
Can you not find a series rating that works?

For the 90° conductor idea, you would definitely need to splice/transition at each end, there is no under 600 volt equipment with 90° terminations
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The meter bank has siemens HQP and HQS circuit breakers and will be fed by fuses. I know JJN bussman fuses is series rated with HQP but I am not even sure if it's series rated with HQS. I need a fuse series rated with BOTH of the breakers

Also I checked calculations and downsizing to 400KCMIL doesn't really do that much.
 
jim dungar said:
I do not believe there is any Listed equipment connection, particularly those on breakers and fusible switches, rated for use with 90°C ampacities, except for some power distribution blocks.
There are many devices that require 90° conductor insulation but still.only use the 75° ratings.
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But just to be clear to anyone reading, you can still do it by splicing 75 degree sized to the 90° sized conductors. Pretty much every splicing connector is rated 90° when used in a standalone fashion. The length of the 75° conductor needed before the transition is somewhat ambiguous, but I believe it was you who recently pointed out the testing standard is 4 ft so that may be a logical minimum length.
 
Tainted said:
The meter bank has siemens HQP and HQS circuit breakers and will be fed by fuses. I know JJN bussman fuses is series rated with HQP but I am not even sure if it's series rated with HQS. I need a fuse series rated with BOTH of the breakers

Also I checked calculations and downsizing to 400KCMIL doesn't really do that much.
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I would be very surprised there is not a series rating for a 65k downstream device. What is the AFC?
 
electrofelon said:
But just to be clear to anyone reading, you can still do it by splicing 75 degree sized to the 90° sized conductors. Pretty much every splicing connector is rated 90° when used in a standalone fashion. The length of the 75° conductor needed before the transition is somewhat ambiguous, but I believe it was you who recently pointed out the testing standard is 4 ft so that may be a logical minimum length.
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In OP he says he needs 40 feet of conductor to lower the available current yet the equipment is literally 10 feet away so 4 feet of 75C conductor on each end leaves him with maybe 2 to 10 feet of 90C conductor remaining, he likely still needs room to coil it up or something to get enough impedance to lower the available current.
 
kwired said:
In OP he says he needs 40 feet of conductor to lower the available current yet the equipment is literally 10 feet away so 4 feet of 75C conductor on each end leaves him with maybe 2 to 10 feet of 90C conductor remaining, he likely still needs room to coil it up or something to get enough impedance to lower the available current.
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Yeah true with that short of length, probably won't make a huge difference. But that in combination with coiling up some extra conductor in say a 4x4 box... Just that one conductor size smaller might make a big difference in hassle and do-ability.
 
electrofelon said:
Yeah true with that short of length, probably won't make a huge difference. But that in combination with coiling up some extra conductor in say a 4x4 box... Just that one conductor size smaller might make a big difference in hassle and do-ability.
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4 foot by 4 foot box?

I would like to see someone get just one loop of 400 or 500 into a 4 inch box.
 
kwired said:
4 foot by 4 foot box?

I would like to see someone get just one loop of 400 or 500 into a 4 inch box.
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Of course I am talking about a 4 ft by 4 ft box - but now they think about it maybe a 4 -11/16 box with an extension ring will do it 😂. Ok seriously now, OP said 40 ft of conductor with enclosures 10 ft apart, so say he needs 30 ft extra of conductor. That would be three loops in the box. Seems doable. Again using the 90° conductor trick, that reduces the conductors a size and maybe gets you one less loop?
 
Is this meter bank feed from a utility transformer and secondary conductors.

Maybe something on there end can help. They like to down size secondary when we can not.

Change location of transformer if underground.
 
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Tainted said:
Fault is 126kA sym rms. 40 feet would reduce it to close to 65kA

See page 56 https://cache.industry.siemens.com/...007/v1/SIE_TA_CircuitBreakerSeriesRatings.pdf

Do you think HQS is series rated with bussman JJN class T fuses? Or is that pertaining to JJS or both JJN and JJS?
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Well if you are over 100k, then yeah thats a tough one 😟. You said page 56 but that is only 100k right? I Cant find any combination, with upstream 800A either fuse or breaker at 200k that gets you the QP ad QS downstream. Do you have a siemens rep you can talk to ? MAybe they can come up with something that will work.
 
electrofelon said:
Well if you are over 100k, then yeah thats a tough one 😟. You said page 56 but that is only 100k right? I Cant find any combination, with upstream 800A either fuse or breaker at 200k that gets you the QP ad QS downstream. Do you have a siemens rep you can talk to ? MAybe they can come up with something that will work.
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I just need 15 feet of 2 sets 500s to make it below 100kA to get a 100kA series rated combination.

Siemens is looking into it
 
Tainted said:
I just need 15 feet of 2 sets 500s to make it below 100kA to get a 100kA series rated combination.

Siemens is looking into it
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IF you can get it down to 100k, looks like you can do it with an upstream breaker but not fuses. Any reason you cant use an enclosed CB? It would need to be the mighty SHND6, and the downstream only need to be 22k QPH and QSH.
 
electrofelon said:
IF you can get it down to 100k, looks like you can do it with an upstream breaker but not fuses. Any reason you cant use an enclosed CB? It would need to be the mighty SHND6, and the downstream only need to be 22k QPH and QSH.
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Circuit breakers in my opinion are really bad at carrying fault currents. And also there is a chance that the main service overcurrent device might blow first before the overcurrent devices downstream. I can do a coordination study between the overcurrent devices but I’d rather use fuses. The fault current is way too high to get good coordination with circuit breakers

The circuit goes something like this:

Service fuse -> fuse -> HQS and HQP breakers

I need the the first and second fuses to be coordinated. If I use a circuit breaker as the second overcurrent device, it might not coordinate well because the fault current is too high
 
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Tainted said:
Circuit breakers in my opinion are really bad at carrying fault currents. And also there is a chance that the main service overcurrent device might blow first before the overcurrent devices downstream. I can do a coordination study between the overcurrent devices but I’d rather use fuses. The fault current is way too high to get good coordination with circuit breakers

The circuit goes something like this:

Service fuse -> fuse -> HQS and HQP breakers

I need the the first and second fuses to be coordinated. If I use a circuit breaker as the second overcurrent device, it might not coordinate well because the fault current is too high
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Fair enough on the coordination. Unless there is something I have missed, it appears you are out of luck using fuses, unless siemens can come up with something that works that I am not seeing. Can you use all QS instead of a mix of QS and QP? Then it would work with a class T or L
 
electrofelon said:
Fair enough on the coordination. Unless there is something I have missed, it appears you are out of luck using fuses, unless siemens can come up with something that works that I am not seeing. Can you use all QS instead of a mix of QS and QP? Then it would work with a class T or L
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Can't use all QS because I have loads that are less than 100A :(

Might be a stupid idea but do you think I can have 800A Bussman JJN and JJS fuses in series and then it will series rate with both HQP and HQS breakers?
 
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