NEC 250.80, 250.92

hhsting

Senior Member
As I have said multiple times, there does not seem to be any guidance in the code for parallel SSBJ's to multiple service disconnects. Last time I ran across this I looped a full sized SSBJ from 1st disco, to CT can lay in lug and back to 2nd disco just to be safe. Have fun at the salon
Ok thanks for your input. Salon should say also acts like SSBJ. I don’t understand you provided full size. I guess one cannot use 250.102(C)(2) for parallel SSBJ


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hhsting

Senior Member
As I have said multiple times, there does not seem to be any guidance in the code for parallel SSBJ's to multiple service disconnects. Last time I ran across this I looped a full sized SSBJ from 1st disco, to CT can lay in lug and back to 2nd disco just to be safe. Have fun at the salon
Fault currents of trough travels thru 1/0 AWG bonding jumper to gnd bar to #4 AWG SSBJ/GEC tap to #4 MBJ to 3/0 AWG neutral to 500 kcmil. Can all the under sized #4 handle fault current of trough?

When you say Full size you mean #1/0 AWG SSBJ and #1/0 AWG MBJ?


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Fault currents of trough travels thru 1/0 AWG bonding jumper to gnd bar to #4 AWG SSBJ/GEC tap to #4 MBJ to 3/0 AWG neutral to 500 kcmil. Can all the under sized #4 handle fault current of trough?

When you say Full size you mean #1/0 AWG SSBJ and #1/0 AWG MBJ?


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Well the fault would go thru both SSBJ'S to each service disconnect's neutral and back to the 500's, so it would be full sized in that sense.

Yes full size would be 1/0 for 500 ungrounded conductors
 

hhsting

Senior Member
Well the fault would go thru both SSBJ'S to each service disconnect's neutral and back to the 500's, so it would be full sized in that sense.

Yes full size would be 1/0 for 500 ungrounded conductors
Trough Fault current would go from trough to bonding jumper to gnd bus bar to GEC tap to MBJ to neutral disco to incoming neutral. If split then Each neutral in disco is 3/0. Two of them combined would 168x2 = 336 kcmil. Note this is still undersized since incoming neutral is 500kcmil.

I don’t think if you resize the conductors to each 200A disco from 4#3/0 AWG to 4#250kcmil would be an option designer would go to.

Direct connection you would have neutral bar bonded to trough which would let fault current directly to incoming neutral.

I don’t see any other option except what post #2 says recommend 250.64(d)(3).
 
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hhsting

Senior Member
Well the fault would go thru both SSBJ'S to each service disconnect's neutral and back to the 500's, so it would be full sized in that sense.

Yes full size would be 1/0 for 500 ungrounded conductors

Trough Fault current would go from trough to bonding jumper to gnd bus bar to GEC tap to MBJ to neutral disco to incoming neutral. If split then Each neutral in disco is 3/0. Two of them combined would 168x2 = 336 kcmil. Note this is still undersized since incoming neutral is 500kcmil.

I don’t think if you resize the conductors to each 200A disco from 4#3/0 AWG to 4#250kcmil would be an option designer would go to.

Direct connection you would have neutral bar bonded to trough which would let fault current directly to incoming neutral.

I don’t see any other option except what post #2 says recommend 250.64(d)(3). What do you think?


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Trough Fault current would go from trough to bonding jumper to gnd bus bar to GEC tap to MBJ to neutral disco to incoming neutral. If split then Each neutral in disco is 3/0. Two of them combined would 168x2 = 336 kcmil. Note this is still undersized since incoming neutral is 500kcmil.

I don’t think if you resize the conductors to each 200A disco from 4#3/0 AWG to 4#250kcmil would be an option designer would go to.

Direct connection you would have neutral bar bonded to trough which would let fault current directly to incoming neutral.

I don’t see any other option except what post #2 says recommend 250.64(d)(3). What do you think?


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I wouldnt worry about the size of the neutral to each disco, If you were going to allow parallel SSBJ's, I would think you want the sizes to add up to 1/0 (2 - #3's) which is the size for the largest ungrounded conductor per 250.102(C)
 

hhsting

Senior Member
I wouldnt worry about the size of the neutral to each disco, If you were going to allow parallel SSBJ's, I would think you want the sizes to add up to 1/0 (2 - #3's) which is the size for the largest ungrounded conductor per 250.102(C)
SSBJ would be 1/0Awg. However, I don’t follow why not worry about size of neutral each disco? That’s just regular neutral it’s not SSBJ. If you size SSBJ to 500 kcmil then each neutral should be sized 500 kcmil or 250 kcmil for each?
 
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SSBJ would be 1/0Awg. However, I don’t follow why not worry about size of neutral each disco? That’s just regular neutral it’s not SSBJ
You just have to get the SSBJ to the neutral. I dont really see why the neutral service conductor taps to each enclosure would need to add up to the pre tap size. In fact, It could be argued that you only size each SSBJ "tap" to the ungrounded conductors serving that enclosure (like we do for the GEC taps) so in that case the #4 would be fine. This is all conjecture of course as the code just doesnt tell is what to do here.
 

hhsting

Senior Member
I wouldnt worry about the size of the neutral to each disco, If you were going to allow parallel SSBJ's, I would think you want the sizes to add up to 1/0 (2 - #3's) which is the size for the largest ungrounded conductor per 250.102(C)
Ignore previous post. SSBJ would be 1/0Awg. I guess the tapped neutral from 500kcmil + MBJ + GEC tap + gnd bus bar + bond to enclosure is one big supply side bonding jumper (SSBJ).

So I have for each disco 3/0 in series with 1/0AWG in series with Gnd bus. Let’s say that’s x kcmil.

X would be in parallel to X which then should be equal to 1/0 AWG.


However what is x? What do you think?
 
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hhsting

Senior Member
You just have to get the SSBJ to the neutral. I dont really see why the neutral service conductor taps to each enclosure would need to add up to the pre tap size. In fact, It could be argued that you only size each SSBJ "tap" to the ungrounded conductors serving that enclosure (like we do for the GEC taps) so in that case the #4 would be fine. This is all conjecture of course as the code just doesnt tell is what to do here.
If that’s the case then why not just do what the code says 250.64(D)(3). It is not certain what can happen if something is undersized just to be safe.


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hhsting

Senior Member
You just have to get the SSBJ to the neutral. I dont really see why the neutral service conductor taps to each enclosure would need to add up to the pre tap size. In fact, It could be argued that you only size each SSBJ "tap" to the ungrounded conductors serving that enclosure (like we do for the GEC taps) so in that case the #4 would be fine. This is all conjecture of course as the code just doesnt tell is what to do here.
If one is not sure then best to follow technique code says. Never know if something is undersized in conjecture

I will just recommended designer to follow code 250.64(D)(3) and do similar to what’s attached.
 

Attachments

If one is not sure then best to follow technique code says. Never know if something is undersized in conjecture

I will just recommended designer to follow code 250.64(D)(3) and do similar to what’s attached.
There are multiple ways to do it. This simplest would just be to use bonding locknuts on the trough to service disconnect conduits. The next easiest is to just put a lay in lug on the trough and run the neuter thru it.

Putting the GEC busbar in the trough as they want seems like a PIA and convoluted - I hate working in troughs.

Personally, I would pass it if they increased the GEC taps to equal 1/0 total size together.
 

hhsting

Senior Member
There are multiple ways to do it. This simplest would just be to use bonding locknuts on the trough to service disconnect conduits. The next easiest is to just put a lay in lug on the trough and run the neuter thru it.

Putting the GEC busbar in the trough as they want seems like a PIA and convoluted - I hate working in troughs.

Personally, I would pass it if they increased the GEC taps to equal 1/0 total size together.
They said they have 1600A main termination that has 500kcmil going to ct cabinet. From CT cabinet they have 2 sets of 3/0awg into trough.

They said they would place 2 sets of 30/ AWG neutral cable in trough connect to ground bus. No GEC tap but their is 2 sets of 3/0awg cable neutral tapped to each disco. So in picture they show incoming neutral connected to ground bus and instead #4 to each disco it’s #3/0 neutral.

That would work right? Bus not too small?
 
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hhsting

Senior Member
There are multiple ways to do it. This simplest would just be to use bonding locknuts on the trough to service disconnect conduits. The next easiest is to just put a lay in lug on the trough and run the neuter thru it.

Putting the GEC busbar in the trough as they want seems like a PIA and convoluted - I hate working in troughs.

Personally, I would pass it if they increased the GEC taps to equal 1/0 total size together.
electrofelon my buddy thank you I appreciate your input


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