250.30 SSBJ

[ramsy]

The OP Isaiah is probably asleep by now in Baton Rouge, LA. As I should be, since hurricane Hillary spared my work early in the AM. Will stay tuned for further developments.

 

[Jpflex]

“I’m not exactly sure what you meant by bonding jumpers for metal conduit not underground being easier but if you told me more info on your underground set up such as if you have one big conduit for all feeders or 3 conduits would be helpful”

If you meant using EMT conduit as a supply side bonding jumper rather than more than 14 parallel SSBJ conductors than yes I believe NEC does not require the conduit to be sized by chart because they assume if it can hold all ungrounded and grounded conductors, then it should be able to handle fault current return path

 

[Isaiah]

I don’t get your SSBJ TOTAL at 14 conductors which should run from the separately derived source enclosure to the first point of disconnect enclosure or bus

If you you are paralleling every ungrounded conductor and SSBJ into one massive conduit ok

However if you have 3 conduits equally separating pairs of ungrounded and grounded conductors in 3 conduits from source to first disconnect then you could not get the required even number of SSBJ in 3 conduits. 14 SSBJ / 3 = 4.66 SSBJ conductors in each of the conduits (not possible)

Also if you don’t have neutral loads you may be able to go with an ungrounded system and not run a neutral (which I think you call 14 SSBJ?) from XO to the first disconnect. Instead you leave xo without anything terminating to it. The SSBJs would not connect at the xo neutral but to the source cabinet ground to first point of disconnect

Here’s the math I got for your project

Primary 125.15 I = 1 AWG @75 deg c

Secondary 3608.54 I = 14 of 250 kcmil conductor parallel x 255i = 3570i

(What the heck are you powering for this many amps a small town or meth lab lol?)


SSBJ 14,500,00 x .125 = 1,812,500 mil

1,812,500 mil / 14 conductors = 129,464.286 mil individual SSBJ X 14 or 2/0 at 133,100 cm each x 14 (would only work in a single conduit as 14 SSBJ can not divide evenly into 3 conduit runs)

It’s not 14 conductors; it’s 14 paralleled 500kCMIL per phase. In other words it’s 42 total conductors—3 conductors A,B,C per conduit plus one SSBJ.
Also it wouldn’t make sense to route 14 ungrounded conductors in a single conduit due to correction factors plus the conduit would be enormous at 40% fill. Lol


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[Jpflex]

It’s not 14 conductors; it’s 14 paralleled 500kCMIL per phase. In other words it’s 42 total conductors—3 conductors A,B,C per conduit plus one SSBJ.
Also it wouldn’t make sense to route 14 ungrounded conductors in a single conduit due to correction factors plus the conduit would be enormous at 40% fill. Lol


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Ok my bad I thought you were asking about SSBJs

500 KCMIL or 500,000 CMIL = 380 i amperes @ 75 deg Celsius x 14 wires per phase = 5,320 i total parallel AMPACITY for secondary

HOWEVER secondary transformer ampacity out put is 3,608.54 i amperes. Your choice of wire would initially seem overkill when resized at 5,320 i but, I believe for continuous loads transformer ampere output and inrush current effect on transformer startup, the 3,608.54 i is multiplied x 1.25 percent = 4,510.64 i ampacity wire needed after considering temperature derating and voltage drop (not calculated)

Sizing secondary transformer ampere output at 3608.54 i x 1.25 for continuous loading conductor sizing = 4,510.67 i ampere conductor needed after derating for temperature and voltage drop. With your paralleled conductors rated for 5,320 i think you look good here?

But what I’m the heck are you powering with that much amperes?

 

[Jpflex]

It’s not 14 conductors; it’s 14 paralleled 500kCMIL per phase. In other words it’s 42 total conductors—3 conductors A,B,C per conduit plus one SSBJ.
Also it wouldn’t make sense to route 14 ungrounded conductors in a single conduit due to correction factors plus the conduit would be enormous at 40% fill. Lol


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That’s why I mentioned 3 conduits for paralleling

 

[augie47]

Odd (to me) that QA is concerned about "residual voltage" with XO connected. I'd be more concerned about voltages with XO not connected,
As you pointed out, IF XO is bonded at the transformer the pointy of connection of the SSBJ seems irrelevant.

 

[Isaiah]

Odd (to me) that QA is concerned about "residual voltage" with XO connected. I'd be more concerned about voltages with XO not connected,
As you pointed out, IF XO is bonded at the transformer the pointy of connection of the SSBJ seems irrelevant.

Yes Augie, I’m going to push back hard on this one.


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