30 OCPD in 600A Main Panelboard

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busman

busman

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Master Electrician / Electrical Engineer
All,

Without going into the weeds. Need to serve a single 400A load at 480V 3-phase. Customer wants some future capacity so I've specified a 600A MCB panelboard. But, this is being constructed in a Conex box and needs one of those wall mounted HVAC units (think Bard, Marvair, etc.). They usually need about a 30A OCPD. Can you think of any creative ways to feed this. Most panelboards what are 600A have about a 100A minimum OCPD that can be installed. I guess I could use 100A conductors for a short distance to a fused disconnect with 30A fuses. Any better ideas. Last resort is to install a second 480V panelboard at about 125A MLO that would take molded case circuit breakers.

As always, thanks for any help.

Mark
 
busman said:
All,

Without going into the weeds. Need to serve a single 400A load at 480V 3-phase. Customer wants some future capacity so I've specified a 600A MCB panelboard. But, this is being constructed in a Conex box and needs one of those wall mounted HVAC units (think Bard, Marvair, etc.). They usually need about a 30A OCPD. Can you think of any creative ways to feed this. Most panelboards what are 600A have about a 100A minimum OCPD that can be installed. I guess I could use 100A conductors for a short distance to a fused disconnect with 30A fuses. Any better ideas. Last resort is to install a second 480V panelboard at about 125A MLO that would take molded case circuit breakers.

As always, thanks for any help.

if it was me, I would set a small 480 to 208/120 transformer and a 125 amp 120/208 panel and have them spec the AC at that voltage. Having 120 available down the road is a better plan, IMHO
Click to expand...
 
Siemens can easily make you a 600A panelboard that has a 400A branch breaker and a bunch of miniature branches too. In fact I specd and installed pretty much exactly that last year on a job. Where I had a 400A subfeed breaker and needed a few dozen 20-100A breakers.
 
Here is a picture. Those breakers in the middle are 250A frame QR, 400A is on the bottom. This was MLO and 120/208, but the Siemens 480 miniature/panelboard breakers (I.e. BQD) have the same mounting as the 240V breakers. Note they actually supplied me with a BQD in the upper right, maybe because this was speced at 22 KAIC and they didnt have stock on a B3100H so they gave me the BQD which is 65K @240. I love panelboards! 🥰
 

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electrofelon said:
Here is a picture.
Click to expand...
Basic questions due to unfamiliarity: the 3 busbars that are visible behind the neutral wire at the bottom run all the way to the top to those double lugs? And then does the assembly with the miniature circuit breakers have its own busbars that connect to the main busbars beneath it?

Cheers, Wayne
 
wwhitney said:
Basic questions due to unfamiliarity: the 3 busbars that are visible behind the neutral wire at the bottom run all the way to the top to those double lugs? And then does the assembly with the miniature circuit breakers have its own busbars that connect to the main busbars beneath it?

Cheers, Wayne
Click to expand...
Correct on both. It's often called a "finger kit" in the field and I think by at least some manufacturers, if you were to buy it separately and install it due to a change or modification in the field. This one was factory built to my specs. Actually the 250A frame QR breakers I supplied because I had them, we were rearranging some distribution equipment. So they provided the appropriate finger kit as a "qr provision" space, and I just bolted them in.
 
busman said:
Most panelboards what are 600A have about a 100A minimum OCPD that can be installed.
Click to expand...

I question this. First, when you say "100A minimum", what exactly do you mean? Do you mean AT or AF? Just tried to logically think through this and if you mean AT, then presumably you mean it would be like a 225 to 250 amp frame that thus only goes down to 100 AT. In other words, they can't physically Mount miniature circuit breakers. Unless you mean they can take 15 to 100 amp miniature breakers but specify you can't put one in that is smaller than 100 (can't imagine that would be a thing).

Do the other manufacturers, say Eaton, not have product offerings that allow you to mount miniatures in with say a 600 amp or 400 amp branch? Siemens seems to allow mounting miniatures in even their largest P4 and P5 panelboards. I have always only used siemens for my factory panel boards so I admit I am not familiar with others' product offerings.
 
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