How to? Multiple 480/277 services?

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11Haze29

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Electrical Engineer
Have existing 1000KVA 480/277V 3ph padmount, underground feed to 1200A MCB Panelboard inside. Owner wants to subdivide the building into four tenants and wants 480/277 metered service to each. Utility Green book says 1000KVA 480/277 transformer has 18,100 A Fault Current. There are no EZ multi paks at 480. Though of wireway trough, with four Main CB/Meter Combos, can find them at 320A continuous and with 300 MCB but only at 10K AIC. All single meter sockets are rated 10K AIC. Though maybe fused disconnect upstream with current limiting fuses, but even with 300A CLF's the let through is around 12KA. The only other option is CT metering cabinet. But with four, 400AF/300A disconnects, four metering cabinetes, and four single socket meters, the space requirement is huge.

I can't find any manufacturer with meter sockets greater than 10KAIC. Can't use series rated, as the combo must be tested by manufacturer and nobody is making it.
While 1600A 208 3ph is easy with a MCB and Multi Pak, 1200A at 480V is very awkward.

Any ideas would be appreciated.
 
did you calculate the actual available short circuit current at the 1200A MCB? It does not take all that much wire to reduce from 18 kA to 10 kA.

what happens if you run four sets of smaller service conductors from the xfmr to 4 meters inside? How long of a run does it take to get to 10 kA?
 
I thought of that also, but, in this case there are four parallel 400MCM CU, and the run is only about 15 feet. So I doubt I would drop from 18K to 10K in that short a distance. Plus, the utility doesn't go by calculated fault at a distance, their install manual uses a Table for the different KVAa and voltages, and the Table lists 1000 KVA @480 is 18,100 Amps. Service equipment has to meet that value. Utility owns the transfomer and I think they already included some dimished value into the Table, as a typical 1000KVA Xfrm @ 5.5% Imp would be 22KA. The transformer is metered on the secondary, but with CT's inside the transformer, and just the one meter.
 
11Haze29 said:
I thought of that also, but, in this case there are four parallel 400MCM CU, and the run is only about 15 feet. So I doubt I would drop from 18K to 10K in that short a distance. Plus, the utility doesn't go by calculated fault at a distance, their install manual uses a Table for the different KVAa and voltages, and the Table lists 1000 KVA @480 is 18,100 Amps. Service equipment has to meet that value. Utility owns the transfomer and I think they already included some dimished value into the Table, as a typical 1000KVA Xfrm @ 5.5% Imp would be 22KA. The transformer is metered on the secondary, but with CT's inside the transformer, and just the one meter.
Click to expand...

they are probably figuring that the grid is not really an infinite source. I doubt they are making a guess as to what it is at your service equipment.

there may not be a good answer for your situation.
 
11Haze29 said:
Have existing 1000KVA 480/277V 3ph padmount, underground feed to 1200A MCB Panelboard inside. Owner wants to subdivide the building into four tenants and wants 480/277 metered service to each. Utility Green book says 1000KVA 480/277 transformer has 18,100 A Fault Current. There are no EZ multi paks at 480. Though of wireway trough, with four Main CB/Meter Combos, can find them at 320A continuous and with 300 MCB but only at 10K AIC. All single meter sockets are rated 10K AIC. Though maybe fused disconnect upstream with current limiting fuses, but even with 300A CLF's the let through is around 12KA. The only other option is CT metering cabinet. But with four, 400AF/300A disconnects, four metering cabinetes, and four single socket meters, the space requirement is huge.

I can't find any manufacturer with meter sockets greater than 10KAIC. Can't use series rated, as the combo must be tested by manufacturer and nobody is making it.
While 1600A 208 3ph is easy with a MCB and Multi Pak, 1200A at 480V is very awkward.

Any ideas would be appreciated.
Click to expand...

Are you sure that no one makes a higher than 10K classs 320 socket? Did you check with a good gear guy at your supply house? EAton has 200 amp 7 jaw 277/480 meter mains rated 22K, but I did not see similar in 320 class. I wonder if they "series rate" with fuses like NF disconnects do? If each unit needs more than 200, you could give them two 200's....Tough situation.
 
11Haze29 said:
Have existing 1000KVA 480/277V 3ph padmount, underground feed to 1200A MCB Panelboard inside. Owner wants to subdivide the building into four tenants and wants 480/277 metered service to each. Utility Green book says 1000KVA 480/277 transformer has 18,100 A Fault Current. There are no EZ multi paks at 480. Though of wireway trough, with four Main CB/Meter Combos, can find them at 320A continuous and with 300 MCB but only at 10K AIC. All single meter sockets are rated 10K AIC. Though maybe fused disconnect upstream with current limiting fuses, but even with 300A CLF's the let through is around 12KA. The only other option is CT metering cabinet. But with four, 400AF/300A disconnects, four metering cabinetes, and four single socket meters, the space requirement is huge.

I can't find any manufacturer with meter sockets greater than 10KAIC. Can't use series rated, as the combo must be tested by manufacturer and nobody is making it.
While 1600A 208 3ph is easy with a MCB and Multi Pak, 1200A at 480V is very awkward.

Any ideas would be appreciated.
Click to expand...

Since the 1200A MDP is inside, you will have to use electronic sub-meters to each tenant, similar to how they do in malls.
Otherwise the tenant services would have to be on the exterior, as well as the service disconnect/480V meters to each tenant.
 
11Haze29 said:
Have existing 1000KVA 480/277V 3ph padmount, underground feed to 1200A MCB Panelboard inside. Owner wants to subdivide the building into four tenants and wants 480/277 metered service to each. Utility Green book says 1000KVA 480/277 transformer has 18,100 A Fault Current. There are no EZ multi paks at 480. Though of wireway trough, with four Main CB/Meter Combos, can find them at 320A continuous and with 300 MCB but only at 10K AIC. All single meter sockets are rated 10K AIC. Though maybe fused disconnect upstream with current limiting fuses, but even with 300A CLF's the let through is around 12KA. The only other option is CT metering cabinet. But with four, 400AF/300A disconnects, four metering cabinetes, and four single socket meters, the space requirement is huge.

I can't find any manufacturer with meter sockets greater than 10KAIC. Can't use series rated, as the combo must be tested by manufacturer and nobody is making it.
While 1600A 208 3ph is easy with a MCB and Multi Pak, 1200A at 480V is very awkward.

Any ideas would be appreciated.
Click to expand...
Are you submetering from the existing 1200 panelboard or are you converting this to four separate services, which can be allowed for multi-tenant applications? Meters could be at tenant space rather than at central location in those instances, which could help with needed space as well as available fault current at the meter socket.

If these will be utility meters you need to know what POCO may or may not allow in addition to what code allows.
 
The existing single meter setup has a 1200A MCB panelboard inside. This will be removed for multiple tenant setup.
Utility does NOT permit submitting, in fact it is expressly forbidden.
 
11Haze29 said:
The existing single meter setup has a 1200A MCB panelboard inside. This will be removed for multiple tenant setup.
Utility does NOT permit submitting, in fact it is expressly forbidden.
Click to expand...

So the MDP will be removed?

Then you can set a 1200A cable tap can (poco furnishes those here) with a wireway like 12x12 , then set poco meters and main fusible safety switches, then pipe to the tenant spaces.

Easy peasy....

The room will have to be properly fire walled, and exterior tenant/poco secured access
 
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