Large Industrial Equipment Greater than 600 Amps Issues with Feeder OCPD ?

[SteveAtx]

Had a Field Labeling Engineer tell us to make our system use less total amperage less (<500 amps) because, mumble mumble mumble, code.... I'll get back with you.

I don't see an issue with large industrial equipment, Greater than 600 Amps 208 VAC, is there something in code or practice that would make this difficult? Or stop us from building Large Industrial Equipment Greater than 600 Amps?

 

[Jraef]

Had a Field Labeling Engineer tell us to make our system use less total amperage less (<500 amps) because, mumble mumble mumble, code.... I'll get back with you.

I don't see an issue with large industrial equipment, Greater than 600 Amps 208 VAC, is there something in code or practice that would make this difficult? Or stop us from building Large Industrial Equipment Greater than 600 Amps?

The NEC isn't going to say anything about it, but your local utility might. 600A at 208V is a 225kVA service transformer JUST FOR THAT ONE LOAD, even higher if it has to start up across-the-line. It's highly likely that your local utility has a policy of not stocking 208V transformers larger than "xxx" kVA. Remember, when THEY own the transformer, THEY have to service / replace it if it fails. So they often will have limitations in order to reduce the inventory of spares they have to keep on hand. Around here (PG&E) the limit of 208Y120V service drops is 1,000kVA, but yours may be different. I did work in Idaho once where the limit was a 300kVA service drop for 208V, so if one load was 75% of that, it doesn't leave a lot of room for other loads at that service.

Bottom line, it's more likely related to the fact that you are building something that big for a 208V service. Most people would have gone to 480V at a much lower level.

 

[Sahib]

Typical service sizes from one POCO-UI, is attached herewith for further information.

https://www.uinet.com/wps/wcm/conne...ERES&CACHEID=6558490041384665b0e4f07a239a91d1

 

[kwired]

The NEC isn't going to say anything about it, but your local utility might. 600A at 208V is a 225kVA service transformer JUST FOR THAT ONE LOAD, even higher if it has to start up across-the-line. It's highly likely that your local utility has a policy of not stocking 208V transformers larger than "xxx" kVA. Remember, when THEY own the transformer, THEY have to service / replace it if it fails. So they often will have limitations in order to reduce the inventory of spares they have to keep on hand. Around here (PG&E) the limit of 208Y120V service drops is 1,000kVA, but yours may be different. I did work in Idaho once where the limit was a 300kVA service drop for 208V, so if one load was 75% of that, it doesn't leave a lot of room for other loads at that service.

Bottom line, it's more likely related to the fact that you are building something that big for a 208V service. Most people would have gone to 480V at a much lower level.

Something tells me the field labeling engineer is trying to give the unit in question a listing and doesn't care about what size of service the POCO will supply at what voltage.

 

[Iron_Ben]

Had a Field Labeling Engineer tell us to make our system use less total amperage less (<500 amps) because, mumble mumble mumble, code.... I'll get back with you.

I don't see an issue with large industrial equipment, Greater than 600 Amps 208 VAC, is there something in code or practice that would make this difficult? Or stop us from building Large Industrial Equipment Greater than 600 Amps?

When I worked for the poco, we hooked up a lot of large 208Y/120 services. 4,000 amps was not uncommon. A decent sized (but not huge) elementary or middle school was a typical example. Once you get to that size I think 480Y/277 is a better choice, but I suppose it's up to the designing engineer, and all have their own preferences and peculiarities. As jraef noted above, 1000 kva was also our largest standard "in stock" size for 208Y/120 padmount transformers. A 4,000 amp 208Y/120 service would pretty much always get a 500 kva padmount, and we're still waiting for the first one to fail due to overload.

 

[kwired]

When I worked for the poco, we hooked up a lot of large 208Y/120 services. 4,000 amps was not uncommon. A decent sized (but not huge) elementary or middle school was a typical example. Once you get to that size I think 480Y/277 is a better choice, but I suppose it's up to the designing engineer, and all have their own preferences and peculiarities. As jraef noted above, 1000 kva was also our largest standard "in stock" size for 208Y/120 padmount transformers. A 4,000 amp 208Y/120 service would pretty much always get a 500 kva padmount, and we're still waiting for the first one to fail due to overload.

They may put in a 4000 amp service, but chances are the actual average load is well below that. Peak demands may not be long enough duration to be a major issue as long as there is long enough cool down time in between.

Someday when they put on a major addition they may just supply it from that 4000 amp service, but maybe the 500 kVA transformer gets increased in size when more load gets added.