7.5KVA Isloated Power Panel

[Alwayslearningelec]

How to I convert this panel to find out how many amp panel it is? Curious? It is fed from 277/480. Why do they list it as a panel as a 7.5 kva islolated power panel? It is a hospital?

Thanks.

 

[skeshesh]

Wow I feel a bit light-headed reading your post!

Let's clarify some things: Where did you read the 7.5KVA rating?

If it's on a single line diagram it could be the load on the panel. If it's fed from a 7.5KVA transformer, then the panel can only supply 7.5KVA (perhaps xfmr can be overloaded further but that's another question). Neither scenario will tell you what the ampere rating of the panel is. You could load a 400A panel to 7.5KVA or feed it from a 7.5KVA transformer as long as OCPD and conductors are sized properly.

They list the panel as such likely because it's being fed from an isolation transformer, hence my guess at the 2nd scenario above.

You're either on site or looking at drawings, either way can't you find out if it's a hospital?

 

[Alwayslearningelec]

Wow I feel a bit light-headed reading your post!

Let's clarify some things: Where did you read the 7.5KVA rating?

If it's on a single line diagram it could be the load on the panel. If it's fed from a 7.5KVA transformer, then the panel can only supply 7.5KVA (perhaps xfmr can be overloaded further but that's another question). Neither scenario will tell you what the ampere rating of the panel is. You could load a 400A panel to 7.5KVA or feed it from a 7.5KVA transformer as long as OCPD and conductors are sized properly.

They list the panel as such likely because it's being fed from an isolation transformer, hence my guess at the 2nd scenario above.

You're either on site or looking at drawings, either way can't you find out if it's a hospital?

Hey, thanks very muchf or the reply. Duh on my part. I meant it IS a hospital. It is a 7.5 kva isolation panel being from from a distribution panel which is being fed from a bus duct riser. No transformer. They are incomplete drawings I am looking at and I am just trying to figure out what loads that panel(at the most) could be feeding. They don't even indicate feeder sizes. Not very critical was jsut curious as to how I could get a ballpark at to the loads that panel is feeding. Thanks.

 

[skeshesh]

Again, typically the KVA rating shown next to the panel is the load. There are "KVA rated" types of isolation panels used in hospitals take a look:
http://ecatalog.squared.com/pubs/El...ts/Hospital Isolation Panels/43100-019-01.pdf

Having said that I'd find it strange to have no isolation transformer. I understand it's fed from a distribution panel, but are you absolutely sure there's no small isolated transformer hidden in the ceiling or something? I'd check out the conduit route to make sure. If you're in the field take a look at the panel. If it doesn't look like a regular panel and more like the isolation style medical ones chances are it a 7.5KVA rated (take a look at the link above).

 

[roger]

This is an Isolation Power System Panelboard, it will have no grounded conductor on the secondary side. There will be some critical commisioning procedures that must take place before putting these systems in service per chapter 4 of NFPA 99. The die-electric strength of the secondary conductors insulation is critical for keeping leakage current at a minimum, this takes an XHHW conductor, there must be less than .0006 A of leakage current in it's unloaded state and not more than .005 A total leakage when in service, this is the alarm threshold. You can not use pulling compound when installing the conductors.

As far as figuring out the load, it is a 7.5 KVA transformer with a 277 v primary to 120 v secondary and as Skeshesh says, it can only supply that much load.

Roger

 

[Alwayslearningelec]

Again, typically the KVA rating shown next to the panel is the load. There are "KVA rated" types of isolation panels used in hospitals take a look:
http://ecatalog.squared.com/pubs/El...ts/Hospital Isolation Panels/43100-019-01.pdf

Having said that I'd find it strange to have no isolation transformer. I understand it's fed from a distribution panel, but are you absolutely sure there's no small isolated transformer hidden in the ceiling or something? I'd check out the conduit route to make sure. If you're in the field take a look at the panel. If it doesn't look like a regular panel and more like the isolation style medical ones chances are it a 7.5KVA rated (take a look at the link above).

Sorry! They have integral 277/480 to 120/208 isolation transformers. Good call!!

 

[Alwayslearningelec]

This is an Isolation Power System Panelboard, it will have no grounded conductor on the secondary side. There will be some critical commisioning procedures that must take place before putting these systems in service per chapter 4 of NFPA 99. The die-electric strength of the secondary conductors insulation is critical for keeping leakage current at a minimum, this takes an XHHW conductor, there must be less than .0006 A of leakage current in it's unloaded state and not more than .005 A total leakage when in service, this is the alarm threshold. You can not use pulling compound when installing the conductors.

As far as figuring out the load, it is a 7.5 KVA transformer with a 277 v primary to 120 v secondary and as Skeshesh says, it can only supply that much load.

Roger

Thanks. So this couls be loaded to 400a??

 

[steve66]

Thanks. So this couls be loaded to 400a??

No, I'm not sure where the 400A came from. The isolation panel is rated at 7500 VA, so at 277V, so it could be drawing about 27 amps max.

These panels typically serve all the loads in an operating room (maybe including the lights, maybe not).

 

[roger]

Thanks. So this couls be loaded to 400a??

As Steve said, I don't know where you came up with 400 Amps. These panels serve small loads in specific areas.

Roger

 

[skeshesh]

No, I'm not sure where the 400A came from. The isolation panel is rated at 7500 VA, so at 277V, so it could be drawing about 27 amps max.

These panels typically serve all the loads in an operating room (maybe including the lights, maybe not).

I may have misled him in my first post (post #2). The point I was trying to make was that the rating of the panel is the maximum ampere rating of the bus in the panel, but that doesnt mean you can load the panel upto it's rating. The loading of the panel will most often be limited by feeder size and/or OCPD.