Load question

[Brnspark]

I have a 45 KVA transformer that is fed with 480 volt 60 amps, feeding a 125 amp Square D QO panel. I have been asked to replace a 50 amp 3 pole breaker with a 100 amp 3 pole breaker for a new piece of equipment we are getting. There are already 3 3 pole 30 amp Breakers plus a few 20 amp receptacle Outlets being fed from this panel. The 100 amp piece of equipment will be running the same time as two of the 30 amp ones. The panel is fed with number 2 wire. Just wondering if I can put that 100 amp breaker in. The equipment doesn't have an FLA on the nameplate, just what size overcurrent protection we need.

 

[iwire]

The sizes of the breakers are meaningless as far as determining the load.

You need to look at each loads labeling to see how much is already used.

 

[Jraef]

And to add on to that, a 45kVA transformer (which implies 3 phase) assuming 208V secondary is good for 125A output total. So without knowing the actual loads, you can't determine if it will work. Again, the breaker sizes mean little.

Also, it's highly unlikely your equipment has no info showing the load in one form or another, it's an almost universal requirement. If it is UL listed, it's an absolute requirement. If it has a label that says "MOCP = 100A", that means Max Over Current Protection. But if it does have that, it will likely also have another value shown called "MCA" which is "Minimum Circuit Ampacity". That gives you the load information.

 

[kwired]

And to add on to that, a 45kVA transformer (which implies 3 phase) assuming 208V secondary is good for 125A output total. So without knowing the actual loads, you can't determine if it will work. Again, the breaker sizes mean little.

Also, it's highly unlikely your equipment has no info showing the load in one form or another, it's an almost universal requirement. If it is UL listed, it's an absolute requirement. If it has a label that says "MOCP = 100A", that means Max Over Current Protection. But if it does have that, it will likely also have another value shown called "MCA" which is "Minimum Circuit Ampacity". That gives you the load information.

But keep in mind that MCA is not necessarily actual load. For most instances with a motor or refrigeration compressor it will have 125% of largest motor factored into it, so at very least you wouldn't need to add anything for continuous loading.