5 KA short circuit amps / symetrical
5 KA short circuit amps / symetrical
(OP)
Received a call today from maintenance. They are going to be hooking up an convection heater. Rating is 55 FLA.
On the front of the panel, it states " short circuit amps - 5KA - symetrical ". Inspector mentioned something to one of the maintenance personnel, that we may have to install a transformer to reduce this?? The feed is fed from an MCC with HRC fuses - IR capacity of 200KA. Why would be need to install a transformer ? There is the main feed from the MCC ( fused ) , then a main switch at the unit itself.... and also fuses inside the console. Am I missing something here. If the unit is capable of putting out 5KA under short circuit conditions, but the fuses are capable of interuppting more than 5 KA, then there should not be a problem..correct ? Possibly the maintenance person got his wires crossed...????
On the front of the panel, it states " short circuit amps - 5KA - symetrical ". Inspector mentioned something to one of the maintenance personnel, that we may have to install a transformer to reduce this?? The feed is fed from an MCC with HRC fuses - IR capacity of 200KA. Why would be need to install a transformer ? There is the main feed from the MCC ( fused ) , then a main switch at the unit itself.... and also fuses inside the console. Am I missing something here. If the unit is capable of putting out 5KA under short circuit conditions, but the fuses are capable of interuppting more than 5 KA, then there should not be a problem..correct ? Possibly the maintenance person got his wires crossed...????






RE: 5 KA short circuit amps / symetrical
The heater don't have nothing to do with the short-circuit current, The 5kA only means that the pannel can resist "without" damage to a short-circuit current of 5kA or less.
So you must calculate the short-circuit current at the pannel and confirme that it is less than 5kA symetrical. If the current is more than 5kA, well maybe you will have to add a transformer to reduce the short-circuit current, or install a pannel with a bigger rating, or...
The firt step is to calculate the short circuit current.
RE: 5 KA short circuit amps / symetrical
RE: 5 KA short circuit amps / symetrical
RE: 5 KA short circuit amps / symetrical
If this is new equipment, you might check with the manufacturer and inquire about tested combination using an upstream current-limiting fuse. They may have already done some testing.
Next time, put the available short circuit current in the purchase spec.
"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg
RE: 5 KA short circuit amps / symetrical
Yes, I see what is missing now....HRC fuses can safely interrupt 200KA....but we have to limit SCCR to 5 KA somehow.
RE: 5 KA short circuit amps / symetrical
RE: 5 KA short circuit amps / symetrical
RE: 5 KA short circuit amps / symetrical
RE: 5 KA short circuit amps / symetrical