is it necessary to do a short circuit for this?

[ptonsparky]

Does make troubleshooting easier, your problem is usually obvious once you remove the right cover.

My tech school instructor used to say working with 480 was easy. You could almost always find the problem where the smoke and burn marks were.

 

[Deetz]

In our Manufacturing facility, we come across the typical 5ka alot. Like someone else said before. It's kind of a go to number for the machine builder. If you go back to them, the engineers of the place may help and up that level. Also there are firms that will do an in depth look if you supply them with the electrical schematic and parts list that you can get from the manufacturer. They do charge a fee though.

 

[kwired]

If the unit has definite purpose contactors for the motor controllers, those I believe by default are only 5kA rated. They may be able to do some things to get a higher rating on the equipment and still use those contactors?

 

[Knightryder12]

If I’m only concerned about sizing a branch circuit off a three phase LV Panelboard to a HAVC unit do I have to go all the way back to the POCO XFMR to get the cable size per short circuit requirement?


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What size transformer is feeding that 208V panel? I have been doing this for a long time and have yet come across a dry type transformer under the size of 225kva let more than 10K through. Also, just because the breakers are rated at 10K aic, does not mean there is 10K available.
And no one is going to pay an EE to do a fault study on a plant that size to replace one piece of mechanical equipment. Whoever designed the HVAC equipment should have designed it with a higher SCCR rating. Its no upcharge to say provide the unit with a 42K SCCR rating. And its a minimal charge to go to 65K.

 

[jim dungar]

Rule of thumb is a standard motor only contributes about 6x FLA as short circuit current.

Upon further review: motors typically contribute only 4X FLA.
You need roughly 250A of Non-VFD motor load to raise SCCR or AIC requirements by 1kA.

 

[MyCleveland]

What size transformer is feeding that 208V panel? I have been doing this for a long time and have yet come across a dry type transformer under the size of 225kva let more than 10K through. Also, just because the breakers are rated at 10K aic, does not mean there is 10K available.
And no one is going to pay an EE to do a fault study on a plant that size to replace one piece of mechanical equipment. Whoever designed the HVAC equipment should have designed it with a higher SCCR rating. Its no upcharge to say provide the unit with a 42K SCCR rating. And its a minimal charge to go to 65K.

It is the EE or EC that must tell the ME or MC what level of SCC the equipment is exposed to, depending on if the job is plan/spec or design build.

 

[Knightryder12]

It is the EE or EC that must tell the ME or MC what level of SCC the equipment is exposed to, depending on if the job is plan/spec or design build.

You are 100% correct. That's how we do it at the firm I am at.