Chiller Protection

[flengineer]

I have a chiller with a MOCP of 500A per the nameplate. The chiller has an internal 600A breaker. Can the breaker at the switchboard be smaller than the internal protection of the chiller?

The mechanical engineer originally specified a chiller with 600A MOCP. The 600A breaker is installed and the inspector has an issue with it not matching the nameplate.

 

[480sparky]

Are you sure it's a breaker installed in the unit, or could it just be a 600a disconnect?

 

[flengineer]

We've been going back and forth with the manufacturer on this. They first said the internal breaker had been calibrated down to 500A, then they said it wasn't. Their final position:

"The electrical components inside the chiller are specifically designed to protect the chiller components downstream of the customer connection point. In the case of this chiller, the primary internal protection is provided by semi-conductor fusing sized in accordance with UL requirements to properly protect the chiller components. The internal circuit breaker in the chiller panel is an optional accessory for customers that desire an external handle for disconnecting power and/or increased short circuit withstand rating. However, the fusing is designed to fully protect the chiller even when the circuit breaker is not present."

 

[480sparky]

I'd say if the ME spec'ed a 600a OCD, and the unit came in with a nameplate rating of 500a for the OCD, then you need to do two things.

1. Install a 500a OCD in the panel.
2. Send the bill to the ME.

 

[flengineer]

:roll: Obviously, you're a contractor. How about we bill the Contractor instead for not coordinating with the shop drawings.

 

[480sparky]

:roll: Obviously, you're a contractor. How about we bill the Contractor instead for not coordinating with the shop drawings.

If the shop drawing said 500a, I'd say go for it.

If the shop drawings said 600a, what are you going to say when he responds with that fact?

 

[Pierre C Belarge]

Yes, one can supply a 600A overcurrent device with a 500A supply, It is that simple.

The design features, such as will the 500A supply hold the load is going to be a phone call you will have to deal with if the installation is not operating properly.

 

[weressl]

I have a chiller with a MOCP of 500A per the nameplate. The chiller has an internal 600A breaker. Can the breaker at the switchboard be smaller than the internal protection of the chiller?

The mechanical engineer originally specified a chiller with 600A MOCP. The 600A breaker is installed and the inspector has an issue with it not matching the nameplate.

1. The mechanical engineer has no business of specifying an electrical device, and
2. the manufacturer will install whatever their UL listing requires,
3. Selective coordination should be used to size the upstream protective device.