Chiller SCCR

[JoeStillman]

How did you pull this off….I would think most would tell you that’s someone else’s problem.

We discovered the problem when we tried to size reactors to put upstream of the chiller. After we selected the reactors, we needed to look into what the voltage drop would be on motor starting. Turned out the reactor would have knocked the voltage down too low. When they give you operating voltage tolerances, they are giving you a maximum upstream impedance. When they give you SCCR, they are giving you a minimum upstream impedance. When they give you a minimum that is greater than the maximum, it is impossible to power the unit at the rated voltage. I wrote them a letter telling them they needed to recall all the chillers that were built that way. That got their attention.

 

[MyCleveland]

When you have time, could you show an example of your logic/calcs please.

What happened to the ME that put you in the position where you needed to consider adding the reactors? Was there no coordination between the engineers?

 

[JoeStillman]

When you have time, could you show an example of your logic/calcs please.

What happened to the ME that put you in the position where you needed to consider adding the reactors? Was there no coordination between the engineers?

The ME had specified 65k but the Approved Shop Drawing didn't give the SCCR. We didn't find the problem until the engineer commissioned by the EC for the SC/AF/TCC study asked the question.

BTW the EC and MC were two desks in one office. We suspected them of being dumb like foxes.

 

[MyCleveland]

The ME had specified 65k but the Approved Shop Drawing didn't give the SCCR. We didn't find the problem until the engineer commissioned by the EC for the SC/AF/TCC study asked the question.

BTW the EC and MC were two desks in one office. We suspected them of being dumb like foxes.

I believe they caved because of the lack of info on the submittal.

I would just delete the last two words in your last sentence…MC has no chance of a change order with missing data in a submittal and the EC is just going to let you and his EE fight through the details.

 

[Tainted]

The cure is for specifying engineers to DEMAND IT up front in project specifications so that these low-baller suppliers have to comply or lose out. And if a low baller squeezes though and the gear shows up with 5kA, force THEM to remove the control panel, send it to a panel shop to be rebuilt and re-listed with a high enough SCCR! Only then will they get the message.

The problem is education. For example my mechanical engineer with a PE license just specifies anything without even thinking about short circuit. I literally had to explain it to him and he thought I was talking gibberish and he couldn't comprehend what short circuit values are and how they vary depending on the circuit. I guarantee he probably learned nothing and will just do what he normally would do.

 

[zbang]

The problem is usually finding an analogy that the listener can understand. For instance, the ME probably knows nothing of wires, but when you explain that a short 6" dia pipe can dump a whole lot more water on the floor than a 200' long 1" pipe, they often get it.