HVAC SCCR

R

Rock86

Senior Member
Location
new york
Occupation
Electrical Engineer / Electrician
Situation: Mechanical engineer sent a cut sheet for a temporary chiller. Voltage, load calc, and OCP all checked to be compatible. The cut sheet says the SCCR is 5kA. I ran an available fault current calculation and the result was over 12kA. I went to my mechanical engineer to discuss this with him and he said that no electrical engineer in his 25 years has ever mentioned a concern for SCCR.

Do I have a valid point telling him the SCCR is underrated for the electrical condition, or am I misunderstanding SCCR vs AFC?

Note: I am not talking about the AIC rating.
 
You are correct. Most manufacturers use the default 5kA and do not provide the components needed for a higher SCCR unless specified at the time of the order.
 
It's a very common issue. I've encountered it with elevator system components as well. To be frank, I don't recall ever encountering a reasonable, all-encompassing solution. I do recall that current-limiting fuses are not a viable option, nor is the placement of series resistance to limit fault current. Getting the manufacturers to only use components that can collectively provide a higher SCCR is not cost-effective for them. If you are in need of a way out of the conundrum, I fear that I have none to offer.
 
Did you calculate the AFC including the branch citcuit conductors to the unit? If so, can you make them much longer to limit the current? Waste of wire, but may be an easy solution.
 
Rock86 said:
Do I have a valid point telling him the SCCR is underrated for the electrical condition, or am I misunderstanding SCCR vs AFC?
Click to expand...
For more than 50 years, NEC 110.10 has said equipment needs to be able to handle/tolerate short circuit currents until the upstream protective devices operate. Over the decades specific sections of the NEC, like for industrial control panels, have had similar verbiage added to them because 110.10 was commonly ignored.

My guess is the mechanical engineers have never been held accountable for their poor specifications. Electrical contractors have been shouldering the cost and headaches of compliance.
 
You might want to enter "HVAC SCCR" in the search bar on this forum. There are a number of threads that address this all too common issue.
 
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