I'm looking at a project where some chillers are being added to an existing normal and emergency system through a new ATS. With adding this new chiller load is there an NEC requirement to calculate or consider the existing Switchbaord load with the new added load? I know there are NEC requirements for quantifying load for services (metering or utility bills) but wasn't sure if there was a requirement for locations downstream of service?
Adding loads to existing Switchboard
- Thread starter philly
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electrofelon
Senior Member
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- Cherry Valley NY, Seattle, WA
So some equipment and all conductor ratings must be evaluated with a load calc: 215.2(A)(1) for feeders, 210.19(A) for branch circuits, 408.30 for panelboards. There is actually no specific requirement that a switchboard be sized to meet the load, but 110.3(A)(7) and 110.3(B) could be cited. But as mentioned the conductors serving that switchboard do. OF course in practice there are times we skip it and just use our experience and judgement.
As with additional motor loads, the important thing to check is with the short time currents additional loads impose on the existing breakers! It might be good to check if your existing breakers have adjustable short-time /instantaneous settings.
As mentioned, the existing conductors might not be able to carry the added loads also!
As mentioned, the existing conductors might not be able to carry the added loads also!
That's interesting. I'm curious why a panelboard would have this requirement and not a Switchboard. Like you said the feeders for both would need to be sized accordingly.
I'm curious what most most would take as a practical approach here when considering monitoring vs looking at loads and feeder sizes themselves?
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