Wanted to toss in some added examples to this thread - just for fun. DISCLAIMER: Although I deal with the NEC, the basics should be similar...
Can someone explain to me in a simple way, with code references, when to derate. I shouldn't sya I am totally lost on when and how to derate, but when I see 400 amp switches fused at 400Amps with 400A rated wire. Where is the derating in that?
There is no need to derate this scenario ***under normal circumstances***, since everything equals out to be 400 Amp Capacity.
Where things could change - thus becoming "NOT NORMAL CIRCUMSTANCES" would be:
- Ambient Temperature is always higher than 30°C,
- Load Amperes is >320 Amperes continuously for 3 Hours or more (LCL)
My question basically was how do you know if an existing distribution is becoming overloaded and how do you determine if you can continue adding loads without the risk of blowing the main fuses feeding that switchgear?
First off - and let me point out that I am not being a smart***, but if the Main OCPD often trips / blows a fuse, then there is a good indicator that either:
- The Service Capacity is being exceeded for an extended period of time,
- There is something faulting out in the Service Equipment,
- A large connected load is drawing excessive starting current.
The way to determine if an existing Service's capacity is, or will become inadequate, is similar to what COOKCC
has mentioned in the above post.
Determine the existing loads and apply it to the new designed loads.
Coincidental loads need to be considered, along with heavy starting loads & LCL (Long Continuous Loads).
When your calculated loads exceed the existing capacity - figured either by a Load Calc, Panel Schedules - or both, then a Service upgrade is needed.
This should be ample to cover your queries.
Let me know if you have further questions.