Isolator Sizing as per IEC/NEC standards 1

[alanElec]

Hi All,

I'm using field isolators to connect HVAC equipments such as AHU'S,package units etc to the Electrical Panel.The main purpose of providing the field isolator is only for isolation and maintanence of equipment.How should i size the Isolators for the equipment?Usully I give a 10% margin over the full load current.Is that Ok?

 

[jraef]

Per the NEC, any switch on a motor circuit must have a motor HP rating equal to or greater than the motor HP, current alone is not adequate because switch of motors requires added considerations. There are added rules for multiple motors and mixed loads.

"Will work for (the memory of) salami"

 

[alanElec]

Per the NEC, any switch on a motor circuit must have a motor HP rating equal to or greater than the motor HP, current alone is not adequate because switch of motors requires added considerations. There are added rules for multiple motors and mixed loads.

Im talking about a single motor load.can u clarify sir?

 

[fx007]

Per NEC, if your equipment manufacturer provide information for Disconnect Switch (read Isolator - same thing), you just use the manufacturer recommended size. Else, take FLA (full load amps) from the manufacturer's catalog x 1,15 and choose the next size up ( example, 472A, choose 600A). I used factor 1,15 on all my projects and was used by my company on all their projects. If single isolator for multiple equipment (within line of eye-sight), you add all FLA for each and then x 1,15. Conductors are calculated FLA x 1,25, C.B. FLA x 1,75 for the 1st or if only one.
If multiple, for all the rest, just straight add the rest of FLA to the 1st, calculated above, and use that load to size cable/CB.
If need, I have my table I always use, just PM your email, and I will send it to you.

Regards