Rateings of disconnect switchs ???

[Davebones]

Have 3 - 150HP motors with 3 - 200amp disconnect switches feeding each .Nameplate amps are 167 amps .By code a 400amp switch should have been used ( 430.110 - "1.15 x 180 = 207 amps " ).What shall I tell my boss the reason we have to upgrade to 400 amp switchs ? I know about risk of opening under load ,any other risks involved to justify expense ??? No vfd involved these are across the line starters .These have 200 amp time/delay Rk1 fuses and have had no problems starting ?

 

[cpal]

Have 3 - 150HP motors with 3 - 200amp disconnect switches feeding each .Nameplate amps are 167 amps .?

First the disconnects should be sized IAW the FLA listed in table 430.250.

What is the voltage? 480?? (180A)

Second are the 200AA disconnects fused??

If not what is the HP rating of thoise disconnects?? (possibly 125Hp)

If those switches are non fused and caompl;y with the exception of 430.110 (A). You may not need to change to larger disconnects.

 

[Davebones]

480V system ,switches are fused at 200 amp , and rated at 125HP .I took the amperage from table 430.250 .This calculation showed me I had wrong size switches installed .PS what is meant by IAW ?

 

[augie47]

Not sure about other manufacturers, but SquareD 200 amp fusible is rated at 125 HP. Using that switch on a 150HP motor would, IMHO, be a violation of 430.110 and 110.3

 

[Davebones]

I understand its a violation ,what I would like to understand is what do I tell MANAGEMENT the risks involved if we leave it like it is.

 

[Pierre C Belarge]

Show management the related codes section(s) and let them take it from there.